Cycling rates of myeloid progenitors in c-kit⁺lin⁻ BM. The cycling rates of progenitors were determined by tritiated thymidine kill assay of sorted c-kit⁺lin⁻ BM cells. Results represent the mean ± range of the assessment of separated cells from two individual mice each from the CCR2 (−/−) and (+/+) groups in which 1,000 cells were plated in methylcellulose in the presence of Epo, PWMSCM, and SLF.