CSF2 and infection: During infection with influenza A virus (IAV), circulating monocytes are recruited into the alveolar niche via CCR2‐dependent signaling pathways.[141, 142] Within this microenvironment, they are exposed to granulocyte–macrophage colony‐stimulating factor (GM‐CSF) secreted by adjacent alveolar type 2 (AT2) epithelial cells.[143]Ex vivo studies have shown that upon GM‐CSF stimulation, these monocyte‐derived precursors markedly increase the expression of lymphocyte antigen 6 complex, locus G (Ly6g).