IL-3 is sufficient for mast cell progenitor survival in vitro. CD34⁺ progenitors were enriched from buffy coats and cultured for 5 days with the cytokines indicated in the figure. (A) The cultured cells were analyzed with flow cytometry, and the frequency of CD117^hiFcεRI⁺ pre–mast cells as a fraction of live singlet cells was quantified. One representative experiment out of 3 is shown. (B) The frequency of CD117^hiFcεRI⁺ pre–mast cells as a fraction of live singlet cells was normalized to the combined IL-3 and IL-6 condition for each buffy coat, and the results from 3 buffy coats were pooled. The bars represent the means ± SEM of each group. One-way ANOVA with Tukey’s multiple comparisons test. ***Adjusted P < .001; ****adjusted P < .0001. (C) The IL-3 receptor (IL-3R) expression on the SSC^loCD14⁻CD34⁺CD117^int/hiFcεRI⁺ blood mast cell progenitors is shown. The red-filled histogram indicates the fluorescence minus 1 control, and the blue line indicates the sample. The analysis was performed on cells from 2 blood donors and yielded similar results.