Regulation of maturation rate of mouse granulocytes

Regenerating mouse bone marrow cells were cultured i.p. in diffusion chambers (DC) to study factors affecting the maturation rate of granulocyte precursors. One day after exposing 3-day-old DC cultures to 3H-thymidine the cultures were harvested, and labelled proliferative and non-proliferative granulocytes were counted in radioautographs. The relative maturation rate--defined as the fraction of proliferative precursors maturing into the non-proliferative compartment per unit time--could be increased by different experimental procedures that inhibit cell production. Inhibition was obtained (a) by increasing culture cellularity; (b) by implanting DC into normal rats or rats with huge s.c. chloroma tumours rather than into mice; and (c) by treating the cells with leucocyte extracts (granulocyte chalone) during the last day of culture. Furthermore, a sudden inhibition of rapidly proliferating granulocytes by leucocyte extracts resulted in an increase (apparently transient) in the absolute number of labelled non-proliferative granulocytes. Such an increae was not detected in experiments involving a stronger or sustained inhibition of granulopoiesis, evidently because the size of the precursor population had been markedly reduced.