Indomethacin blocks the immunosuppressive activity of rat testicular macrophages cultured in vitro.

Macrophages are a prominent resident cell type in the interstitial tissue of the testis in several mammalian species. This presence in an immunologically-privileged site prompted an investigation of their ability to initiate and regulate lymphocyte proliferation in vitro. Isolated rat peripheral blood lymphocytes (PBL) were cultured either directly with isolated rat testicular (Tm) or peritoneal (Pm) macrophages or with the conditioned medium from cultures of these cells (Ts or Ps). The presence of Tm and Ts reduced the proliferative response of PBL to 65% +/- 3% and 65% +/- 4% of that observed in the control cultures. Stimulation of the Tm with lipopolysaccharide (LPS) did not significantly alter this effect. Dialysis of Ts (to remove molecules < 14,000 MW) before addition to PBL cultures did significantly reduce the amount of inhibition, with PBL proliferation reaching 93% +/- 4% of the control. LPS in conjunction with indomethacin (IDM) or interferon gamma (IFN gamma) induced PBL proliferation at levels comparable to or significantly greater than those of the controls (104% +/- 4% and 113% +/- 6%, respectively). The collective addition of IDM, IFN gamma and LPS to Tm cultures increased PBL proliferation over control levels (119% +/- 5% for Ts and 133% +/- 6% for Tm). Prostaglandin levels in macrophage-conditioned medium were measured by specific radioimmunoassay and were significantly greater in Ts (13.1 +/- 0.4 ng/ml PGE2 and 16.8 +/- 0.6 ng/ml PGF2 alpha) than in Ps (both below the assay minimum sensitivities). The results indicate that the rat testicular macrophages produce high basal levels of prostaglandin E2 and F2 alpha. These products appear largely responsible for the inhibition by these cells of mitogen-induced PBL proliferation in vitro, and may contribute to both the immune-privileged status and the normal physiology of the rodent testis.