Lecture on immunoglobulins
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Immunoglobulins are glycoprotein molecules produced by plasma cells that function as antibodies. They have two main roles: as antigen receptors that bind to antigens, and as effector molecules that help eliminate or inactivate antigens. The basic immunoglobulin structure consists of two heavy chains and two light chains held together by disulfide bonds. The five major human immunoglobulin classes are IgG, IgM, IgA, IgD, and IgE, which differ based on their heavy chain composition. IgG is the most abundant immunoglobulin in blood and provides long-term immunity. IgM is the first immunoglobulin made in a primary response and can bind five antigens at once. IgA is found primarily in mucos
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Lecture on immunoglobulins
- 2. Immunoglobulins:Structure and Function • Definition: Glycoprotein molecules that are produced by plasma cells in response to an immunogen and which function as antibodies Immune serum Ag adsorbed serum 1 2 + - albumin globulins Mobility Amountofprotein
- 3. Immunoglobulin Has Two Roles • Antigen Receptor – Recognition of and binding to antigens such as toxins, viruses, and exposed molecules on the surface of pathogenic organisms – V domain function • Effector Molecule – Elimination or inactivation of the foreign antigen or the cell that bears the antigen – C domain function
- 4. Basic Immunoglobulin Structure • Immunoglobulins - heterogeneous • Myeloma proteins - homogeneous immunoglobulins
- 5. Immunoglobulin Structure • Heavy & Light Chains • Disulfide bonds – Inter-chain – Intra-chain CH1 VL CL VH CH2 CH3 Hinge Region Carbohydrate Disulfide bond
- 6. Immunoglobulin Structure • Variable & Constant Regions – VL & CL – VH & CH • Hinge Region CH1 VL CL VH CH2 CH3 Hinge Region Carbohydrate Disulfide bond The first 108 amino acids in light chains and first 118 amino acids in heavy chains constitute the variable region
- 7. Immunoglobulin Structure • Domains – VL & CL – VH & CH1 - CH3 (or CH4) • Oligosaccharides CH1 VL CL VH CH2 CH3 Hinge Region Carbohydrate Disulfide bond
- 8. IgG molecule
- 9. Immunoglobulin Fragments: Structure/Function Relationships • Fab – Ag binding – Valence = 1 – Specificty determined by VH and VL Papain Fc Fab • Fc – Effector functions
- 10. Immunoglobulin Fragments: Structure/Function Relationships • Fab – Ag binding • Fc – Effector functions • F(ab’)2 Pepsin Fc Peptides F(ab’)2
- 11. Human Immunoglobulin Classes Depending on the heavy chain make up, the immunoglobulins are differentiated into 5 major classes • IgG - Gamma heavy chains • IgM – Mu heavy chains • IgA - Alpha heavy chains • IgD - Delta heavy chains • IgE - Epsilon heavy chains
- 12. Human Immunoglobulin Subclasses • IgG Subclasses – IgG1 - Gamma 1 heavy chains – IgG2 - Gamma 2 heavy chains – IgG3 - Gamma 3 heavy chains – IgG4 - Gamma 4 heavy chains • IgA subclasses – IgA1 - Alpha 1 heavy chains – IgA2 - Alpha 2 heavy chains
- 13. Human Immunoglobulin Light Chain Types • Kappa • Lambda In human beings, 60% light chains are of Kappa variety and 40% are of Lamda type
- 14. Human Immunoglobulin Light Chain Subtypes • Lambda light chains – Lambda 1 – Lambda 2 – Lambda 3 – Lambda 4
- 15. IgG • Structure – Monomer (7S) IgG1, IgG2 and IgG4 IgG3
- 16. IgG Predominant Ig of blood (75- 80%) 1 unit, smallest Longest half-life Antibody seen in secondary immnue response Passive transfer Crosses placental barrier – Rh iso-immunization Agglutination Opsonization Complement Actn.
- 17. IgM • Structure – Pentamer (19S) – Extra domain (CH4) – J chain C4 J Chain
- 18. IgM It can combine with 5 antigens simultaneously 3rd highest serum Ig First Ig made by fetus and B cells Major Ig of primary response No hinge region Natural antibodies are IgM in nature It cannot cross the placenta Agglutination, C’ act.
- 19. IgA • Structure – Serum - monomer – Secretions (sIgA) • Dimer (11S) • J chain • Secretory component J ChainSecretory Piece
- 20. Origin of Secretory Component of sIgA
- 21. IgA Serum-monomer 2nd highest serum Ig 2 units J chain secretory component produced by epithelial cells Major secretory Ig (Mucosal or Local Immunity) – Tears, saliva, gastric and pulmonary secretions Prevents attachment & penetration of microorganisms Does not fix complement (unless aggregated)
- 22. IgD • Structure – Monomer – Tail piece Tail Piece
- 23. IgD 1 unit 4th highest serum Ig Long hinge region. Found as membrane receptor on early B cells. Does not bind complement Not in all species.
- 24. IgE • Structure – Monomer – Extra domain (CH4) C4
- 25. IgE 1 unit Least common serum Ig Extra CH domain binds IgE specific receptors on basophils and mast cells. Ag binding induces degranulation. Parasitic immunity Binds to Fc receptor on eosinophils Type I Hypersensitivity Allergy Does not fix complement
- 26. IgE-Induced Degranulation of Mast Cells In Allergy
- 27. Clinical aspect • Paraproteinemias – Multiple myeloma – Bence-Jones proteinuria – Waldenstrom’s macroglobulinemia – Hyper gamma globulinemia
- 28. Multiple myeloma • When Ig secreting cells are transformed into malignant cells, one clone alone is enormously proliferated • This is seen in electrophoresis as the myeloma band or monoclonal band or M band • It is characterised by paraproteinemia, anemia, lytic bone lesions and proteinuria
- 29. • Bone marrow examination reveals large number of malignant plasma cells • Spontaneous pathological fracture of weight bearing bones, ribs and vertebrae may occur • X-ray shows punched out osteolytic lesions • Hypercalcemia and hypercalciuria • Raised beta-2 microglobin • Immunity is depressed • Prognosis is good
- 30. Bence-Jones proteinuria • Seen in 20% of patients with multiple myeloma • Monoclonal light chains are excreted in urine • They precipitate when heated between 45ºC and 60ºC; but redissolving at higher than 80ºC and lower than 45ºC • Bradshaw’s test