Expression of EE372 receptors on adult erythroid progenitor cells expanded ex vivo. (A) Using conditions developed by Panzenbock et al,40 erythroid progenitor cells were expanded from the marrow of transgenic (EE372) and control mice (wt, wild-type). EE372 expression was assayed using an antibody specific to the hEGF receptor extracellular domain. PE, phycoerythrin fluorescence intensity. FALS, forward angle light scatter. (B) Example estimate of EE372 receptor densities. Phycoerythrin molecular equivalent microbeads were used to generate a calibration profile (3,800, 12,000, 34,000, 124,000, and 300,000, reading left to right). This profile (and regression analyses) then were used to estimate EE372 receptor densities on marrow cells expanded ex vivo (see inset).