A regulatory mechanism for the number of pluripotential haemopoietic progenitor cells in mice.

Large changes in the pattern of regeneration of haemopoietic progenitor cells (CFU-S) are reported as a result of simply altering the time interval between administration of certain cytotoxic agents and whole-body irradiation. These results suggest a negative feedback control for the number of CFU-S, which has an appreciable time delay. A high inverse correlation between the number of maturing granulocytic cells (with ring-shaped nuclei) at the time of irradiation and the subsequent regeneration of CFU-S is consistent with these cells producing some substance that controls the number but not the proliferation rate of the CFU-S. The possibility is considered that this mechanism is an important control in the biological regulation of haemopoiesis.