An investigation of the relationship between sPD-1, sPD-L1 and severe pneumonia patients admitted to ICU and its clinical significance.

Background: Soluble programmed cell death 1 (sPD-1) and its ligand (sPD-L1) have emerged as potential biomarkers for early identification and risk stratification in patients with severe pneumonia (SP). However, there is a lack of robust laboratory evidence supporting their clinical utility. This study aimed to explore the relationship between sPD-1/sPD-L1 levels and clinical outcomes in SP patients. Methods: This study included SP patients admitted to the Department of Critical Care Medicine at the Affiliated Hospital of Zunyi Medical University between November 2022 and December 2023. Patients were categorized into survivor and non-survivor groups based on 28-day clinical outcomes. Baseline characteristics and laboratory data were collected upon admission. Serum levels of sPD-1 and sPD-L1 were quantified using enzyme-linked immunosorbent assay. Cox regression analysis was performed to identify prognostic factors, and a nomogram was developed to predict outcomes. The predictive performance of sPD-1, sPD-L1, and their combined indices was evaluated using receiver operating characteristic (ROC) curve analysis. Results: A total of 125 patients with severe pneumonia (SP) were included in this study. Compared to survivors, non-survivors were older, had more severe disease (as indicated by higher SOFA and APACHE II scores), and exhibited lower body mass index (BMI), hemoglobin levels, lymphocyte counts, CALLY index, and albumin levels. Additionally, non-survivors showed significantly elevated levels of systemic inflammatory markers (NLR, PLR, MLR, CLR, CAR, and SII) and higher serum sPD-1 concentrations. Multivariate Cox regression analysis identified age, SOFA score, and sPD-1 levels as independent risk factors for poor prognosis in SP patients. Restricted cubic spline (RCS) curves revealed a linear relationship between age, SOFA score, and the risk of poor prognosis. A nomogram incorporating age, SOFA score, and sPD-1 levels demonstrated strong predictive performance for 28-day mortality in SP patients, with an area under the curve (AUC) of 0.80. Incorporating sPD-1 measurements significantly improves the prognostic accuracy of both SOFA and APACHE II scores in critically ill patients. Conclusion: sPD-1 levels were significantly elevated in non-surviving SP patients, suggesting its potential role as a biomarker for disease severity and immune dysregulation. The combination of sPD-1 with other clinical parameters may provide valuable insights into the prognosis and immune status of SP patients.