免疫学课件Antigen

Antigen Weilin Chen,Ph.D Institute of immunology,ZJUhttp:/ Lecture 21.Introduction2.Specificity3.Requirements for immunogenicity4.Types of antigens5.Superantigen,immunological adjuvants and mitogenIntroduction1.Antigen(Ag)the substances that induce a specific immune response(recognized by TCR or BCR)and subsequently react with the products of a specific immune response.Introduction 2.Properties of Ag-immunogenicity immunoreactivity(antigenicity)3.Complete antigenIntroduction4.Hapten-A substance that is non-immunogenic but which can react with the products of a specific immune response.5.Immunogen Tolerogen AllergenSpecificitySpecificity1.Antigenic determinant(epitope)-the portion of the antigen that binds specifically with the binding site of an antibody or a receptor on a lymphocyte.-the size of an epitope is approximately equivalent to 5-7 amino acids.录像：Ag.mp4(Karl Landsteiner l868-1943)1930 Nobel PrizeSpecificitydescriptionexample One epitopehaptensMany epitopes of the same specificitypolysaccharidesMany epitopes of different specificityproteinsReprensentation of some possible antigenic structuresSpecificity2.structure of epitope conformational determinant sequential determinant3.Epitopes recognized by B cells Epitopes recognized by T cellsB cell epitopeT cell epitopeDegradationNatural proteinAntigenic peptideT cell epitopeB cell epitope and T cell epitopeAntigenT and B cell epitopes in a protein antigenSpecificity T cell epitope B cell epitopeReceptor TCR BCRMHC necessary non-necessary Character linear short natural polypeptide peptide polysaccharidesSize 812 aa(CD8+T)5 15 aa 1217aa(CD4+T)5 7monosaccharidesType linear determinant conformational determinant;linear determinant Location everywhere of Ag surface of Ag Specificity4.Hapten-carrier effectSmon antigen and cross-reactionA.Contribution of the Immunogen1.Foreignness -The immune system normally discriminates between self and non-self such that only foreign molecules are immunogenic.Factors influencing immunogenicityFactors influencing immunogenicityA.Contribution of the Immunogen2.Chemical Composition-In general,the more complex the substance is chemically the more immunogenic it will be.Carbohydrates（polysaccharides）：haptens Lipids：rarely immunogenic Nucleic acids：poor immunogens Proteins：virtually all proteins are immunogenicFactors influencing immunogenicity3.Size-There is not absolute size above which a substance will be immunogenic.In general,the larger the molecule the more immunogenic it is likely to be.Factors influencing immunogenicity4.Chemical Complexity-an increase in the chemical complexity of a compound is accompanied by an increase in its immunogenicityFactors influencing immunogenicity5.Conformation and accessibility 6.Physical form-In general particulate antigens are more immunogenic than soluble ones and denatured antigens more immunogenic than the native form.Factors influencing immunogenicityB.Contribution of the Biological System1.Genetic Factors-Some substances are immunogenic in one species but not in another.Similarly,some substances are immunogenic in one individual but not in others(i.e.responders and non-responders).2.Other factors The very young and the very old Woman and man Immunosuppressive agentFactors influencing immunogenicityFactors influencing immunogenicityC.Method of Administration1.Dose-The dose of administration of an immunogen can influence its immunogenicity.2.Route-Generally the subcutaneous route is better than the intravenous or intragastric routes.The route of antigen administration can also alter the nature of the response3.AdjuvantsTypes of antigensTh:Thymus-dependent antigen(TD-Ag)Thymus-independent antigen(TI-Ag)Relative:Xenogenic antigen Allogenic antigen Autoantigen Heterophilic antigen Idiotypic antigenTypes of antigensTD-Ag T-dependent antigens are those that do not directly stimulate the production of antibody without the help of T cells.Proteins are T-dependent antigens.Types of antigensTI-Ag T-independent antigens are antigens which can directly stimulate the B cells to produce antibody without the requirement for T cell help In general,polysaccharides are T-independent antigens.The responses to these antigens differ from the responses to other antigens.(A)TI-1 Ag(B)TI-2 Ag Types of antigensXenogenic Ag -An antigen found in more than one species.Types of antigensAllogenic Ag -individuals of a species differ in alleles(are allogeneic)and the antigenic diffences will cause an immune response to allografts.The antigens concerned are often of the MHC and are referred to as alloantigens.Types of antigensAutoantigen -The antigens of an organisms own cells and cell products are self antigens to the immune system of that organisn.-Clones of immune cells reactive with self antigens are normally eliminated.Types of antigensHeterophilic Ag(Forssman antigen)-A cross-reacting antigen that appears in widely ranging species such as humans and bacteria.-Postinfectious glomerulonephritis:group A Streptococcu