Detection of membrane-bound FL on leukemic cells by flow cytometric analysis. Serially transplanted 199 leukemic spleen cells were transferred to liquid culture and maintained in the presence of KL, IL-3, and IL-7 plus G418 for 4 weeks before analysis. Cells were assayed for capacity to bind a soluble human flt3R-Fc fusion protein. The solid line histogram represents specific staining (79.3% positive) above background (shaded line histogram). See Materials and Methods for details.