Antigen Presentation 2022-23 Past Paper PDF

Title: Antigen Presentation CRN No: 15569(Male), 15581 (Female) Block: 1.2 Subject/Discipline: Immunology Expert: Dr.Sayed A.Quadri Block Coordinator: Dr.Sayed A.Quadri Learning objectives 14. Explain how T and B lymphocytes recognize antigens. 15. Why does the immune system require specialize...

Title: Antigen Presentation CRN No: 15569(Male), 15581 (Female) Block: 1.2 Subject/Discipline: Immunology Expert: Dr.Sayed A.Quadri Block Coordinator: Dr.Sayed A.Quadri Learning objectives 14. Explain how T and B lymphocytes recognize antigens. 15. Why does the immune system require specialized system of antigen presentation for effective immune responses. 16. What kind of molecules plays a critical role in antigen presentation to T-lymphocytes. 17. What cell type (s) play important roles in the capture of invading microorganisms? Explain this role. 18. Explain how immune responses of CD8+ T- lymphocytes are initiated by dendritic cells. Define “cross presentation”. 19. Explain in general terms the molecular structure of MHC class I and class II molecules. Briefly discuss the major biological and functional characteristics of MHC molecules and the cells that express the various classes of MHC molecules 20. Describe in general terms how peptides originating from proteins outside the cell may be absorbed by MHC class II molecule ( briefly discuss the role of the CLIP peptide in this context) and explain how proteins of intracellular origin are presented by MHC class I molecule(Briefly discuss the role of TAT proteins in this process). 21. Explain the biological relevance of the extreme polymorphism of MHC molecules. 22. What molecules on T-lymphocytes contribute to their specificity of either class I or class II MHC associated peptide antigens. 23. Describe in what ways the two classes of MHC molecules play a role effector functions by CD4+ and CD8+ lymphocytes Terms to be familiar MHC molecules (Major Histocompatibility Complex )  Proteins present on the surface of cells. APC (Antigen Presenting Cells)  Cells that process and display antigen to T-lymphocytes Naïve T-Lymphocytes - ‫ساذجة‬  T-cells that haven't come in contact with antigen Co-stimulation and Co-stimulatory signals Additional signals required for T-cells activation  Clonal expansion  Proliferation (increase in number) of a particular clone of lymphocyte (antigen specific lymphocyte) Cytokines  Proteins released by several types of cells that act on other cells (adjacent – paracrine, or distant-endocrine)  Also called the cell messengers Lymphoid organs  Organs where lymphocytes mature (primary) or accumulate (secondary) Lymphocyte recirculation  continuous movement of lymphocytes from – blood - peripheral lymphoid organs – lymph - blood  Lymphocyte differentiation  Clonal proliferation culminates in formation of effector cells / memory cells. Effector cells  Lymphocytes which produce an immune response – antibody producing plasma cells from B-Lymphocytes and Cytotoxic Lymphocytes(CTL) and T-helper cells (TH cells) from T-lymphocytes. Memory cells  Some lymphocytes differentiates into long lived cells and are responsible for secondary immune response.  Lymphocyte repertoire Total collection of lymphocyte specificities. Characteristics of adaptive IS Specificity (one lock for one key), Diversity (several locks for different keys), Clonal Expansion, Non-reactivity to Self (no locks for self keys). Keys: Antigens Locks: Lymphocytes  Rule 1 Each lymphocyte clone has a distinct antigen receptor unique for a specific antigen.  Lymphocytes recognize antigens by antigen receptors on their surfaces Lymphocyte Antigen Antigen Receptor Antigen recognition by B-lymphocytes B-lymphocytes recognize Recognize antigens by “membrane bound antibodies” on their surface. Recognize a variety of antigens (proteins, polysaccharides, fats and nucleic acids). B-Lymphocytes recognize antigen directly Antigen recognition by T-lymphocytes T-lymphocytes recognize  peptide antigen bound to and displayed by MHC on APCs- by their T-Cell Receptor (TCR) T-Lymphocytes recognize antigen in bond form  Rule 2 T-lymphocytes recognize antigen when the antigen is presented by another cell on its surface with MHC. Why does the immune system require specialized system of antigen presentation for effective immune responses ? Why does the immune system require specialized system of antigen presentation for effective immune responses ? a. Antigen may enter through any body site. b. Antigen specific lymphocyte has to come in contact with its homologous antigen (1 in 1 million)-----should locate & react ASAP. c. Different types of antigen may require different responses. (antigens in the cytosol and nucleus vs. antigens in the vesicle). d. Sometimes IS needs to react to the same microbe in different ways depending on its stage of infection. Immune system has developed highly specialized system for capture and display of antigen. What kind of molecules plays a critical role in antigen presentation to T-lymphocytes? Molecules THAT play a critical role in antigen presentation to T-lymphocytes  MHC molecules present on cell surface.  Antigen is bound with MHC molecule on cell surface.  Antigen- MHC complex displayed on surface of APC.  T-Lymphocytes recognize antigen only when it is displayed on surface of APC with MHC.  Each individual’s MHC is unique.  T-Lymphocytes recognize antigen only with MHC of same individual – MHC restriction.  T-Lymphocytes recognize antigen by TCR.  What kind of molecules plays a critical role in antigen presentation to T-lymphocytes Antigen TCR Capture Process Present Capp[pp  Binding to lectin Function of Dendritic cells receptor – phagocytosis/ Receptor-mediated endocytosis Stimulation Capture antigen through TLR & other PRR + Cytokines IL-1 & TNF Loose adhesiveness Get activated & express CCR7 Migrate to L.N Present antigen to Lymphocytes Explain in general terms the molecular structure of MHC class I and class II molecules. Briefly discuss the major biological and functional characteristics of MHC molecules and the cells that express the various classes of MHC molecules ‫تكبيل‬ ‫اليدين‬  MHC molecules M=Major H=Histo C=Compatibility HLA (Human Leukocyte Antigens) is a synonym of MHC molecules.  Membrane proteins on APCs that display peptide antigen for recognition by T-lymphocytes.  2 types of MHC molecules – Class I & II. CD 8 binding CD 4 binding  Rule 3 CD 4+ T-lymphocytes recognize antigen with MHC II molecules. And CD 8+ T-lymphocytes recognize antigen with MHC I molecules. Biological and functional characteristics of MHC 1. MHC genes are highly polymorphic  Rule 4 MHC molecule exhibit high level of polymorphism. (different variants of the genes in a population) And T-lymphocytes recognize antigen with self MHC molecules only : MHC restriction. 2. 3.  4. 5. 6.  7. 8. 9. Cells that express MHC 21. Describe in general terms how peptides originating from proteins outside the cell may be absorbed by MHC class II molecule ( briefly discuss the role of the CLIP peptide in this context) and explain how proteins of intracellular origin are presented by MHC class I molecule(Briefly discuss the role of TAT proteins in this process). Packaging and loading of cargo  Endocytic vesicle Explain the biological relevance of the extreme polymorphism of MHC molecules  Polymorphisms present in antigen binding groove.  This determines ability of a MHC molecule to present a specific antigen.  MHC polymorphism ensure at least few individuals have MHC that can present a particular antigen and ensure survival of the species Describe in what ways the two classes of MHC molecules play a role effector functions by CD4+ and CD8+ lymphocytes.