CSF2 and infection: The mechanism behind AM depletion is poorly described and probably differs depending on the causative infection/inflammation and the context: AMs could die from being infected or from exposure to local inflammatory cytokines [such as IFNs (74, 76)] or depletion of survival factors such as GM-CSF (77–79), or they could migrate into the lung tissue and differentiate into a phenotypically different cell type lacking the typical AM surface markers such as Siglec F (42).