IFN-gamma and LPS overcome glucocorticoid inhibition of priming for superoxide release in human monocytes. Evidence that secretion of IL-1 and tumor necrosis factor-alpha is not essential for monocyte priming.
We examined the interaction between IFN-gamma, LPS, and glucocorticoids on release of oxygen radicals by human monocytes cultured in vitro. After 48 h culture, monocytes released low amounts of superoxide anion (O2-) when stimulated by PMA or FMLP. Monocytes incubated with either IFN-gamma or LPS became "primed" and released greater amounts of O2- in response to stimuli. Monocytes incubated with hydrocortisone, methylprednisolone, dexamethasone, or prednisolone alone showed decreased release of O2-. Prednisone and progesterone, which are not active glucocorticoids, had no effect. When glucocorticoids were co-incubated with IFN-gamma or LPS, the effect of hydrocortisone and other active steroids was blocked, and the monocytes released high O2-. However, when monocytes were preincubated with hydrocortisone for 24 h before addition of IFN-gamma or LPS, priming for enhanced O2- production by LPS was partially inhibited whereas there was no effect on IFN-gamma priming. We suggest that IFN-gamma and LPS can block the anti-inflammatory effects of glucocorticoids, contributing to increased inflammation at tissue sites; however, the mechanism of this effect may differ for the two macrophage activators. To investigate the mechanisms of priming by IFN-gamma and LPS, we examined the effects of these agents and of hydrocortisone on secretion of IL-1 and TNF-alpha. Both IL-1 and TNF-alpha primed monocytes for enhanced release of O2- in response to PMA. LPS caused monocytes to secrete both IL-1 beta and TNF-alpha. LPS-induced secretion of TNF-alpha and IL-1 beta was completely blocked by hydrocortisone, but the priming effect of LPS on O2- release was only partly blocked. IFN-gamma did not cause monocytes to secrete IL-1 beta or TNF-alpha, under our culture conditions (mononuclear cells cultured in Teflon in endotoxin-free modified Earle's salt solution without serum). Therefore, priming by LPS and IFN-gamma, and the inhibition of priming by glucocorticoids involve mechanisms that extend beyond regulation of secretion of IL-1 and TNF-alpha.