The in vitro colony-forming cell has been studied in murine bone marrow during a phase of enhanced granulopoiesis secondary to irradiation-induced neutropenia. It is suggested that the in vitro colony-forming cell derives from a primitive proliferating granulocytic precursor cell. The primary bone marrow response to neutropenia appears to occur in this committed myeloid stem cell compartment, the size of which appears inversely related to the blood neutrophil level. Because of these findings, a humoral regulator of granulopoiesis with a primary site of action at the committed myeloid stem cell level has been postulated.

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© 1971 by American Society of Hematology, Inc.
1971
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