Immunoglobulin

1. IMMUNOLOGY Immunoglobulin Chen Weilin, Ph.D Institute of immunology, ZJU

2. immunoglobulin • Introduction • the basic structure of immunoglobulins • Fuction of immunoglobulins • the structures and properties of immunoglobulin classes 5. Monoclonal antibody

3. immunoglobulin Introduction Immunoglobulins (Ig) - Glycoprotein molecules which are produced by plasma cells in response to an immunogen and which function as antibodies. The immunoglobulins derive their name from the finding that when antibody-containing serum is place in an electrical field the antibodies, which were responsible for immunity, migrated with the globular proteins - secreted Ig(sIg) ; membrane Ig(mIg)

4. immunoglobulin Introduction

5. immunoglobulin Introduction Antibody(Ab) - Serum protein formed in response to immunization; antibodies are generally defined in terms of their specific binding to the immunizing antigen.

6. immunoglobulin basic structure of the immunoglobulins

7. immunoglobulin basic structure of the immunoglobulins 1.Heavy Chain and Light Chain heavy chain (H chain) 50-75Kd 450-550aa isotype:IgM,IgD,IgA,IgE,IgG H chain: μ δ α ε γ light chain (L chain) 25Kd 214aa classes of L chain: κ λ

8. immunoglobulin basic structure of the immunoglobulins 2.variable region and constant region variable region(V region) Light Chain - VL (110 aa) Heavy Chain - VH (110 aa) HRV(hypervariable region) CDR(complementarity-determining region) FR(framework region)

9. immunoglobulin basic structure of the immunoglobulins CDR binds with epitope of antigen

10. immunoglobulin basic structure of the immunoglobulins 2.variable region and constant region constant region(C region) Light Chain - CL (110 aa) Heavy Chain - CH (330-440 aa) CH1, CH2, CH3,( CH4)

11. immunoglobulin basic structure of the immunoglobulins 3. Hinge Region - between the CH1 and CH2 region of the H chain - be made of cysteine and proline residues cysteine:be involved in formation of interchain disulfide bonds proline residues:prevent folding in a globular structure • flexibility: allow the two Fab arms to open; close to accommodate binding to epitope; be cleaved by proteases. - IgM and IgE have no hinge region

12. immunoglobulin Domains of immunoglobulin Domains - 3D images of the immunoglobulin molecule shows that it is not straight as depicted in Figure. Rather, it is folded into globular regions each of which contains an intra-chain disulfide bond. These regions are called domains. 1. Light Chain Domains - VL and CL 2. Heavy Chain Domains - VH, CH1,CH2, CH3 (or CH4)

13. immunoglobulin Domains of immunoglobulin

14. immunoglobulin Domains of the Ig

15. immunoglobulin

16. immunoglobulin Immunoglobulin fragments

17. immunoglobulin J chain and SP Joining chain -J chain a ploypeptide chain Join the units together

18. immunoglobulin J chain and SP Secretory piece -SP,SC

19. immunoglobulin Function of immunoglobulins Functions of V regions - recognition and binding to antigen - HVR (CDR) - neutralization of toxins; immobilization of microorganisms; neutralization of viral activity

20. immunoglobulin Function of C regions (Fc portion) 1. Activation of complement: IgM, IgG1,3; IgA 2. Binding to Fc receptor of cell • opsonization, enhancement of Ag uptake by DC and M • ADCC • Participation in type I hypersensitivity 3. Passage through the placenta (IgG) and mucosa (sIgA)

21. immunoglobulin Opsonization of antibody

22. immunoglobulin Antibody-dependent cell-mediated cytotoxicity (ADCC)

23. immunoglobulin IgG • IgG is the major Ig in serum - 75% of serum Ig • IgG is the major Ig in extra vascular spaces • c) Fixes complement - Not all subclasses fix equally • well; IgG4 does not fix complement • d) Binding to cells - Macrophages, monocytes, PMN's and some lymphocytes have Fc receptors for the Fc region of IgG.

24. immunoglobulin IgM a) IgM is the 3rd most common serum Ig. b) IgM is the first Ig to be made by the fetus and the first Ig to be made by a virgin B cells when it is stimulated by antigen. c) As a consequence of its pentameric structure, IgM is a good complement fixing Ig. Thus, IgM antibodies are very efficient in leading to the lysis of microorganisms d) As a consequence of its structure, IgM is also a good agglutinating Ig . e) IgM binds to some cells via Fc receptors.

25. immunoglobulin IgA a) IgA is the 2nd most common serum Ig. b) IgA is the major class of Ig in secretions – tears, saliva, colostrum, mucus. Since it is found in secretions secretory IgA is important in local (mucosal) immunity. c) Normally IgA does not fix complement, unless aggregated. d) IgA can binding to some cells - PMN's and some lymphocytes.

26. immunoglobulin IgA

27. immunoglobulin IgD a) IgD is found in low levels in serum; its role in serum uncertain. b) IgD is primarily found on B cell surfaces where it functions as a receptor for antigen. IgD on the surface of B cells has extra amino acids at C-terminal end for anchoring to the membrane. It also associates with the Ig-alpha and Ig-beta chains. c) IgD does not bind complement.

28. immunoglobulin IgE • IgE is the least common serum Ig • since it binds very tightly to Fc receptors on basophils and mast cells even before interacting with antigen. • b) Involved in allergic reactions • c) IgE also plays a role in parasitic • helminth diseases • d) IgE does not fix complement

29. immunoglobulin Monoclonal antibody