Unveiling Ventilator-Associated Pneumonia: S100A8 as a Promising Biomarker Through Integrated RNA-Seq Analysis.

Background and Objectives: Ventilator-associated pneumonia (VAP) was a common and severe complication of invasive mechanical ventilation. The traditional VAP diagnostic model relied on laboratory microbiological cultures. However, VAP had unclear pathogenesis, and its accurate identification was difficult due to the varying levels of pathogen detection in different laboratories. There was an urgent need for new diagnostic biomarkers for VAP. Methods: The transcriptome of VAP patients was analyzed and computed using bioinformatics techniques in this study. The screen identified differentially expressed genes (DEGs) from the chemokine CC family, the S-100 family, and the α-defensin family, which are highly associated with immune-related antimicrobial functions. Single-cell landscape data revealed an increase in MTRNR2L12+ cells and a decrease in naïve CD4+ T cells, ciliated cells, and CD8+ T cells in VAP patients, indicating a significant change in the homeostatic profile in patients. Moreover, this paper explored differential gene expression at the single-cell level. Results: The study analyzed 46 VAP samples and 48 normal samples to explore VAP pathogenesis and identify potential biomarkers. Both bulk RNA seq and scRNA-seq analysis revealed that S100A8 was highly expressed in the VAP group. This phenomenon was caused by the cellular level differential expression of B cells. In contrast, the reduced FN1 and HLA-DRB5 expressions in the VAP group may be influenced by the expression of T cells, macrophages, and ciliated cells. Western blot experiments detected S100A8 expression in the patient samples. Conclusion: In this study, we combine bulk RNA-seq and scRNA-seq analyses to screen and validate the potential of S100A8, a gene with consistent expression, as a biomarker, providing a new perspective for VAP diagnosis.