When stimulated by an infectious agent or allergen, white blood cells within the body produce proteins called antibodies. Antibodies have the ability to bind selectively to a specific protein or compound, called an antigen, and the antibody-antigen binding stimulates the immune system to engulf and destroy the foreign object. Since the body produces specific antibodies in response to specific allergens or infectious agents, medical tests to assess the levels of antibodies can indicate the presence of an underlying disorder. There are a number of medical laboratory tests to detect antibodies and indicate infection.
ELISA
An enzyme-linked immunosorbent assay, or ELISA test, can be used to detect antibodies in a blood sample. The test relies on antibody-antigen binding as a way to detect the antibody. During an ELISA test, a known antigen is bound to a membrane, and the membrane is treated with the patient's sample. If an antibody against the test antigen is present in the patient, the antibody will bind to the membrane, and if the antibody is not present in the sample, no binding will occur. After allowing time for antibody binding, the doctor will test for the presence of the antibody on the membrane. A positive ELISA test indicates that a patient's tissue contains a specific antibody, and may indicate a patient has a specific disease.
Immunoprecipitation
Another antibody detection method is immunoprecipitation, or IP. During an IP experiment, a patient's blood is exposed to a specific antigen. If the antibody being tested is present within the patient's tissue, it will bind to the antigen, and all other antibodies will remain unbound. If the specific antibody is not present, none of the antibodies will bind to the antigen. After allowing time for antibody-antigen binding, all the antibodies, along with any antigen bound to the antibodies, are removed from the sample and analyzed by further laboratory methods. If the doctor or research technician can detect the antigen in the purified antibody sample, this indicates the presence of the antibody being tested. If the researcher cannot detect any bound antigen, this suggests the antibody is not present in the sample. This antibody detection method is used to test for the presence of antibodies that help diagnose hepatitis C virus infections, reports Clinical Experimental Immunology.
Cell Screening
Another common antibody detection method is cell screening, which allows researchers to detect antibodies in cells under the microscope. The University of Mississippi Medical Center reports that this type of testing is commonly used to help screen pregnant women or patients requiring blood or tissue transfusions to help detect antibodies that may generate an immune response that can complicate transfusions. Cell screening makes use of cells that contain specific antigens. The screening cell population is incubated with a patient's serum sample, and antibodies from the sample are allowed to bind to antigens on the screening cells. Researchers can then detect antibody-antigen binding by analyzing the screening cells for the presence of antibodies. If the researchers find antibody-antigen complexes in the screening cells, this indicates the presence of the antibody within the patient sample.
References
- Clinical and Diagnostic Virology: A nitrocellulose membrane based IgM capture enzyme immunoassay for etiological diagnosis of dengue virus infections
- Clinical Experimental Immunology: A new approach to cytochrome CYP2D6 antibody detection in autoimmune hepatitis type-2 (AIH-2) and chronic hepatitis C virus (HCV) infection: a sensitive and quantitative radioligand assay
- University of Mississippi Medical Center: Antibody Detection
