BIOM2004 W2 Lecture 2

Introduction to the Immune System

Dr R Furmonaviciene

  • Please choose the best definition of Immune System :
  • Immune system is composed of organs, cells and cellular networks;
  • Immune system is composed of organs, cells and antibodies;
  • Immune system is composed of organs, cells and sub-cellular structures

BIOM2004 W1

Revision MCQ:

  • Learning Outcomes:
  • Discuss the key events of an immune response to bacterial invasion
  • Compare and contrast innate and adaptive immunity
  • Actively participate in pre-session, during-session and post-session learning; to start using OneClass Notebook (see Blackboard)

BIOM2004 W2 Lecture 2

Antigens

Immune system is activated by danger signals

Immune system is activated by molecular patterns

Viruses and bacteria invade by using their surface proteins to attach to host cells or they produce proteins and hydrophobic molecules like LPS to damage host cells

Proteins and other molecules which activate immune system are called antigens

Cells involved in immune response recognise antigens by using their receptors

Receptors usually bind to small areas of antigens, called epitopes

Antigens

This Photo by Unknown Author is licensed under CC BY

Summarise key events here:

Example of an Immune Respose:

What Happens When We Get a Splinter?

Summarise key events here:

Splinter and

Bacterial Invasion

Splinter

The barrier of skin is damaged

The cells are injured

The splinter is covered in bacteria

Bacteria can easier enter the tissues and blood stream

Danger signals will attract immune cells

Innate and possibly adaptive immune response will be initiated

Defensins, phagocytes and dendritic cells may be activated

T cells and B cells may participate in defense

Immune memory cells may be formed

Bacteria gets eliminated

Tissues heal

Immune response stops

Example of an Immune Respose:

What Happens When We Get a Splinter?

Key Events in More Detail

Antigen presentation

MHC class molecules on dendritic cells pick up antigenic peptides and

present them to T cells waiting in the lymph nodes;

This activates T cells and they enter blood stream and travel to the site of infection to clear the pathogens

B Lymphocytes are also activated in the lymphnode.

When informed about danger and activated, T cells form clones (or groups of identical T cells with the right specificity)

T helper cells inform B cells, and B lymphocytes also form clones.

Effective Immune Response

After the infection is cleared, immune response needs to be switched off (autoimmune diseases may result if this is not happening)

Memory cells are left after the infection is cleared, so that immune system can remember pathogen and react faster next time this pathogen comes across

Therefore secondary immune response (response to a seen pathogen) is stronger than primary response (response to a new pathogen)

Phases of an Immune Response

Primary and Secondary Immune Response

Innate and Adaptive Immunity

Compare and contrast Innate and Adaptive immunity

Adaptive immune responses develop later and consist of activation of lymphocytes. The kinetics of the innate and adaptive immune responses are approximations and may vary in different infections.

Innate and adaptive immunity

Cellular

Immune

response

Humoral

Surprise Task: Which Splinter is Better: Glass Splinter or Wooden Splinter?

Innate and Adaptive Immunity:

How Immune Response is Switched Off?

Task:

Read the following paper

https://www-proquest-com.proxy.library.dmu.ac.uk/docview/2434147450?OpenUrlRefId=info:xri/sid:summon&accountid=10472

Damage-associated molecular patterns in trauma

Borna, ReljaLand Walter Gottlieb.European Journal of Trauma and Emergency Surgery; Heidelberg Vol. 46, Iss. 4,  (Aug 2020): 751-775. DOI:10.1007/s00068-019-01235-w

and answer the question below:

How Can Danger-Associated Molecular Patterns (DAMPs) promote tissue healing?

Please place your answer in OneClass Notebook on Blackboard

Can you briefly explain the picture?

Immune system is regulated by stimulating and suppressive molecular patterns

Activation of Immune System

We are constantly surrounded

  • by bacteria
  • viruses
  • parasites

Activation of Immune System: Which Way to Go?

Post-Lecture Task

Read the following research paper and discuss briefly

The innate and adaptive events of immune response

to COVID-19.

https://www.frontiersin.org/articles/10.3389/fimmu.2020.01662/full

Optional catch-up time: text me via MS Teams

BIOM2004 W3 Lecture 3

Cytokines

Dr R Furmonaviciene

  • Learning Outcomes:
  • Discuss the definition and functions of cytokines
  • Discuss briefly how cytokines can be dis-regulated
  • Actively participate in pre-session, during-session and post-session learning; to start using OneClass Notebook (see Blackboard)

BIOM2004 W3 Lecture 3

Write your definition of Cytokines here:

Bite 1

Cytokines:

Groups and Functions

Soluble Mediators = cytokines

Membrane receptors and counter-receptors

How do cells communicate?

stimulus

Cytokine gene

Cytokine

Cytokine Receptor

Gene activation

Cytokine-producing cell

Target cell

Biological effects

Autocrine action

Paracrine action

Endocrine action

Circulation

Cytokine effects

Activated macrophage

IL-12: activates NK cells, induces differentiation of CD4+ Th cells into Th1 cells

IL-8: Chemotactic factor – recruits neutrophils, basophils and T cells to site of infection

Systemic Effects

Local Effects

IL-1: Activates vascular endothelium and lymphocytes Local tissue destruction and increases access of effector cells into tissue

TNF: Activates vascular endothelium and increases vascular permeability – increased entry of IgG complement and cells to tissue and increase drainage to lymph nodes

IL-6: Lymphocyte activation and increased antibody production

IL-1: Fever and production of IL-6

TNFa: Fever, mobilisation of metabolites, shock

IL-6: Fever, acute-phase protein production

Inflammatory cytokines

Cytokine definition

Cytokine is the general term for a large group of molecules involved in signalling between cells during immune responses. Cytokines signal between lymphocytes, phagocytes, and other cells of the body.

  • All cytokines are proteins or glycoproteins
  • The different cytokines fall into a number of categories. The principal subgroups are: interferons, interleukins, chemokines and colony-stimulating factors.

Main functions of cytokines

  • Stimulators of immature lymphocyte growth and differentiation
  • Mediators of natural immunity
  • Regulators of mature lymphocyte activation, growth and differentiation
  • Regulators of immune-mediated inflammation

Cytokine redundancy

  • Redundant = different cytokines may have the same function, e.g.:

Cytokine pleotropism

  • Pleotropic = one cytokine having many functions, e.g.:

Cytokine regulation

  • Production of antagonistic cytokines, e.g. IL-10 inhibits the synthesis of TNFalpha
  • Production of dedicated inhibitor molecules, e.g. IL-1 receptor antagonist (IL-1ra) is produced by the same cells that secrete IL-1; IL-1 and IL-1ra compete for the same receptor
  • Cytokines may be regulated by activating proteases, e.g. during activation the amino terminus of TGFbeta is removed to release the active form of the cytokine

Interferons

Interferons

  • INTERFERONS LIMIT THE SPREAD OF CERTAIN VIRAL INFECTIONS. IFNs induce a state of antiviral resistance in uninfected cells. They are produced very early in infection and are important in delaying the spread of a virus until such time as the adaptive immune response has developed.
  • one group of interferons (IFNα and IFNβ) is produced by cells that have become infected by a virus;
  • another type, IFNγ, is released by activated Th1 cells.

Anti-virus cytokine response

Interferons (IFNs)

Induce resistance to viral replication in all host cells

Increase MHC Class I expression and antigen presentation in all cells

Activate NK cells to kill virus-infected cells

Virus-infected host cell

Interleukins

TCR

CD3

CD4

CD4+/T helper cell

TCR

CD3

CD4

Interleukin-2 (IL-2)

Interferon gamma (IFN)

TCR

CD3

CD4

Interleukin-5 (IL-5)

Interleukin-13 (IL-13)

Interleukin-4 (IL-4)

Th1 (T helper 1) – Cell mediated immune responses, e.g. intracellular bacteria, activate phagocytes

Th2 (T helper 2) – Humoral immune responses, e.g. IgE production, activate B cells

Cytokines can be used to define

T cell subsets

  • INTERLEUKINS are a large group of cytokines produced mainly by T cells

CYTOKINE SECRETION FROM T-helper CELLS CONTROLS B CELL PROLIFERATION AND DIFFERENTIATION

B cell development is influenced by cytokines from T cells and APCs, and by direct interactions with Th2 cells. IL-4 is most important in promoting division, and a variety of cytokines including IL-4, IL-5, IL-6, IL-10, and IFNγ influence development into antibody-forming cells (AFCs).

Colony stimulating factors

Bone Marrow

Blood

Pluripotent hematopoietic stem cell

neutrophil

monocyte

GM-CSF

Granulocyte/ macrophage progenitor

M-CSF

G-CSF

Granulocyte/macrophage colony stimulating factor (GM-CSF)

Macrophage colony stimulating factor (M-CSF)

Granulocyte colony stimulating factor (G-CSF)

CS factors

  • COLONY STIMULATING FACTORS (CSFs) DIRECT THE DIVISION AND DIFFERENTIATION OF LEUKOCYTE PRECURSORS

Chemokines

Chemokines

  • Chemokines regulate normal cell traffic, tissue architecture, and inflammatory cell recruitment. The two largest chemokine families are designated CCL or CxCL, distinguished by the arrangement of their cysteine residues. CCL chemokines attract monocytes, lymphocytes and eosinophils. Most CxCL chemokines attract neutrophils, although some act on lymphocytes.
  • CCL11 – Eotaxin – attract eosinophils
  • CxCL8 – IL-8 – attracts neutrophils

Other cytokines

  • OTHER CYTOKINES INCLUDE TNF α AND TNF β, AND TGF β

What Can Go Wrong with Cytokines?

Discuss an example of cytokine dis-regulation here:

How does cytokine storm start?

Toxic shock syndrome (cytokine storm)

This occurs due to overproduction of cytokine during bacterial infection. This condition may develop within few hours following infection (e.g. by E coli, Klebsiella pneumoniae, Neisseria meningitidis). The symptoms of septic shock include drop in blood pressure, diarrhea, fever and hemorrhagic blood clotting in various organs.

The reason for septic shock is bacterial endotoxins stimulate macrophages to over produce IL-1 and TNF-alpha.

Anti-cytokine therapy in RA

  • Rheumatoid arthritis (RA) is an autoimmune disease characterised by inflammation of the joints and a progressive loss of joint function.
  • New therapies for RA include the use of anti-cytokine reagents to block the action of TNFalpha or IL-1beta, e.g. Etanercept is a recombinant protein consisting of a portion of a TNF receptor fused to the Fc portion of human immunoglobulin IgG to prolong its circulating half-life.

Disfunctions of cytokine receptors

Polymorphisms in the genes encoding cytokine receptors have been shown to correlate with an increased susceptibility to:

  • infection;
  • severe combined immune deficiency (SCID); and
  • inflammatory conditions.
  • Further examples are the mutations in the IFNγ receptor (IFNγR) or IL-12 receptor (IL-12R), which increase susceptibility to mycobacterial infection.

BIOM2004 W4 Lecture 4

Cells of Innate Immune Response

Dr R Furmonaviciene

  • Learning Outcomes:
  • Discuss the cell types involved in innate immune response
  • Discuss briefly how these cells recognise antigens
  • Actively participate in pre-session, during-session and post-session learning; to start using OneClass Notebook (see Blackboard)

Write your summary here:

Bite 1

Cells of Innate Immune Response:

Cell types and Functions

Learning Outcomes

To discuss the functions

of

NK cells,

phagocytes,

dendritic cells

What Key Cells Types Participate in an Immune Response?

The mechanisms of innate immunity provide the initial defense against infections. Adaptive immune responses develop later and consist of activation of lymphocytes. The kinetics of the innate and adaptive immune responses are approximations and may vary in different infections.

Innate and adaptive immunity

Cellular

Immune

response

Cellular

Humoral

Humoral

Key Cells and Proteins Involved in an Immune Response

  • Innate immune response involves key cell types:
  • Dendritic cells, phagocytes, NK cells, basophils, eosinophils
  • Adaptive immune response involves
  • B cells and T cells (lymphocytes)
  • Cytokines (defensive proteins and peptides) are produced by all cells mentioned
  • Antibodies are produced by B cells only

Cells of the innate immune system:

Neutrophils have multilobed nucleus, because of which these cells are also called polymorphonuclear leukocytes, and the faint cytoplasmic granules.

Phagocytose pathogens

Inflammatory cells

Phagocytes: Neutrophils, Monocytes and Macrophages

Microbes may be ingested by different membrane receptors of phagocytes; some directly bind microbes, and others bind opsonised microbes. The microbes are internalised into phagosomes, which fuse with lysosomes to form phagolysosomes, where the microbes are killed by reactive oxygen and nitrogen intermediates and proteolytic enzymes. NO, nitric oxide; ROS, reactive oxygen species.

Phagocytosis

Notatki:

Microbes may be ingested by different membrane receptors of phagocytes; some directly bind microbes, and others bind opsonized microbes.

The microbes are internalised into phagosomes, which fuse with lysosomes to form phagolysosomes, where the microbes are killed by reactive oxygen and nitrogen intermediates and proteolytic enzymes.

Phagocytosis is an active, energy-dependent process of engulfment of large particles (>0.5 μm in diameter). Microbial killing takes place in the vesicles formed by phagocytosis, and in this way, the mechanisms of killing, which could potentially injure the phagocyte, are isolated from the rest of the cell.

  • NK cells recognize ligands on infected cells or cells undergoing other types of stress, and kill the host cells. In this way, NK cells eliminate reservoirs of infection as well as dysfunctional cells.
  • NK cells respond to IL-12 produced by macrophages and secrete IFN-gamma, which activates the macrophages to kill phagocytosed microbes.

NK cell

functions

Role of dendritic cells in antigen capture and presentation

Notatki:

Mature dendritic cells express high levels of class II MHC molecules with bound peptides as well as co-stimulators required for T cell activation (APCs – Antigen Presenting Cells).

This process of maturation can be reproduced in vitro by culturing bone marrow-derived immature dendritic cells with cytokines (such as tumour necrosis factor and granulocyte-macrophage colony-stimulating factor) and microbial products (such as endotoxin).

Thus, by the time these cells become resident in lymph nodes, they have developed into potent APCs with the ability to activate T lymphocytes. Naive T cells that recirculate through lymph nodes encounter these APCs. T cells that are specific for the displayed peptide-MHC complexes are activated, and an immune response is initiated.

Resting (immature) dendritic cells express membrane receptors that bind microbes, such as mannose receptors. Dendritic cells use these receptors to capture and endocytose microbial antigens, and begin to process the proteins into peptides capable of binding to MHC molecules.

Dendritic cells also express Toll-like receptors that recognise microbial molecules and activate the cells to secrete cytokines and start their process of maturation.

Dendritic cells that are activated by microbes and by locally produced cytokines, such as tumor necrosis factor, lose their adhesiveness for epithelia and begin to express a chemokine receptor called CCR7 that is specific for chemokines produced in the T cell zones of lymph nodes. The chemokines attract the dendritic cells bearing microbial antigens into the T cell zones of the regional lymph nodes.

Receptors of Innate Recognition

Receptors have broad recognition (poly-specific)

Dendritic Cell Toll-like receptors (TLRs) recognize a wide variety of PAMPs

The basic steps in TLR signaling, illustrated only for TLR2 and TLR4, are applicable to all TLRs.

TLRs

https://www.frontiersin.org/articles/10.3389/fimmu.2016.00556/full

Innate and Adaptive Immunity Timeline

(Paper link – optional extra reading)

What Can Go Wrong with Cells of Innate Immune Response? Dendritic cells and Monocytes in Atherosclerosis

Immunity 2017 47, 621-634DOI: (10.1016/j.immuni.2017.09.008)

https://www.cell.com/immunity/fulltext/S1074-7613(17)30419-3

Macrophages and DCs may contribute to plaque formation

Paper link – optional extra reading

Notatki:

Regulation of Innate Immune Processes Related to Monocyte-Macrophages in Atherosclerosis

Lesional macrophages originate from bone-marrow-derived hematopoietic stem and progenitor cells (HSPCs), which give rise to circulating monocytes. In certain instances, these stem cells first populate the spleen and then undergo extramedullary hematopoiesis. Proliferation and release of HSPCs can be exacerbated by elevated cellular cholesterol and by somatic mutations leading to clonal hematopoiesis, such as those that occur in aging and myeloproliferative disease (MPD). This process can also be stimulated by stress-induced activation of the sympathetic nervous system (SNS). The major subpopulation of monocytes that contribute to atherosclerosis progression are Ly6chi monocytes, which enter lesions in response to subendothelially retained apolipoprotein-B-containing lipoproteins (LPs) and subsequent chemokine release by activated endothelial cells. After differentiation into macrophages, these myeloid cells undergo a variety of phenotypic changes under the influence of the factors listed in the figure. Those macrophages on the inflammatory end of the spectrum secrete proteins and carry out processes that promote atherosclerosis progression, whereas those on the resolution end of the spectrum promote lesion regression.

Do you remember an example of a cytokine and it’s function?

Inflammation and Immunobiology

(BIOM2004)

T CELLS

Dr Naomi Martin

HB 1.32

naomi.martin@dmu.ac.uk

  • Aims: to learn more about T lymphocytes
  • Learning objectives:
  • Describe and discuss T cell structure and function
  • Describe and discuss T cell development
  • Describe and discuss T cell activation and the function of different types of T cell

LEARNING AIMS & OBJECTIVES

This defence can be NON-SPECIFIC or SPECIFIC

  • This defence can be NON-SPECIFIC or SPECIFIC
  • Non-specific mechanism of defence
  • Does not distinguish between infective agents

THE IMMUNE SYSTEM

LO: to learn more about T lymphocytes

This defence can be NON-SPECIFIC or SPECIFIC

  • This defence can be NON-SPECIFIC or SPECIFIC
  • Specific mechanisms of defence
  • Responds specifically to particular infective agents

THE IMMUNE SYSTEM

LO: to learn more about T lymphocytes

A small leukocyte (white blood cell) with a single round nucleus, occurring especially in the lymphatic system

  • A small leukocyte (white blood cell) with a single round nucleus, occurring especially in the lymphatic system
  • Role in specific immune defence
  • MAIN JOB IS TO FIGHT INFECTION

LYMPHOCYTES

LO: to learn more about T lymphocytes

Cellular immunity is mediated by T cells

  • Cellular immunity is mediated by T cells
  • Same lineage as B cells – progenitor identical
  • Depends on where it becomes immunocompetent
  • T cells develop in the Thymus
  • T cells do not produce antibodies

T LYMPHOCYTES

LO: Describe and discuss T cell structure and function

T cells have antigen receptors that are structurally related to antibodies

  • T cells have antigen receptors that are structurally related to antibodies

T LYMPHOCYTES

LO: Describe and discuss T cell structure and function

T cells have antigen receptors that are structurally related to antibodies

  • T cells have antigen receptors that are structurally related to antibodies

T LYMPHOCYTES

LO: Describe and discuss T cell structure and function

Develop in the Thymus (in the upper chest)

  • Develop in the Thymus (in the upper chest)
  • Each T cell possesses a unique antigen-binding molecule called the T cell receptor (TCR)

T LYMPHOCYTES

LO: Describe and discuss T cell structure and function

These antigen receptors help recognise antigens only in the form of peptides displayed on the surface of antigen-presenting cells

  • These antigen receptors help recognise antigens only in the form of peptides displayed on the surface of antigen-presenting cells

T LYMPHOCYTES

LO: Describe and discuss T cell structure and function

Only recognise antigen that is bound to cell membrane proteins called major histocompatibility complex (MHC) molecules.

  • Only recognise antigen that is bound to cell membrane proteins called major histocompatibility complex (MHC) molecules.

T LYMPHOCYTES

LO: Describe and discuss T cell structure and function

A number of different subsets exist – defined by surface antigens, function or cytokine production

  • A number of different subsets exist – defined by surface antigens, function or cytokine production
  • MHC class I (found on all nucleated cells)
  • MHC class II (found on APC)
  • MHC class III (found on hepatocytes, macrophages)

T LYMPHOCYTES

LO: Describe and discuss T cell structure and function

T CELL DEVELOPMENT

LO: Describe and discuss T cell development

Thymus section showing lobular organization:

This section shows the two main areas of the thymus lobule – an outer cortex of immature cells (C) and an inner medulla of more mature cells (M).

T CELL DEVELOPMENT

LO: Describe and discuss T cell development

Selection of the T cell repertoire occurs in the thymus

  • Selection of the T cell repertoire occurs in the thymus
  • Recognition
  • CENTRAL TOLERANCE
  • Mechanism whereby the immune system is impaired in its response to respond to self-antigens
  • Many T cells are eliminated
  • Selection mechanisms operate to shape the T-cell repertoire

T CELL MATURATION

LO: Describe and discuss T cell development

Positive selection

Positive selection

only T cells with a receptor that bind with affinity to self-peptide MHC survive – others are eliminated by apoptosis – ENSURES MHC RECOGNITION

Negative selection

T cells with a receptor that bind with high avidity to self-antigen or self-antigen presented by MHC undergo apoptosis – ENSURES SELF-TOLERANCE

T CELL MATURATION

LO: Describe and discuss T cell development

T cell precursor goes from bone marrow to the thymus

  • T cell precursor goes from bone marrow to the thymus
  • In the cortex of the thymus, positive selection occurs
  • This is a check to see if the T cells interact with MHC
  • Cells that are able to interact with MHC receive survival signals
  • Those that do not interact do not receive a survival signal and die by apoptosis

T CELL MATURATION

LO: Describe and discuss T cell development

Those T cells which interact with MHC class I are differentiated into CD8 or cytotoxic T cells

  • Those T cells which interact with MHC class I are differentiated into CD8 or cytotoxic T cells
  • T cells which interact with MHC class II are differentiated into CD4 or helper T cells

T CELL MATURATION

LO: Describe and discuss T cell development

Differentiated T cells now go to the medulla of the thymus

  • Differentiated T cells now go to the medulla of the thymus
  • Negative selection occurs in the medulla
  • This checks how well the T cells bind with self MHC peptides

T CELL MATURATION

LO: Describe and discuss T cell development

M

If this interaction is too strong, the cell will not receive survival signals and will undergo apoptosis

  • If this interaction is too strong, the cell will not receive survival signals and will undergo apoptosis
  • Without this negative selection, self-reactive T cells capable of inducing autoimmune diseases are produced
  • Mature T cells are then released to the lymph nodes

T CELL MATURATION

LO: Describe and discuss T cell development

After passing through these checks of positive and negative selection, the T cells are released into the lymph nodes and are now mature naïve T cells

  • After passing through these checks of positive and negative selection, the T cells are released into the lymph nodes and are now mature naïve T cells

T CELL MATURATION

LO: Describe and discuss T cell development

On recognition of peptide-MHC by their TCR, a naïve T cell (Th0) becomes activated  differentiate  proliferate

  • On recognition of peptide-MHC by their TCR, a naïve T cell (Th0) becomes activated  differentiate  proliferate
  • The activation required recognition of antigens displayed on APCs, co-stimulators and cytokines produced by the APCs and the T cells themselves
  • These signals tell the cells what to do

LO: Describe and discuss T cell activation and the function of different types of T cell

T CELL ACTIVATION

  • They become differentiated into distinct populations

LO: Describe and discuss T cell activation and the function of different types of T cell

T CELL ACTIVATION

  • Clustering of surface receptors such as TCR, CD4, CD28 and CD45 results in activation of intracellular signal transducers

Three signals are necessary for full T cell activation

  • Three signals are necessary for full T cell activation
  • SIGNAL 1: generated by the interaction of MHC-peptide with the TCR
  • The interaction between the TCR and ag/MHC alone is not enough to sustain the contact between the T cells and APC

LO: Describe and discuss T cell activation and the function of different types of T cell

T CELL ACTIVATION

  • SIGNAL 2: generated by the interaction of CD28 on the T cell and members of the B7 family on the APC; this is called the co-stimulatory signal
  • Integrins and their receptors on the T cell and APC strengthen this interaction so that the TCR and CD28 can receive prolonged and sustained signals

LO: Describe and discuss T cell activation and the function of different types of T cell

T CELL ACTIVATION

SIGNAL 3: cytokine stimulation

  • SIGNAL 3: cytokine stimulation
  • Signals through the integrins also enhance T cell activation

LO: Describe and discuss T cell activation and the function of different types of T cell

T CELL ACTIVATION

HELPER TH (CD4+) cells secrete cytokines which stimulate the proliferation and differentiation of T cells, B cells, macrophages & other leukocytes

  • HELPER TH (CD4+) cells secrete cytokines which stimulate the proliferation and differentiation of T cells, B cells, macrophages & other leukocytes
  • Helper T cells release molecules which warn the immune system of the presence of a danger

LO: Describe and discuss T cell activation and the function of different types of T cell

TYPES OF T CELLS – HELPER TH

In 1986, Mosmann and colleagues observed that individual clones of helper T cells could be separated into two classes depending upon the specific cytokines the cells secrete in response to antigenic stimulation

  • In 1986, Mosmann and colleagues observed that individual clones of helper T cells could be separated into two classes depending upon the specific cytokines the cells secrete in response to antigenic stimulation

LO: Describe and discuss T cell activation and the function of different types of T cell

TYPES OF T CELLS – HELPER TH

T.R. Mosmann, et al., “Two types of murine helper T cell clone: I. Definition according to profiles of lymphokine activities and secreted proteins,” Journal of Immunology, 136:2348-57, 1986.

The two helper T cell classes also differ by the type of immune response they produce:

  • The two helper T cell classes also differ by the type of immune response they produce:
  • Th1 cells primarily produce interferon (IFN)-ɣ and interleukin (IL)-2
  • Th1 cells – generate responses against intracellular parasites such as bacteria and viruses, cell-mediated responses

LO: Describe and discuss T cell activation and the function of different types of T cell

TYPES OF T CELLS – HELPER TH

Th2 cells produce IL-4, IL-5, IL-6, IL-10, and IL-13

  • Th2 cells produce IL-4, IL-5, IL-6, IL-10, and IL-13
  • Th2 cells – produce immune responses against helminths and other extracellular parasites, humoral response e.g. IgE production

LO: Describe and discuss T cell activation and the function of different types of T cell

TYPES OF T CELLS – HELPER TH

Interestingly, the cytokines produced by each Th subset tend to both stimulate production of that Th subset and inhibit development of the other Th subset.

  • Interestingly, the cytokines produced by each Th subset tend to both stimulate production of that Th subset and inhibit development of the other Th subset.
  • IFN-ɣ produced by Th1 cells has the dual effect of both stimulating Th1 development and inhibiting Th2 development.
  • Th2-secreted IL-10 has the opposite effect.

LO: Describe and discuss T cell activation and the function of different types of T cell

TYPES OF T CELLS – HELPER TH

CYTOTOXIC Tc (CD8+) cells kill cells that produce foreign antigens

  • CYTOTOXIC Tc (CD8+) cells kill cells that produce foreign antigens
  • Attach themselves to other cells in the body, if this cell is diseased or pathogenic, the T cell will either
  • Force the cell to undergo apoptosis
  • Secrete enzymes which will kill the cell

LO: Describe and discuss T cell activation and the function of different types of T cell

TYPES OF T CELLS – CYTOTOXIC TC

Responsible for the direct killing of infected, damaged, and dysfunctional cells, including tumour cells

  • Responsible for the direct killing of infected, damaged, and dysfunctional cells, including tumour cells
  • Once inside cells, these pathogens are not accessible to antibodies and can be eliminated only by the destruction or modification of the infected cells on which they depend
  • Powerful and accurately targeted

LO: Describe and discuss T cell activation and the function of different types of T cell

TYPES OF T CELLS – CYTOTOXIC TC

Cytotoxic T cells kill their targets by programming them to undergo apoptosis (nuclear fragmentation)

  • Cytotoxic T cells kill their targets by programming them to undergo apoptosis (nuclear fragmentation)
  • Recognise
  • Peptide fragments
  • MHC I
  • Cytotoxins

LO: Describe and discuss T cell activation and the function of different types of T cell

TYPES OF T CELLS – CYTOTOXIC TC

https://highered.mheducation.com/sites/0072495855/student_view0/chapter24/animation__cytotoxic_t-cell_activity_against_target_cells__quiz_1_.html

LO: Describe and discuss T cell activation and the function of different types of T cell

TYPES OF T CELLS – CYTOTOXIC TC

  • Calcium-dependent release of specialized lytic granules
  • e.g. perforin – forms transmembrane pores
  • e.g. granzymes – act as digestive enzymes

CD4+ helper T cells bind to MHC class II molecules

  • CD4+ helper T cells bind to MHC class II molecules
  • Found on mononuclear phagocytes, B cells, dendritic cells
  • CD8+ cytotoxic T cells bind to MHC class I molecules
  • Found on all nucleated cells (including cells expressing MHC II)

T CELL RECEPTOR

LO: Describe and discuss T cell activation and the function of different types of T cell

Consists of 2 polypeptides α and β, or γ and δ

  • Consists of 2 polypeptides α and β, or γ and δ
  • Each polypeptide chain has 2 regions (1 variable, 1 constant)
  • Each T cell has a unique TCR on its surface
  • Hundreds of millions
  • Similar to immunoglobulin chains
  • Variable and constant regions = diversity

T CELL RECEPTOR

LO: Describe and discuss T cell activation and the function of different types of T cell

α β

  • α β
  • Recognise antigens BUT only in conjunction with MHC proteins (immunoglobulins recognise free antigens)
  • The complementary determining regions form the binding site for antigen/MHC molecule

T CELL RECEPTOR

LO: Describe and discuss T cell activation and the function of different types of T cell

Small subset of T cells, about 1-5% total T cell population

  • Small subset of T cells, about 1-5% total T cell population
  • TCR glycoproteins ɣδ, instead of αβ
  • Enriched (>50 % of the T cell population) in epithelial cell-rich compartments like skin, the digestive tract, and reproductive organ mucosa

LO: Describe and discuss T cell activation and the function of different types of T cell

TYPES OF T CELLS – GAMMA DELTA Tɣδ

Role in immunoregulation & immunosurveillance

  • Role in immunoregulation & immunosurveillance
  • Cytotoxic
  • Kill infected & activated cells
  • Engage death receptors (FAS)
  • Release cytotoxic effector molecules (Perforin)
  • Undergo functional programming in the thymus
  • Sense cellular stress
  • Contribute to different stages of the inflammatory response
  • Major role in RESOLUTION of the immune response

LO: Describe and discuss T cell activation and the function of different types of T cell

TYPES OF T CELLS – GAMMA DELTA Tɣδ

Not MHC restricted

  • Not MHC restricted
  • Recognise whole proteins rather than peptides
  • Role in the resolution of the immune response
  • Functions of γδ T cells differ according to = functional plasticity
  • their tissue distribution
  • the structure of their antigen receptors
  • how and what stage of the immune response they have become activated

TYPES OF T CELLS – GAMMA DELTA Tɣδ

  • Aims: to learn more about T lymphocytes
  • Learning objectives:
  • Describe and discuss T cell structure and function
  • Describe and discuss T cell development
  • Describe and discuss T cell activation and the function of different types of T cell

LEARNING AIMS & OBJECTIVES

Adaptive Immunity: B Cells

BIOM2004

Week 6

Adaptive Immunity: B Cells How B Cells Contribute to an Immune Response? Learning aims: How do B cells get activated? How different antibody classes protect us from pathogens?

A. Light micrograph of a plasma cell in tissue. B. Electron micrograph of a plasma cell. (Courtesy of Dr. Noel Weidner, Department of Pathology, University of California, San Diego, California.)

Morphology of Activated B Cells

Activated B lymphocytes become plasma cells or activated B cells, secreting immunoglobulins (or antibodies)

The activation of B cells is initiated by specific recognition of antigens by the surface Ig receptors of the cells. Antigens stimulate the proliferation and differentiation of the specific B cell clone. Depending on the antigen, different classes of antibodies can be produced.

B Cell Clonal Expansion

Changes in Antibody Structure during B Cell Activation

In the course of immune response, depending on the signals, coming to B cells, antibody structures may change which will result in stronger binding or secretion of different antibody class.

Antibody Structure and Function

IgG molecule

Antibody model by Mike Clark

https://www.csap.cam.ac.uk/network/mike-clark/

Antibodies have 2 functions

Function 1:

To bind specifically to pathogen/antigen – mediated via the variable region (V region). Thereby each antibody recognises a unique antigen (Ag) to give a total repertoire large enough to recognise almost anything.

Antigen binding

  • This model of lysozyme bound to an antibody molecule. The heavy chains of the antibody are colored red, the light chains are yellow, and the antigen is colored blue.

Antigen Binding

Cellular Receptor Binding

Function 2:

To recruit other cells and molecules of the immune system – feature of the constant region (C region) of the Ab – 5 main forms of C region – one for each Ab ‘type’. However, for membrane bound Ab the C region is inserted into the membrane – once V region recognises Ag the C region transmits a signal that activates the B cell.

Biological activity

Protective Functions of Antibodies

Receptors for IgG have either two or three extracellular immunoglobulin domains.

Motifs (ITAM, ITIM) on the intracellular segments or on associated polypeptides are targets for tyrosine kinases involved in initiating intracellular signaling pathways.

Fc receptors

Immunoglobulin Structure

Heavy chain

Light chain

Immunoglobulin G (IgG)

Molecular weight approximately 150 kilodalton (kDa)

composed of 2 heavy chains of 50kDa each and 2 light chains of 25kDa each

heavy chains linked by disulphide bonds and each heavy chain linked to light chain by disulphide bond

in any given antibody the 2 heavy chains and the 2 light chains are identical – so each antibody has 2 identical antibody binding regions

IgG molecules are cleaved by the enzymes papain (A) and pepsin (B) at the sites indicated by arrows. Papain digestion allows separation of two antigen-binding regions (the Fab fragments) from the portion of the IgG molecule that binds to complement and Fc receptors (the Fc fragment). Pepsin generates a single bivalent antigen-binding fragment, F(ab’)2.

Proteolytic fragments of an IgG molecule

The 5 classes of immunoglobulins are distinguished by the Constant region of their heavy chains

ClassHeavy chainSubclassesLight Chain
IgGgg1, g2, g3, g4k or l
IgMmNonek or l
IgAaa1, a2k or l
IgEeNonek or l
IgDdNonek or l

Minor differences in the amino acid sequences of the a and g heavy chains leads to categorisation of subclasses

Five classes – G, M, A, E, D

Immuno-globulinIgGIgMIgAIgEIgD
Normal Levels (mg/dl)620 – 140045 – 25080 – 3500.002 – 0.20.3 – 3.0

IgG: Most abundant class in serum (about 80%) – IgG1 > IgG2 > IgG3 > IgG4.

IgG1 and IgG3 bind with high affinity to Fc receptors on phagocytic cells for opsonisation (IgG 4 intermediate and IgG 2 low).

IgG3 is the most effective complement activator (then IgG1; IgG2 less efficient and IgG4 can’t).

IgG1, IgG3 and IgG4 readily cross the placenta and have an important role in protecting the fetus (passive immunity).

  • A model of IgG1
  • IgG3
  • IgM H chains have five domains with disulfide bonds cross-linking adjacent Ch3 and Ch4 domains.
  • IgA. The J chain is required to join the two subunits.
  • This diagram of IgD shows the domain structure and a characteristically large number of oligosaccharide units.
  • IgE.

Different Structures of Different Antibody Classes

Immunoglobulin M (IgM)

  • 5% to 10% of total serum Ig.
  • Monomeric IgM is membrane bound on B cells.
  • Plasma cells secrete pentameric IgM (5 monomers held together by a J (joining) chain.
  • IgM is the first class produced in a primary response to antigen

Y

Y

Y

Y

Y

Y

Monomeric

Pentameric

(1) In free solution, deer IgM adopts the characteristic star-shaped configuration.

(2) IgM antibody (arrow) in ‘crab-like’ configuration with partly visible central ring structure bound to a poliovirus virion.

IgA

Only 10% to 15% of total serum Ig.

BUT predominant class in external secretions (breast milk, saliva, tears and mucus in bronchial, genitourinary and digestive tracts).

Daily production of IgA is greater than for any other class.

Secretory IgA in secretions – dimer of tetramer with a J chain and secretory component.

Binding to bacterial and viral surface antigens prevents attachment of pathogens to mucosal cells.

Y

Y

Y

Y

Mast Cell

Fc Receptor specific for IgE

Granule

IgE

Allergen

Immunoglobulin E

IgE serum levels are elevated in people with parasite infection or allergy (eczema, hay fever, asthma, anaphylactic shock).

IgE binds to Fc receptors on blood basophils and tissue mast cells – cross-linking by allergen induces release of granule contents (pharmacologically active mediators).

Immunoglobulin D

  • About 0.2% of total serum immunoglobulin.
  • Together with IgM is the major membrane bound Ig expressed by mature B cells.
  • No biological effector function has been described for IgD.

Antibodies can be designed and used for diagnostics and therapy

Search research papers to find an example of an antibody used in diagnostic test – optional task for your independent extra reading

Immunoglobulins (Ig) or antibodies are:

  • produced by B cells
  • become secreted – circulating antibodies
  • when membrane bound act as B cell surface receptor (BCR)
  • all activated B cells produce a vast array of Ig/Ab with a variety of antigen specificities
  • BUT each B cell produces Ig/Ab with a single specificity (produced Abs bind one antigen)

Summarising Comments

Please use module Discussion Board for your questions or message me on MS Teams 

BIOM2004 W1 Lecture 1

Introduction to the Inflammation and Immunobiology Module

Dr R Furmonaviciene

  • Learning Outcomes:
  • To clarify all doubts about the learning goals, study themes and assessments; to be able to tell your colleagues this information
  • To discuss your ideas about how immune system is activated
  • To actively participate in pre-session, during-session and post-session learning

BIOM2004 W1 Lecture 1

  • Learning themes and sessions
  • Finding your way online
  • Assessments
  • Communication
  • All can be found on Blackboard site of the module,

BIOM2004 Module Content

How many credits?

How many lecturers?

How many assessments?

When is the first assessment due?

How many credits?

How many credits?

How many lecturers?

How many lecturers?

Find the answer in ‘Staff Contacts’

On Blackboard

How many assessments?

How many assessments?

Look for the answer in the module Template

(Information about the module site on Blackboard)

Quiz (MCQs)

Exam

When is the first assessment due?

When is the first assessment due?

We have formative (unmarked) assessments to help you to prepare for the summative ones (marked)

Formative Quiz (MCQ) Week 4 (some examples of MCQs)

Summative Quiz (MCQ) Week 29

We will give you all the details closer to the dates – please attend all sessions

Study Materials for Lecture 1:

  • You Tube video about P Matzinger (available on Blackbaord) (compulsory)
  • Conversation with P Matzinger text (available on Blackboard)

  • Which answers are right?

Quick Quiz about Polly Matzinger after you examined the pre-session material about her 

Legends of allergy/immunology: Polly Matzinger

Allergy, Volume: 75, Issue: 8, Pages: 2136-2138, First published: 21 January 2020, DOI: (10.1111/all.14191)

Notatki:

Danger Model. Professional antigen‐presenting cells (Macrophages or DC) are activated to stimulate T cells by endogenous cellular alarm signals released from distressed or damaged cells

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How immune system gets activated?

Immune system is activated by molecular patterns signaling danger, e.g.:

bits of RNA or DNA,

hydrophobic molecules,

proteolytic enzymes

What parts of immune system react to danger?

P Matzinger mentions lymph nodes,

B, T, dendritic cells,

MHC molecules as being involved in an immune response

Give some examples of danger signals and non-dangerous events (these will not triger immune response)

Danger signals: e.g.: allergens which are harmful proteins or they may mimic danger- signalling molecules; microbial, viral proteins

Non-dangerous events: development of the fetus, apoptosis during development of the fingers, where unnecessary cells disappear by apoptosis

  • Structure?
  • Function?
  • Activation?

Suggest your best definition of the ‘Immune System’…

Immune system is composed of organs, cells and molecules

Immune system is activated by danger signals

Organs, cells and molecules work together as a defensive network

Final Task:

Read the following paper

https://www-proquest-com.proxy.library.dmu.ac.uk/docview/2434147450?OpenUrlRefId=info:xri/sid:summon&accountid=10472

Damage-associated molecular patterns in trauma

Borna, ReljaLand Walter Gottlieb.European Journal of Trauma and Emergency Surgery; Heidelberg Vol. 46, Iss. 4,  (Aug 2020): 751-775. DOI:10.1007/s00068-019-01235-w

and answer the question below:

How Can Danger-Associated Molecular Patterns (DAMPs) promote tissue healing?

Study Materials for Lecture 2:

Read the following paper

https://www-proquest-com.proxy.library.dmu.ac.uk/docview/2434147450?OpenUrlRefId=info:xri/sid:summon&accountid=10472

Damage-associated molecular patterns in trauma

Borna, ReljaLand Walter Gottlieb.European Journal of Trauma and Emergency Surgery; Heidelberg Vol. 46, Iss. 4,  (Aug 2020): 751-775. DOI:10.1007/s00068-019-01235-w

and answer the question below:

How Can Danger-Associated Molecular Patterns (DAMPs) promote tissue healing?

Dr Umakhanth Venkatraman GIRIJA

umakhanth.venkatramangirija@dmu.ac.uk

Complement

in the

Immune system

C

C

C

C

BIOM2004

Inflammation & Immunobiology

Learning ObjectivesLearning Outcomes
1. Complement components & activationWhat is complement pathway?Which cells produce complement proteins?What are the different types of pathways ?What are the different target recognition mechanisms?How do the pathways get activated?What are the various effector mechanisms and the fate of the target cells?
2. Regulation of ComplementWhat is Complement Regulation? Why is regulation of complement important?What are the types of complement regulators?Learn with examples

Targets Pathogens

  • Bacteria
  • Virus
  • Fungi
  • Protozoa

Targets Damaged Self-Cells

  • Physical damage
  • Chemical damage
  • Neoplasm

Importance

Complement, part of innate immune system, is a network of ~40 different proteins. It can recognise (bind) to and eliminate a wide range of target cells and also bridge adaptive immunity

How does Complement work

Complement, part of innate immune system,

is a network of ~40 different proteins.

They (have to) work via defined pathways to carefully eliminate pathogens and not human cells

The 40 different proteins have to work in an organised manner

What are Complement Pathways?

  • Biochemical pathways that are part of innate immune system
  • They ‘recognise’ pathogens or target cells via different ways
  • They ‘function’ via enzymatic cascade and ‘eliminate’ pathogens or target cells via various mechanisms

CLASSICAL

Pathway

It is based on recognition, complement pathways are classified in to three different types

LECTIN

pathway

ALTERNATIVE

Pathway

Where are Complement Proteins Produced?

LIVER

MACROPHAGES

  • Majority of the complement proteins are produced by liver and macrophages
  • They are also produced by endothelial/epithelial cells, cells of immune system such as dendritic cells, T- & B- lymphocytes, mast cells and Natural killer cells

Target recognition & activation

Enzymatic cascade

Target elimination

COMPLEMENT

Antigen-Antibody

Pathogen

C1q

C1r, C1s proteases

C1q, a multimeric protein in complex with

C1r & C1s proteases (C1-complex)

binds antigen-antibody complex

Target recognition & activation

Enzymatic cascade

Target elimination

Antibody ‘dependent’ pathway

C1q upon binding to a target undergoes a conformational change to activate the associated serine proteases C1r and C1s and this triggers an enzymatic cascade and the classical pathway

1

CLASSICAL

Pathway

Pathogen

Glycans are chains of sugars (also called as oligosaccharides) that decorate cell surface of both pathogens and human cells – but what is the key difference between them?

Human cell

Mannose sugar at terminal position in microbial glycan

Mannose sugar NOT at terminal position in human glycan

MBL

MBL

As a result, pathogen can be recognized by a protein called human mannose-binding lectin (MBL) via recognition of terminal mannose

Human cell cannot be recognized by human mannose-binding lectin (MBL)

Pathogen

Antibody ‘independent’ pathway

Lectins along with the partner proteases directly bind to carbohydrate structures on microbial or target cell surfaces; undergo a conformational change to trigger the enzymatic cascade and pathway

2

Mannose present at terminal position

MBL

Mannose-Binding Lectin (MBL) in complex with MBL-associated serine proteases (MASPs) bind pathogens directly via the terminal mannose sugars on the surface of pathogens

MASPs

Target recognition & activation

Enzymatic cascade

Target elimination

LECTIN

pathway

Pathogen

H2O

C3

Spontaneous hydrolysis of C3 protein

generates C3b that binds to

–OH or –NH2 groups on pathogens

C3 is an abundant complement protein in the serum (~ 1.2 mg/ml)

There is constant hydrolysis of C3 in the serum, which in the presence of proteins factor B & properdin generate C3b and trigger the alternative pathway.

3

Target recognition & activation

Enzymatic cascade

Target elimination

C3b

ALTERNATIVE

Pathway

Antibody-Antigen

Pathogen

C1q

C1r, C1s proteases

MBL

Complement recognizes target cells via multiple ways and accordingly, the pathways are classified; Fill the boxes

1

2

3

MASPs

H2O

C3

C3b

Antibody-Antigen

Pathogen

C1q

C1r, C1s proteases

MBL

Complement recognizes target cells via multiple ways and accordingly, the pathways are classified

1

2

3

MASPs

H2O

C3

C3b

ALTERNATIVE

Pathway

CLASSICAL

Pathway

LECTIN

pathway

Target recognition & activation

Enzymatic cascade

Target elimination

C3b

Pathogen

2. Coats “Eat me signal”

Phagocyte

1. “Punches holes” and destroys

Pathogen

Pathogen

3. “Calls for help” from other cells

C3a

C5a

C3a

C5a

Target recognition & activation

Enzymatic cascade

Target elimination

1. “Punches holes” and destroys

Pathogen

Target recognition & activation

Enzymatic cascade

Target elimination

CLASSICAL pathway as an example

Explore more

Cytosol

Plasma membrane

Antigens

C4

Antibody

C2

C1

C4b

C4a

Released into blood/extracellular fluid (call for help)

C2b

C2a

C3 convertase

C3

C3b

C3a

C5

C5a

C5b

C6

C7

C8

Cell leakage and death

Poly C9

Membrane Attack Complex (MAC) (C5b-C9)

The Classical Pathway Cascade

Pathogen

CLASSICAL

ALTERNATIVE

LECTIN

The three pathways recognise targets differently, but converge at C3b and follow the same route to eliminate pathogens e.g. via cell lysis

Complement killing

E. coli

Lysed E. coli

(Electron microscopy image; Kuby, Immunology, 2003)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3820029/

SELF-DIRECTED LEARNING # 1

W7 Complement_DR GIRIJA

  • There are five major classes of antibodies. Which ones activate classical pathway of activation?
  • An antibody has Fc and Fab regions. Which of this region binds to C1q?

SELF-DIRECTED LEARNING # 2

W7 Complement_DR GIRIJA

You have now learnt that lectin pathway of complement is activated by mannose binding lectin (MBL) and MBL-associated serine proteases (MASPs). MBL recognises mannose on the target cell surface.

  • Are there any other components/proteins other than MBL that activate lectin pathway? Learn some examples along with what ligands they can recognise
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7408476/

C3b

Pathogen

2. Coats “Eat me signal”

Phagocyte

Target recognition & activation

Enzymatic cascade

Target elimination

Pathogen

Macrophages have C3b receptors and bind to C3b (complement fragment) coated on target cells during the enzymatic cascade process

What is the “Eat me” signal ?

C3b

Pathogen

C3b

C3b

Macrophage

C3b receptors

CLASSICAL

LECTIN

ALTERNATIVE

C3b

Coated by any or all of the three pathways

Formation of Phagosome

Fusion of Phagosome and lysosome to form phagolysosome

Macrophage engulfs C3b coated pathogen

Lysosomal enzymes degrade the pathogen-complement complex

Degraded fragments released as debris from macrophage

Complement C3b mediated phagocytosis is very effective in clearing pathogens

“Eat me signal”

Pathogen

3. “Call for help” from other cells

C3a

C5a

C3a

C5a

Target recognition & activation

Enzymatic cascade

Target elimination

Signals (phosphorylation)

C3b

C4b

C2a

C4b

C3d

C2a

CD19

CD21

B-cell

C3d receptor

B-cell activation and proliferation

Antibody production and Memory cell formation

By stimulating antibody production, Complement bridges innate and adaptive immune system. This is vital for mounting a strong and long lasting immune response towards invading pathogens.

Complement stimulates antibody production

Macrophage

Neutrophil

Basophil

Eosinophil

Mast cell

C3a

C5a

C3a

C5a

Call for help from other immune cells

Complement activation products such as C3a & C5a act as anaphylatoxins and interact with many other cells of immune system and can cause inflammation

Chemotaxis

Phagocytosis

Cytokine production

Degranulation

Oxidative burst

Learning ObjectivesLearning Outcomes
1. Complement components & activationWhat is complement pathway?Which cells produce complement proteins?What are the different types of pathways ?What are the different target recognition mechanisms?How do the pathways get activated?What are the various effector mechanisms and the fate of the target cells?
2. Regulation of ComplementWhat is Complement Regulation? Why is regulation of complement important?What are the types of complement regulators?Learn with examples

Complement

SELF

(Do NOT attack)

NON SELF

(Attack)

ALTERED SELF

(Attack)

What are Regulators of Complement Activation (RCA)?

Regulatory proteins bind to various complement components and inhibit their “inappropriate activation” by

  • destabilizing activation complexes
  • mediating specific proteolysis of activation-derived fragments

Inappropriate complement activation = (a) unnecessary pathway initiation and activation in the serum or extracellular fluid and (b) activation on self-cells

DAF

MAC-IP

MCP

Human cell

  • DAF = Decay Accelerating Factor (dissociates C3 convertase)
  • MAC-IP = Membrane Attack Complex – Inhibitory Protein (inhibits polymerization of C9)
  • MCP = Membrane Cofactor of Proteolysis (degrades C4b and C3b)
  • Pathogens, in general, do not have complement regulators.
  • Exception: They may adapt to innate immune system and acquire them

Membrane bound Regulators of Complement Activation prevent self-attack in a range of ways

Soluble Regulators in the plasma or extracellular fluid are recruited on host cell surface to prevent complement self-attack

C1 INH

Factor

I

Factor

H

Protein

S

SIALIC ACID (N-acetyl Neuraminic acid derivatives) and GLYCOSAMINOGLYCANS of Human Cell facilitate binding of regulators from blood

  • Difference in the cell surface carbohydrate composition of host versus microbial cells favours the host.
  • Pathogens generally lack or have significantly lower levels of sialic acid and hence cannot recruit complement regulators, thus susceptible to complement attack

Complement Lectures – Summary

Complement network provides front line immune defence against pathogens, altered self cells and allergens.

Complement can be initiated by Classical, Lectin and the Alternative pathways. They eliminate the targets cells by multiple mechanisms: Lysis, phagocytosis and cell signalling.

Human Complement regulation is very important to prevent self-damage. There are a number of membrane-bound and soluble complement regulators that prevent complement self-damage. Pathogens normally cannot use these human regulatory mechanisms, however there are exceptions.

http://www.annualreviews.org/doi/abs/10.1146/annurev-immunol-032713-120154

Complement general review

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4543182/pdf/kjped-58-239.pdf

Complement Regulation

Recommended books and journal articles:

Further reading

  • Abul K Abbas, Andrew H Lichtman and Shiv Pillai. Cellular and molecular ImmunologyElsevier, 2014, 8th edition
  • Owen, Punt and Stranford. Kuby Immunology; Palgrave Macmillian. 2015. 7th edition.
  • Peter J. Delves, Seamus J. Martin, Dennis R. Burton and Ivan M. Roitt. ROITT’S ESSENTIAL IMMUNOLOGY; 2011, 12th edition

Books

Dr Umakhanth Venkatraman GIRIJA

umakhanth.venkatramangirija@dmu.ac.uk

BIOM2004

Inflammation & Immunobiology

Major Histo Compatibility (MHC)

or Human Leukocyte Antigen (HLA)

Learning ObjectivesLearning Outcomes
1. Types, Structure and functionsWhat is MHC?What are the different types of MHC?What are the structural features of MHC proteins?What is the function of MHC and how is it important?What are polygenic and polymorphic properties of MHC? How are they important?
2. Antigen processing and presentationAntigen processing and presentation by MHC-IExpression of MHC-IMolecular processing and presentation of antigenic peptidesAntigen processing and presentation by MHC-IIExpression of MHC-IIMolecular processing and presentation of antigenic peptides

MHC

Organ Transplantation

is the process of taking organs from one individual to another individual

Genetically identical individuals

Genetically different individuals

Inherited Genes must be involved in the process of

transplant rejection

Notatki:

Transplantation of organs, cells and tissues between genetically identical individuals are accepted, while that of between genetically different individuals were rejected. This showed that “inherited genes” must be involved in the process of rejection.

Major Histo Compatibility (MHC)

Tissue

Suitability / matching

Inherited Genes must be involved in the process of

transplant rejection

MHC complex

is a collection of genes arrayed within a long stretch of DNA on chromosome 6 in humans

MHC is called as Human Leukocyte Antigen (HLA) complex

MHC = HLA

Notatki:

The human MHC was discovered by searching for cell surface molecules in one individual that would be recognized as foreign by another individual. It was discovered that individuals who had received multiple blood transfusions and patients who had received kidney transplants contained antibodies that recognised cells from the blood or kidney donors. The proteins recognized by these antibodies were called human leukocyte antigen (HLA).

Long arm

Short arm

Chromosome 6

MHC Class II

MHC Class I

  • Class I and II have common structural features
  • Both have roles in antigen presentation

Class III

  • Class III include complement proteins and cytokines
  • Critical to immune function

MHC is of three types: Class I, II and III

2-micro globulin

Transmembrane segment

Cytoplasmic tail

1

2

3

Membrane-proximal domains (Ig-G like)

Membrane-

distal domains

1

2

1

2

(Peptide)-binding cleft

MHC Class I

MHC Class II

Notatki:

MHC class I: Composed of a polymorphic αlpha-chain (made up of three domains alpha-1,2 and 3) that are non-covalently attached to a non polymorphic Beta2-microglobulin.

MHC class II: composed of a polymorphic alpha-chain (made up of two domains alpha-1 and -2) non-covalently attached to a polymorphic beta chain (made p of two domains beta -1 and -2). The peptide binding groove is marked with arrows i.e. this is the region/cleft to which the peptides to be presented (displayed) will bind.

  • Ends of peptide binding cleft is CLOSED
  • Can accommodate only shorter peptides: 8-11 amino acids
  • Ends of peptide binding cleft is OPEN
  • Can accommodate longer peptides: 10-30 amino acids

MHC class I

MHC class II

Arrows indicate closed cleft (MHC-I) and open cleft (MHC-II);

Circles drawn to show the peptides which are reddish orange in colour

MHC presents both “SELF” and “NON-SELF” peptides

MHC displaying

“FOREIGN” peptides

  • To signal immune cells for elimination of pathogens

MHC displaying “SELF” peptides

  • To show the cell is healthy
  • To maintain tolerance to self-proteins

Pathogen

Human cell

DP

DQ

DR

B

A

C

1

Polygenic

  • Multiple MHC genes code for same function i.e. display peptides
  • Each MHC molecule can bind many peptides

DP

DQ

DR

B

A

C

1

DP

DQ

DR

B

A

C

1

Polymorphic

  • MHC genes are the most polymorphic genes in mammalian genome
  • As a result, MHC proteins are variable in individuals
  • >5000 MHC alleles have been estimated so far

DP

DQ

DR

B

A

C

1

MHC

Polymorphic

Polygenic

High degree of variability in the population

Fight range of microbial infections

MHC – Interesting Research Facts

Cheetahs have low MHC diversity

MHC – Interesting Research Facts

  • MHC genes are known to be involved in mate choice in a number of species (e.g. in fish, birds, mammals)
  • The more MHC variation seems to be preference for pairing
  • Outcome – species diversity

Learning ObjectivesLearning Outcomes
1. Types, Structure and functionsWhat is MHC? How was it discovered ?What are the different types of MHC?What are the structural features of MHC proteins?What is the function of MHC and how is it important?What are polygenic and polymorphic properties of MHC? How are they important?
2. Antigen processing and presentationAntigen processing and presentation by MHC-IExpression of MHC-IMolecular processing and presentation of antigenic peptidesAntigen processing and presentation by MHC-IIExpression of MHC-IIMolecular processing and presentation of antigenic peptides

MHC

MHC class I

MHC Class I expression is found throughout the body

  • ALMOST ALL NUCLEATED CELLS express MHC Class I
  • Constitutive expression
  • Red Blood Cells (RBCs) are non-nucleated and do not express MHC
  • Lymphocytes express highest levels of MHC Class I
  • 5 X 105 MHC Class I molecules per lymphocyte
  • Fibroblasts, muscle cells, liver cells and some neural cells express very low levels of MHC Class I

MHC-I

Intracellular human proteins

(Normal, Cancer)

Short Peptides

PROTEASOME

(Proteasomes are multiprotein enzyme complexes and are involved in Proteolytic degradation of proteins)

Viral infections

(always intracellular)

viral proteins synthesized intra-cellularly in the host (human)

(Chlamydia, Mycobacterium, Neisseria, Salmonella)

Some bacterial infections are also intracellular

MHC-I

How peptides are formed ?

(Endogenous pathway)

Notatki:

In the MHC class I pathway, protein antigens in the cytosol (self, intracellular bacteria or viruses) are processed by proteasomes and the generated peptides are transported into the endoplasmic reticulum (ER). Proteasomes are large multiprotein enzyme complexes with a broad range of proteolytic activity. They are found in the cytoplasm and nuclei of most cells. Its structure appears like a cylinder. It performs essential function in cells by degrading damaged and misfolded proteins. Proteasomes have been adapted to process foreign proteins so that they offer a specialized role in antigen presentation.

Transporter associated with Antigen Processing (TAP)

Endoplasmic

Reticulum

Golgi

MHC I

Displayed MHC I +

peptide recognized by cytotoxic T-cell (CD8+)

How MHC-I delivers the peptides on cell surface ? (Endogenous Pathway)

MHC-I

Notatki:

How MHC class-I delivers peptides on the cell surface? Proteins degraded by proteasome enter Endoplasmic Reticulum via TAP (Transporter associated with Antigen Processing), where they bind to MHC-I. MHC-I – peptide complex is then carried by golgi and presented on the cell surface via vesicles. Cytotoxic CD8+ T-cells recognize this complex and via T-cell receptor. CD8+ T-cell proliferates and releases enzymes like perforin, granulozymes which puncture or degrade the entire cell

  • Proteins degraded by proteasome enter ER via TAP, where they bind to MHC-I
  • MHC-I + peptide complex is carried by golgi and presented on cell surface
  • Cytotoxic CD8+ T-cells recognize this complex and via T-cell receptor
  • CD8+ T-cell proliferates and releases enzymes like perforin, granulozymes which puncture or degrade the entire cell

Viral / Intracellular bacteria infected cell / cancer cell has to die (cannot be repaired)

MHC-I

MHC class II

MHC-II

Extracellular bacteria or extracellular pathogens

Drugs bound to proteins

Soluble foreign antigens (allergens)

MHC class II presents peptides derived from …

MHC Class II expression – restricted to Antigen-Presenting Cells (APCs)

Dendritic Cells

Macrophages

B cells

Professional APCs

MHC Class II ExpressionConstitutiveNeed activation (TLR signalling)Constitutive

TLR – Toll Like Receptors are pattern recognition molecules on cell surfaces

MHC Class II expression – restricted to Antigen-Presenting Cells (APCs)

Non-Professional APCs

Fibroblasts (skin)

Glial cells (Brain)

Pancreatic beta cells

Thyroid epithelial cells

Vascular endothelial cells

  • Deputize professional APCs for short periods
  • When? During sustained inflammation
  • Require activation for expression of MHC II and costimulatory molecules

Lysosomal enzymes degrade bacterial proteins in phago-lysosomes

3

Toll Like Receptors (TLR)

Bacteria

Flagella

LPS

Lipo

peptides

1

Bacteria

Endosome

Lysosomes

2

Endoplasmic

Reticulum

Invariable chain occupies MHC-II binding site temporarily

4

Antigen Presenting Cell

Lysosomal enzymes also remove the invariable chain

6

Golgi

5

7

  • Free MHC II picks up the processed bacterial peptide
  • Special vesicular structure delivers the complex on cell surface

CD4+ T-cells

MHC II + peptide

recognized by

T-helper cell

MHC-II

MHC-II: Exogenous pathway – How antigens are recognised, processed and delivered on cell surface?

Notatki:

Recognition: Extracellular pathogens and antigens are captured from the environment by specialised antigen presenting cells (APCs) such as Macrophages and Dendritic cells. APCs use specialised receptors (e.g. Toll Like Receptors TLRs) to recognize specific structures on pathogens such as Lipopolysaccharides, flagella, lipopeptides.

Internalization: This recognition helps in efficient internalization of the pathogens in membrane bound vesicles called endosomes.

Processing of internalized pathogens and generation of peptides: Fusion of endosomes and lysosomes produce special vesicles called phagolysosomes and this allows the lysosomal enzymes degrade the internalized pathogenic antigens into short peptides.

Synthesis of MHC-II molecules and their protection: Class II MHC molecules are synthesized in the Endoplasmic Reticulum and are capped with an invariable chain. The invariable chain blocks the MHC II peptide binding cleft so that no other peptides or proteins within the ER make contact with the cleft.

Transportation of MHC-II: MHC-II with the invariable chain is transported via Golgi apparatus to the phagolysosomes where the processed pathogenic peptides are available (refer step 3)

Peptide binding to MHC-II: Lysosomal enzymes remove the invariable chain from the MHC-II. This makes the MHC-II cleft free and this allows the pathogenic peptides to bind to the MHC-II.

Display of MHC-II-Peptide complex on the cell surface: Fusion of the phagolysosome with the plasma membrane of the APC via vesiculotubular extension allows the delivery of MHC-II-peptide complex to be delivered on the surface of the APC. The MHC-II displayed peptide will now be recognized by T-Helper cell. TH cells proliferate releasing chemokines and switch on the immune network by stimulating CD8+ cells and B-cells.

MHC-I

MHC-II

  • Extracellular antigens internalized by antigen presenting cells via endosomes
  • Fusion of endosomes and lysosomes allow the lysosomal enzymes degrade the internalized antigens into short peptides.
  • MHC-class II with the invariant chain is synthesized in ER, but the chain is later removed by lysosomal enzymes.
  • This allows the free MHC-II to bind to the short peptides, which are then transported to the cell surface via special vesicles.
  • Displayed MHC-class II + peptide complex is recognized by CD4+ T-cells. T-cells proliferate releasing chemokines and switch on the immune network by stimulating CD8+ cells, B-cells, etc.

MHC-I

MHC-II

Present on all nucleated cells

Present only on antigen presenting cells

Binds endogenous antigens

Binds exogenous antigens

Present antigens (short peptides

8-11 amino acids) to

CD8+ cytotoxic T-lymphocytes

Present antigens (peptides of

11-30 amino acids) to

CD4+ helper T-lymphocytes

Presence of foreign or over abundant (e.g. cancer) antigens induces cell destruction (and is the only way)

Presence of foreign or over abundant (e.g. cancer) antigens induces antibody formation and invites inflammatory cells

SELF-DIRECTED LEARNING # 1

W8_MHC_DR GIRIJA

Red-Blood Cells (RBC) are non-nucleated and do not express MHC. Platelets also lack nucleus, but do they express MHC?

Do platelets express MHC?

RBC

SELF-DIRECTED LEARNING # 2

W8_MHC_DR GIRIJA

We discussed about the mechanisms of antigen presentations by MHC (which is HLA in humans). The below link for research paper could be a very useful source for additional self-directed learning.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5159193/
  • How can the knowledge be translated in to clinical medicine? What are the potential applications? (as a minimum, read this section of the paper: Concluding remarks and future perspectives)

  • What is MHC/HLA? What are its functions?
  • What are the different types of MHC? What are their structural properties?
  • What is the importance of polymorphic and polygenic features of MHC?
  • Endogenous pathway: What is the mechanism of antigen processing and presentation by MHC class I.
  • Exogenous pathway: What is the mechanism of antigen processing and presentation by MHC class II.
  • Summarise the differences between MHC class I and class II.

MHC – Some Sample Questions

SELF READING BUILDING ON THE LECTURE CONTENT

IS VERY IMPORTANT FOR YOUR LEARNING EXPERIENCE AND ALSO FOR THE EXAMINATIONS

Recommended reading

  • Peter J. Delves, Seamus J. Martin, Dennis R. Burton and Ivan M. Roitt. ROITT’S ESSENTIAL IMMUNOLOGY; 2011, 12th edition
  • Abul K Abbas, Andrew H Lichtman and Shiv Pillai. Cellular and molecular ImmunologyElsevier, 2014, 8th edition
  • Owen, Punt and Stranford. Kuby Immunology; Palgrave Macmillian. 2015. 7th edition.

Books

Journal articles

https://www.ncbi.nlm.nih.gov/pubmed/27614798

Mucosal Immunity

Dr Umakhanth Venkatraman GIRIJA

umakhanth.venkatramangirija@dmu.ac.uk

BIOM2004

Inflammation & Immunobiology

Learning ObjectivesLearning Outcomes
1. What are the mucosal organs?Name the major mucosal systems and the organs involved:Gastrointestinal systemRespiratory systemUrogenital systemWhat is a mucosal tissue? What does it secrete?
2. Gastrointestinal System
2.a. Different types of cells, secretory products and their antimicrobial natureOverview of the GI system and Intestinal Epithelial cellsSpecialized cells: Goblet cells, Stem cells, Paneth cells – their structure, functionsAntimicrobial secretions: Defensins, Phospholipase and lysozyme – What are they? What are their mode of action?
2.b. Antigen sampling, presentation and maintenance of immune toleranceWhat are M-cells?How antigens are sampled in the GI system and presented to the immune system? What is the outcome?Importance of Immune homeostasis in the GI systemThe role of Treg cells and IL-10

Mucosal Immunity

Learning ObjectivesLearning Outcomes
1. What are the mucosal organs?Name the major mucosal systems and the organs involved:Gastrointestinal systemRespiratory systemUrogenital systemWhat is a mucosal tissue? What does it secrete?
2. Gastrointestinal System
2.a. Different types of cells, secretory products and their antimicrobial natureOverview of the GI system and Intestinal Epithelial cellsSpecialized cells: Goblet cells, Stem cells, Paneth cells – their structure, functionsAntimicrobial secretions: Defensins, Phospholipase and lysozyme – What are they? What are their mode of action?
2.b. Antigen sampling, presentation and maintenance of immune toleranceWhat are M-cells?How antigens are sampled in the GI system and presented to the immune system? What is the outcome?Importance of Immune homeostasis in the GI systemThe role of Treg cells and IL-10

Mucosal Immunity

Food antigens (Innocuous/safe)

Commensals (Symbiotic microbes)

Pathogen Entry & breaching the intestinal barrier

Immune System does not react

Immune System maintains tolerance

Immune System has to defend

What are the Mucosal organs / systems?

Sinus

Trachea

Lungs

Respiratory Tract

Oral cavity

Oeso

phagus

Stomach

Gastrointestinal

Tract

Intestine

Bladder

Vagina

Uterus

Urogenital

Tract

Kidney

Mammary glands

Lacrymal gland

Salivary

gland

Conjunctiva

Immunobiology, Fig 11.1, 7th edition; Garland Science (2008)

A range of mechanisms: physical, biochemical and immunological

What is Mucosal tissue ?

They cover the cavities in the body and also the blood vessels and organs

Mucus is a thick slippery jelly like fluid:

For example in nose, stomach, urogenital tract

A tissue that is able to “secrete mucus”

Where?

across an epithelial cell layer

Contribute to “immune defence”

Learning ObjectivesLearning Outcomes
1. What are the mucosal organs?Name the major mucosal systems and the organs involved:Gastrointestinal systemRespiratory systemUrogenital systemWhat is a mucosal tissue? What does it secrete?
2. Gastrointestinal System
2.a. Different types of cells, secretory products and their antimicrobial natureOverview of the GI system and Intestinal Epithelial cellsSpecialized cells: Goblet cells, Stem cells, Paneth cells – their structure, functionsAntimicrobial secretions: Defensins, Phospholipase and lysozyme – What are they? What are their mode of action?
2.b. Antigen sampling, presentation and maintenance of immune toleranceWhat are M-cells?How antigens are sampled in the GI system and presented to the immune system? What is the outcome?Importance of Immune homeostasis in the GI systemThe role of Treg cells and IL-10

Mucosal Immunity

Gastrointestinal Tract

Combined total surface area of small and large bowel is about 40m2 (comparable to a studio apartment)

About 1000 different microbial species live in our GI tract and 1014 bacterial cells in our gut; they are commensals or friendly microbes

Physical barriers and Secretions

Mucus

Antimicrobial secretion

1

Connective tissue

Muscle tissue

Epithelial cell layer

2

Villi

Helps in nutrient absorption and also makes it difficult for pathogenic invasion

Gastrointestinal Tract

T-lymphocyte

B-lymphocyte

Macrophage

3

Immune response

  • Cellular: MHC class I & II
  • Humoral (Ab) response

Lymphoid Tissue (Peyer’s patch)

Gastrointestinal Tract

Intestinal Epithelial Cells – What is special in them?

Epithelial cell

Special cells

Crypt

Lymphoid tissue

(Peyer’s patch)

Goblet (cup shaped) cells

Present in the crypt of the epithelium

  • Secrete MUCUS
  • Microbial infection leads to transient excess mucus secretion (within milliseconds)

95% water + 5% Mucins

Mucins are heavily glycosylated proteins; Glycosylation gives mucus the viscosity and also protect mucins from protease degradation

Mucins bind to microbes and eliminate them

19 different type of mucins

MUCUS

Goblet cells

Consistent excess

mucus production

over weeks or months

could be indication of cancer

  • Paneth cells present in the crypt along with stem cells
  • Paneth cells functionally similar to neutrophils
  • Stem cells have a role in epithelial replenishment

Paneth cells

Stem cells

Paneth and Stem cells

Defensins

(Antimicrobial peptides)

Strongly hydrophobic

Positively charged

Antimicrobials secreted by Paneth cells

Small:

18-45 amino acids

  • -defensins (secreted by paneth cells and neutrophils)
  • -defensins

DNA/RNA functions interfered

Cell membrane disrupted & Cell contents leak

DNA

RNA

Cell membrane

(-ve charge)

Defensin (+ve charge)

Microbe

How do Defensins work?

Lysozyme

(Muraminidase)

  • Binds to N-acetyl muramic acid of bacterial cell wall
  • Cell wall integrity lost
  • Kills bacteria

Phospholipase A2

  • Binds to bacterial cell membranes
  • Bacterial cellular lysis and death

Other Antimicrobials

Learning ObjectivesLearning Outcomes
1. What are the mucosal organs?Name the major mucosal systems and the organs involved:Gastrointestinal systemRespiratory systemUrogenital systemWhat is a mucosal tissue? What does it secrete?
2. Gastrointestinal System
2.a. Different types of cells, secretory products and their antimicrobial natureOverview of the GI system and Intestinal Epithelial cellsSpecialized cells: Goblet cells, Stem cells, Paneth cells – their structure, functionsAntimicrobial secretions: Defensins, Phospholipase and lysozyme – What are they? What are their mode of action?
2.b. Antigen sampling, presentation and maintenance of immune toleranceWhat are M-cells?How antigens are sampled in the GI system and presented to the immune system? What is the outcome?Importance of Immune homeostasis in the GI systemThe role of Treg cells and IL-10

Mucosal Immunity

M-cells

Specialized epithelial cells (similar

to macrophages)

Present above organized lymphoid

follicles called payer’s patches

Have irregular small villi

Coated with glycolipids and proteins;

help them interact with antigens and microbes

Peyer’s patch (Lymphoid tissue)

How do M-cells function?

Antigens

Bacteria

  • M-cells can uptake antigens as well as whole bacteria by a process similar to phagocytosis
  • Antigens sampled by professional antigen presenting cells (e.g. Dendritic cells, macrophages)

Immune signalling following M-cell

Phagocytosis/Pinocytosis/Transcytosis

CD4 +

Helper

T-cell

IL-2

IL-2

CD4 +

Helper

T-cell

CD4 +

Helper

T-cell

CD4 +

Helper

T-cell

T-cell proliferation

B-cell

Pathogens /

Infections

IL-2

IL-2

B-cell

B-cell

B-cell proliferation

Y

Y

Y

Notatki:

Phagocytosis – It is cell eating or engulfment of other cells; Pinocytosis – is cell drinking during which a cell absorbs some extra cellular fluid that contain small solutes and brings them inside; Transcytosis – transcellular transport of macromolecules

  • Antigen presenting cells (Dendritic cells) presenting a pathogenic peptide via MHC-Class II stimulates CD4+ T-cell to secrete IL-2.
  • IL-2 signal leads to T-cell and B-cell proliferation mounting an immune response against pathogens.
  • MHC class I presentation will lead to CD8+ cell proliferation (not ideal for the mucosal system, but where essential, this has to happen)

Epithelial cell layer

Villi

Gastrointestinal Tract

B-cell

T-cell

Interleukin-10 (IL-10) maintains immune homeostasis

TREG

IL-10

IL-10

IL-10

IL-10

  • Dendritic cells constantly sample antigens by protruding between epithelial cells.
  • Sampling of commensals or non-pathogenic antigens and presentation to T-cells, render the T-cells to become T-regulatory cells (TREG).
  • TREG then secrete IL-10 (Interleukin-10) which is anti-inflammatory (stops inflammation).

Failure of immune balance / homeostasis leads to inflammatory bowel disease and other intestinal disorders

SELF-DIRECTED LEARNING # 1

W11_MUCOSAL IMMUNITY

In this week-11 lecture, we briefly discussed about defensins, the types of defensins and how can they defend against microbes.

You have also learnt about complement in an earlier lecture.

Human Neutrophil Peptide-1, one of the defensins, also interplays with complement. Below paper link would be an useful reading resource. If you do not get access to full paper, at least read the abstract.

https://www.ncbi.nlm.nih.gov/pubmed/17448537
  • Which components of complement do defensins interact with?
  • What is the outcome of defensin-complement interaction?

Learning ObjectivesLearning Outcomes
3. Respiratory System
2.a. Lymphoid organs/glands of airwaysImportance and the functions ofNasal Associated Lymphoid Tissue (NALT)TonsilsAdenoids
2.b. Epithelial layers of different airwaysCommon infectious diseases in the respiratory tractCells and macromolecules associated with trachea, bronchioles, alveoliPulmonary Surfactant: What is the composition? What are Surfactant Proteins? What is their structural architecture? How do they eliminate pathogens?Respiratory Distress Syndrome
3. Urogenital System
Brief overviewKey components that provide immunity:Antibodies, Antimicrobial peptides, NK cells, Neutrophils
4. Antibody Response in the Mucosal SystemProperties of IgA and secretory mechanism into lumenClass switch recombination: signalling and mechanism

Mucosal Immunity

Learning ObjectivesLearning Outcomes
3. Respiratory System
2.a. Lymphoid organs/glands of airwaysImportance and the functions ofNasal Associated Lymphoid Tissue (NALT)TonsilsAdenoids
2.b. Epithelial layers of different airwaysCommon infectious diseases in the respiratory tractCells and macromolecules associated with trachea, bronchioles, alveoliPulmonary Surfactant: What is the composition? What are Surfactant Proteins? What is their structural architecture? How do they eliminate pathogens?Respiratory Distress Syndrome
3. Urogenital System
Brief overviewKey components that provide immunity:Antibodies, Antimicrobial peptides, NK cells, Neutrophils
4. Antibody Response in the Mucosal SystemProperties of IgA and secretory mechanism into lumenClass switch recombination: signalling and mechanism

Mucosal Immunity

  • Rhinovirus
  • Respiratory Syncytial virus (RSV)
  • Parainfluenza virus
  • Influenza virus

Infectious

Respiratory Diseases

Upper respiratory tract

Examples

  • Streptococcus pneumoniae
  • Mycobacterium tuberculosis
  • Haemophilus influenzae

Lower respiratory tract

Examples

Tonsils

Adenoid

NALT

  • Tonsils and Adenoid are small glands
  • Antigens are directly delivered and processed

Nasal Associated Lymphoid Tissue

  • First lymphoid site that contacts antigens from the environment

Lymphoid organs of Airways

Tonsils

Adenoid

Surface area of tonsil crypts is ~300cm2

Maximizes the chances for antigen processing and clearance before pathogens can access respiratory tract

Ideally suited to sample antigens entering the airways

Learning ObjectivesLearning Outcomes
3. Respiratory System
2.a. Lymphoid organs/glands of airwaysImportance and the functions ofNasal Associated Lymphoid Tissue (NALT)TonsilsAdenoids
2.b. Epithelial layers of different airwaysCommon infectious diseases in the respiratory tractCells and macromolecules associated with trachea, bronchioles, alveoliPulmonary Surfactant: What is the composition? What are Surfactant Proteins? What is their structural architecture? How do they eliminate pathogens?Respiratory Distress Syndrome
3. Urogenital System
Brief overviewKey components that provide immunity:Antibodies, Antimicrobial peptides, NK cells, Neutrophils
4. Antibody Response in the Mucosal SystemProperties of IgA and secretory mechanism into lumenClass switch recombination: signalling and mechanism

Mucosal Immunity

CLARA cells

Bronchiole

Small airways

Surfactant

Trachea

GOBLET cells

Large airways

Cilia

SP-A,B,C,D

Alveoli

Type I cells

Type II cells

Epithelial layers of different airways

SP = Surfactant Protein

Pulmonary Surfactant =

Phospholipids

+

Proteins

(Surfactant proteins)

Pulmonary Surfactant maintains the surface tension in the airways

  • Hydrophobic peptides
  • Interact with phospholipids to lower the surface tension within alveolus

Surfactant proteins

SP-A

SP-D

SP-B

SP-C

  • Glycoproteins
  • Immunomodulatory properties

N-terminal domain (cysteine rich)

Collagen domain

Carbohydrate Recognition Domain

(CRD)

Neck

CRD recognizes and binds to

  • carbohydrate targets (mannose, fucose) on pathogens
  • DNA, Phospholipid and other protein structures on apoptotic cells

X 6 =

SP-A (Hexamer)

SP-D (Tetramer)

Surfactant Proteins SP-A and SP-D are multimeric

and recognize a range of ligands

SP-A

Pathogen

Pathogen

SP-A (CRD) binds to mannose / fucose moieties on pathogens, undergoes a conformational change to facilitate binding

Multiple SP-A and SP-D can bind to the pathogen, cause aggregation and eliminate them by biophysical means (via cough and sputum)

Pathogen elimination

mechanism – 1

  • SP-A and SP-D bind to the pathogens
  • Macrophages have receptors for SP-A and SP-D, which then present the bound pathogens or antigens for phagocytosis

Pathogen

Pathogen elimination

mechanism – 2

Macrophages with SP-A and

SP-D receptors

Normal

alveoli

Both SP-A and SP-D can bind to DNA, exposed proteins or phospholipids of apoptotic cells in the alveolar region and help in their elimination by phagocytosis

Apoptotic cells with blebs, exposed cell membrane and DNA

SP-A

SP-D

Alveoli collapse RDS

Respiratory Distress Syndrome

Lungs

Airway

Normal

alveoli

Collapsed

alveoli

Common in babies born <34 weeks of gestational age develop RDS

Lungs have not developed fully enough to produce surfactant (which normally keeps the alveoli open after exhaling)

If surfactant is not present, baby has to work hard to reopen alveoli

Interesting Research Facts

  • Spike-protein (also called as S-protein) of Corona virus is recognised by SP-D
  • SP-D receptors on phagocytes recognise the SP-D bound to Corona virus
  • Corona virus should be engulfed by the phagocytes

Envelope-protein

Spike-protein

Membrane-protein

https://www.frontiersin.org/articles/10.3389/fmed.2020.00254/full

Interesting Research Facts

https://www.researchgate.net/publication/6410295

Seems easy

But the battle is complex

Because, Corona virus/cytokine storm can destroy the alveolar cells leading to reduced blood oxygenation, impaired surfactant production including SP-D, fibrosis, oedema and respiratory failure

Corona virus

Cytokine storm

Learning ObjectivesLearning Outcomes
3. Respiratory System
2.a. Lymphoid organs/glands of airwaysImportance and the functions ofNasal Associated Lymphoid Tissue (NALT)TonsilsAdenoids
2.b. Epithelial layers of different airwaysCommon infectious diseases in the respiratory tractCells and macromolecules associated with trachea, bronchioles, alveoliPulmonary Surfactant: What is the composition? What are Surfactant Proteins? What is their structural architecture? How do they eliminate pathogens?Respiratory Distress Syndrome
3. Urogenital System
Brief overviewKey components that provide immunity:Antibodies, Antimicrobial peptides, NK cells, Neutrophils
4. Antibody Response in the Mucosal SystemProperties of IgA and secretory mechanism into lumenClass switch recombination: signalling and mechanism

Mucosal Immunity

Urogenital Tract

  • Lacks M-cells
  • IgG and also IgA dominate the mucosal urogenital tract (while IgA is the dominant in GI and Respiratory tract)
  • Antimicrobial defensins, lactoferrin, lipcalin and Tamm-horsfall protein (THP) exclusively binds to fimbriae and enhances bacterial washout via urine
  • Natural Killer Cells and Neutrophils play a major role in pathogen elimination by direct killing

Learning ObjectivesLearning Outcomes
3. Respiratory System
2.a. Lymphoid organs/glands of airwaysImportance and the functions ofNasal Associated Lymphoid Tissue (NALT)TonsilsAdenoids
2.b. Epithelial layers of different airwaysCommon infectious diseases in the respiratory tractCells and macromolecules associated with trachea, bronchioles, alveoliPulmonary Surfactant: What is the composition? What are Surfactant Proteins? What is their structural architecture? How do they eliminate pathogens?Respiratory Distress Syndrome
3. Urogenital System
Brief overviewKey components that provide immunity:Antibodies, Antimicrobial peptides, NK cells, Neutrophils
4. Antibody Response in the Mucosal SystemProperties of IgA and secretory mechanism into lumenClass switch recombination: signalling and mechanism

Mucosal Immunity

Antibody immune response

dominates

mucosal system

IgG IgA IgM IgE IgD

Systemic antibody levels

Mucosal antibody levels

Relative %

IgG IgA IgM IgE IgD

IgG is the dominant Ab in Systemic response

IgA is the dominant Ab in Mucosal response

IgA

IgA

IgA

IgA

IgA

IgA

Resistant to proteases

Stable in acidic environments of GI tract

Higher affinity to antigens

Less inflammatory: good for GI (binds very weakly to complement)

Secretory component is antimicrobial

J-chain

Dimeric

IgA

Plasma B cells are White Blood Cells (WBCs) secreting large volumes of Antibodies (Ab)

Two IgA molecules linked together by a third molecule called the Joining chain (J-chain)

1

2

3

4

Dimeric IgA can bind 4 antigens !

Antigen-IgA complex agglutinates in the lumen

(IgA DOES NOT activate COMPLEMENT)

Clearance via Peristaltic movement

Peristalsis – contraction and relaxation of muscles to pass the food through GI tract and finally the waste

Agglutination of antigens and elimination by peristalsis is a better choice than complement activation, because the latter could be more stressful to the system in a mucosal area

Dimeric IgA – an effective mucosal antibody

Dimeric IgA binds to the poly Ig receptor (secretory component) on epithelial cell and taken up by Endocytosis

Epithelial cell

Lumen (food pipe)

Apical

Surface

Basolateral Surface

Plasma cell in the lymphoid tissue secretes dimeric IgA

Dimeric IgA + extracellular domain of poly Ig receptor RELEASED INTO THE LUMEN

Naive Plasma-B cells express IgM or IgD

IgD

IgM

In a mucosal immune response, it shifts to IgA

IgA

How

Antibody Class Switching

Antibodies

Heavy chain

Light chain

C

C

C

C

C

C

V

V

V

V

Ag

Ag

Constant

region

Variable region detects different antigens from bacteria, virus, cancer cell

and this variability is formed by hyper mutation (VDJ recombination)

  • Carries out the effector functions by interacting with immune network
  • This determines the type of antibody e.g. IgM, IgG, IgA, IgD and IgE

Class Switching

Basics

V D J

IgM

IgD

IgG

IgA

IgE

S

S

S

S

S

S

S

S

V D J

IgA

Class switch recombination

allows the heavy chain gene coding for IgA antibody

IgA

V D J

DNA repair

DNA repair

AID

AID

AID

AID

2. Upon breakage, the intervening sequences will be lost. VDJ and IgA sequences are then recombined by class switch recombination and DNA repair mechanisms. This leads to secretion of IgA antibody.

(this intervening sequence will be lost)

1. Upon receiving the appropriate cytokine signal, Activation Induced cytidine Deaminase makes double strand breaks in S (Switch) regions upstream of IgA and IgM

T-cell

B-cell

Pathogen

Gamma-Interferon

Y

IgG

IL-4

Y

Y

IgA

TGF-Beta

IgE

Y

  • B-cell normally makes IgM and IgD antibodies. Upon receiving an appropriate cytokine signal (which depends on the type of T-cell), B-cell switches to form a different class of antibody (the above list only contains example cytokines). This is called Antibody Switching.
  • B-cell then transforms into plasma cell and a plasma blast produces enormous number of the specific antibody

T-Helper cell 1

T-Helper cell 2

T-regulatory cells

Depending on the pathogen and site of infection

Summary

Gastro intestinal, respiratory and uro-genital tracts form the major components of mucosal systems in our body.

Physical barriers (villi, M-cells, goblet cells) and antimicrobial secretions (defensins, lysozyme, phospholipase) try to maintain the ever active GI tract free of infections.

T-regulatory cells help to maintain immune tolerance via IL-10 secretion. This helps the mucosal immune system to stop constant inflammatory response in the GI tract.

Mucosal Immunity

Summary

While cell mediated immune response has a role to play in mucosal immune defence, it is the humoral (antibody) mediated response which dominates.

IgA is the dominant antibody in GI and respiratory tract, while both IgG and IgA dominate the urogenital tract.

Epithelial cells of mucosal system comprise many special cells which secrete antimicrobials that help in fighting infections.

Antibody class switching is the mechanism used by B-cells to produce IgA in the mucosal surface which transfer to the lumen by endocytosis.

Mucosal Immunity

  • What are the various mucosal organs in our body?

Mucosal Immunity (part-1) – some sample questions

1. Mucosal organs/systems

2. Physical barriers and Secretions

3. Antigen sampling and immune response

4. Maintenance of immune tolerance

  • What are goblet cells and stem cells in the mucosal lining?
  • What is mucus? Outline how it provides defence against pathogens.
  • What are Paneth cells? What is their role in mucosal immunity?
  • Describe the various antimicrobial secretions that support our immune system in the gastro intestinal system.
  • Describe the role of M-cells in antigen sampling and explain the fate of such antigens.
  • Explain how immune homeostasis or tolerance is maintained in the gastro intestinal system.

Mucosal Immunity (part-2) – Practice questions

  • What features of IgA make it an ideal antibody in mucosal immunity?
  • Explain the mechanism of transfer of IgA across the epithelial surface.
  • What is Antibody Class Switching? What are the major cytokine signals that mediate antibody class switching?

Antibody response in the mucosa

Immune response in Respiratory tract

Immune response in Urogenital tract

  • What are the major structural features and their associated immunological role in the respiratory tract ?
  • What is the composition of Pulmonary surfactant?
  • What are the different types of Surfactant proteins? Explain their role in airway immunity.
  • What is Respiratory Distress Syndrome. Why is it caused?
  • What are the major immunological features of urogenital system?

Reading

Books

  • Peter J. Delves, Seamus J. Martin, Dennis R. Burton and Ivan M. Roitt. ROITT’S ESSENTIAL IMMUNOLOGY; 2011, 12th edition
  • Abul K Abbas, Andrew H Lichtman and Shiv Pillai. Cellular and molecular ImmunologyElsevier, 2014, 8th edition
  • Owen, Punt and Stranford. Kuby Immunology; Palgrave Macmillian. 2015. 7th edition.

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