Time-dependency of cell death on the induction of MARCO transcript with the lac switch system. (A) The wild-type HL-60 cells or the transformant cells were treated with IPTG for the indicated periods and assayed with a cell counting kit. On the vertical axis, the O.D. from wild-type HL-60 cells is shown as 100%, while 0% indicates the O.D. from cell-free cultures. (•) Wild-type HL-60 cells; (▴) mock-transfected HL-60 cells; (○) NF-1 cells. (B) Cells were cultured for the indicated periods with IPTG, and viable cell number was counted by Trypan blue dye exclusion assay. (C) Cells were cultured as in (B), and cell counting was proceeded microscopically. (•) Wild-type HL-60 cells; (▴) mock-transfected HL-60 cells; (○) NF-1 cells. In each panel, values represent the mean of triplicate assays with standard error of means (SEM). This result is representative of five independent experiments.