Antibody detection is crucial in medicine for identifying diseases. Enzyme immunosorbent assays (ELISA) detect antibodies and antigens, with indirect sandwich and competitive ELISA techniques used. Commercial kits for detecting tuberculosis and HIV/AIDS are available, but may not be as reliable as sputum smear microscopy. Fluorescent antibody tests are used to detect malaria antibodies, which can reveal transfusion-induced malaria and strong disease symptoms.
Antibody detection is important in medicine for detecting disease, as antibodies are large proteins that can detect viruses and bacteria. Antibody detection is done in the laboratory and in the field to examine the bonds between antibodies and antigens and to identify an antibody by its distinctive color change when a substrate molecule that reacts with an enzyme is attached to it while still bound to the antigen. The detection test is known as an enzyme immunosorbent assay (ELISA). Prior to the development of ELISA, the only assays in the 1960s were radioimmunoassays that identified antibodies based on their specific radioactivity. The early 1970s saw the development of several ELISA techniques to identify specific antibodies.
The indirect sandwich ELISA technique for detecting antibodies prepares a buffered solution containing a disease antigen and binds it to a plastic plate. Then, a primary antibody from a patient is introduced to bind to the antigen. Next, a secondary antibody with an enzyme attached is introduced and a substrate for the enzyme is added. This causes a reaction that changes the color of the enzyme, signaling that the two antibodies have bound, if the patient’s antibody is positive for that disease antigen. The intensity of the color change indicates the amount of disease detected by the antibody; this color strength is then measured quantitatively by a spectrometer.
Another ELISA technique that works when patient samples are crude or impure is competitive ELISA, when an unlabeled antibody is incubated with the patient’s antigen sample. The bound antibody/antigen complex is washed so that unbound antibody is removed and a secondary antibody coupled with an enzyme specific to the primary antibody is introduced to bind with the antigen. With the addition of a substrate to the enzyme, if the disease is detected by the antibody, the enzyme will produce chromogenic or fluorescent properties as a signal. A field test used by Israeli doctors uses a test tube filled with protein fragments and antibodies and the introduction of a blue liquid. If the blue liquid turns red within ten minutes, the particular antigen in the tube is being recognized by the antibody for that particular disease.
In hard-to-reach areas of developing countries, laboratories are not easily accessible. Many commercial antibody detection kits have been sold to healthcare professionals for testing for tuberculosis, especially pediatric and human immunodeficiency virus-related tuberculosis/autoimmune deficiency syndrome (HIV/AIDS). One study including 68 specific studies found that these kits were not as reliable as sputum smear microscopy.
Malaria is another disease for which antibody detection uses a fluorescent antibody test procedure. This procedure is useful for screening blood donors because transfusion-induced malaria may not be shown with a simple blood test. If a patient shows repeated negative blood samples, but shows strong disease symptoms, the fluorescent marker test can reveal this. When examined under a microscope, malaria antibodies often show an apple-green color that is positive for the malaria parasite.
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