G-CSF is required for the thermally mediated acceleration of neutrophil recovery after TBI. G-CSF concentrations were determined by ELISA in the serum (A-B), intestinal lysates (50 μg; C-D), and bone marrow lysates (40 μg; E-F) of C57BL/6 mice given either 3 Gy (A,C,E) or 6 Gy (B,D,F) TBI. (G-H) Ly6G⁺ cells counts were performed in mice that have been given anti–G-SF neutralizing antibody (G) or isotype control antibody (H) given immediately after 3 Gy TBI and 2 hours after heat treatment. Hatched bars indicate mice that received antibody treatment. Each graph is a representative of at least 3 separate experiments. n = 3-5 mice per group. *P < .03, TBI alone group versus TBI followed by heat. †P < .04, TBI + heat + anti–G-SF group versus the TBI + heat group. n.d. indicates not detected.