TRANSFORMING GROWTH-FACTOR-BETA-1 REGULATION OF MACROPHAGE ACTIVATION DEPENDS ON THE TRIGGERING STIMULUS

We have examined the effects of transforming growth factor beta1 (TGF-beta1) on the regulation of murine bone marrow-derived macrophage function. TGF-beta, added simultaneously with or up to 4 h before interferon-gamma (IFN-gamma) plus lipopolysaccharide (LPS), inhibited macrophage leishmanicidal activity, nitrite (NO2-) production and secretion of prostaglandin E2. In contrast, no effect of TGF-beta could be demonstrated on macrophages stimulated with IFN-gamma plus tumor necrosis factor-alpha (TNF-alpha) under the same conditions. These results suggested that TGF-beta inhibited LPS-induced triggering of macrophage activation, which was confirmed by studies with IFN-gamma-primed cells. Interestingly, when macrophages were pretreated with TGF-beta for 24 h, NO2- production in response to IFN-gamma plus TNF-alpha was also inhibited. Although control and IFN-gamma/LPS-stimulated macrophages were found to secrete latent TGF-beta, only the IFN-gamma/LPS cultures produced biologically active TGF-beta. Significantly, active TGF-beta was present at concentrations shown earlier to inhibit macrophage function.