Overview of the Immune System and Immunotoxicology

This chapter is designed to introduce the diversity and complexity of the immune system in terms of general overview that will be expanded upon in the following chapters. The immune system is briefly described with emphasis on the cells providing innate (cell lacking antigen specificity) and adaptive (cells with antigen specificity) immunity. The regulatory factors (cytokines and growth factors) that influence immune cell development, activation, proliferation, differentiation, and function are mentioned. The positive aspects of immunity, which include defenses against infections and cancers, as well as the negative aspects, including different hypersensitivities that can lead to pathophysiological conditions and autoimmune diseases, are described. Mechanisms to circumvent immune responses to self-constituents via tolerogenic processes (processes that prevent responses to antigens) are contrasted with immunogenic responses (immunity to antigens). Throughout the chapter mechanisms that can lead to health problems due to the effects of toxins or toxicants are introduced and many of these immunotoxicological disturbances are more fully explained in the following chapters.