The use of KIM-1 antagonists to inhibit signaling between a T cell and asecond cell, e.g., an antigen-presenting cell, is disclosed. Such inhibitionis useful for treatment of diseases including various autoimmune diseases andgraft-versus-host disease. Also disclosed is the use of a KIM-1 antagonist toinhibit secretion of IFN-.gamma. by lymphocytes or other immune cells in amammal. Inhibition of IFN-.gamma. is useful for treatment of inflammatorydiseases or disorders, e.g., inflammatory bowel disease.