Binding of merocyanine 540 to normal and leukemic erythroid cells

Normal erythroid cells and both uninduced and induced erythroleukemia cells were stained with the leukemia-specific fluorescent probe merocyanine 540 and its analogs. The external membranes of normal intact cells bound the dye, but this general low-affinity binding was completely abolished by the addition of competing serum. In contrast, erythroleukemia cells bound the dye even in the presence of serum; binding was not affected by reversing the sign of the charge carried by MC540, but was abolished upon removal of certain hydrophobic side chains. When the erythroleukemia cells were induced to differentiate, the distribution of dye-binding regions was altered by the cell such that staining became localized to one region of the membrane. Concomitantly, conconavalin A binding sites were redistributed and became localized in the same region of the membrane as the merocyanine binding sites. Merocyanine 540 is thus shown to bind to a hematopoietic surface feature whose topological distribution is subject to cellular control during differentiation. This leukemia-specific marker may be one of several eliminated during enucleation of mammalian erythroid cells.