Vagal nerve stimulation blocks peritoneal macrophage inflammatory responsiveness after severe burn injury

Large surface area burn injuries lead to activation of the innate immune system, which can be blocked by parasympathetic inputs mediated by the vagus nerve. We hypothesized that vagal nerve stimulation (VNS) would alter the inflammatory response of peritoneal macrophages after severe burn injury. Male BALB/c mice underwent right cervical VNS before 30% total body surface area steam burn and were compared with animals subjected to burn alone. Peritoneal macrophages were harvested at several time points following injury and exposed to lipopolysaccharide (LPS) in culture conditions. The inflammatory response of peritoneal macrophages was measured by analyzing changes in nuclear factor κB p65 phosphorylation using flow cytometry. We found that peritoneal macrophages isolated from mice subjected to burn injury were hyperresponsive to LPS challenge, suggesting burn-induced macrophage activation. We identified a protective role for VNS in blocking peritoneal macrophage activation. Analysis of the phosphorylation state of nuclear factor κB pathway mediator, p65 Rel A, revealed a VNS-mediated reduction in p65 phosphorylation levels after exposure to LPS compared with burn alone. In combination, these studies suggest VNS mediates the inflammatory response in peritoneal macrophages by affecting the set point of LPS responsiveness.