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In the zone of equivalence, the formation of precipitin complexes is optimal. Extensive lattices of antigen and antibody are formed by cross-linking. At high concentrations of antigen, the average size of antibody-antigen complexes is once again small because few antibody molecules are available to cross-link antigen molecules together.
Immunoprecipitation of intact protein complexes (i.e. antigen along with any proteins or ligands that are bound to it) is known as co-immunoprecipitation (Co-IP). Co-IP works by selecting an antibody that targets a known protein that is believed to be a member of a larger complex of proteins.
Firstly, the antigen and antibody rapidly form antigen-antibody complexes within few seconds and this is followed by a slower reaction in which the antibody-antigen complexes forms lattices that precipitate from the solution. [25] [26] A special ring test is useful for diagnosis of anthrax and determination of adulteration in food. [27] [28]
Immunodiffusion is a laboratory technique used to detect and quantify antigens and antibodies by observing their interactions within a gel medium. [1] This technique involves the diffusion of antigens and antibodies through a gel, usually agar, resulting in the formation of a visible precipitate when they interact.
As more antigen is added, the amount of protein precipitated increases until the antigen/antibody molecules are at an optimal ratio. This is known as the zone of equivalence or equivalence point. When the amount of antigen in solution exceeds the amount of antibody, the amount of precipitation will decrease. This is known as the antigen excess ...
The antigen diffuses radially into the medium, forming a circle of precipitin that marks the boundary between the antibody and the antigen. [1] [2] The diameter of the circle increases with time as the antigen diffuses into the medium, reacts with the antibody, and forms insoluble precipitin complexes.
In immunology the particular macromolecule bound by an antibody is referred to as an antigen and the area on an antigen to which the antibody binds is called an epitope. In some cases, an immunoassay may use an antigen to detect for the presence of antibodies, which recognize that antigen, in a solution.
Immunochemical techniques include: enzyme-linked immunosorbent assay, immunoblotting (e.g., Western blot assay), precipitation and agglutination reactions, immunoelectrophoresis, immunophenotyping, immunochromatographic assay and cyflometry. One of the earliest examples of immunochemistry is the Wasserman test to detect syphilis.