Guinea-pigs injected with testis autoclavate (WT) in incomplete adjuvant develop antibody but no delayed hypersensitivity or testicular lesions. These animals fail to develop delayed hypersensitivity or a lesion when subsequently injected with antigen in complete adjuvant. Animals similarly treated, and then given repeated injection of immune cells from animals treated with whole testis and complete adjuvant, develop both delayed hypersensitivity and the characteristic orchitis. 2. Guinea-pigs injected with a purified fraction (designated H) with incomplete adjuvant fail to develop either circulating antibody, delayed hypersensitivity or a testicular lesion. Animals subsequently injected with this antigen and complete adjuvant, develop delayed hypersensitivity but no circulating antibody or testicular lesion. Three of the five animals similarly treated and given repeated injections of serum containing anti-testis antibody also develop orchitis. 3. A sequential study of fourteen animals killed at daily intervals after they were injected with WT and complete adjuvant, showed that antibody was first detected in the testis on the same day as delayed hypersensitivity first appeared. Circulating antibody was not detected until 2 days later. The specific testicular antigen showed first signs of disappearing on the 10th day, by which time histological evidence of orchitis was first detected. 4. Antibody was not detected in the testes in any animal in the absence of delayed hypersensitivity.
