Science dealing with the body's defenses against disease-causing microorganisms and disorders of those defenses.
Starting with vaccine against smallpox in 1796, immunology has arrived at a comprehensive and sophisticated understanding of the role of microorganisms in disease and of the formation, mobilization, action, and interaction of antibodies and antigen-reactive cells. It covers treatment of allergies , immunosuppression after organ transplants to prevent rejection, and study of autoimmune diseases and immunodeficiencies . {{link=AIDS">AIDS has stimulated intensive research in the last of these.