1、Immunoglobulin1.The structure and Function of Immunoglobulin(antibody)2.Ig genes and synthesis of protein3.Diversity of Ig and its mechanism 4.Application of antibodyIntroduction Antibody(Ab)-protein produced by plasma cells in response to immunization and binds specifically to particular Ag.-Ab is
2、generally defined in terms of their specific binding to the immunizing Ag IntroductionImmunoglobulins(Ig)-The Igs are globulin which function as Abs or similar to Abs in chemical structure.-Igs derive their name from the finding that when Ab-containing serum is place in an electrical field,they migr
3、ate with the globular proteins-secreted Ig(sIg);membrane Ig(mIg)Structure and function of the IgRodney Porter 1917-1985Nobel Prize in 1972Gerald Edelman 1929-Nobel Prize in 1972for their discoveries concerning the chemical structure of antibodies1)Heavy Chain and Light Chain heavy chain(H chain)5075
4、Kd 450550aa H chain:isotype:IgM,IgG,IgA,IgE,IgD IgG:IgG14 IgA:IgA1,IgA2 1,structure1)Heavy Chain and Light Chain light chain(L chain)25Kd 214aa classes of L chain:1 4structure of the Ig2.variable region and constant region variable region(V region)Light Chain-VL(110 aa)Heavy Chain-VH(110 aa)HVR or C
5、DR FR HVR or CDRHVR:hypervariable regions CDR:the complementarity determining regions.CDR are found in both the H and the L chains.Framework regionsFR(framework region)regions between the CDR in the V region are called the FR.VL and VH:Ag binding site constant region(C region)Light Chain-CL(110 aa)H
6、eavy Chain-CH(330-440 aa):CH1,CH2,CH3,(CH4)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 regionDomains -globular regions of 3D images of the Ig are called domains.1.Light Ch
7、ain Domains 2.VL,CL2.Heavy Chain Domains VH,CH1,CH2,CH3(or CH4)Domains of IgDomains of IgJ chain and SP J chain (Joining chain)a polypeptide chainJoin the monomer to polymerJ chain and SP Secretory piece(SP)Ig fragmentsHeterogeneity of Ig1.Classification of Ig class subclass IgG1IgG4 type subtype 1
8、2 3 42.Diversity of Ig induced by exogenous factors3.Serotypes of Ig induced by endogenous factors(1)Isotype(2)The genes for isotype variants are present in all healthy member of a species.(2)Allotype This refers to genetic variation between individuals within a species.(3)Idiotype Variation in the
9、V domain,particularly in CDR,produces idiotype.Function of antibodyNeutralization of microbes and microbial ToxinsNeutralization of microbes and microbial ToxinsNeutralization of microbes and microbial ToxinsOpsonization and phagocytosis of microbesopsonization:a process by which phagocytosis is fac
10、ilitated by the deposition of opsonins(Ab or C3b)on the antigen.Ab-dependent cell-mediated cytotoxicity,ADCCComplement activationMucosal immunity Rearrangement of Ig genes and synthesis of IgOrganization of Ig gene lociThree separate loci encode,respectively,all the Ig heavy chains,the Ig light chai
11、n,and the Ig light chain.Each locus is on a different chromosome.Rearrangement of V region of Ig moleculeMechanisms of V(D)J RecombinationV(D)J Recombinase:Rag-1/Rag-2Recombination signal sequences(RSS)RSS=heptamer+spacer+nonamer12/23 ruleLooping out and inversionConserved heptamer(7 bp)and nonamer(
12、9 bp)sequences,separated by 12-or 23-bp spacers,are located adjacent to V and J exons(for and loci)or to V,D,and J exons(in the H chain locus).The V(D)J recombinase recognizes these recombination signal sequences and brings the exons together Recombination of V and J exons may occur by deletion of i
13、ntervening DNA and ligation of the V and J segments if the V gene is in the opposite orientation,by inversion of the DNA followed by ligation of adjacent gene segments.Synapsis:Portions of the antigen receptor chromosome are made accessible to the recombination machinery,and two selected coding segm
14、ents and their adjacent RSSs are brought together by a chromosomal looping event and held in position for subsequent cleavage,processing,and joining.Cleavage:Double-strand breaks are enzymatically generated at RSS-coding sequence junctions using machinery that is lymphoid specific.process of V(D)J r
15、ecombinationCoding end processing:The broken coding ends(but not the signal/RSS ends)are modified by the addition or removal of bases,and thus greater diversity is generated.Joining:The broken coding ends as well as the signal ends are brought together and ligated by a double-strand break repair pro
16、cess found in all cells that is called non-homolgous end joining.process of V(D)J recombinationConsequences of VDJ recombinationIg gene recombination and expressionAllelic exclusion and Isotype exclusionIg gene recombination and expression Generation of Diversity of Ig Diversity(repertoire)is the to
17、tal of all the Ab specificities that an organism is capable of expressing.History -Germ line theory -Somatic mutation Generation of Diversity of IgCurrent conceptsuCombinatorial diversity V-D-J-C or V-J-C H-LuJunctional diversity P-nucleotide N-region insertionuSomatic hypermutation antigen stimulat
18、ion Combinatorial diversity Junctional diversity Junctional diversitySomatic hypermutationPreparation and application of Ab1)Preparation of Ab lPolyclonal antibodylMonoclonal antibodylGenetic engineering antibodyGenetic engineering antibodyGenetic engineering antibodyFab antibodyFv antibodySingle ch
19、ain fragment variable,ScFvSingle domain antibodyMinimal recognition antibody,MRUbispecific antibodyWolf E,Hofmeister H,Kufer P,et al.BiTEs:bispecific antibody constructswith unique anti-tumor activity.Drug Discover Today.2005,10(18):1237-1244 Preparation and application of Ab2)Application of AbScientific researchDiagnosisTherapyProphylaxis
