This was a prospective observational study. The subjects of this study included 101 patients with gastroenterological disease who underwent elective abdominal surgery via laparotomy at the National Defense Medical College Hospital. Blood samples were taken on the preoperative day (Pre) and the first postoperative day (POD1). We calculated CD4+ T-cell count and PD-1 expression on CD4+ T cells by flow cytometer. The occurrence of postoperative infectious complications was defined according to a combination of clinical findings and the results of laboratory and other tests. The postoperative infectious complications in this study included incisional surgical site infections (SSIs), organ/space SSIs, enterocolitis, urinary tract infections, and pneumonia. Incisional and organ/space SSIs were diagnosed according to the definitions stated in the guidelines issued by the Center for Disease Control and Prevention.