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Chapter 1 : Introduction to Part I
This is an introductory chapter to immunology. The immune system is a collection of organs and vessels in the body involved in producing and delivering the cells and molecules that protect from infections. Immunology is the study of the immune system and its products and mechanisms of defense. Innate defense mechanisms against foreign invaders include mechanical barriers, secreted products, and inflammatory cells. Innate resistance is present at all times in normal individuals. Its effectiveness may be modulated by physiological conditions. The adaptive immune system is quiescent until it is stimulated by a specific infection or vaccination (immunizing event). Agents that stimulate the adaptive system of immunity are recognized as foreign by the immune system and are called immunogens or antigens. The adaptive system is capable of exquisitely distinguishing among different microorganisms and significantly alters its intensity and response time upon reexposure. There are two major arms of the immune response: humoral and cellular. Humoral immunity is mediated by soluble protein molecules known as antibodies. Cellular immunity is mediated by specifically sensitized white blood cells known as lymphocytes. The hallmark of an inflammatory response is the passage of proteins, fluid, and cells from the blood into focal areas in tissues. The term immunopathology is a misnomer: “immune” means protection or exemption from; “pathology” is the study of disease. Thus, immunopathology literally means the study of the protection from disease, but in usage it actually means the study of how immune mechanisms cause diseases.