Monocyte programmed death ligand-1 expression is an early marker for predicting infectious complications in acute pancreatitis

BACKGROUND: Acute pancreatitis (AP) is a life-threatening disease that requires early identification of patients at risk of developing infectious complications. Immunosuppression is an initial event that is key to AP pathogenesis. The programmed cell death 1 (PD-1) and programmed cell death ligand 1 (PD-L1) system is reported to mediate evasion of host immune surveillance in many diseases; however, the relationship between PD-1/PD-L1 expression and these parameters or infectious complications in AP has not been elucidated. This study was conducted to determine whether PD-1 and PD-L1 are upregulated and to reveal the relationship between PD-1/PD-L1 expression and the development of infectious complications in AP. METHODS: Sixty-three patients with AP and 32 sex- and age-matched healthy control subjects were prospectively enrolled. On days 1 and 3 after the onset of AP, we measured PD-1 expression in peripheral CD4(+) T cells and PD-L1 and human leukocyte antigen-DR (HLA-DR) expression in CD14(+) monocytes using flow cytometry. Plasma interleukin (IL)-10 levels were measured by enzyme-linked immunosorbent assay. RESULTS: Compared with healthy volunteers, the percentages of PD-1-expressing CD4(+) lymphocytes and PD-L1-expressing CD14(+) monocytes were increased in patients with AP on days 1 and 3 after onset, especially those with infectious complications. Moreover, increased PD-1/PD-L1 expression was associated with increased occurrence of infectious complications, decreased circulating lymphocytes, and increased plasma IL-10 concentration. Multivariate regression analysis indicated that the increased percentage of PD-L1-expressing CD14(+) monocytes was an independent risk factor for infectious complications in AP. Area under the ROC curve analysis showed the combination of Acute Physiology and Chronic Health Evaluation II score and PD-L1 and HLA-DR expression in CD14(+) monocytes had high accuracy in predicting infectious complications in patients with AP. CONCLUSIONS: The PD-1/PD-L1 system plays an essential role in the early immunosuppression of AP. PD-L1 expression in CD14(+) monocytes may be a new marker for predicting risk of infectious complications in patients with AP.