IgE-induced mast cell survival is mediated by soluble factors. (A-B) Survival of FcRγ^-/- BMMCs supplemented with supernatant of IgE(-Ag)–treated FcRγ^+/+ BMMCs. BMMCs from FcRγ^+/+ and FcRγ^-/- mice were cultured in the absence (A) and presence (B) of 100% supernatant from IgE-treated (1 μg/mL, Sup(+)[▴]) or untreated (Sup(-)[⬡]; ○ indicates no supernatant) WT BMMCs for 12 hours, and then tested in the survival assay. (C) IgE-induced survival of FcϵRI^- BMMCs when cocultured with FcϵRI⁺ BMMCs. BMMCs were infected with pMX-FcRγ-IRES-GFP and the viability of the bulk population was analyzed for both FcϵRI⁺ (GFP⁺) and FcϵRI^- (GFP^-) populations. IgE concentration was 0 μg/mL (○), 1 μg/mL (⬡), and 10 μg/mL (▴). (D) Coculture of FcRγ^-/- and FcRγ^+/+ BMMCs in transwell chambers. Either FcRγ^-/- or WT (FcRγ^+/+) BMMCs were cultured in upper and lower chambers with indicated combinations in the presence (▪) or absence (□) of 1 μg/mL IgE. The viability of cells in the upper chamber was analyzed 4 days after IL-3 depletion. Data are expressed as the mean ± SD for triplicate assays. Similar results were obtained from 3 independent experiments.