Differentiation of myeloid cells and 1,25-dihydroxyvitamin D3

It is well established that 1,25(OH)(2)D-3 induces monocyte/macrophage (Mo/M phi) colonies when added to culture of granulocyte/macrophage progenitors. Recently, we demonstrated that one of the target cells of 1,25(OH)(2)D-3 in Mo/M phi differentiation is the neutrophilic promyelocyte that is believed to belong to the neutrophilic lineage. This fact overthrows the established theory that normal hematopoietic precursors are committed to respective cell lineages and do not deviate from their own lineage. The lineage switching from the promyelocyte to Mo/M phi was suggested to be operating in vivo because 1,25(OH)(2)D-3 is a physiological substance produced by M phi. More recently, we have shown that transient exposure (24 h) of promyelocytes to 1,25(OH)(2)D-3 causes Mo/M phi differentiation. This strategy could be useful for examining the effects of 1,25(OH)(2)D-3 on the growth and differentiation of normal myeloblasts and myeloid progenitor cells. Recent advances in molecular biology have enabled investigators to identify a number of genes involved in Mo/M phi differentiation induced by 1,25(OH)(2)D-3. Some of these may be the determinant genes for Mo/M phi differentiation; however, further studies are required to determine the underlying mechanisms of Mo/M phi differentiation.