SYNERGISTIC COOPERATION BETWEEN T-CELL LYMPHOKINES FOR INDUCTION OF THE NITRIC-OXIDE SYNTHASE GENE IN MURINE PERITONEAL-MACROPHAGES

The ability of T cell-derived cytokines to induce the expression of th e nitric oxide synthase (NOS) gene in murine peritoneal macrophages wa s examined. IL-2 or TNF-alpha alone had no effect either on gene expre ssion or enzyme activity, whereas IFN-gamma had only modest activity. When IL-2 or TNF-alpha were used in combination with IFN-gamma, there was a marked cooperative induction of both mRNA and enzyme activity. T he cooperative effects were truly synergistic, as the consequences of combined cytokine treatment were many times greater than was seen with any of the agents acting independently. The expression of NOS mRNA an d enzyme activity in response to combined lymphokine treatments was a continuous process reaching optimal levels between 24 and 48 h after s timulation. Concentration dependency for both IL-2 and TNF-alpha sugge sted that their effects were mediated through interaction with the cor responding defined cell surface receptors. Human rTNF-alpha was as eff ective a stimulus as murine TNF-alpha; because human TNF-alpha is reco gnized only by the p55 Type II TNF receptor, this structure appears to mediate the response to TNF-alpha. When IL-2 and TNF-alpha were added at saturating doses in the presence of IFN-gamma, there was an additi ve effect on NOS mRNA expression suggesting that IL-2 and TNF-alpha co operate with IFN-gamma through at least partially distinct intracellul ar signaling pathways. Expression of NOS mRNA in response to IFN-gamma /IL-2 or IFN-gamma/TNF-alpha treatment required protein synthesis, sug gesting that cooperative cytokine induction of NOS involves the interm ediate expression of new gene products. Such molecular controls for re gulation of inducible macrophage gene expression can be contrasted wit h regulatory control of other inflammatory genes such as IP-10 and TNF -alpha.