Ontogeny of immunosuppressive activity, MHC antigens and leukocytes in the rat testis

The levels of immunosuppressive activity and the presence of MHC antigens and leukocytes were studied in the immature and the sexually mature rat testis. The immunosuppressive activities were measured from high-molecular weight (greater than 5 kDa) fractions of testis extracts using the protectin bioassay. The presence of MHC antigens and leucocytes was studied using the indirect immunoperoxidase method. In the immature rats, clusters of class I MHC antigen positive cells and a few cells expressing class II MHC antigen were present in the testicular interstitium. In the sexually mature rats, all the cells were MHC I+, and MHC II+ cells were numerous in the testicular interstitium. The seminiferous epithelium was MHC-negative in both the immature and the sexually mature testis. W3/25+ leukocytes were present in the interstitium and the tubular wall in both the immature and the sexually mature rat testis, but not in the seminiferous epithelium at any age. At 20-30 days of age, the testicular extracts were neutral or slightly stimulated 3H-TdR incorporation into peripheral blood lymphocytes, but at 44-60 days of age they inhibited lymphocyte proliferation significantly. In gel filtration, a peak of immunosuppressive activity was observed at approximately 400 kDa (protectin A) in both 20- and 60-days-old rat testes. A smaller peak was present at approximately 200 kDa in both age groups. This study shows that the testicular immunoregulatory microenvironment is different in the immature and the sexually mature rats. This may be important in such age-dependent human diseases as mumps orchitis and the testicular relapses of acute lymphoblastic leukemia.