Dominant negative effect of KIT^W42 in Ba/F3^Del-Tyr814 cells. (A) Flow cytometric analysis of the surface binding of ACK2 MoAb (ECD). Cells were incubated with either ACK2 MoAb (—) or negative control antibody (---). (B) Viability assays. After plating cells (2 × 10⁴), viable cells were counted at daily intervals using trypan blue dye. Three independent experiments were performed with comparable results, and the result of a representative experiment is shown. Each point represents the mean of triplicate samples. Bars are the standard error. In some points, the standard error was too small to be shown by bars. (C) Incorporation of [³H]-thymidine. Proliferation of cells for rmIL-3 (10 ng/mL) and rmSCF (100 ng/mL) was measured with [³H]-thymidine incorporation assay. Three independent experiments were performed with comparable results, and the result of a representative experiment is shown. Each value represents the mean of triplicate samples, and the standard error was less than 5%. Asterisks indicate the presence of the statistical significance (P < .01) when compared with the value of either Ba/F3^Del-Wildor Ba/F3^Del-Tyr814 cells at the absence of rmIL-3 and rmSCF.