1-ALPHA,25-DIHYDROXYVITAMIN D-3 PROMOTES MONOCYTOPOIESIS AND SUPPRESSES GRANULOCYTOPOIESIS IN CULTURES OF NORMAL HUMAN MYELOID BLAST CELLS

Primitive myeloid blast cells were (2-10 x 10(6)) purified from 18-22-week fetal liver-derived mononuclear cell preparations by negative selection followed by counterflow cell elutriation. The cells, when maintained in liquid culture in the presence of 100 U/ml interleukin-3 (IL-3) for the first 5 days and 10 U/ml IL-3 and 30 ng/ml granulocyte colony-stimulating factor thereafter, underwent considerable proliferation resulting in an similar to 30-fold increase in cell number by day 14. Analyses of cell morphology and of the numbers of cells that expressed the neutrophil-associated antigen CD15, the monocyte-associated antigen 61D3, and enzymes alpha-naphthyl acetate esterase (ANAE), human leukocyte elastase, and cathepsin G revealed that proliferation of the cells was associated with their concomitant differentiation toward neutrophils and monocytes. The cultures generated predominantly neutrophils; by day 14, wells seeded with 2 x 10(5) cells produced similar to 5 x 10(6) neutrophils as opposed to only similar to 3.5 x 10(5) cells with a monocytoid morphology. This predominance of granulocytopoiesis over monocytopoiesis was confirmed by the numbers of cells that had acquired expression of the CD15 antigen and ANAE, which were approximately 2 x 10(6) and 1 x 10(5), respectively. By contrast, parallel cultures containing 100 nM 1 alpha,25-dihydroxyvitamin D-3 (VitD(3)) generated more monocytes than neutrophils. At day 14, VitD(3)-treated cultures contained similar to 2 x 10(6) cells with morphologies consistent with their differentiation toward monocytes and similar to 1 x 10(6) ANAE-positive cells, compared with similar to 9.5 x 10(5) cells having morphologies of granulocyte-series cells and similar to 4.5 x 10(4) CD15-positive cells. In both control and VitD(3)-treated cultures, the enzymes cathepsin G and human leukocyte elastase were expressed almost exclusively by cells that were differentiating toward neutrophils. These data reveal that VitD(3) promotes monocytopoiesis and suppresses granulocytopoiesis of primitive blast cells.