Stimulation of erythroid colony formation in vitro by erythropoietin immobilized on agarose-bound lectins.

WGA and the PHA-E covalently linked to beaded agarose were employed to prepare an immobilized form of Ep. Agarose-PHA-E-Ep complexes induced the formation of sheep and human erythroid colonies in plasma clot and methylcellulose cultures without detectable leaching of Ep. Approximately 85% to 95% of the colonies formed were attached or juxtaposed to the agarose beads. The dose-response curve of the agarose-PHA-E-Ep complexes for erythroid colony formation was similar to that of unbound Ep, and after removal of cells adherent to the beads, the immobilized Ep could be reused. Attachment of erythroid colonies to agarose-lectin-Ep complexes was due to lectin-cell surface interactions. These results support the concept that Ep acts at the surface of its target cells.