A pathogen entering the body stimulates the immune response. The body responds to the invading organisms, or antigens, by producing antibodies. These antibodies act as flags, binding to the antigens and signaling other cells to come and destroy them. Antibodies also remain in the bloodstream after the pathogen is destroyed, ready to react if the pathogen returns a second time. Because each antibody is specific to a certain antigen, they can be used to detect the presence of a disease in an individual.
Procedure
The Enzyme-Linked Immunosorbent Assay, or ELISA, can be used to test for antibodies. It has multiple uses, such as testing for diseases such as HIV and SARS, drug use, and pregnancy. In ELISA, first a test sample and then a primary antibody solution are added to a microplate strip. If antigens are present in the test sample, they will have bound to the wells on the microplate strip, and antibodies will bind to those antigens. If not, they will be removed when the well is rinsed out. A second antibody is then added to the microplate strip, and the unbound antibodies are again rinsed out. The second group of antibodies are labeled with an enzyme which, when exposed to a chromogenic enzyme substrate, will change color.
The color-changing enzyme shows up
as the second band on a pregnancy test.
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