(A) GM-pu4 was found to be NSE-positive. The GM-pu4 clone was tested for NSE activity. The dark staining cells are NSE-positive. The activity was verified as being monocyte-specific by the ability of NaF to inhibit the reaction. (B) GM-pu4 cells have phagocytic activity. GM-pu4 cells were incubated with latex beads for 1 or 4 hours. The engulfment of beads was evaluated by flow cytometry and with a fluorescent microscope. The clear tracing on the histogram plot are cells that did not receive beads. For visualization, cells were spun onto slides and stained with Wright-Giemsa. The figure shows the same two cells viewed with bright field or UV.