Stimulation of Hematopoiesis by Femoral Marrow Curettage in Sublethally Irradiated Mice

Femoral bone marrow curettage produced an intense stimulus on hematopoietic stem cells (HSC) in sublethally irradiated mice 4 days after curettage. A similar but lesser stimulation of ⁵⁹Fe incorporation into spleen and red cells was observed. Previous investigations have shown that this effect is not observed in unirradiated mice. Histologic studies of the curetted femurs indicated a rapid regeneration of a primitive mesenchymal tissue within the medullary cavities during the period of stimulation. It is suggested that the primitive mesenchymal cells synthesize a humoral factor that is capable of stimulating HSC in a marrow microenvironment of depleted cellularity. The observations are consistent with a hypothesis of inhibition of HSC response to a similar stimulus in a normocellular marrow by a mechanism of cell-cell interaction. The humoral factor affects HSC similar to fetuin, spleen extract, and alpha globulin fractions.