Figure 3.4

Antibody-antigen fit Antibodies have specific binding sites, which latch onto corresponding sites on the surface of an invading cell.

different from the others. A large antigen can stimulate production of a range of antibodies, which attach themselves to different parts of its surface.

Once produced, antibodies continue circulating in the blood in small quantities. This is the basis of the immune response, which prepares the body for further invasions by the same germ. It also allows doctors to discover a patient's past history of infection, by examining the antibodies in a sample of the patient's blood.

The antibody's ''seek and find" ability has a lot of potential medical uses, not only to combat diseases but also to help diagnose illnesses and detect the presence of drugs and abnormal substances in the blood. The body produces only minute amounts of each antibody, however, and blood samples have mixtures of many different types. Researchers needed to duplicate large numbers of identical antibodies. The means to do this came with the development of hybridoma technology for producing monoclonal antibodies, described in Chapter 2. Monoclonal antibodies (mAbs) are the products of cloned cell cultures derived from single original B-cells, as shown in Figure 3.5.