Abstract
Local regulation of hematopoietic differentiation in the marrow requires close interactions with components of the microenvironment. In this study, we explored the capacity of human marrow hematopoietic progenitor cells to adhere in vitro to the extracellular matrix (ECM) secreted by human marrow fibroblasts. When marrow mononuclear cells were incubated on ECM-coated dishes, all types of progenitors adhered to this substrate through an active process requiring divalent cations and serum factors. The proportion of erythropoietic progenitors attached to ECM in two hours was at least twofold higher than that of granulopoietic progenitors. Moreover, in the erythroid lineage, the capacity to adhere to ECM increased with the degree of differentiation of the progenitor: 28% of CFU-E adhered to ECM as compared with 13% of immature BFU-E. Thus, ECM-mediated adherence varied both with the cell lineage and the maturation stage of the progenitor. Purified fibronectin could substitute for ECM in the adhesion assay, and ECM- mediated adhesion of CFU-E and BFU-E was partially inhibited by a polyclonal antifibronectin antibody, which implies that fibronectin may be one ECM component involved in progenitor cell adhesion. Incomplete inhibition of progenitor adhesion to ECM by the antifibronectin antibody, however, as well as the lower proportion of precursors attaching to purified fibronectin as compared with ECM suggest that other matrix molecules may also mediate erythroid progenitors attachment to ECM. These observations support the idea that hematopoietic progenitor cells may regulate their differentiation in part through the modulation of adhesive interactions with a number of constituents of the microenvironment.
