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A technique that uses a fluorochrome to indicate the occurrence of a specific antigen-antibody reaction. The fluorochrome labels either an antigen or an antibody. The labeled reactant is then used to detect the presence of the unlabeled reactant. The use of a labeled reactant (such as an antibody which both detects and indicates the antigen) to reveal the presence of an unlabeled one is termed direct immunofluorescence. The use of a labeled indicator antibody, which reacts with an unlabeled detector antibody that has previously reacted with an antigen, is termed indirect immunofluorescence. Substitution of a light meter for the human eye permits a quantitative measurement in immunofluorometry. See Immunoassay
any set of methods of fluorescent analysis used in immunology, histochemistry, virology, bacteriology, mycology, and parasitology.
The combination of immunochemical reactions with fluorescence microscopy makes possible the detection of tissue and cellular antigens, including those involved in autoimmune diseases and in malignantly degenerated cells. The method is also useful in studying the patterns of antibody synthesis and in identifying the causative agents of many viral and microbial diseases. Specific antibodies are tagged with a fluorescent dye (for example, acridine orange) that will not alter their properties and then introduced to the specimen, so that only the parts of the specimen containing antigen will fluoresce. When the formation of antigen-antibody complexes is being investigated by immuno-fluorescence, the antibodies are tagged with a dye whose fluorescent properties will change when the antibodies combine with antigen.