Inhibition of HSPC proliferation by basophil-derived CCL3. (A) KLS⁺ cells were isolated from the femoral and tibial BMs of CD45.1⁺ congenic mice, labeled with CFSE, and cocultured with or without CD45.2⁺ WT or CCL3^−/− mouse-derived basophils (Ba). The division times of KLS⁺ cells were analyzed with FlowJo software at day 4. Basophil-mediated proliferation inhibition was calculated as follows: proliferation inhibition = (1 − division time of KLS⁺ cells in the presence of Ba/division time of KLS⁺ cells in the absence of Ba) × 100. Representative results from 3 independent experiments and means ± SD from 3 independent experiments are shown in the left and right panels, respectively. *P < .05 by an unpaired Student t test. (B) CD45.2⁺ MCPT8-DTR mouse-derived total BM cells were intravenously injected into sublethally irradiated CD45.1⁺ congenic mice to establish the BM chimera. DT (400 ng/mouse) was intravenously injected at the indicated time points. The same dose of mutated DT (Glu52) was injected as a control in a similar manner. (C) The numbers of CD34⁻KLS⁺ and CD150⁺CD48⁻KLS⁺ HSCs in the tibial BMs at 24 days after BM transplantation. Data represent means ± SD from 4 independent experiments. *P < .05 by the Mann-Whitney U test. (D) The numbers of donor-derived total WBCs excluding TCR-β chain⁺ T cells, CD19⁺ B cells, and Ly6G⁺ granulocytes in the PB. Means ± SD were calculated from 11 DT- or 8 DT (Glu52)–treated mice. *P < .05; **P < .01; N.S., no significant difference by the Mann-Whitney U test.