Direct and Indirect Effects of Murine Interleukin‐2, Gamma Interferon, and Tumor Necrosis Factor on Testosterone Synthesis in Mouse Leydig Cells

Abstract

It was recently observed that treatment of patients with a high dosage of human interleukin (IL‐2) resulted in suppression of plasma concentrations of testosterone. A murine model was developed to assess the direct and indirect effects of murine IL‐2 and the secondarily released cytokines, gamma interferon (INFγ), and tumor necrosis factor (TNFα), on testosterone production in isolated Leydig cells. Pretreatment for 24 hours with IL‐2 (100 to 500 IU/ml) or INFγ (100 to 1000 IU/ml) significantly decreased testosterone production in response to luteinizing hormone (LH; P < 0.02 and 0.005, respectively). The combinations of INFγ with either TNFα or IL‐2 produced enhanced suppressive effects on Leydig cell testosterone production. Steroidogenic precursors (22‐hydroxycholesterol, 17α‐hydroxypregnenolone, and dehydroepiandrosterone) restored testosterone secretion to control levels after preincubation with INFγ or TNFα. In contrast, the inhibition of testosterone synthesis produced by either IL‐2 or INFγ plus TNFα could be reversed by 17α‐hydroxypregnenolone and dehydroepiandrosterone, but not by 22‐hydroxycholesterol (P < 0.01). Dibutryl cyclic adenosine monophosphate was also ineffective in reversing the inhibitory effects of these cytokines on synthesis. Although IL‐2 directly inhibited synthesis in isolated Leydig cells, it stimulated testosterone production (P < 0.005) in minced murine testes. This suggests that IL‐2 releases regulatory factors from other cells that were able to overcome the direct inhibitory effect of IL‐2. This stimulatory effect was not caused by INFγ and TNFα because INFγ alone or with TNFα inhibited (P < 0.005) testosterone production in minced testes. These results suggest that INFγ inhibits production by affecting LH‐stimulated events occurring before cholesterol side‐chain cleavage. IL‐2 and the combined effect of INFγ and TNFα additionally inhibit the cholesterol side‐chain cleavage enzyme.