CYTOKINE SECRETION BY MACROPHAGES IN THE RAT TESTIS

The rat testis contains a large population of resident macrophages, th e physiological roles of which are yet to be established. To investiga te the functional capacity of these cells, we have analyzed the secret ion of the cytokines interleukin (IL)-1, IL-6, tumor necrosis factor a lpha (TNF alpha), and granulocyte macrophage-colony stimulating factor (GM-CSF) by isolated testicular macrophages (TMs) and, for comparison , by isolated rat peritoneal macrophages (PMs). Cells were cultured fo r 48 h in serum-free medium alone or with lipopolysaccharide (LPS, 10 mu g/ml) and/or recombinant interferon-gamma (rIFN gamma, 200 U/ml). S pecific bioassays were used to measure cytokines in the media collecte d from cultures. Basal production of IL-1, TNF alpha, and IL-6 by TMs and PMs were similar, but TMs produced 8-fold greater levels of GM-CSF than did PMs. LPS, alone or in combination with IFN gamma, significan tly enhanced the secretion of all cytokines by PMs (340-840% increase) . LPS a lone had little effect on TM secretion except to reduce GM-CSF levels some 4-fold. The addition of LPS and IFN gamma increased IL-1, IL-6, and TNF alpha levels (200-750% increase) and reduced GM-CSF lev els to 45% of basal levels. Treatment of cultures with indomethacin to minimize prostaglandin production enhanced the LPS-induced effects in both cell types. Expression of the mRNA for each cytokine in cultures of testicular and peritoneal macrophages, as well as in intact testis , was confirmed by reverse transcription polymerase chain reaction. Th ese studies indicate that macrophages resident within the rat testis h ave a novel cytokine secretion profile and an altered responsiveness t o inflammatory activators compared with macrophages from the peritonea l cavity. This may be important in physiological processes in the test is and may contribute to the dysfunctional afferent immune activity th ought to underlie the immunologically privileged status of the testes.