Immunoregulatory activity in adult rat testicular interstitial fluid: roles of interleukin-1 and transforming growth factor (beta)

Studies on the effect of rat testicular interstitial fluid (IF) on T- cell function have reported both stimulatory and inhibitory actions. Specific cytokines produced within the testis, particularly interleukin- 1 (IL-1) and transforming growth factor (beta) (TGFbeta), may contribute to these apparently conflicting observations. In proliferation assays employing lectin- or antibody-activated thymocytes or mature T cells in vitro, adult rat testicular IF stimulated T-cell activation and/or proliferation at low assay doses and was inhibitory at higher doses. The stimulatory activity was blocked by recombinant IL-1 receptor antagonist. The inhibitory activity was not affected by a polyspecific TGF(beta) antiserum. The biological characteristics of the inhibitor were distinct from those of a similar, but considerably less potent, activity in platelet-depleted serum. These data demonstrate that rat testicular IF contains biologically significant concentrations of IL-1 but has a predominantly inhibitory action on T-cell responses. The factor predominantly responsible for this inhibitory activity displays a relatively large apparent molecular weight, is protease sensitive and partially heat labile, but does not appear to be one of the known mammalian TGF(beta) isoforms.