M-CSF protects against P. aeruginosa infection by inducing increased myelopoiesis of transplanted HS/PCs. (a) Lethally irradiated CD45.2 mice were transplanted with 2,500 CD45.1 HS/PCs, treated with three doses of control PBS or M-CSF during transplantation (−1 h, 5 h, and 18 h), challenged after 1 wk by intraperitoneal injection of 500 CFU of P. aeruginosa, and analyzed for bacterial load and myeloid donor cells 1 d after infection or for survival. (b and c) Survival of mice after HS/PC transplantation and bacterial infection (arrow) for PBS control (n = 13) or mice treated with three doses of 10 µg of baculovirus-expressed rmM-CSF (n = 8; b) or three doses of 10 µg rhM-CSF (n = 10; c). Transplanted, not infected (black line; n = 4) and irradiated (XR), untransplanted and uninfected control mice (dashed line; n = 6) are shown. P < 0.001 (rmM-CSF) and P < 0.05 (rhM-CSF) by a Mantel-Cox test. (d) Bacterial load in indicated organs 18 h after infection of transplanted mice treated with rhM-CSF or control PBS. (e and f) Median of donor monocytes (CD11b⁺, Ly6C⁺) and monocyte-derived macrophages (CD11b⁺, Ly6C⁺, F4/80^int) in the liver or granulocytes (Ly6G⁺, CD11b⁺) and mononuclear phagocytes (Ly6G⁻, CD11b⁺) in the spleen of PBS control or M-CSF–treated recipient mice 1 d after infection (e) or 9 d after transplantation of uninfected mice (f). Gating strategy is shown in Fig. S1. All data are representative of at least two independent experiments. (d–f) P-values were obtained by Mann-Whitney U tests. **, P < 0.01; ***, P < 0.001.