Percentage of HL-60 cells staining positive for nonspecific esterase after treatment with various concentrations of recombinant mactinin. Cells were incubated for 3 days with mactinin, then harvested and stained. The percentage of untreated HL-60 cells positive for staining was subtracted. Each value is the mean ± SD for a minimum of two assays of 100 cells each. The result of treatment with 100 nM 12-O-tetradecanoylphorbol-13-acetate is also shown (circle).