INITIAL CYTOKINE EXPOSURE DETERMINES FUNCTION OF MACROPHAGES AND RENDERS THEM UNRESPONSIVE TO OTHER CYTOKINES

The functional properties of infiltrating macrophages (M phi) must be tightly regulated to facilitate appropriate responses to complex condi tions in an inflammatory focus. This study was designed to ascertain w hether uncommitted M phi that have been exposed to combinations of cyt okines with opposing functions develop properties dictated by one cyto kine or by cytokine mixtures. Uncommitted rat bone marrow-derived M ph i (BMDMs) were incubated with IFN-gamma, TNF-alpha, TGF-beta, IL-4, IL -6, and IL-10 alone or sequentially in combinations. After 48 h, funct ion was assessed by nitric oxide (NO) generation, uptake of apoptotic neutrophils, and beta-glucuronidase expression. IFN-gamma followed 4 h later by TNF-induced NO generation. The pretreatment of BMDMs before IFN-gamma priming with TNF, TGF-beta, and IL-4 suppressed NO generatio n by 87%, 92%, and 85%, respectively; IL-10 had no effect. The same cy tokines administered at 4 h after IFN priming had no effect on NO gene ration. The uptake of apoptotic polymorphonuclear leukocytes was augme nted by TNF (40% vs 29% controls; p < 0.05) and decreased by IFN-gamma , IL-10, and IL-4. The TNF response was unaffected by subsequent treat ment with IFN-gamma, IL-4, or IL-10. Similarly, the decreased polymorp honuclear leukocyte uptake induced by IFN-gamma, IL-4, or IL-10 was un affected by the subsequent addition of TNF. beta-glucuronidase express ion was increased by TGF-beta and decreased by IFN-gamma, These respon ses were not modified by cytokines with the opposing function. Thus, t he functional response of BMDMs to complex mixtures of cytokines was d etermined by the first cytokine to which they were exposed. Once activ ated, BMDMs become unresponsive to alternative activating signals, a f inding which has obvious implications for M phi function in vivo.