Mild heating increased the number of neutrophils and granulocytic progenitors in the bone marrow after TBI. (A) Bone marrow was isolated from the femur and tibia of C57BL/6 mice that received 3 Gy TBI with or without heat treatment, and then erythrocytes were lysed and total number of bone marrow cells was quantified. (B) The percentage of Ly6G⁺ cells was determined by flow cytometry. Neutrophil numbers were calculated using the percentage of Ly6G⁺ cells and the total bone marrow cell counts. (C-F) C57BL/6 mice were left untreated (NT), treated with TBI alone, or with 3 Gy TBI followed 2 hours later with a heat treatment. At 12 and 48 hours after treatment, bone marrow was isolated from one femur and tibia from each mouse and filtered. Erythrocytes were lysed and total number of cells quantified. Number of HSCs (C), multipotent progenitor (D), granulocyte-macrophage progenitor (E), and pre-granulocyte-macrophage progenitor (F) cells were determined using the percentage of each cell population as determined by flow cytometry and the overall bone marrow cell count. (G-H) CFU assays were performed using 2 × 10⁴ bone marrow cells from mice given either 3 Gy (G) or 6 Gy (H) TBI with or without heat treatment. The bone marrow cells were mixed in methylcellulose with rmSCF, rmIL-3, and rhIL-6. On day 12, colonies were scored on coded plates for unbiased counts. Colony types were identified on a morphologic basis. The number of CFUs per femur was calculated. Each graph is representative of at least 2 separate experiments. n = 3-5 mice per group. †P < .04, compared with untreated mice. *P < .04, TBI alone mice versus TBI followed by heat treatment.