中科院细胞与分子免疫学课程Chapter3+Antibodies+and+Antigens-new2

Section II Recognition of Antigens,Three classes molecules used in adaptive immunity,Section II Recognition of Antigens,Chapter 3 Antibodies and Antigens Chapter 4 The Major Histocompatibility Complex,Chapter 5Antigen Processing and Presentation to T Lymphocytes Chapter 6Antigen Receptors and Accessory Molecules of T Lymphocytes,Chapter3 Antibodies and Antigens,Natural Distribution and Production of Antibodies,Antibodies are distributed: - through out the body - on the surface of a limited number of cell types. -Phagocytes -NK cells -Mast cellsProduction : B lymphocytes,Binding antigen phase: -In recognition phase - Membrane antibody function as BCR Nave B cell changed into activated phase -In effector phase - Secreted form Eliminate the antigen,70-kg adult human : 3g of antibodies Two thirds of the antibody: IgAAntibodies that enter the circulation have limited half-lives. -IgG, has a half-life of about 3 weeks.,Several interesting numbers:,Molecular Structure of Antibodies,A symmetric core structure:-two identical light chains and heavy chains.,Ig domain:,Ig domain:,Barrel under construction,A barrel made of many staves arranged in a folded over sheet,Ig domain: about 110 amino acid residues fold independently in a globular motif Ig super-family: All molecules that contain this motif,Terms should to be known:,Both the heavy chains and light chains have: - N terminal variable regions in antigen recognition- C terminal constant regions in effector functions,Structural Features of Variable Regions and Their Relationship to Antigen Binding,Three hypervariable segments in antigen binding,Crystallographic analyses of antigen-antibody complexes,Complementarity-determining regions (CDRs): Region: The three hypervariable regions of a VL domain and VH domain are brought together in three-dimensional space to form an antigen-binding surface. Character: a surface complementary to the three-dimensional structure of the bound antigen,Structural Features of Constant Regions and Their Relationship to Effector Functions,On the basis of differences in the structure of their heavy chain C regions, antibody molecules can be divided into distinct classes and subclasses.,Isotypes: classesIgG - Gamma () heavy chainsIgM - Mu () heavy chains IgA - Alpha () heavy chains IgD - Delta () heavy chains IgE - Epsilon () heavy chains ,Immunoglobulin Isotypes,IgM (kappa),IgG (kappa),Subtypes：In humans, IgA and IgG isotypes can be further subdivided into closely related subclasses, or subtypes, called IgA1 and IgA2, and IgG1, IgG2, IgG3, and IgG4.,IgG1,IgG4,IgG3,IgG2,Immunoglobulin Allotypes（同种异型）,Definition - Antigenic determinants specified by allelic forms of the Ig genes,minor structural differences in amino acid sequences located in the conserved portions.,IgG2 (kappa)Person 2,IgG2 (kappa)Person 1,Immunoglobulin Idiotypes（独特型）,IgG1 (kappa)Person2anti-B,IgG1 (kappa)Person 1anti-A,- By the hypervariable regions of the Ig variable domains.,Antibody molecules are flexible, permitting them to bind to different arrays of antigens.,Character of Hinge Regions ：,There are two classes, or isotypes, of light chains, called and ., and ,Character of Light chain,About 60% of antibody molecules have light chains, and about 40% have light chains. B cell lymphomas,Antibodies may be expressed in secreted or membrane-associated forms, which differ in the amino acid sequence of the carboxy terminal end of the heavy chain C region.,Identify the functional domain,Papain: Fab + FCPepsin:F(ab)2,Features Related to Effector Functions,Fc portions perform distinct functions.,ADCC: Antibody-dependent cell-mediated cytotoxity,Activation of complement,Healthy E. coli,Electron micrographs of the effect of antibodies and complement upon bacteria,Activation of complement,Antibody + complement- mediated damage to E. coli,Fc region determines the tissue distribution of antibody molecules,IgA : the only isotype in mucosal secretions and milk. IgG: Fc receptor expressed in the placenta and the intestine,Antigen,Features of Biologic Antigens,Antigen: Any substance that may be specifically bound by an antibody molecule or T cell receptor.Immunogens: Molecules that stimulate immune responses Hapten: Small chemicals, such as dinitrophenol, may bind to antibodies but cannot activate B cells on their own.Carrier:To generate antibodies specific for hapten, macromolecules were commonly attach them to immunization, the macromolecules were called carrier.,Terms to remember :,DNP-BSA,Hapten,Carrier:,Immunogens,Antigen:,Determinant /epitope: Antibody binds to only a portion of the macromolecule, which is called a determinant or an epitope.,Polyvalency / multivalency: The presence of multiple identical determinants in an antigen.,Different epitopes of a single protein molecule may influence the binding of antibodies.Steric hindrance: two determinants are close to one another. Allosteric effects: first antibody binding cause a conformational change.,Determinants may be Covalent structure: liner determinantsNoncovalent folding: conformational determinants,Structure and Chemical Basis of Antigen BindingThe antigen-binding sites of most antibodies are planar surfaces.The binding is noncovalent, reversible binding.,Affinity :The strength of the binding between a single combining site of an antibody and an epitope of an antigen.,Character of Antibody binding:,Kd = dissociation constant = antigen concentration binding 50% antibody present in a solutionTypical human antibody Kd: 10-7 M-10-9 M,2. Avidity: The overall strength of attachment,3. Would the affinity be different in the same antibody ?,For polyvalent antigen can form into large masses,Changes in antibody structure during humoral immune responses,Affinity mutationSwitch from membrane to secreted formIsotype switching,Monoclonal Antibodies,Antigen,Spleen cell+ Myloma cell,Selection,Screening,Tetrahydrofolate,Aminopterin,Selection of Myloma cell lines :,Aminopterin-treated Cells can use Salvage