129 Stimulating the Cholinergic Anti-inflammatory Pathway Alters Inflammatory Cell Mobilization after Burn Injury

Abstract

Abstract Introduction Severe burn injury causes a systemic inflammatory response (SIRS) that is characterized by mobilization of inflammatory cells into the circulation and is associated with distant organ injury that can lead to significant morbidity and mortality. The cholinergic anti-inflammatory pathway, mediated by the vagus nerve, regulates the anti-inflammatory response to injury and infection. We have previously shown in models of burn injury that stimulating the vagus nerve may be a potential therapy aimed at limiting SIRS. Here, we hypothesized that stimulating the vagus nerve (VNS) would limit the SIRS response by altering the mobilization and trafficking of inflammatory cells after burn injury. Methods Wild type 10–12-week-old C57BL/6 mice were injured with a 30% total body surface area steam burn. A separate cohort of animals was treated with electrical stimulation of the cervical vagus nerve for 10 minutes immediately post-burn. Bone marrow, blood and lung tissue were collected 24 hours after burn injury. Flow cytometry of bone marrow was performed to measure Lineage- c-kit± Sca-1+ (LSK) hematopoietic stem cells (HSC), then further analyzed to quantify changes in Long-term (LT) HSC, short-term (ST) HSC, and Multipotential Progenitor (MPP) compartments. Bone marrow, blood and perfused lung tissue were analyzed by flow cytometry using a panel of myeloid cell markers. Results Severe burn injury decreased bone marrow LSK expression by 50% compared to sham, with LT-HSC and MPP expression decreasing to a greater degree than ST-HSCs. VNS did not alter burn-induced changes in any bone marrow HSC cell type. Burn injury was associated with increased mobilization of CD45+CD11b+ monocytes and CD11b+Ly6Chi inflammatory monocytes into the peripheral blood and lung, while increased CD11b+Ly6Clo patrolling monocytes and Gr1+Ly6C- neutrophils was seen in the lung only. VNS significantly prevented the burn-induced increase in CD45+ inflammatory cells, CD11b+Ly6Clo patrolling monocytes and Gr1+Ly6C- neutrophils in the lung (see Figure), reducing their expression to sham levels, despite only modest changes to myeloid cell expression in the blood. Conclusions VNS attenuates myeloid cell cell trafficking to the lung after severe burn injury despite having no effect on emergency myelopoiesis in the bone marrow. Further studies are needed to define the mechanism by which the cholinergic anti-inflammatory pathway attenuates the SIRS response to burn.