Lectin receptor proximity on HL-60 leukemia cells determined by fluorescence energy transfer using flow cytometry

Fluorescence energy transfer using flow cytometric measurements was utilized to determine the proximity of concanavalin A receptors on the surface of HL-60 promyelocytic leukemia cells before and after induction of differentiation. The HL-60 cells were induced to differentiate into granulocytes using dimethylsulfoxide and into macrophages using 12-O-tetradecanoylphorbol-13-acetate. Concanavalin A was labeled with either fluorescein (donor chromophore) or tetramethylrhodamine (acceptor chromophore), and these species were used to determine lectin proximity. With granulocytic differentiation, the amount of concanavalin A bound remained constant, but a decrease in receptor density was observed. During macrophage differentiation, however, both receptor density and receptor number increased. The increase in concanavalin A binding during differentiation appears to be a result of maturation rather than an initiating event.