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
body. These organs can be classified functionally nto two main groups. The primary lymphoid organs provide appropriate microenvironments for the development and maturation of lymphocytes. The secondary lymphoid organs rap antigen from defined tissues or vascular spaces and are sites where mature lymphocytes can interact effectively with that antigen. Blood vessels and lymphatic systems connect these organs, uniting them into a functional whole Carried within the blood and lymph and populating the Macrophage Interacting with
