defense system that has evolved to protect animals from invading pathogenic microorganisms and ancer. It is able to generate an enormous variety of cells and molecules capable of specifically recognizing and eliminat ing an apparently limitless variety of foreign invaders. These cells and molecules act together in a dynamic network whose omplexity rivals that of the nervous system. Functionally, an immune response can be divided into two related activities--recognition and response. Immune
cell receptor when complexed with MHC,are called antigens. The molecular properties of antigens and he way in which these properties ultimately contribute to immune activation are central to our understanding of the mmune system. This chapter describes some of the molecu- Complementarity of Interacting Surfaces of Antibody(left) lar features of antigens recognized by B or T cells. The chap and Antigen(rig ter also explores the contribution made to immunogenicity by the biological system of the host; ultimately the biological system determines whether a molecule that combines with a a Immunogenicity Versus Antigenicity Bor T cells antigen-binding receptor can then induce an im
