(a) Cultured skin-derived MCs were triggered by C48/80 (10 µg/ml), codeine (50 µg/ml), or C48/80 + codeine for different times. Cell surface MRGPRX2 expression was determined as in Figure 3. The data are presented as mean ± SEM of n = 8 individual experiments. **P < 0.01 for codeine versus c48/80, #P < 0.05 for codeine versus codeine + c48/80. (b) Ex vivo skin MCs were stimulated, and HR was measured as in Figure 1. C48/ 80, compound 48/80; h, hour; HR, histamine release; MC, mast cell; MFI, mean fluorescence intensity.