SEROLOGY RXN.pptx

Antigen/Antibody Interaction An antigen-antibody interaction is a bimolecular association similar to an enzyme-substrate reaction but with a difference. 1. It does not lead to an irreversible chemical alteration in the antibody or antigen. 2. It involves various non-covalent interaction between the...

Antigen/Antibody Interaction An antigen-antibody interaction is a bimolecular association similar to an enzyme-substrate reaction but with a difference. 1. It does not lead to an irreversible chemical alteration in the antibody or antigen. 2. It involves various non-covalent interaction between the antigenic determinant of the antigen & the variable region domain of the antibody molecule Antigen/Antibody reactions The exquisite specificity of antigen-antibody interaction has led to the development of various immunologic assays. This has played a vital role in; Diagnosing diseases, monitoring the level of the humoral immune response Identifying molecules of biological or medical interest. An antigen reacts only with antibodies elicited by itself or a closely related antigen The results of many immunologic tests are expressed as a titer; A titer is the highest dilution of the specimen eg serum, that gives a positive reaction in the test. SEROLOGIC DIAGNOSIS Antibodies can be used as sensitive & specific tools to detect, identify & quantitate the antigens from a virus, bacteria, fungi, parasite etc. Immunologic techniques can detect, identify & quantitate antigen in clinical specimen Evaluate the antibody response to infection Ascertain individual’s history of exposure to infectious agents Many serologic assays are designed to give a positive or negative result Antigen/Antibody reaction cont. Most serologic tests are designed to determine the presence of either antigen or antibody. Although Ag-Ab rxn are highly specific, cross reaction can occur Cross reaction occur if 2 different antigens share identical epitope/possess similar chemical properties Cross-reactivity is often observed among polysaccharide antigens that contain similar oligosaccharide residues Some Examples of Ag/Ab RXN Precipitation reactions Agglutination reactions Radioimmunoassay Enzyme-Linked Immunosorbent Assay (ELISA) Western blotting Immunofluorescence Immunoelectron microscopy Selected techniques/purpose/Egs Technique Purpose Examples Latex agglutination Quantitation & detection of antigen & antibody Streptococcal Ags, fungal Ags Hemagglutinat Antiviral antibody, serotype of virus ion inhibition strain Identification of influenza Complement fixation Fungal, viral antibody Quantitate specific antibody titer Radioimmunoa Quantitation of antigen or antibody ssay (RIA) Viral antigen (rotavirus), viral antibody(anti-HIV) ELISA Same as RIA Same as RIA Western blot Detection of antigen-specific antibody Confirmation of anti-HIV seropositivity Immunofluores Population analysis of antigencence flow positive cells cytometry Immunophenotyping Ouchterlony Detect & compare antigen & immunodouble antibody diffusion Fungal antigen & antibody MONOCLONAL ANTIBODIES Monoclonal antibodies are the products of hybrid cells generated by the fusion & cloning of spleen cells from an immunized mouse & myeloma cells, which produces a hybridoma. The myeloma provides immortalization to the antibody-producing B-cells of the spleen Each hybridoma clone is a factory for one antibody molecule, yielding a monoclonal antibody that recognizes only one epitope Monoclonal antibodies can also be prepared through genetic engineering Monoclonal antibodies recognize individual epitopes on an antigen Monoclonal antibodies are commercially available for some antigens, especially for lymphocyte cell surface antigens