MSU crystals injected i.p. are taken up by macrophages and induce secretion of IL-1α. IL-1α stimulates production of G-CSF (here by fibroblasts and endothelial cells), which causes release of neutrophils from bone marrow to blood and further to tissue. NADPH oxidase (Phox), a normal constituent of macrophages (and neutrophils), reduces the amount of IL-1α secreted from macrophages; consequently, it reduces the production of G-CSF and the mobilization of neutrophils from bone marrow and their recruitment to the site of inflammation, where they may activate macrophages further. Professional illustration by Patrick Lane, ScEYEnce Studios.