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Immunoglobulin Structure & Function

Immunoglobulin Structure & Function. Assigned Reading Performance Ojectives Key terms Key Concepts Content Outline Short Answer Questions. Angels & Devils. Assigned Reading. Chapter: 5 pp107-142 Janis Kuby’s Immunology 3rd Ed. Basic Structure B Cell Receptor

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Immunoglobulin Structure & Function

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  1. Immunoglobulin Structure & Function • Assigned Reading • Performance Ojectives • Key terms • Key Concepts • Content Outline • Short Answer Questions

  2. Angels & Devils

  3. Assigned Reading • Chapter: 5 pp107-142 • Janis Kuby’s Immunology 3rd Ed

  4. Basic Structure B Cell Receptor Antigenic Determinants of Igs Immunoglobulin Superfamily Ig Classes Monoclonal Antibodies (MABS) Immunoglobulin Sequencing Studies Immunoglobulin Fine Structure Content Outline

  5. Background

  6. Tiselius

  7. Electrophoresis

  8. General Structure of Immunoglobulins • Electron microscopy • Crystallography • Hinge region • light & heavy chains • binding site • domains • fragments

  9. IgG Crystal

  10. X - Ray Crystallography • Crystallized Antigen or Antigen - Antibody Complex • Electron Density Map of the Molecule • Three Dimensional Images

  11. Antibodies contain a flexible hinge region • EM evidence • Location • Chemical Structure • Advantages

  12. Antibody Flexibility • EMs of same conc of antibody mixed with different conc of antigen • Ag-Ab complexes form different shapes • Ag is inflexible • AB MUST BE FLEXIBLE

  13. Ag-Ab Complexes

  14. Immunoglobulin flexible hinge

  15. Hinge Prolines

  16. Advantages of hinge • Rotation around central point • Bind antigens at various distances • Bind various ratios of antigens Blocks or binds to antigens over a wide range of concentrations

  17. Structure of IgG

  18. IgG: Domains

  19. IgG: Enzyme hydrolysis

  20. Ag-Ab complexes after Pepsin

  21. B Cell Receptor • BEFORE IMMUNIZATION • Ig genes are organized & Igs assembled • Anchored on membrane as specific receptors for immunogen • AFTER IMMUNIZATION • different expression of Ig genes • lose anchor>> secreted • different class of Ig secreted

  22. Antigenic Determinants of Igs • Immunoglobulins are immunogenic • Inject human antibodies into a mouse • Mouse develops anti-Human antibodies • Use these antibodies to probe structure of immunoglobulins • Three classes of anti-antibodies • Isotypes • Allotypes • Idiotypes

  23. Antibody Classes: Outline • 5 classes of antibodies • Concentration of classes • Structure and function of • IgG • IgM • IgA • IgD • IgE

  24. Immunoglobulin Classes • Immunoglobulin A IgA,mA • Immunoglobulin D IgD, mD • Immunoglobulin E IgE, mE • Immunoglobulin G IgG,mG • Immunoglobulin M IgM,mM

  25. Immunoglobuin concentrations

  26. Ig Superfamily

  27. IgG: Physicochemical Properties • Molecular weight • Sedimentation constant 7S • Total 146,000 • Heavy chain 51,000 • Isotypes 4 • Heavy chain domains 4 • Carbohydrate (%) 2-3 • half life (days) 21

  28. Structure of IgG

  29. IgG: Domains

  30. IgG subclasses

  31. IgG: Functions • Bind antigen in tissue fluids • Promote destruction of antigen • activates complement • Promote phagocytosis • binds to Fc receptors on macrophages • Passive protection of fetus • binds to receptors on placenta • transferred to fetal circulation

  32. Functions of IgG Domains • VH + VL Antigen binding • CH1 Complement binding c4b • CH2 complement binding C1q • CH3 Macrophage binding,Fc receptor • CH2 +CH3 neutrophil & K cell binding, bind to placental syncytiotrophoblast

  33. Primary vs Secondary Response

  34. IgM:Physicochemical Properties • Molecular weight • Sedimentation constant 19 S • Total 900,000 • Heavy chain 65,000 • Isotypes 1 • Heavy chain domains 5 • Carbohydrate (%) 12 • half life (days) 5

  35. IgM: Structure

  36. IgM: Heavy chains

  37. IgM: Functions • Antigen receptor for B cell • Short term protection • binds tightly to antigen • (high avidity)

  38. IgA:Physicochemical Properties Serum Secretory • Molecular weight • Sedimentation constant 7S 11S • Total 160,000 385,000 • Heavy chain 52-56,000 52,56,000 • Isotypes 2 2 • Heavy chain domains 4 4 • Carbohydrate (%) 7-11 7-11 • Half life (days)6 6

  39. Structure of IgA

  40. IgA dimers

  41. EM of IgA

  42. Secretion of IgA

  43. IgA: Functions • Protects body surfaces against invading microbes • Secretory IgA - • transported to epithelium • secreted in mucus, milk & tears • Blood IgA - • transported to liver • binds to hepatocytes • secreted into bile

  44. J chain • Small polypeptide chain • found in polymeric classes of antibodies • Acts as a clasp to join prototype subunits • produced by same cell that makes antibodies

  45. J chain structure

  46. J chain: Beta sheets

  47. J Chain: Barrel

  48. IgE: Physicochemical Properties • Molecular weight 188,000 • Sedimentation constant 8S • Total 188,000 • Heavy chain 72,500 • Isotypes 1 • Heavy chain domains 5 • Carbohydrate (%) 12 • half life (days) 2

  49. Structure of IgE

  50. Molecular model of IgE

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