Autoimmune encephalomyelitis: activation of thymus lymphocytes against syngeneic brain antigens in vitro.

Thymus lymphocytes of normal adult rats were autosensitized in vitro against soluble antigens extracted from the brains of syngeneic rats. Injection of the autosensitized lymphocytes into syngeneic rats led to the development of brain lesions suggestive of autoimmune encephalomyelitis. Injection of control lymphocytes or the antigen extract alone did not cause lesions. Since sensitization in vitro requires the presence of lymphocytes programmed with specific receptors, the results indicate that normal rats have lymphocytes capable of recognizing central nervous system self-antigens. Hence, regulatory mechanisms, inoperative in vitro, probably function in vivo to prevent immune activation of self-recognizing lymphocytes and autoimmunity. This concept suggests a new approach to exploring the pathogenesis of autoimmune diseases.