Adhesive properties of human erythroblastic precursor cells

Interactions between hematopoietic precursor cells and their surrounding marrow environment are essential for hematopoietic differentiation. These occur in part through the production of regulatory molecules by marrow stromal cells and their local concentration by components of the extracellular matrix (ECM), but direct cell-cell or cell-matrix contacts are likely to also play an essential role. During the past several years, we have characterized the adhesive properties of human hematopoietic precusor cells on two substrates, marrow fibroblastic ECM and purified plasma fibronectin (Fn). We have shown that adhesion to marrow ECM and Fn was a selective property of erythroblastic cells and was expressed by normal erythroblastic progenitors (CFU-E and BFU-E), as well as by erythroleukemic cell lines (K 562), but only a small proportion of CFU-GM. Furthermore, attachment to Fn was very precisely regulated during erythroblastic differentiation as shown by the loss of Fn-adhesion in reticulocytes derived from purified immature erythroblasts induced to differentiate in vitro. The physiological relevance of these results is not well understood, but we speculate that adhesion to ECM components helps stem cells to locate in a favorable environment, and that loss of this property in reticulocytes is required before they cross the marrow-blood barrier.