REGULATION OF TUMOR-NECROSIS-FACTOR-ALPHA AND IL-1-BETA SYNTHESIS BY THROMBOXANE A(2) IN NONADHERENT HUMAN MONOCYTES

Synthesis of TNF-alpha and IL-1 beta by monocytes/macrophages can be p artially regulated by the eicosanoid, PGE(2). We report here that inhi bition of both PGE(2) and thromboxane A(2) (TXA(2)) synthesis by a pro staglandin H synthase inhibitor, NS-398, had no effect on the synthesi s of either TNF-alpha or IL-1 beta, even though the addition of PGE(2) to these treated cells dose-dependently inhibited TNF-alpha and IL-1 beta synthesis. Because TXA(2) is a major eicosanoid product of stimul ated human monocytes, we examined its influence on cytokine production . Inhibition of thromboxane synthase by carboxyheptyl imidazole (CI) r esulted in inhibition of TNF-alpha (61+/-4.3%; n=8; p <0.001) and IL-1 beta (54+/-4.2%; n=8; p <0.001) synthesis by serum-treated zymosan-st imulated nonadherent human monocytes. This effect was observed when cy tokine production was measured by ELISA or bioactivity assays. Further more, the addition of a TXA(2) agonist, carbocyclic TXA(2), to CI-trea ted monocytes dose-dependently restored the levels of TNF-alpha and IL -1 beta synthesis to those found with serum-treated zymosan stimulatio n alone. Inhibition of TXA(2) activity by the thromboxane receptor ant agonists, pinane TXA(2) or SQ 29,548, also inhibited the production of TNF-alpha (67+/-2.4% and 65+/-2.7%, respectively; n=8; p <0.001) and IL-1 beta (59+/-3.3% and 70+/-1.2%, respectively; n=8; p <0.001). Trea tment with CI resulted in a partial decrease in TNF-alpha mRNA levels (60+/-12.0%; n=4), but had little or no effect on IL-1 beta mRNA level s. These novel observations implicate TXA, as an important paracrine o r autocrine facilitator of TNF-alpha and IL-1 beta production in stimu lated human monocytes and suggest that levels of TNF-alpha and IL-1 be ta synthesis are determined in part by the balance between TXA(2) and PGE(2) production in human monocytes.