Constitutive CCL3 expression by a restricted progenitor cell type in mouse BM. (A) Total BM cells were harvested from the tibial bones of untreated mice. Rat immunoglobulin G2a (IgG2a) was used as an isotype control, shown in the upper panel. Expression of MPO, CD16/32, or CD34 was determined in total BM cells (black contour lines) or in lineage^low CCL3-expressing cells (red contour lines). Representative results from 3 independent experiments are shown. (B) CCL3 and c-kit expression was determined in lineage^lowCD34⁺MPO⁺ cells (R1 and R2). Percentages of CCL3⁺ cells in c-kit^high and c-kit^low regions are shown. Rat IgG2a was used as an isotype control. Representative results from 3 independent experiments are shown. (C) Total BM cells (1 × 10⁷) harvested from the femoral and tibial bones of untreated and primary BM chimeric mice were intravenously injected into sublethally irradiated recipient mice to establish the primary and secondary BM chimeras, respectively. Eight weeks after transplantation, the proportion of CCL3⁺c-kit⁻ cells among lineage^lowCD34⁺MPO⁺ cells was compared with that in untreated BM cells. Data represent means ± standard deviation (SD) from 4 independent experiments. *P < .05; N.S., no significant difference by Dunnett’s test.