Human graft versus host disease.

Human graft versus host disease is composed of 2 distinct clinical entities, acute graft versus host disease and chronic graft versus host disease, which have different pathogenesis. Acute graft versus host disease is produced by the attack of donor immunocompetent T or null lymphocytes against recipient histocompatibility antigens. The null lymphocytes may attack antigens shared by the donor and recipient and are autocytotoxic lymphocytes which can produce acute graft versus host disease in recipients of identical twin transplants. The cessation of acute graft versus host disease occurs when suppressor lymphocytes appear in the recipient's peripheral circulation. Chronic graft versus host disease is produced by immunocompetent lymphocytes that differentiate in the recipient. Its control is unknown. Some patients with chronic graft versus host disease have in vivo activated suppressor lymphocytes which produce a secondary immunoincompetence and an increased susceptibility to bacterial sepsis and death.