Objective:To observe the dynamic changes of soluble programmed cell death protein 1 (sPD-1) and cellular immunity and humoral immunity in patients with sepsis and septic shock, and to explore the relationship between sPD-1 and immunosuppression in sepsis.Methods:This study was a prospective cohort study. Patients with sepsis and septic shock admitted to the ICU of General Hospital of Ningxia Medical University from June 2018 to December 2018 were included as the study subjects, ordinary postoperative patients admitted to the ICU during the same period were included as the non-sepsis group, and healthy volunteers matched in age and sex were included as healthy controls. The sPD-1, lymphocyte count, serum immunoglobulin and lymphocyte subsets of peripheral blood on the first, third and seventh days after admission to the ICU were detected. The changes of sPD-1 and various immune indices in each group were compared, and the correlation between the indices was analyzed. For healthy controls and non-sepsis patients, only blood samples were tested on the day of inclusion.Results:A total of 90 patients [58 males and 32 females, aged (58.36±17.46) years] were included in this study, including 29 cases of sepsis, 31 cases of septic shock, 15 cases of non-sepsis, and 15 volunteers were recruited as healthy control group. The 28-day fatality rate of patients in the sepsis and septic shock groups was 28.3%. On the first day of ICU admission, the sPD-1 concentration were significantly higher in the septic shock group and sepsis group than those in the non-sepsis group and healthy control group [512.64 (216.85, 1039.41) pg/mL vs. 261.90 (191.96, 421.99) pg/mL vs. 191.56 (151.26, 232.66) pg/mL vs. 200.51 (162.14, 241.26) pg/mL, all P<0.05]. The sPD-1 concentration in the septic shock group was significantly higher than that in the sepsis group, and this phenomenon persisted for at least one week ( P<0.05). The lymphocyte count on the first day in the sepsis and septic shock groups were significantly lower than those in the healthy control and non-sepsis groups (all P<0.05), and the lymphocyte count in the septic shock group remained lower levels until the seventh day of ICU admission (all P<0.05). The percentage of lymphocytes and total T lymphocytes in the sepsis and septic shock groups were significantly lower than those in the healthy control and non-sepsis groups (all P<0.05), while the percentage of total B lymphocytes did not differ between groups (all P>0.05). The percentage of CD8+ T lymphocytes on the seventh day of ICU admission in the septic shock group was still significantly lower than that in the sepsis group [(18.36±2.23)% vs. (28.28±2.97)%, P<0.05]. The levels of serum immunoglobulin IgG and IgM were significantly lower in the sepsis and septic shock group than those in the healthy control and non-sepsis groups (all P<0.05), and the IgG and IgM in the sepsis and septic shock groups returned to normal on the seventh day of ICU admission. The area under the ROC curve was used to evaluate the predictive value of sPD-1 on poor prognosis, and the results showed that sPD-1 on the seventh day of ICU had a good predictive value for 28-day prognosis in patients with sepsis and septic shock, and the best cut-off value was 286.52 pg/mL, with a sensitivity of 100.00% and specificity of 56.25%. Conclusions:Immunosuppression occurs in patients with sepsis and septic shock in the early stage, and the duration of immunosuppression in patients with septic shock is prolonged, but humoral immunosuppression plays a major defense in the early stage, and cellular immunosuppression is dominant in the later stage.