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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.
The Uhlenhuth test, also referred to as the antigen–antibody precipitin test for species, is a test which can determine the species of a blood sample. It was invented by Paul Uhlenhuth in 1901, based on the discovery that the blood of different species had one or more characteristic proteins .
Precipitation occurs with most antigens because the antigen is multivalent (i.e. has several antigenic determinants per molecule to which antibodies can bind). Antibodies have at least two antigen binding sites (and in the case of immunoglobulin M there is a multimeric complex with up to 10 antigen binding sites), thus large aggregates or gel ...
In addition to the binding of an antibody to its antigen, the other key feature of all immunoassays is a means to produce a measurable signal in response to the binding. Most, though not all, immunoassays involve chemically linking antibodies or antigens with some kind of detectable label.
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.
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.
Blood compatibility testing is routinely performed before a blood transfusion.The full compatibility testing process involves ABO and RhD (Rh factor) typing; screening for antibodies against other blood group systems; and crossmatching, which involves testing the recipient's blood plasma against the donor's red blood cells as a final check for incompatibility.