ABSTRACT
The evolution of a complex system required to recognize and eliminate non-self entities needs necessarily to be balanced by mechanisms that prevent recognition and response to self antigens. This chapter theme is to discuss how tolerance from self is achieved. The mechanisms involved in clonal deletion and clonal anergy are discussed, with special reference to the role of T regulatory cells (Tregs). We also describe experimental and medical approaches to induce tolerance that could have significant clinical value. The reverse side of tolerance is autoimmunity, when immune responses directed against self cause a variety of diseases that may affect all organs and tissues. The roles of autoantibodies and self-reacting T lymphocytes as primary causes of autoimmune disease are discussed. The diversity of autoimmune diseases is also associated with a diversity of pathogenic factors, including genetic determinants, functional aberrations, and molecular mimicry. The importance of animal models for the understanding the pathogenesis of autoimmune diseases is emphasized.
