Up-regulation of programmed cell death 1 ligand 1 on neutrophils may be involved in sepsis-induced immunosuppression: an animal study and a prospective case-control study.

Background: Recent studies have shown that neutrophils may display an antigen-presenting function and inhibit lymphocyte proliferation by expressing programmed cell death 1 ligand 1 (PD-L1). The current study was performed to investigate the effect of neutrophils and their pathophysiological significance during sepsis.

Methods: Neutrophil PD-L1 expression was determined in both septic mice (n = 6) and patients (n = 41). Neutrophils from septic mice were subtyped into PD-L1 and PD-L1 populations to determine their phenotypes and functions. Septic neutrophils were cocultured with lymphocytes to observe the effect of septic neutrophils on lymphocyte apoptosis.

Results: The PD-L1 level on neutrophils from septic mice was significantly up-regulated (21.41 ± 4.76%). This level increased with the progression of sepsis and the migration of neutrophils from the bone marrow to the blood and peritoneal cavity. The percentages of CD11a, CD62L, and C-C chemokine receptor type 2 were lower, whereas the percentages of CD16 and CD64 were higher on PD-L1 neutrophils than on PD-L1 neutrophils. The migratory capacity of PD-L1 neutrophils was compromised. Septic neutrophils induced lymphocyte apoptosis via a contact mechanism, and this process could be reversed by anti-PD-L1 antibody. PD-L1 was also up-regulated on neutrophils from patients with severe sepsis (14.6% [3.75%, 42.1%]). The levels were negatively correlated with the monocyte human leukocyte antigen-DR level and positively correlated with the severity of septic patients. Neutrophil PD-L1 was a predictor for the prognosis of severe sepsis, with an area of 0.74 under the receiver operating curve.

Conclusions: PD-L1 is up-regulated on neutrophils during sepsis, which may be related to sepsis-induced immunosuppression.