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
Damage-associated molecular patterns in trauma
Borna, Relja; Land 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.
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
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)
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
- 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
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
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
| Class | Heavy chain | Subclasses | Light Chain |
| IgG | g | g1, g2, g3, g4 | k or l |
| IgM | m | None | k or l |
| IgA | a | a1, a2 | k or l |
| IgE | e | None | k or l |
| IgD | d | None | k 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-globulin | IgG | IgM | IgA | IgE | IgD |
| Normal Levels (mg/dl) | 620 – 1400 | 45 – 250 | 80 – 350 | 0.002 – 0.2 | 0.3 – 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
Damage-associated molecular patterns in trauma
Borna, Relja; Land 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
Damage-associated molecular patterns in trauma
Borna, Relja; Land 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 Objectives | Learning Outcomes |
| 1. Complement components & activation | What 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 Complement | What 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)
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
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 Objectives | Learning Outcomes |
| 1. Complement components & activation | What 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 Complement | What 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 Immunology, Elsevier, 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 Objectives | Learning Outcomes |
| 1. Types, Structure and functions | What 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 presentation | Antigen 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 Objectives | Learning Outcomes |
| 1. Types, Structure and functions | What 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 presentation | Antigen 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 Expression | Constitutive | Need 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.
- 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 Immunology, Elsevier, 2014, 8th edition
- Owen, Punt and Stranford. Kuby Immunology; Palgrave Macmillian. 2015. 7th edition.
Books
Journal articles
Mucosal Immunity
Dr Umakhanth Venkatraman GIRIJA
umakhanth.venkatramangirija@dmu.ac.uk
BIOM2004
Inflammation & Immunobiology
| Learning Objectives | Learning 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 nature | Overview 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 tolerance | What 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 Objectives | Learning 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 nature | Overview 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 tolerance | What 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 Objectives | Learning 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 nature | Overview 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 tolerance | What 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 Objectives | Learning 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 nature | Overview 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 tolerance | What 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.
- Which components of complement do defensins interact with?
- What is the outcome of defensin-complement interaction?
| Learning Objectives | Learning Outcomes |
| 3. Respiratory System | |
| 2.a. Lymphoid organs/glands of airways | Importance and the functions ofNasal Associated Lymphoid Tissue (NALT)TonsilsAdenoids |
| 2.b. Epithelial layers of different airways | Common 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 overview | Key components that provide immunity:Antibodies, Antimicrobial peptides, NK cells, Neutrophils |
| 4. Antibody Response in the Mucosal System | Properties of IgA and secretory mechanism into lumenClass switch recombination: signalling and mechanism |
Mucosal Immunity
| Learning Objectives | Learning Outcomes |
| 3. Respiratory System | |
| 2.a. Lymphoid organs/glands of airways | Importance and the functions ofNasal Associated Lymphoid Tissue (NALT)TonsilsAdenoids |
| 2.b. Epithelial layers of different airways | Common 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 overview | Key components that provide immunity:Antibodies, Antimicrobial peptides, NK cells, Neutrophils |
| 4. Antibody Response in the Mucosal System | Properties 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 Objectives | Learning Outcomes |
| 3. Respiratory System | |
| 2.a. Lymphoid organs/glands of airways | Importance and the functions ofNasal Associated Lymphoid Tissue (NALT)TonsilsAdenoids |
| 2.b. Epithelial layers of different airways | Common 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 overview | Key components that provide immunity:Antibodies, Antimicrobial peptides, NK cells, Neutrophils |
| 4. Antibody Response in the Mucosal System | Properties 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
Interesting Research Facts
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 Objectives | Learning Outcomes |
| 3. Respiratory System | |
| 2.a. Lymphoid organs/glands of airways | Importance and the functions ofNasal Associated Lymphoid Tissue (NALT)TonsilsAdenoids |
| 2.b. Epithelial layers of different airways | Common 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 overview | Key components that provide immunity:Antibodies, Antimicrobial peptides, NK cells, Neutrophils |
| 4. Antibody Response in the Mucosal System | Properties 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 Objectives | Learning Outcomes |
| 3. Respiratory System | |
| 2.a. Lymphoid organs/glands of airways | Importance and the functions ofNasal Associated Lymphoid Tissue (NALT)TonsilsAdenoids |
| 2.b. Epithelial layers of different airways | Common 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 overview | Key components that provide immunity:Antibodies, Antimicrobial peptides, NK cells, Neutrophils |
| 4. Antibody Response in the Mucosal System | Properties 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 Immunology, Elsevier, 2014, 8th edition
- Owen, Punt and Stranford. Kuby Immunology; Palgrave Macmillian. 2015. 7th edition.
