CD4 and alkaline phosphatase measurement: In our study, PD-1 expression in CD4+ lymphocytes and PD-L1 expression in CD14+ monocytes were correlated with peripheral lymphocyte count and plasma IL-10 concentration, suggesting that the PD-1/PD-L1 system takes part in the development of immunosuppression in AP by regulating lymphocyte proliferation and IL-10 production.