Histological and serological features of experimental autoimmune thymitis in guinea-pigs.

Guinea-pigs injected with thymus or muscle in complete Freund's adjuvant developed experimental autoimmune thymitis'. Thymitis was defined by accumulations of lymphocytes around Hassall's corpuscles in the thymic medulla and by distortion and compression of reticulin fibres towards the cortico-medullary junction. Thymitis occurred in five of eight animals injected with thymus and four of four animals injected with muscle. Immunized guinea-pigs showed delayed hypersensitivity responses to tissues used for immunization; these responses were not tissue specific. Circulating antibody responses, detected by immunofluorescence, did show specificity in that muscle induced the formation of antibody to the myoid antigen of skeletal muscle striations and to thymic myoid cells, and thymus induced antibody to the cytoplasm of lymphocytes and epithelial-reticular cells of the thymus. Thymectomy 1 day before immunization did not influence the immune responses of immunized guinea-pigs, although we previously showed that it did prevent the development of a myasthenic' neuromuscular block which occurs in animals with experimental autoimmune thymitis. It would appear that this block is not due directly to the delayed hypersensitivity or circulating antibody responses we have demonstrated, but to a humoral substance released from a thymus damaged by autoimmune thymitis.