Immunology

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 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-proquestcom.proxy.library.dmu.ac.uk/docview/2434147450?Op enUrlRefId=info:xri/sid:summon&accountid=10472 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 harmful chemicals If this is true, how do we survive? 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 Local Effects Systemic 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 IL6 TNFa: Fever, mobilisation of metabolites, shock IL-6: Fever, acutephase 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 (8-25kDa). • The different cytokines fall into a number of categories. The principal subgroups are: interferons, interleukins, chemokines and colony-stimulating factors. Main functions of cytokines 1) Stimulators of immature lymphocyte growth and differentiation 1) Mediators of natural immunity 1) Regulators of mature lymphocyte activation, growth and differentiation 1) Regulators of immune-mediated inflammation Cytokine redundancy • Redundant = different cytokines may have the same function, e.g.: TNFalpha IL-1beta + + fever induction Cytokine pleotropism • Pleotropic = one cytokine having many functions, e.g.: TNFalpha + fever induction + induction of adhesion molecule expression on endothelium + induction of leukocyte adhesion 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 Many interleukins cause other cells to divide and differentiate. 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 Tumor necrosis factors TNFα and TNFβ, and transforming growth factor-β (TGFβ), have a variety of functions, but are particularly important in mediating inflammation and cytotoxic reactions. 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 produceIL-1andTNF-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 halflife. 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. • E.g. mutations in the IL-7R α chain result in a reduced number of T cells; • whereas those with deficiency in the common cytokine receptor γ chain (γc), a component of IL-2, IL-4, IL-7, IL-9, and IL-15 receptors, have reduced numbers of T and NK cells and impaired B cell function, in part attributable to the lack of T cell help • 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 Immun e respons e Cellul ar Humora l Humora l 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. Phagocytos is A. 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. B. 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 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/1 0.3389/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/fullte xt/S1074-7613(17)30419-3 Macrophages and DCs may contribute to plaque formation Paper link – optional extra reading 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 • 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 • 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 • 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 • 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 LYMPHOCYTES LO: Describe and discuss T cell structure and function • 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) • 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 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. 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 • 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 • 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 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 selfantigen 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 • 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 • 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 • Negative selection occurs in the medulla • This checks how well the T cells bind with self MHC peptides T CELL MATURATION M LO: Describe and discuss T cell development • 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 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 • The activation required recognition of antigens displayed on APCs, costimulators and cytokines produced by the APCs and the T cells themselves • These signals tell the cells what to do e.g. APC (DC, macrophage, phagocytes) produce IL12 which activates APC and also induces generation and differentiation on T cells, which then produce IFNɣ and IL2 (activated macrophages and induces MHCII expression, promotes differentiation of memory cells). 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 • 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 • 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 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 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: • 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 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. • 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 • 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 • 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) • 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/00724958 55/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 in target cell membranes • e.g. granzymes – act as digestive enzymes • 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 • 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 • 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 • 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 • 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 • 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 A. 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. B. A view of the interacting surfaces of lysozyme (in green) and a Fab fragment of a monoclonal anti-hen egg lysozyme antibody (VH in blue and VL in yellow) is provided. The residues of hen egg lysozyme and of the Fab fragment that interact with one another are shown in red. A critical glutamine residue on lysozyme (in magenta) fits into a “cleft” in the antibody. 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 Clas s Heavy chain Subcl asses Light Chain IgG  1, 2, 3, 4 k or l IgM m None k or l IgA  1, 2 k or l IgE e None k or l IgD d None k or l Minor differences in the amino acid sequences of the  and  heavy chains leads to categorisation of subclasses Five classes – G, M, A, E, D Immunoglobulin 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). 1) A model of IgG1 2) IgG3 3) IgM H chains have five domains with disulfide bonds cross-linking adjacent Ch3 and Ch4 domains. 4) IgA. The J chain is required to join the two subunits. 5) This diagram of IgD shows the domain structure and a characteristically large number of oligosaccharide units. 6) IgE. Carbohydrate side chains are shown in blue. 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 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 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 postsession 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, in the module handbook or other information folders 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) 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-proquestcom.proxy.library.dmu.ac.uk/docview/2434147450?Op enUrlRefId=info:xri/sid:summon&accountid=10472 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 https://www-proquestcom.proxy.library.dmu.ac.uk/d ocview/2434147450?OpenUrlR efId=info:xri/sid:summon&acc ountid=10472 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 bl 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 Importanc 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 ComplemComplement, 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 MBLassociated 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 C3 H2O 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 C3 H2O 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 C3 H2O C3b ALTERNATIVE Pathway CLASSICAL Pathway LECTIN pathway Target recognition & activation Enzymatic cascade Target elimination C3b Pathogen 2. Coats “Eat me signal” 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) Pathogen The Classical Pathway Cascade 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” 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 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 membranebound 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, 8 th edition • Owen, Punt and Stranford. Kuby Immunology; Palgrave Macmillian. 2015. 7 th 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-I o Expression of MHC-I o Molecular processing and presentation of antigenic peptides • Antigen processing and presentation by MHC-II o Expression of MHC-II o Molecular processing and presentation of antigenic peptides MHC is the process of taking orgaGenetically identical individuals Genetically different individuals Inherited Genes must be involved in the process of transplant 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 Chromosome 6 Long arm Short arm 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 2 1 3 Membrane-proximal domains (Ig-G like) Membranedistal domains 1 2 1 2 (Peptide)-binding cleft MHC Class I MHC Class II • 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  Polygen • 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  Polymorp• 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 (polymorphism = occurrence of different forms of same gene among the individuals or population) 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-I o Expression of MHC-I o Molecular processing and presentation of antigenic peptides • Antigen processing and presentation by MHC-II o Expression of MHC-II o Molecular 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) PROTEASOME Short Peptides (Proteasomes are multiprotein enzyme complexes and are involved in Proteolytic degradation of proteins) Viral infections (always intracellular) viral proteins synthesized intracellularly in the host (human) (Chlamydia, Mycobacterium, Neisseria, Salmonella) Some bacterial infections are also intracellular MHC-I How peptides are fo(Endogenous path 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 • 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 phagolysosomes Flagella 3 1 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 MHC II + peptide recognized by T-helper cell MHC-II MHC-II: Exogenous pathway – How antigens are recognised, processed and delivered on cell surface? MHC-III • 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/ 1. 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, 8 th edition • Owen, Punt and Stranford. Kuby Immunology; Palgrave Macmillian. 2015. 7 th 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 Objectives Learning Outcomes 1. What are the mucosal organs? • Name the major mucosal systems and the organs involved: o Gastrointestinal system o Respiratory system o Urogenital system • What 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 cells • Specialized cells: Goblet cells, Stem cells, Paneth cells – their structure, functions • Antimicrobial 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 system • The 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: o Gastrointestinal system o Respiratory system o Urogenital system • What 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 cells • Specialized cells: Goblet cells, Stem cells, Paneth cells – their structure, functions • Antimicrobial 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 system • The 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 Oral cavity Tract Oeso phagus Stomach Gastrointestinal Tract Intestine Bladder Vagina Uterus Urogenita 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: o Gastrointestinal system o Respiratory system o Urogenital system • What 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 cells • Specialized cells: Goblet cells, Stem cells, Paneth cells – their structure, functions • Antimicrobial 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 system • The role of Treg cells and IL-10 Mucosal Immunity GastrointestinCombined 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 1 Antimicrobial secretion Connective tissue Muscle tissue Epithelial cell layer Villi 2 Helps in nutrient absorption and also makes it difficult for pathogenic invasion GastrointestinT-lymphocyte B-lymphocyte Macrophage 3 Immune response a. Cellular: MHC class I & II b. Humoral (Ab) response Lymphoid Tissue (Peyer’s patch) GastrointestinIntestinal 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 MUC US 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 and secrete a number of antimicrobials • 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 (epithelial cells) 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: o Gastrointestinal system o Respiratory system o Urogenital system • What 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 cells • Specialized cells: Goblet cells, Stem cells, Paneth cells – their structure, functions • Antimicrobial 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 system • The 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? Bacteria Antigens ❑ 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 • 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 GastrointestinaB-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 1. Which components of complement do defensins interact with? 2. 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 of o Nasal Associated Lymphoid Tissue (NALT) o Tonsils o Adenoids 2.b. Epithelial layers of different airways • Common infectious diseases in the respiratory tract • Cells and macromolecules associated with trachea, bronchioles, alveoli • Pulmonary 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: o Antibodies, Antimicrobial peptides, NK cells, Neutrophils 4. Antibody Response in the Mucosal System • Properties of IgA and secretory mechanism into lumen • Class 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 of o Nasal Associated Lymphoid Tissue (NALT) o Tonsils o Adenoids 2.b. Epithelial layers of different airways • Common infectious diseases in the respiratory tract • Cells and macromolecules associated with trachea, bronchioles, alveoli • Pulmonary 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: o Antibodies, Antimicrobial peptides, NK cells, Neutrophils 4. Antibody Response in the Mucosal System • Properties of IgA and secretory mechanism into lumen • Class 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 of o Nasal Associated Lymphoid Tissue (NALT) o Tonsils o Adenoids 2.b. Epithelial layers of different airways • Common infectious diseases in the respiratory tract • Cells and macromolecules associated with trachea, bronchioles, alveoli • Pulmonary 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: o Antibodies, Antimicrobial peptides, NK cells, Neutrophils 4. Antibody Response in the Mucosal System • Properties of IgA and secretory mechanism into lumen • Class 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 II cells Type I 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 Objectives Learning Outcomes 3. Respiratory System 2.a. Lymphoid organs/glands of airways • Importance and the functions of o Nasal Associated Lymphoid Tissue (NALT) o Tonsils o Adenoids 2.b. Epithelial layers of different airways • Common infectious diseases in the respiratory tract • Cells and macromolecules associated with trachea, bronchioles, alveoli • Pulmonary 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: o Antibodies, Antimicrobial peptides, NK cells, Neutrophils 4. Antibody Response in the Mucosal System • Properties of IgA and secretory mechanism into lumen • Class 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 of o Nasal Associated Lymphoid Tissue (NALT) o Tonsils o Adenoids 2.b. Epithelial layers of different airways • Common infectious diseases in the respiratory tract • Cells and macromolecules associated with trachea, bronchioles, alveoli • Pulmonary 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: o Antibodies, Antimicrobial peptides, NK cells, Neutrophils 4. Antibody Response in the Mucosal System • Properties of IgA and secretory mechanism into lumen • Class switch recombination: signalling and mechanism Mucosal Immunity Antibody immune response dominates mucosal system 0 20 40 60 80 100 IgGIgG IgA IgAIgM IgMIgE IgDIgE IgD Systemic antibody levels Mucosal antibody levels Relative % IgG IgG IgA IgAIgM IgMIgE IgDIgE IgD IgG is the dominant Ab in Systemic response IgA is the dominant Ab in Mucosal response 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 How IgA 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 V D J IgM IgD IgG IgE IgA S S S S S S S S V D J IgA Class switch recombination allows the heavy chain gene coding for IgA antibody DNA repair V D J IgA 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 GammaInterferon Y IgG IL-4 TGF-Beta Y YIgA IgE • B-cell normally makes IgM and IgD antibodies. Upon receiving an appropriate cytokine signal (which depends on the type of Tcell), 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 • 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, 8 th edition • Owen, Punt and Stranford. Kuby Immunology; Palgrave Macmillian. 2015. 7 th edition. Books