Impairment of cell-mediated immune responses by infection with Mycobacterium lepraemurium

The effect of chronic infection with Mycobacterium lepraemurium upon cell-mediated immune responses was studied in Lewis rats. Rats infected for 40 to 175 days were completely protected from attempted induction of experimental adjuvant disease, and the severity of experimental allergic encephalomyelitis in leprous rats was markedly attenuated. Full manifestations of each autoimmune disease were expressed in littermate control groups. Skin homograft rejection by infected rats was significantly impaired (P less than 0.001) as was the delayed-type hypersensitivity response to sheep erythrocytes (P less than 0.02). It is suggested that chronic infection with M. lepraemurium exerts a nonspecific inhibitory effect on cell-mediated immunity by perturbation of normal lymphocyte recirculation and by induction of immuno-suppressor cell activity.