In vivo stimulatory effect of macrophage colony-stimulating factor on the number of stroma-initiating cells

The in vivo effect of human macrophage colony-stimulating factor (M-CSF) on the number of cells that formed stromal colonies in an in vitro culture sy stem (stroma-initiating cells; SICs) was investigated. We found that the nu mber of SICs in the femurs of C57BL/6 mice was significantly increased by t he treatment with M-CSF. We also found that the SICs were resistant to at l east three different chemotherapeutic reagents, 5-fluorouracil (5-FU), cyta rabine, and cyctophosphamide, because the femoral cells of mice treated wit h these reagents contained higher numbers of SICs than those of untreated m ice. M-CSF treatment also increased the number of SICs of the reagent-pretr eated mice. The SICs detected in our culture system were present only in Ma c-1(-)CD45(-) cells, and the M-CSF treatment of 5-FU-pretreated mice actual ly increased the number of Mac-1(-)CD45(-) SICs. The Mac-1(-)CD45(-) SiCs c ollected from mice that were pretreated with 5-FU and then treated with M-C SF formed stromal colonies under in vitro culture conditions that did not c ontain M-CSF but did contain a high concentration of fetal calf serum. This result suggested that SICs collected following the treatment procedure did not necessarily require the presence of M-CSF for their in vitro prolifera tion. Our study indicated that M-CSF has the ability to increase the number of progenitor or precursor cells for bone marrow stromal cells in vivo sys tem. J Cell Physiol 178:267-273, 1999. (C) 1999 Wiley-iiss, Inc.