Defective KIT expression and response to KitL in mast cells of WBB6F₁-tg/tg mice. (A) Flow cytometry of the surface expression of KIT in mast cells obtained from colonies and BMMCs. Mast cell colonies developed from bone marrow cells (i-ii), and BMMCs cultured in the presence of IL-3 alone (iii-iv) or IL-3 + KitL (v-vi) were harvested and incubated with FITC-conjugated anti-KIT antibody or isotype control. The staining profiles with anti-KIT antibody (thick line) and with isotype control (thin line) were shown. The data were representative of 3 independent experiments. (B) Response to KitL of BMMCs derived from WBB6F₁-+/+ or WBB6F₁-tg/tg mice. BMMCs were incubated in the medium containing 10 ng/mL IL-3 and various concentration of KitL, and the response to KitL was detected with uptake of ³H-TdT. The bars represent the mean ± SE of 3 experiments. In some cases, the SE was too small to be shown by bars.