AIDS is caused by a virus called Human Immunodeficiency Virus or HIV. The presence of this virus is detected by screening the blood of a person for special kinds of proteins called antibodies which are produced in the body in response to viral infection.
A characteristic feature of antibody molecules is that they are highly specific. They bind only to certain regions of the viral – proteins which act as the antigen. This is similar to a key fitting only a specific lock. AIDS detection tests are actually based on detecting the binding of the antibodies present in the blood with an artificially synthesized antigen attached to a solid surface.
If the HIV antibody is present in the blood, it binds with the synthetic antigen. This reaction can be confirmed by tests which give a coloured product.
