(a, b) Cultured skin-derived MCs were stimulated for the times indicated (10 µg/ml of C48/80, 30 µM of SP, 50 µg/ml of codeine). (a) MRGPRX2 surface expression (net MFI, Figure 1) plotted as a function of time; mean ± SEM and n = 9. *P < 0.05; **P < 0.01 versus C48/80; #P < 0.05 versus codeine. (b) Representative histograms of a; red: isotype, blue: MRGPRX2. (c) Intracellular MRGPRX2 expression by flow cytometry and fluorescence microscopy (on cell permeabilization, left panel) in comparison with MRGPRX2 at the cell surface (intact cells, right panel) at 1 hour after codeine or PBS treatment (control); one representative of n = 3. Bar = 25 µm. C48/80, compound 48/80; h, hour; MC, mast cell; MFI, mean fluorescence intensity; SP, substance P.