Bone marrow response to single small doses of irradiation: implications for stem cell functional organization.

The data collected in 107 experiments over 23 months have been pooled to indicate the responses of cellularity, stem cell (CFU-S) number, and CFU-S proliferation rate (CFU-S in S-phase) during early recovery of the bone marrow from 1.5 and 2.6 Gy irradiation. The bone marrow differentials and numbers of granulocyte-macrophage progenitors (CFC-GM) were determined after irradiation with 1.5 Gy. The CFU-S proliferation rate was examined also in mice irradiated with 3.5-5.0 Gy. The data are discussed in the light of various hypotheses about the functional organization of the CFU-S population. It is proposed that the control of the CFU-S production rate is primary rather than the control of CFU-S numbers.