Immunosuppressive activity in the rat seminiferous tubules

Rat seminiferous tubule segments in defined stages of the epithelial cycle were isolated by transillumination-assisted microdissection. The segments were cultured together with ConA-stimulated peripheral blood lymphocytes (PBL) and incorporation of 3H-labelled thymidine was measured. Tubule segments in stages II-VIII of the seminiferous epithelial cycle inhibited PBL proliferation significantly more than stages IX-I. Inhibition was lowest in stages IX-XII and increased progressively to reach a maximum in stages II-VIII. In a more detailed analysis, tubules in stages V and VI inhibited PBL proliferation significantly less than stage II tubules. No significant difference was observed between stages II and VII. The immunosuppressive activity had molecular weights of approximately 25 kDa and approximately 65 kDa in stage II-VIII seminiferous tubules. In stage II-VI seminiferous tubules activity was present also at approximately 10 kDa. The results suggest that the seminiferous tubules produce high-molecular weight immunosuppressive activity in a stage-dependent way. In addition to its contribution to the immunologically privileged milieu of the testis this activity may also be involved in the physiological regulation of DNA synthesis in the seminiferous epithelium.