CXCR2 and susceptibility to pneumonia measurement: The absence/expression of CXCR2 from all lung cells in CXCR2−/− (global knockout) mice as well as cell type-specific absence in lung endothelial cells in CXCR2fl/flCdh5Cre+ and epithelial cells in CXCR2fl/flShhCre+ mice was validated by flow cytometry following IL-1β stimulation and found to be increased in WT mice after pneumonia induction (Supplementary Fig. 1).