Hydrocortisone promotes clonal granulopoiesis in cultures of normal human bone marrow--a "nutritional" advantage or true stimulation of growth?

The generation of normal human hemopoietic clones is promoted, in tissue culture, by physiological as well as pharmacological concentrations of hydrocortisone. In part this may reflect a facilitative, nutritional effect of the hormone which may be more evident in particular culture media. However, the findings, in liquid suspension cultures, of an increase in the absolute number of cells and a rise in the mitotic index in the presence of hydrocortisone, point to a real stimulation of cellular proliferation. Measurements of the number of clones early in culture, and the size of clones after longer intervals, indicate respectively that the hormone influences both recruitment of clonogenic cells into cytokinesis and amplification of established clones. The target cell in both processes may be the same, namely a morphologically recognizable entity, in the granulocyte lineage, having limited proliferative potential. Evidence in support of this interpretation includes the high cloning efficiency, small mean clonal size and brief clonal lifespan. These features suggest that members of the myeloblast-promyelocyte-myelocyte hierarchy are likely candidates, but whether the action of hydrocortisone is exerted directly on these cells, or on a more mature accessory population, remains to be determined.