Production of soluble CD34 by human myeloid cells

CD34, a glycophosphoprotein present in lymphohaematopoietic stem and progen itor cells, as well as in other cell types, exists in both transmembrane an d intracytoplasmic forms. Transmembrane CD34 expression, which is high in t he earliest haematopoietic precursors, decreases as cells mature. However, to our knowledge, there is no information on whether a decrease in transmem brane CD34 can also predict a release of the molecule from the cell membran e into the extracellular fluid. To investigate the above possibility, we st udied conditions (incubation time, cell density and proliferative status) i n human myeloid cells (lines KG-1a, KG-1 and cord blood-derived cells) that may cause a decrease in surface CD34 and the generation of a soluble form of the molecule. The latter, as demonstrated by Western blot analysis, adds more complexity to the proposed structural features and functional propert ies of CD34 in myeloid cells.