Effect of 787F mutation on MC function. (A) SCF treatment does not rescue BMMCs carrying the 787F mutation from apoptosis induced by IL-3 deprivation. BMMCs were cultured with indicating concentrations of SCF for 48 hours, and apoptosis was measured using annexinV/PI staining. BMMCs without cytokines or treated with 5 ng/mL IL-3 were used as negative and positive controls, respectively. BMMC cultures generated from individual animals were analyzed. One representative experiment of 4 is shown (*P = .02; **P = .002; ***P = 4 × 10⁻⁴; n = 3). (B) Kit^787F BMMCs do not reconstitute MC-deficient Kit^W/Kit ^W-v mice in vivo. Kit^W/Kit^W-v mice were reconstituted with 3 × 10⁶ wild-type (wt) or Kit^787F (787F) BMMCs intraperitoneally, PECs were analyzed by FACS, and the number of c-Kit^high, T1/ST2^high peritoneal MCs were assessed 6 weeks later (*P = .006; **P = 3 × 10⁻⁴; n = 3-5). (C) MCs from Kit^787F mice do not produce IL-6 upon SCF stimulation. BMMCs from wild-type and Kit^787F mice were left untreated or treated with increasing concentration of SCF for 48 hours, and IL-6 was measured in supernatants by ELISA. Mean values from 4 independent experiments ± SEM are shown (*P = .04; **P = 7 × 10⁻⁶; n = 4-8). (D) Stimulation with SCF (100 ng/mL) does not further increase IL-6 production induced by IgE and antigen in Kit^787F BMMCs. Cells were stimulated for 3 hours, and IL-6 was measured in supernatants by ELISA (***P < 5 × 10⁻⁴). Mean values from 3 independent experiments ± SD are shown. RANTES (E) or IL-6 (F) production induced by PMA and ionomycin or LPS is comparable in wild-type and Kit^787F BMMCs. Cells were stimulated for 48 hours, and concentration of IL-6 or RANTES was measured in the supernatants. Mean values from 3 independent experiments ± SEM are shown.