Bulk-RNA cell type deconvolution revealed increases in circulating HSPCs and S100A8/9-high neutrophils alongside reductions in naïve CD4 T cells in patients later diagnosed with postoperative pneumonia, while gene-set enrichment analysis revealed upregulation of neutrophil degranulation and myeloid-leucocyte-mediated immunity. Here, CD4 is linked to susceptibility to pneumonia measurement.