Recent studies have demonstrated that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure of C57Bl/6 mice results in an enhanced inflammatory response to intraperitoneal injection of sheep red blood cells (SRBC). This response is characterized by an increase in total peritoneal cells (PEC) as well as an increase in relative and absolute numbers of neutrophils (PMN) harvested 16 to 40 hr following injection of SRBC. The mechanisms whereby TCDD increases cellular influx are unknown. In the present studies, the role of the proinflammatory cytokines interleukin 1 (IL-1) and tumor necrosis factor (TNF) in TCDD-induced hyperinflammation was examined. Intraperitoneal administration of recombinant IL-1 beta (0.4 U) or TNF alpha (10 ng) resulted in an enhanced peritoneal inflammatory response compared to phosphate-buffered saline-injected control animals measured 20 hr following injection of SRBC. The effect of exogenous cytokines mimicked the effects of exposure to 5 mu g/kg TCDD. When endogenous IL-1 activity was blocked using an IL-1 receptor antagonist (IL-1ra, 1 mg every 3 hr), the PMN influx was significantly decreased in control animals but not in animals exposed to 20 mu g/kg TCDD. When endogenous TNF activity was blocked using a TNF-soluble receptor (rhuTNFR:Fc, 100 mu g), the numbers of total PEC and macrophages (MAC) harvested from control mice were reduced, while in mice exposed to 20 mu g/kg TCDD, inhibition of TNF activity dramatically reduced the numbers of PEC, MAC, and PMN. Following rhTNFR:Fc treatment, there was no difference between TCDD-treated and control mice in inflammatory cell influx. These results demonstrate that TNF plays a major role in mediating TCDD-induced hyperinflammation. In support of this conclusion, a dose-dependent increase in plasma TNF alpha was measured by ELISA in TCDD-treated mice following SRBC injection. (C) 1994 Academic Press, Inc.
