Early STAT3 Activation and Delayed STAT5 Dominance Define the Acute Leukocyte Signaling Response to Trauma and May Correlate with Clinical Outcomes.

Major trauma dysregulates the immune system, leaving injured patients at increased risk of infection. Despite extensive research to define the effect of trauma on the immune system, there are no effective interventions to restore immune function in injured patients. We previously used single-cell phosphoproteomics to identify pathways for immunomodulation in COVID-19 induced critical illness. We hypothesized that trauma would also be associated with definable changes in leukocyte signaling, providing therapeutic targets. To test this hypothesis, we used mass cytometry to assess signaling phosphoproteins and associated surface markers at single-cell resolution in a cohort of critically injured patients. We find that injury causes an acute increase in STAT3 signaling across leukocyte populations, followed by a shift from STAT3 to STAT5 predominance in T cells over the first 72 hours after injury. We used computational clustering to identify subpopulations of T cells and found that injury causes an increase in activated CD4 memory T cells. We assessed the relationship between phosphoprotein levels and clinical outcomes and identified significant correlations between early phospho-STAT3 levels in T cells, monocytes, and neutrophils and clinical outcomes, including ICU and hospital length of stay. These data demonstrate that severe injury is associated with cell-type-specific changes in the signaling phosphoproteome in circulating leukocytes, which may underlie clinical outcomes from injury.