on a plate and then serum hopefully containing antibodies is mixed with the antigen. Then the complex is detected through fluorescence or a chromogen reaction. Low concentrations of antibodies or antigens can be detected using immunofiltration techniques. This basically filters a large volume of fluid through a porous pad. The antigen or antibody can be captured. This has been adapted for strip testing that can be used in a clinic. Testing for TORCH infections can be done with this type of testing. Pregnancy tests done at home are strip testing, also called lateral flow testing. In such cases, urine is allowed to adhere to an absorbent pad. This hydrates the dried reagents and, if antigens are present, a stripe will form.
USING FLUORESCENT ANTIBODY METHODS Fluorescent antibody techniques can be used by attaching a fluorescent marker to the constant region of a specific antibody. Cells can also be labeled with fluorescent antibodies in related testing. In direct fluorescent antibody testing a monoclonal antibody is bound to a fluorescent label. This is done to test for Group A streptococcus in a throat swab and to detect Mycoplasma infections and Legionella infections. Fluorescent antibodies bind to the bacteria so they can be detected on a slide. Indirect fluorescent antibody testing looks instead for antibodies in patient’s serum. It is used to check for syphilis. Syphilis organisms are prepared from a laboratory animal that are smeared on a glass slide. If the antibodies are present, they won’t wash off the slide and, when a secondary antibody is added that has a fluorogen added to it, there will be fluorescent bacteria seen on a slide. This is a confirmatory test to the VDRL test for syphilis. A related test is the fluorescent ANA test, which detects antinuclear antibodies. This is a test for autoimmune diseases and will be generally positive in a variety of autoimmune diseases. In order for it to work, the cells must be permeable to the anti-DNA antibody. It checks for the presence of anti-nuclear antibodies in the patient’s serum. The results are determined as a titer. Flow cytometry can be combined with fluorescence in order to count cells that pass through an automated, cell-counting system that will specifically detect fluorescing cells. 246
