Radiation-induced enlargement of granulocytic and macrophage progenitor cells in mouse bone marrow.

The peak sedimentation velocity of C57BL mouse bone marrow progenitors of granulocytes and macrophages (GM-colony-forming cells, GM-CFC's) increased from 4.3 mm/h to 7-8 mm/h by 2 days after 250 rad whole body irradiation and slowly returned to normal over the next 3 weeks. Ppreliminary irradiation and/or endotoxin injection did not prevent this radiation-induced change. Some change in sedimentation velocity was seen with as little as 100 rad irradiation. Neither buoyant density nor cell cycle changes could account for the sedimentation velocity data which therefore indicate a major volume increase in the GM-CFC's. This size enlargement affected all subpopulations of GM-CFC's which consequently maintained their size relationship with one another.