In immunofluorescence testing, the fundamental tool is a fluorescent antibody, a fluorescent dye-labeled monoclonal antibody. For diagnosis, the two ways that fluorescent antibodies (FAbs) can be used.
1. Direct Testing
An unknown test specimen or antigen is fixed to a slide during direct testing and exposed to a fluorescent antibody solution of a known composition. They will bind to it if the antibodies are complementary to antigens in the material.
It is observed by the fluorescent microscope after the slide is rinsed to remove unattached antibodies. The presence of Ab-Ag complexes and a positive outcome are indicated by fluorescing cells or particles. These tests are useful in the identification and location of antigens on cell or tissue surfaces and in the identification of syphilis, gonorrhea, chlamydiosis, whooping cough, Legionnaires’ disease, plague, trichomoniasis, meningitis, and listeriosis disease agents.
2. Indirect Testing
Fluorescent antibodies are antibodies made to react with another antibody’s Fc region (remember that antibodies can be antigenic) in indirect testing methods. An antigen of a known character (for example, a bacterial cell) is combined with a test serum of an unknown antibody content in this scheme.
To visualise whether the serum contains antibodies that are attached to the antigen, a fluorescent antibody solution that can react with the unknown antibody is applied and rinsed off. Fluorescent aggregates or cells are shown in a positive test, indicating that the fluorescent antibodies have been combined with the unlabeled antibodies. No fluorescent complexes will appear in a negative test. To diagnose syphilis (FTA-ABS) and various viral infections, this method is frequently used.