PERSPECTIVES

the robust supply of monocytes that can be rapidly mobilized from blood. With the rev-elation that AAMs derive locally, the idea of a more primitive precursor for macrophages localized within tissues now takes on a greater semblance of logic. After liver injury, hema-topoietic stem cell–derived macrophages assume an alternative, healing phenotype and boost tissue repair, even in mice with normal monocytes ( 4). Their natural residence in tis-sue may serve as a source of macrophages in IL-4–induced, proliferation-mediated infl am-mation. Thus, although Jenkins et al. clev-erly break the mold of assuming that infl am-matory macrophages must be recruited fro