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Immunoglobulin Structure and Function

Immunoglobulin Structure and Function. By Associate Lecturer Mortadha H AL-Hussainy. Faculty of Veterinary Medicine Kufa University. Immunogobulin, Ig. What is Immunoglobulin? Immunoglobulin are the critical ingredients of humoral acquired immune response.

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Immunoglobulin Structure and Function

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  1. ImmunoglobulinStructure and Function By Associate Lecturer Mortadha H AL-Hussainy Faculty of Veterinary Medicine Kufa University

  2. Immunogobulin, Ig What is Immunoglobulin? Immunoglobulin are the critical ingredients of humoral acquired immune response. The immunoglobulins are a group of glycoproteins present in the serum and tissue fluids of all mammals.

  3. Immunoglobulins:Structure and Function Definition: Glycoprotein molecules that are produced by plasma cells in response to an immunogen and which function as antibodies - + albumin Amount of protein globulins γ β α1 α2 Immune serum Ag adsorbed serum Mobility

  4. General Functions of Immunoglobulins Effector functions Fixation of complement Binding to mast cells , macrophages, NK cell • Ag binding • Can result in protection • Valence (Usually require Ag binding)

  5. Basic Immunoglobulin Structure Immunoglobulins - heterogeneous Myeloma proteins - homogeneous immunoglobulins

  6. Two Forms of Immunoglobulin Membrane-bound receptor Soluble antibody

  7. Immunoglobulin Structure Variable(V) & Constant (C) Regions VL & CL VH & CH Hinge Region Disulfide bond Carbohydrate CL VL CH2 CH3 CH1 Hinge Region VH

  8. Structural Regions

  9. hypervariable region • also called Complementarity Determining Regions(CDRs),

  10. 超变区（hyper-variable region, HVR),又称互补决定区(complementary determining region, CDR）

  11. IgG molecule Used with permission from: Dr. Mike Clark, Immunology Division, Department of Pathology Cambridge University, Cambridge, England

  12. Enzymatic Digestion Products of Immunoglobulins

  13. Immunoglobulin Fragments: Structure/Function Relationships Fab Ag binding Valence = 1 Specificity determined by VH and VL Papain Fc Fab • Fc ( crystallizable) • Effector functions

  14. Domains of Immunoglobulin

  15. Functions of the domains on Ig： VH, VL — antigen binding sites； CH1～3, CL — genetic markers of Ig； CH2(IgG), CH3(IgM) — C1q binding sites； CH2～CH3(IgG) — binding to placenta； CH3(IgG) — FcγR binding site； CH4(IgE) — FcεR binding site.

  16. Function of Immunoglobulins • Recognition of antigen 识别抗原 • Activation of complement 激活补体 • Opsonization 调理作用 • Antibody-dependent cell-mediated cytotoxicity,ADCC抗体依赖性细胞毒作用 • Mediate hypersensitivity type I 超敏反应

  17. Immunoglobulin Classes and Subclasses Immunglobulin molecules are divided into distinct classes and subclasses in terms of the differences in amino acid sequence of constant region of heavy chain, i.e.γ,α,μ,δ,andεchains.

  18. Immunoglobulin Classes of Mammals IgG - Gamma (γ) heavy chains IgM - Mu (µ) heavy chains IgA - Alpha (α) heavy chains IgD - Delta (δ) heavy chains IgE - Epsilon (ε) heavy chains

  19. Five Classes of Immunoglobulin

  20. IgG has a family of subclass, IgG1, IgG2, IgG3, IgG4(cattle has no) • IgA is divided into two subclasses, IgA1 and IgA2(sheep).

  21. Light Chain Types of Immunoglobulin Kappa (κ) Lambda (λ) All light chains have protein molecular weights of approximately 23,000 but can be divided into two distinct types, namely λchain,κchain, respectively

  22. B Cell Antigen Receptor (BCR) Ig-α Ig-β Ig-β Ig-α

  23. IgA Structure Serum - monomer Secretions (sIgA) Dimer (11S) J chain Secretory component Secretory Piece J Chain

  24. IgA Structure Properties 2nd highest serum Ig Major secretory Ig (Mucosal or Local Immunity) Tears, saliva, gastric and pulmonary secretions Does not fix complement (unless aggregated) Binds to Fc receptors on some cells

  25. IgD Structure Properties 4th highest serum Ig B cell surface Ig Does not bind complement

  26. IgE Structure Properties Least common serum Ig Binds to basophils and mast cells (Does not require Ag binding) Allergic reactions Parasitic infections (Helminths) Binds to Fc receptor on eosinophils Does not fix complement

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