CSF1 and COVID-19: Regarding ontogeny, monocyte-derived macrophages, which replenish tissue-resident macrophages only in some tissues (e.g., gut) (6), are the major source of pathogenic macrophages in inflamed tissues affected by inflammatory diseases and COVID-19 (7), and they are oppositely instructed by macrophage CSF (M-CSF) or granulocyte macrophage CSF (GM-CSF) (8–14).