This study establishes that the principal T cell growth-stimulating factor in IF collected from normal rat testes is bioactive IL-1, indicating also that the levels of this activity in IF are biologically significant. In addition, we have confirmed the presence in normal IF of a factor (or factors) that inhibits the in vitro activation and/or proliferation of T cells, whether stimulated by the lectin PHA or by a T-cell receptor-activating antibody. Similar results were obtained when homologous (rat) or heterologous (mouse), and mature (peripheral blood lymphocytes and splenocytes) or immature (thymocyte), T-cell culture systems were used. This inhibitory activity appears to be due to one or more mac-romolecular factors that are either produced or activated in the testis. It has been demonstrated that a homologous PHA-activated rat thymocyte culture system provides a convenient, reproducible, and quantifiable assay for this bioactivity, which can be utilized in studies of its biological function. birth control pills
There was an earlier report of a lymphocyte growth-stimulating activity in rat IF with molecular characteristics comparable to those of IL-1 a; however, this is the first study to confirm that this activity is inhibited by a specific antagonist of IL-1 and therefore is attributable to the presence of one of the IL-1 forms. This confirmation was considered important, as several unrelated cytokines have the capacity to stimulate lectin-induced T-cell proliferation in vitro, including tumor necrosis factor (TNF)cx, IL-2, IL-4, and IL-6. TNFa, in particular, has recently been demonstrated to be present in testicular IF. Moreover, inhibin and 3-endorphin, hormones produced by the testis, also stimulate lymphocyte growth in vitro.