What are some examples of diseases caused by T cells?

T cell–mediated autoimmune diseases are usually limited to a few organs and usually are not systemic. Examples of T cell–mediated hypersensitivity reactions against environmental antigens include contact sensitivity to chemicals like therapeutic drugs and substances found in plants ( poison ivy)). Tissue injury also may accompany T cell responses to microbes. For example, in tuberculosis, a T cell–mediated immune response develops against protein antigens of Mycobacterium tuberculosis, and the response becomes chronic because the infection is difficult to eradicate. The resultant granulomatous inflammation causes injury to normal tissues at the site of infection.