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The immune system exists to protect the host from infection, and its evolutionary history must have been shaped largely by this challenge. Other aspects of immunology, such as allergy, autoimmunity, graft rejection, and immunity to tumors are treated as variations on this basic protective function in which the nature of the antigen is the major variable.
The first part of the lecture summarizes our understanding of immunology in conceptual terms and introduces the main players: the cells, tissues, and molecules of the immune system. The middle part of the lecture deal with three main aspects of adaptive immunity: how the immune system recognizes and discriminates among different molecules; how individual cells develop so that each bears a unique receptor directed at foreign, and not at self, molecules; and how these cells are activated when they encounter microbes, and the effector mechanisms that are used to eliminate these microbes from the body. The last part of the lecture examines the role of the immune system in causing rather than preventing diseases, focusing on allergy, autoimmunity, and graft rejection as examples. Finally, we consider how the immune system can be manipulated to the benefit of the host, emphasizing endogenous regulatory mechanisms and the possibility of vaccinating not only against infection, but also against cancer and immunological diseases.