chapter  Chapter 3
18 Pages

Antigens

WithConstantin A. Bona, Francisco A. Bonilla

Antigens are molecules which interact with specific lymphocyte receptors: surface T cell antigen receptors; and B cell immunoglobulin receptors (cell surface and secreted). Antigens are often conceptualized in rather gross terms. We speak of immune responses to proteins or complex polysaccharides, and envision the antigen as a unit macromolecule. However, the immune system does not “see” antigens this way. A particular B or T cell interacts with only a very restricted portion of a macromolecule (Figure 3–1). The part of the antigen interacting with the B or T cell receptor is called an antigenic determinant, or epitope. Thus, antigens are molecules bearing one or more epitopes which, by definition, may be recognized by specific receptors in an immune system. The appropriate descriptive adjective is antigenic, while the property described is antigenicity. <italic>Diagram of the a-carbon structure of influenza virus hemagglutinin</italic>. The membrane-anchored portion of the molecule is toward the left. The right end of the molecule is solvent-exposed and receptor-binding. The shaded areas A-E represent major antigenic sites for antibody binding. (Adapted from Wilson and Cox, 1990.)