Trauma-Hemorrhage-Induced Neutrophil Priming Is Prevented by Mesenteric Lymph Duct Ligation

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Abstract
Our objective in this study was to test the hypothesis that priming of neutrophils (PMN) in vivo by trauma-hemorrhagic shock (T/HS) is mediated by factors carried in intestinal lymph that prime PMNs by enhancing their responses to inflammatory mediators. Previous studies have shown that T/HS-induced lung injury is mediated by factors contained in mesenteric lymph and that ligation of the main mesenteric lymph duct (LDL) can prevent T/HS-induced lung injury. Since T/HS-induced lung injury is associated with PMN infiltration, one mechanism underlying this protective effect may be the prevention of PMN priming and activation. Therefore, we assessed the ability of T/HS to prime PMN responses to inflammatory agonists, and the ability of mesenteric lymph duct division to protect against such T/HS-induced PMN priming in an all-rat system. PMN were collected from male rats 6 h after laparotomy (trauma) plus hemorrhagic shock (30 mmHg for 90 min; T/HS) or trauma plus sham shock (T/SS). Uninstrumented rats were used as controls (UC). In a second set of experiments, rats were subjected to T/HS with or without mesenteric lymph duct division. PMN were then stimulated with chemokine (GRO, MIP-2) and lipid (PAF) chemoattractants, and cell calcium flux was used to quantify responses to those agonists. T/SS primed PMN responses to GRO, MIP-2, and PAF in comparison to UC rats, but the addition of shock (T/HS) amplified PMN priming in a significant manner, especially in response to GRO. Mesenteric lymph duct division prior to T/HS diminished PMN priming to the levels seen in T/SS. This reversal of priming was significant for GRO and GRO/MIP-2 given sequentially, with the other agonist regimens showing similar trends. The results support the concept that trauma and hemorrhagic shock play important additive roles in inflammatory PMN priming. Entry of gut-derived inflammatory products into the circulation via mesenteric lymph seems to play a dominant role in mediating the conversion of physiologic shock insults into immunoinflammatory PMN priming. Shock-induced gut lymph priming enhances PMN responses to many important chemoattractants, most notably the chemokines, and mesenteric lymph duct division effectively reverses such priming to priming levels seen in trauma without shock.