抗原专业知识.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,文档仅供参考，不能作为科学依据，请勿模仿；如有不当之处，请联系网站或本人删除。,Antigen,1.Concept,2.Immunogenicity and specificity,3.Requirements for immunogenicity,4.Types of antigens,5.Superantigen and adjuvants,KNOWLEDGE POINTS,Concept,1.,Antigen,(Ag),the substances that are recognized by TCR/BCR or antibody and induce a specific immune response.,Antigen,2.,Properties of Ag,-immunogenicity,-antigenicity or immunoreactivity,(react with the products of a specific immune response),Ag,T,B,T,浆细胞,致敏,T,细胞,抗体,免疫原性,Ag,T,B,T,浆细胞,致敏,T,细胞,抗原性,抗体,3.,Immunogen,-A substance that induces a specific immune response.,Complete Ags,：,have the properties of,immunogenicity,and,immunoreactivity,.,Hapten,（半抗原）,：,have the property of,immunoreactivity,but not immunogenicity.,-A substance that is non-immunogenic but which can react with the products of a specific immune response.,Antigen,Haptens,are small molecules which could never induce an immune response when administered by themselves but which can when coupled to a carrier molecule.,hapten+carrier complete Ag,5.,Tolerogen,allergen,Tolerogen:,an antigen that induces a state of specific immunological unresponsiveness,Allergen:,a substance capable of inducing allergy or specific hypersensitivity.,pollens,dust,drugs,and foods,Antigen,Foreignness and specificity,.,Foreignness,-The immune system normally discriminates between self and non-self such that only foreign molecules are immunogenic.,.,specificity,1.,epitope,(antigenic determinant),抗原决定簇（基），表位,-,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 5-15 amino acids,.,Antigen,epitope,Antigen,description,example,One epitope,haptens,Many epitopes,of the same specificity,Many polysaccharides,homopolymers,Many epitopes of different specificity,proteins,Representation of some possible antigenic structures,2.,the types of epitope,sequential epitope,:,All of the amino acid or sugar residues that form a given epitope are positioned sequentially in the linear sequence of a protein or polysaccharide antigen.,conformational epitope:,Some epitopes form only when the critical residues are brought together in space through folding of the polypeptide or polysaccharide chain into its normal three-dimensional conformation.,Antigen,Binding site for antigen,Binding site for antigen,构象表位 线性表位,B cell epitope,T cell epitope,Antigen,Antigen,T cell epitope B cell epitope,Receptor,TCR BCR,APC,MHC,necessary unnecessary,Character,linear short natural polypeptide,peptide polysaccharides,linear determinant conformational,determinant;linear,determinant,Location,Ag surface of Ag,Antigen,3.epitope-carrier effect,Antigen,Antigen,4,.common antigen and cross-reaction,Factors influencing immunogenicity,A.,Contribution of the antigen,1.,chemical Composition,protein,polysaccharide,nuclear acid,2.,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.,Antigen,3.,chemical complexity-,In general,the more complex the substance is chemically the more immunogenic it will be.,An increase in the chemical complexity of a compound is accompanied by an increase in its immunogenicity,4.conformation,5.Accessibility,(,如氨基酸残基的位置,),6.physical form,-In general particulate antigens are more immunogenic than soluble ones.,Antigen,Antigen,B.,Contribution of the host,1.,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.,Age,gender,-Age can also influence immunogenicity.Usually the very young and the very old have a,diminished ability to mount and immune response in response to an immunogen.,Antigen,C.,Method of Administration,1.,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 response,3.,Adjuvants,Antigen,Types of antigens,Th:,Thymus-dependent antigen(TD-Ag),Thymus-independent antigen(TI-Ag),Relative:Xenogenic antigen,Allogenic antigen,Autoantigen,Heterophilic antigen,Idiotypic antigen,Antigen,TD-Ag,Thymus,-dependent antigens are those that do not directly stimulate the production of antibody without the help of T cells.,B cell epitope T cell epitope,Humoral immunity and cellular immunity,Antibody:five types,Immune memory,Proteins are thymus-dependent antigens.,Antigen,TI-Ag,Thymus-independent antigens are antigens which can directly stimulate the B cells to produce antibody without the requirement for T cell help In general.,only B cell epitope,Humoral immunity,Antibody:IgM,No Immune memory,polysaccharides are TI-antigens.,Antigen,TI-Ag,Thymus-independent antigens can be subdivided into Type 1 and Type 2 based on their ability to polyclonally activate B cells.,Type 1 TI-Ag(LPS)are polyclonal activators while Type 2 are not.,Antigen,Xenogenic Ag,-,An antigen found in more than one species.,Allogenic Ag,-,individuals of a species differ in alleles(are allogeneic)and the antigenic differences will cause an immune response to allografts.,The antigens concerned are often of the MHC and are referred to as alloantigens.,Antigen,Autoantigen,-,The antigens of an organisms own cells and cell products are self antigens to the immune system of that organism.,-Clones of immune cells reactive with self antigens are normally eliminated.,Antigen,Types of antigens,Heterophilic Ag,(Forssman antigen),-,A cross-reacting antigen that appears in widely ranging species such as humans and bacteria.,Postinfectious glomerulonephritis:,group A,Streptococcus,glomerular basement membrane,Antigen,Forssman antigen,豚鼠 免疫家兔,肝、脾、肾等组织乳剂,分离,血清,与豚鼠组织发生反应,结合绵羊红细胞,Heterophilic Ag,(Forssman antigen),idiotypic Ag,-,The combined antigenic determinants(idiotopes)found on antibodies of an individual that are directed at a particular antigen;such antigenic determinants are found only in the variable region.,Antigen,Endogenous antigen,MHC I pathway,activate CD8,Exogenous antigen,MHC II pathway,activate CD4,Superantigen and adjuvant,Superantigen(SAg),-When the immune system encounters a conventional TD-Ag,only a small fraction(1 in 10,4,-10,6,)of the T cell population is able to recognize the antigen and become activated(monoclonal/oligoclonal response).However,there are some antigens which polyclonally activate some subtypes of the T cells(up to 20%).These antigens are called superantigens.,-SE(AE)T cell SPAB cell,Antigen,Antigen,Antigen,Adjuvant,-it is a substance which,when mixed with an immunogen,enhances the immune response against the immunogen.The use of adjuvants,however,is often hampered by undesirable side effects such as fever and inflammation.,-CFA,IFA,BCG,CP,LPS,CpG,Antigen,Some Key Points,An antigen is defined by any molecule which is recognized by an B cell surface antibody(B cell antigen receptor)or secreted antibody,or by a T cell antigen receptor.,An antigenic determinant(=,epitope,)is a defined site of recognition of an antigen by either specific B cell or T cell receptors.,An immunogen is an antigen that initiates an immune response upon recognition by antigen receptors(various properties influence immunogenicity).,T cell receptors only recognize antigenic peptides when presented by MHC molecules expressed on the surface of antigen presenting cells.,Superantigens,stimulate a larger number of T cells than normal antigens by reacting both with the MHC presenting molecule and a large subset of T cell receptors.,Antigen,Test,1.Which of the following antigens is most likely to be a hapten?-(),A.Red blood cells,B.Penicillin,C.Serum albumin,D.Staphylococcus Aureus,E.Lipopolysaccharide,2.Which of the following is the first requirement for a compound to be immunogenic?-(),A.Molecular size,B.Chemical complexity,C.Foreignness,D.Physical form,E.Dose administered,3.Which of the following is most likely regarding T cell epitopes?-(),A.They are recognized in the context of an MHC molecule,B.They require processing before the B cell can bind to them,C.They are generally hydrophilic,D.They are often made up of nucleotides,E.They may include amino acids from several sites in the molecule,that end up near each other in the final 3-D conformation,Antigen,Thanks!,