An in vitro analysis of murine hemopoietic fibroblastoid progenitors and fibroblastoid cell function during aging.

We determined the number of fibroblastoid progenitors (fibroblastoid colony-forming units, CFU-F) in femurs and spleens derived from (CBA X C57BL)F1 mice of different ages. The femoral CFU-F population size increased from 350 at 1 week of age and plateaued at approximately 1900 CFU-F at 8 weeks of age. The mean incidence of CFU-F per 10(6) femoral marrow nucleated cells decreased from 82 at 8 weeks of age to 55 at 70 weeks of age; however, due to an increase in femur cellularity, there was no decrease in the CFU-F population size. The splenic CFU-F population decreased from 1700 at 1 week of age to 180 at 8 weeks of age; no further change was observed in mice up to 70 weeks' old. Analysis of colony-stimulating activity production by fibroblastoid colonies derived from young (6 weeks) and aged (70 weeks) mouse femoral marrow demonstrated no difference. These results indicate that there is no change in CFU-F numbers or fibroblastoid cell colony-stimulating activity production associated with the age-related increase in hemopoietic organ cellularity and hemopoietic progenitor content observed in this mouse strain. There were, however, major changes in the CFU-F population sizes during development of both femoral marrow and spleen in the first 2 months after birth.