Transcript IMMUNOLOGY
IMMUNOLOGY Immunoglobulin And Antibody Xiaojian wang, Ph.D. Institute of Immunology ZJU School of Medicine Tel: 88206268 [email protected] immunoglobulin 1. Introduction 2. The structure of immunoglobulins 3. Heterogeneity of immunoglobulins 4. Functions of immunoglobulins 5. The structures and properties of immunoglobulin classes 6. Production of antibodies immunoglobulin Antibody(Ab) Globulin produced by plasma cells in response to antigen and binds specifically to particular Ag. Ab is generally defined in terms of their specific binding to the immunizing Ag Immunoglobulins (Ig) The Igs are globulin which function as Abs or similar to Abs in chemical structure. immunoglobulin Not all of Ig have the functions of Ab, e.g. Patients with multiple myeloma have very high levels of Ig, but not Ab (to irrelevant things)) Secreted Ig (sIg)- mediated humoral immunity Membrane Ig (mIg): BCR B cell receptor immunoglobulin Electrophoretic mobility of serum proteins immunoglobulin I. Basic structure of the immunoglobulin 1. Heavy Chain and Light Chain heavy chain (H chain) 50-75Kd 450-550aa H chains: , , , , Isotypes: IgM, IgG, IgA, IgE, IgD Light chain (L chain) 25Kd 214aa Types of L chains: , immunoglobulin In any given Ig, all the H chains are identical. An antibody molecule has either two light chains or two light chains, but never one of each. In humans, about 60% of Ab molecules have light chains, and 40% have light chains. Market changes in this ratio can occur in patients with monoclonal B cell tumors. immunoglobulin 2. Variable region and constant region 1) Variable region (V region) Light Chain - VL (110 aa) Heavy Chain - VH (110 aa) immunoglobulin HVR (hypervariable region): 9-12aa, 3 HVRs CDR (complementarity-determining region): CDR1, CDR2, CDR3 FR (framework region): 15-30aa immunoglobulin Antigen peptide Antigen peptide CDR binds with epitope of antigen immunoglobulin 2) Constant region (C region) Light chain - CL (110 aa) Heavy chain - CH (330-440 aa) CH1, CH2, CH3, (CH4) immunoglobulin 3. Hinge Region - between the CH1 and CH2 region - rich in proline residues flexibility: allow the two Fab arms to bind epitope; be cleaved by proteases. - IgM and IgE have no hinge region immunoglobulin Structure of the immunoglobulins immunoglobulin 4.Domains of immunoglobulin 3D images of the Ig molecule show that it is not straight as depicted in Figure. It is folded into globular regions, each of which contains an intra-chain disulfide bond. These regions are called domains. Light Chain Domains - VL and CL Heavy Chain Domains -VH, CH1, CH2, CH3 IgA, IgD,IgG (CH4 in IgE and IgM) Binding of an antigen by an antibody. Downloaded from: StudentConsult (on 1 June 2006 01:58 PM) © 2005 Elsevier immunoglobulin Functions of the domains on Ig VH和VL: 抗原结合部位 CH1-3和CL: Ig 遗传标志 CH2(IgG)、 CH3(IgM): 补体结合部 位 CH2-CH3(IgG):结合并通过胎盘 Fab Fc CH3(IgG) CH4 (IgE)：FcR结合部 位 immunoglobulin II. Other components in the Ig 1. Joining chain J chain is a small acidic protein that is synthesized by all plasma cells that secrete polymeric Igs (i.e. IgM and sIgA). Join the momomer to polymer 2. Secretory piece (SP) immunoglobulin Secretory component (SC) is a single glycopeptide with MW of 70KD. Produced by mucosa epithelial cells Functions: protect sIgA, resist proteolysis in extra secretory liquid. lumen III. Immunoglobulin fragments Fab(fragment of antigen binding) Fc (fragment crystalizable) immunoglobulin Heterogenecity of Ig Characterist of Ig 1.Binding to antigen 2.Immunogenicity immunoglobulin Heterogenecity of Ig Isotype Isotypes are the antigenic features of a class of Ig H (e.g. chain is different from ). Isotypes of one species can induce immune response in another species. immunoglobulin Classes and subclasses of Ig IgG- (gamma) IgA- (alpha) IgM- (Mu) IgD- (delta) IgE- (epsilon) subclass IgG1~IgG4, IgA1~IgA2,IgM1~Igm2 Type and subtype Type: κ(Kappa) λ(lambda) subtype: λ1~λ4 Allotype immunoglobulin This refers to genetic variation between individuals within a species. CH和CL上的一个或数个氨基酸残基的差异--遗传标志 Gm1-30 Idiotype (Id) immunoglobulin Variation in the V domain ,particularly in CDR, produces idiotype. Functions of immunoglobulins immunoglobulin Functions of V regions Recognition and binding to antigen - HVR (CDR) - neutralization of toxins (e.g. diphtheria, tetanus); - immobilization of microorganisms; - neutralization of viral activity Antibody: monomer(IgG,IgE)---2价 dimer(sIgA) --4价 Petamer(IgM) --5价 Neutralization Toxin receptors Host cell Bacterial toxins Neutralization by antibody Forming phagosome Fc receptor Phagocytosis of antibody-antigen complex by macrophage neutralization of viral activity immunoglobulin Function of C regions (Fc portion) 1. Activation of complement: IgM, IgG Ab( IgM、IgG )+Ag--- C1q----补体经典途径 IgG4、IgA和IgE的凝聚物----补体旁路途径 2. Binding to Fc receptor of cells Opsonization: enhancement of Ag uptake by macrophages (M) Antibody-dependent cell-mediated cytotoxicity (ADCC): NK cells. Participation in type I hypersensitivity: IgE 3. Passage through the placenta (IgG, CH2) and mucosa (sIgA) immunoglobulin Opsonization of antibody immunoglobulin Antibody-dependent cell-mediated cytotoxicity (ADCC) passage through the placenta(IgG) and mucosal(SIgA) Passage through mucosal(SIgA) immunoglobulin Function of immunoglobulins Characteristic and function of Different class of Ig immunoglobulin IgG (1)单体分子； (2)四个亚类； (3)血清中含量最高(75%Ig)； (4)半衰期最长(20～23天)； (5)3～5岁达成人水平(8.0～ 17mg/ml)； (6)可与SPA结合。 (7）唯一能通过胎盘的Ig IgG immunoglobulin 1. Fixes complement –IgG1 and IgG3 fix complement well; IgG4 does not fix complement. 2. Opsonization: enhancement of Ag uptake by macrophages (M) 3. Antibody-dependent (ADCC): NK cells cell-mediated cytotoxicity 3. Crosses the placenta IgG is the only class of Ig that can crosses the placenta and it confers a high degree of passive immunity to the newborn IgM 1. Penatmer 900kd immunoglobulin Macroglobulin 2. IgM is the first Ig synthesized in life 3.IgM is the first Ig produced in primary immune response. 4. IgM is a good complement fixing Ig 5. IgM is also a good agglutinating Ig 6. IgM is mIgM ( IgD) of B cells : 7. Half time: 5 Days immunoglobulin IgA 1. IgA : monomer and secretary serum IgA (IgA1) monomer secretory IgA (IgA2) dimer 2. sIgA exists in secretions such as tears, saliva, colostrum, important role in mucus local and has (mucosal) immunity. 3. IgA can be transmitted from mother to newborn IgD immunoglobulin 1. IgD is found at low levels in serum; its role in serum remains unclear. 2. IgD is primarily found on naive B cell surfaces where it functions as a receptor for antigen. 3. Membrane IgD disappear in activated or memory B cell immunoglobulin IgE 1. IgE is the least common serum Ig. It binds very tightly to Fc receptors on basophils and mast cells even before interacting with antigen. 2. Involved in allergic reactions. 3. IgE also helps to clear parasites worms) by eosinophils. (e.g. Five Classes/Isotypes immunoglobulin Production of antibodies 1) Polyclonal antibody 2) Monoclonal antibody 3) Genetic engineering antibody pAb Ag bearing more than one epitopes Immunizing mouse B cells Clonal proliferation Polyclonal antibody immunoglobulin Georeges Kohler and Cesar Milstein, 1984, monoclonal antibody immunoglobulin Monoclonal antibody production immunoglobulin Human Monoclonals? It would be very nice to have available human monoclonals - much more useful therapeutically Problems Hard to get antigen-primed B cells In vitro primed SCID mice Knock-out mice No good immortal partners Can sometimes transform antibody-secreting B cells (EBV) immunoglobulin Genetically engineered antibody Chimeric Ab Mouse V gene + human C gene expression vector CDR-grafted Ab Mouse CDR gene Bispecific antibody human framework region immunoglobulin mouse Ab Chimeric Ab CDR-grafted Ab immunoglobulin Being Used Now... Humanized antibodies, where mouse CDR regions are combined with human framework and constant regions Anti CD20 (B cell antigen) against non-Hodgkins Lymphoma Anti-HER2 (human epidermal growth factor receptor 2) against breast cancer - Herceptin More than 200 such drugs in clinical trials Sample questions 1. Which of the following antibodies contains Joining chain---------------- ( ) A. IgG1 B. IgG2 C. sIgA D. IgE E. IgD Answer=C 2. Which of the following immunoglobulins can cross the placenta in humans------( ) A. IgA B. IgM C. IgE D. IgG E. IgD Answer=D 3. Describe the structure of an Ig molecule and how this structure enables it to bind to a specific antigen.