IL-3 promotes mast cell progenitor proliferation, whereas IL-5 supports mast cell progenitor survival. (A) Gating of pre–mast cells (pre-MCs) after culture of c-Kit⁺ progenitors for 5 days. (B) Quantification of pre-MCs after culture of c-Kit⁺ progenitors in various cytokine conditions. Points in each group represent individual buffy coats. Values are normalized to the IL-3 condition of each donor. One-way analysis of variance, Dunnett’s post hoc with no cytokines as control group. (Ci) The proliferative response of mast cell progenitors was analyzed by CellTrace Far Red signal in pre-MCs. The control refers to analysis of all live cells after culture without cytokines, as pre-MCs were virtually absent. (Cii) Quantification of the results in panel Ci (n = 3). (D) Analysis of the proliferative response of mast cell progenitors to various concentrations of IL-5. IL-3 served as positive control. Representative of 2 independent experiments. The study used 10 ng/mL IL-3, 20 ng/mL IL-5, 10 ng/mL GM-CSF, 1 U/mL EPO, 50 ng/mL thrombopoietin (TPO), 50 ng/mL Flt3L, and 22.5 to 100 ng/mL IL-33 unless otherwise specified. ****P < .0001. ns, not significant.