BPI and bacterial pneumonia: Recent studies have demonstrated the significant involvement of NETs in the pathogenesis of severe infectious diseases.28 In addition, immature neutrophils were found to express the BPI gene, which has previously been associated with adverse outcomes in severe infections.27 Arginase 1 (ARG1), recognized as an inhibitor of T cell activation,27 was also found to be highly expressed in immature neutrophils from patients with severe bacterial pneumonia (Fig. 5d).