We also showed that GRIM neutrophils suppress other immune cell populations in CF airways, including macrophages via activation of the inhibitor PD-1 pathway (12) and T cells via secretion of arginase 1 (Arg1) from the primary granules, which cleaves the essential amino acid arginine required by T cells for T-cell receptor signaling (13). This evidence concerns the gene ARG1 and cystic fibrosis.