A visual examination of the presence and the distribution of particular antigens on or in cells and tissues using antibodies that have been coupled with fluorescent molecules such as rhodamine and fluorescein. In the direct method, the fluorescent probe combines directly to the antigen of interest. In the indirect method, two antibodies are used in sequence. The first is the one specifically against the antigen under study. Subsequently, the tissue is incubated with a second antibody, prepared against the first antibody. The second antibody has been conjugated previously with a fluorescent dye, which renders the complex visible. The indirect method is often preferred because, if one wants to localize more than one antigen, only one fluorescently labeled antigen need be used, provided the first antibody in each case is from the same species of animal. The second fluorescent antibody is generally commercially available. See Chronology, 1941, Coons et al.
Subjects: Genetics and Genomics.