Upregulated PD-L1 delays human neutrophil apoptosis and promotes lung injury in an experimental mouse model of sepsis

PD-L1 is a ligand for PD-1, and its expression has been shown to be upregulated in neutrophils harvested from septic patients. However, the effect of PD-L1 on neutrophil survival and sepsis-induced lung injury remains largely unknown. In this study, PD-L1 expression correlated negatively with rates of apoptosis in human neutrophils harvested from patients with sepsis. Coimmunoprecipitation assays on control neutrophils challenged with interferon-gamma and LPS showed that PD-L1 complexes with the p85 subunit of phosphatidyl 3-kinase (PI3K) to activate AKT-dependent survival signaling. Conditional CRE/LoxP deletion of neutrophil PD-L1 in vivo further protected against lung injury and reduced neutrophil lung infiltration in a cecal ligation and puncture (CLP) experimental sepsis animal model. Compared with wild-type animals, PD-L1-deficient animals presented lower levels of plasma tumor necrosis factor-alpha and interleukin-6 (IL-6) and higher levels of IL-10 after CLP, and reduced 7-day mortality in CLP PD-L1-knockout animals. Taken together, our data suggest that increased PD-L1 expression on human neutrophils delays cellular apoptosis by triggering PI3K-dependent AKT phosphorylation to drive lung injury and increase mortality during clinical and experimental sepsis.