05醫(yī)學免疫學03第四章抗體

1、 Immunoglobulin And AntibodyXiaojian wang, Ph.D.Institute of ImmunologyZJU School of MedicineTel: 88206268 課程網站： 右下角-課程總覽-搜索：醫(yī)學免疫學 /G2S/Template/View.aspx?action=view&courseType=0&courseId=27447IMMUNOLOGYimmunoglobulin1.Introduction2.The structure of immunoglobulins3.Heterogeneity of immunog

2、lobulins4.Functions of immunoglobulins5.The structures and properties of immunoglobulin classes6.Production of antibodiesimmunoglobulinAntibody(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 bin

3、ding to the immunizing Ag Immunoglobulins (Ig)The Igs are globulin which function as Abs or similar to Abs in chemical structure. 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 humo

4、ral immunity Membrane Ig (mIg): BCR B cell receptorimmunoglobulinimmunoglobulinElectrophoretic mobility of serum proteins1. 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: , im

5、munoglobulinI. Basic structure of the immunoglobulinIn 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 ra

6、tio 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) immunoglobulinimmunoglobulin HVR (hypervariable region): 9-12aa, 3 HVRs CDR (complementarity-determining reg

7、ion): CDR1, CDR2, CDR3 FR (framework region): 15-30aaimmunoglobulinCDR binds with epitope of antigenAntigen peptideAntigen peptide 2) Constant region (C region) Light chain - CL (110 aa) Heavy chain - CH (330-440 aa) CH1, CH2, CH3, (CH4)immunoglobulinimmunoglobulin3. Hinge Region - between the CH1 a

8、nd 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 regionStructure of the immunoglobulinsimmunoglobulin3D images of the Ig molecule show that it is not straight as depicted in Figure. It is folded into glo

9、bular regions, each of which contains an intra-chain disulfide bond. These regions are called domains.Light Chain Domains - VL and CLHeavy Chain Domains -VH, CH1, CH2, CH3 IgA, IgD,IgG (CH4 in IgE and IgM) 4.Domains of immunoglobulinimmunoglobulinDownloaded from: StudentConsult (on 1 June 2006 01:58

10、 PM) 2005 Elsevier Binding of an antigen by an antibody.immunoglobulinFunctions of the domains on IgVH和和VL: 抗原結合部位抗原結合部位CH1-3和和CL: Ig 遺傳標志遺傳標志CH2(IgG)、 CH3(IgM): 補體結合部補體結合部位位CH2-CH3(IgG):結合并通過胎盤結合并通過胎盤CH3(IgG) CH4 (IgE)：FcR結合部結合部位位FabFcII. Other components in the Ig1. Joining chainJ chain is a small

11、 acidic protein that is synthesized by all plasma cells that secrete polymeric Igs (i.e. IgM and sIgA).Join the momomer to polymerimmunoglobulin2. Secretory piece (SP)Secretory component (SC) is a single glycopeptide with MW of 70KD. Produced by mucosa epithelial cells Functions: protect sIgA, resis

12、t proteolysis in extra secretory liquid. immunoglobulinlumenIII. Immunoglobulin fragmentsFab(fragment of antigen binding)Fc (fragment crystalizable) immunoglobulinHeterogenecity of IgCharacterist of IgBinding to antigenImmunogenicityIsotype Isotypes are the antigenic features of a class of Ig H (e.g

13、. chain is different from ).Isotypes of one species can induce immune response in another species.immunoglobulinHeterogenecity of IgClasses and subclasses of Ig IgG- (gamma)IgA- (alpha)IgM- (Mu)IgD- (delta)IgE- (epsilon) subclass IgG1IgG4, IgA1IgA2,IgM1Igm2 Type and subtype Type: (Kappa) (lambda) su

14、btype: 14immunoglobulinAllotypeimmunoglobulinThis refers to genetic variation between individuals within a species. CH和和CL上的一個或數個氨基酸殘基的差異上的一個或數個氨基酸殘基的差異- 遺傳標志遺傳標志Gm1-30Idiotype (Id) immunoglobulinVariation in the V domain ,particularly in CDR, produces idiotype.Functions of immunoglobulinsFunctions

15、of V regions Recognition and binding to antigen - HVR (CDR) - neutralization of toxins (e.g. diphtheria, tetanus); - immobilization of microorganisms; - neutralization of viral activityAntibody: monomer(IgG,IgE)-2價價 dimer(sIgA) - 4價價 Petamer(IgM) - 5價價immunoglobulinNeutralizationBacterial toxinsHost

16、 cellToxin receptorsNeutralization by antibodyPhagocytosis of antibody-antigen complex by macrophageFc receptorForming phagosomeneutralization of viral activityFunction of C regions (Fc portion)1. Activation of complement: IgM, IgG Ab( IgM、IgG )+Ag- C1q-補體補體經典途徑經典途徑 IgG4、IgA和和IgE的凝聚物的凝聚物-補體旁補體旁路途徑路途

17、徑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: IgE3. Passage through the placenta (IgG, CH2) and mucosa (sIgA)immunoglobulinimmunoglobulinOpsonizatio

18、n of antibodyimmunoglobulinAntibody-dependent cell-mediated cytotoxicity (ADCC)passage through the placenta(IgG) and mucosal(SIgA)Passage through mucosal(SIgA)Function of immunoglobulinsimmunoglobulinCharacteristic and function of Different class of Ig (1) (1)單體分子；單體分子； (2) (2)四個亞類；四個亞類； (3) (3)血清中含

19、量最高血清中含量最高(75%Ig)(75%Ig)； (4) (4)半衰期最長半衰期最長(20(202323天天) )； (5)3 (5)35 5歲達成人水平歲達成人水平(8.0(8.017mg/ml)17mg/ml)； (6) (6)可與可與SPASPA結合。結合。 (7 (7）唯一能通過胎盤的）唯一能通過胎盤的IgIgIgGimmunoglobulinIgGimmunoglobulin1. Fixes complement IgG1 and IgG3 fix complement well; IgG4 does not fix complement.2. 2. Opsonization: e

20、nhancement of Ag uptake by macrophages (M)3. 3. Antibody-dependent cell-mediated cytotoxicity (ADCC): NK cells4. 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 newbornIgMimmunoglobulin1. Penatmer 900kd Macrogl

21、obulin2. 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 DaysIgAimmunoglobulin1. IgA : monomer and secretary2. serum IgA (I

22、gA1) monomer3. secretory IgA (IgA2) dimer4. 2. sIgA exists in secretions such as tears, saliva, colostrum, mucus and has important role in local (mucosal) immunity.5. 3. IgA can be transmitted from mother to newbornIgDimmunoglobulin1. IgD is found at low levels in serum; its role in serum remains un

23、clear.2. IgD is primarily found on naive B cell surfaces where it functions as a receptor for antigen. 3. 3. Membrane IgD disappear in activated or memory B cellIgEimmunoglobulin1. IgE is the least common serum Ig. It binds very tightly to Fc receptors on basophils and mast cells even before interac

24、ting with antigen.2. Involved in allergic reactions.3. IgE also helps to clear parasites (e.g. worms) by eosinophils.Five Classes/IsotypesProduction of antibodiesimmunoglobulin1) Polyclonal antibody2) Monoclonal antibody3) Genetic engineering antibodybearing more than one epitopesAgB cellsClonal pro

25、liferationPolyclonal antibodyImmunizing mousepAbGeoreges Kohler and Cesar Milstein, 1984, monoclonal antibodyimmunoglobulinimmunoglobulinMonoclonal antibody productionHuman Monoclonals?It would be very nice to have available human monoclonals - much more useful therapeuticallyProblemsHard to get antigen-primed B cellsIn vitro primedSCID miceKnock-out miceNo good immortal partnersCan sometimes transform antibody-secreting B cells (EBV)immunoglobulinGen