Effective immune responses are critical for control of a variety of infectious disease including bacterial, viral and protozoan infections as well as in protection from development of tumors. Central to the development of an effective immune response is the T lymphocyte which, as part of the adaptive immune system, is central in achieving sterilization and long lasting immunity. While the normal immune responses is tightly regulated there are also notable defects leading to pathologic diseases. Inactivity of tumor antigen-specific T cells, either by suppression or passive ignorance allows tumors to grow and eventually actively suppress the immune response. Conversely, hyperactivation of antigen-specific T cells to self antigens is the underlying basis for many autoimmune diseases including: multiple sclerosis; arthritis; and diabetes. Secondary to their central role in a wide variety of physiologic and pathophysiologic responses my lab takes a broad-based approach to studying T cell responses.