Stroma-derived factor 1α induces a selective inhibition of human erythroid development via the functional upregulation of Fas/CD95 ligand

CXC chemokine receptor 4 (CXCR4), the high-affinity receptor for stroma-derived factor 1 alpha (SDF-1 alpha), shows distinct patterns of expression in human CD34(+) haematopoietic progenitor cells induced to differentiate in vitro along the granulocytic and erythroid lineages. In serum-free liquid cultures supplemented with stem cell factor (SCF), interleukin 3 (IL-3) and granulocyte colony-stimulating factor, the expression of surface CXCR4 progressively increased in cells differentiating along the granulocytic lineage. The addition in culture of 200 ng/ml of SDF-1 alpha, a concentration which maximally activated intracellular Ca2+ flux, only modestly affected the expression levels of CD15 and CD11b granulocytic antigens, as well as the total number of viable cells. On the other hand, in liquid cultures supplemented with SCF, IL-3 and erythropoietin, SDF-1 alpha induced the downregulation of glycophorin A erythroid antigen, accompanied by a progressive decline in the number of viable erythroblasts. Moreover, in semisolid assays, SDF-1 alpha significantly reduced the number of plurifocal erythroid colonies (erythroid blast-forming units; BFU-E), whereas it did not affect granulocyte-macrophage colony-forming units (CFU-GM). We also demonstrated that the inhibitory effect of SDF-1 alpha on glycophorin A(+) erythroid cell development was mediated by the functional upregulation of CD95L in erythroid cultures. These data indicate that SDF-1 alpha plays a role as a negative regulator of erythropoiesis.