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

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.

126 Early Transcriptomic Response to Burn injury: Prolonged Inflammatory Response is Associated with Mortality

Introduction Burn injuries are associated with high morbidity and mortality. Burn care has improved significantly in the last few decades with emphasis on early surgical management, improvements in local wound care, and specialized critical care. While survival rates are improving, mortality remains high in certain patient populations, including those with larger burns. Burn injury induces a systemic hyperinflammatory response with detrimental side effects. Prior studies have offered early insights into the biochemical changes that occur after severe burn injury. The underlying cellular response is still largely unknown. The goal of this work is to characterize the blood transcriptome of severe burn injury and compare this response between patients who live or subsequently die of their injuries. Methods Burn patients presenting to a regional center between 2012–2017 were prospectively enrolled. Blood was collected on admission and at predetermined timepoints (Hours 2, 4, 8, 12, 24) over the first 24 hours. mRNA was isolated and a transcriptomic microarray was used to measure global transcript levels over time. To identify differentially regulated genes (FDR≤0.1) by injury severity, patients were grouped by burn size (TBSA >20%) and mortality. Microarray data was analyzed using bioinformatics software and pathway analysis. Descriptive statistics were generated with Mann-Whitney, Chi-Square, and Fisher’s exact test as appropriate. Results Sixty-eight patients were included in this analysis, most patients were male with a median age of 41 (IQR, 30.5–58.5) years, and TBSA of 20% (IQR, 11–34%). Thirty-five patients suffered %TBSA injury >20%, and this group experienced greater mortality (26% vs. 3%, p=0.008). There were no significant differences in age, race, or gender. Comparative analysis of genes from patients with < />20% TBSA revealed 1250, 444, 209, 20, 865, and 557 differentially regulated genes at hours 0, 2, 4, 8, 12 and 24 respectively. Pathway analysis reveals an initial upregulation in several immune/inflammatory pathways within the >20% TBSA groups between hours 0–2 followed by shutdown between hours 12–24. Immune pathways include Th17 activation pathway and natural killer cell signaling, inflammatory pathways include EIF2 signaling. These pathways remain upregulated in the group of patients with >20% TBSA who died. Conclusions Severe burn injury is associated with an early proinflammatory immune response followed by shutdown of these pathways. Burn patients who die show continued upregulation in the first 24 hours after injury in several proinflammatory pathways compared to those who live.

Psychological aspects in early adjustment after severe burn injury

Burn injury is one of the most serious traumatic events with possible psychological and psychosocial consequences. Health status perception is one of the main health outcomes. The severity of psychological symptoms does not always correlate with that of the burn injury, suggesting that early screening for psychological vulnerabilities may be beneficial. The aim of our study was to identify the personality, clinical, and sociodemographic characteristics related to patient´s subjective perception of health, depression, and anxiety, in a sample of 52 adult patients with severe burn injury shortly before discharge from specialty Burn clinic. Subjective health perception was predicted by depression (β = -.143, t(47) = -3.94, P < .001) and neuroticism (β = -.106, t(43) = -4.83, P < .001), and it correlated positively with extraversion (r = .2858, P = .0465) and conscientiousness (r = .3663, P = .0096). Depression was predicted by neuroticism (F(1,49) = 18.4; P < .001) and correlated with attachment avoidance (r = .29, P = .0383) and negatively with extraversion (r = -.32, P = .0220). Anxiety was related to attachment anxiety (F(1,49) = 4.25; P = .045), neuroticism (F(1,49) = 15.75; P < .001), and agreeableness (r = -.36, p = .0101). Unemployed patients experienced higher levels of depression and anxiety. This research suggests that personality traits and adult attachment may play an important role in the acute phase of the recovery from a severe burn injury. These findings can be relevant for early intervention and holistic rehabilitation.

Persistent Systemic Inflammation in Patients With Severe Burn Injury Is Accompanied by Influx of Immature Neutrophils and Shifts in T Cell Subsets and Cytokine Profiles

Severe burn injury causes local and systemic immune responses that can persist up to months, and can lead to systemic inflammatory response syndrome, organ damage and long-term sequalae such as hypertrophic scarring. To prevent these pathological conditions, a better understanding of the underlying mechanisms is essential. In this longitudinal study, we analyzed the temporal peripheral blood immune profile of 20 burn wound patients admitted to the intensive care by flow cytometry and secretome profiling, and compared this to data from 20 healthy subjects. The patient cohort showed signs of systemic inflammation and persistently high levels of pro-inflammatory soluble mediators, such as IL-6, IL-8, MCP-1, MIP-1β, and MIP-3α, were measured. Using both unsupervised and supervised flow cytometry techniques, we observed a continuous release of neutrophils and monocytes into the blood for at least 39 days. Increased numbers of immature neutrophils were present in peripheral blood in the first three weeks after injury (0.1–2.8 × 106/ml after burn vs. 5 × 103/ml in healthy controls). Total lymphocyte numbers did not increase, but numbers of effector T cells as well as regulatory T cells were increased from the second week onward. Within the CD4+ T cell population, elevated numbers of CCR4+CCR6- and CCR4+CCR6+ cells were found. Altogether, these data reveal that severe burn injury induced a persistent innate inflammatory response, including a release of immature neutrophils, and shifts in the T cell composition toward an overall more pro-inflammatory phenotype, thereby continuing systemic inflammation and increasing the risk of secondary complications.