The healthy immune system is capable of responding to foreign pathogens while remaining tolerant to self tissue. When tolerance to tissue fails,
autoimmunity ensues. In order to treat the cause of autoimmune disease, physicians must understand the immunologic mechanism of tolerance. We
will discuss the general principles of autoimmunity, factors that affect the development and severity of autoimmunity, such as environment and genetics, and different immunopathogenic mechanisms of autoimmunity.