Low-density neutrophil heterogeneity and spleen tyrosine kinase as therapeutic targets in sepsis.

Sepsis is a leading cause of death for which host-directed therapies are urgently needed. We performed high-dimensional flow cytometry, measurement of soluble biomarkers, and lipopolysaccharide (LPS) stimulation of neutrophils to characterize neutrophil heterogeneity and function in patients with sepsis. We observed that in patients with sepsis, low-density neutrophils (LDNs) are elevated and phenotypically diverse populations of innate immune cells with varying degrees of maturity and myeloperoxidase expression. Spleen tyrosine kinase (SYK) expression was found to be higher in whole blood neutrophils and LDNs of patients with sepsis compared with healthy donors. Importantly, SYK+ LDNs associated with increased levels of intracellular myeloperoxidase (MPO) and soluble biomarkers. Furthermore, SYK+ LDNs correlated with clinical outcomes of sepsis disease severity, including sequential organ failure assessment score, mechanical ventilation, and vasopressors. Functionally, the SYK inhibitor R406 suppressed changes in neutrophil features of activation from normal-density neutrophils and LDNs, including the SYK+ and SYK- neutrophil subsets, and MPO release from LDNs following LPS stimulation of sepsis neutrophils. Combined, these results establish LDNs as a heterogenous population of neutrophils that express high levels of SYK and support SYK inhibition as a potentially novel therapeutic target aimed at suppressing overactive neutrophils in sepsis.