(a,b) Resting MCs (rest MCs), IgE-sensitized MCs (sens MCs) or antigen-activated MCs (act MCs) were cocultured with naïve splenic B cells. After 3 days, the culture supernatants were analysed by ELISA for secreted IgM (a) or IgG (b). Results are expressed as mean absorbance values at 405 nm + SEM and represent 4 independent experiments (n = 5). (c,d) Naïve splenic IgM+ B cells were FACS-sorted before cultured alone or with act MCs for three days. The culture supernatant were analysed by ELISA for secreted IgM (c) and IgG (d). Results are expressed as mean absorbance values at 405 nm + SEM and represent 2 independent experiments (n = 6). (e,f) Naïve splenic B cells were cultured together with antigen-activated MCs, separated or not by a transwell membrane system (TW). Additional cultures were set up with naïve splenic B cells cultured with conditioned medium (CM) from 3-days old cultures of act MCs. After 3 days the culture supernatants were analysed by ELISA for secreted IgM (e) or IgG (f). Results are expressed as mean absorbance values at 405 nm + SEM and represent 3 (e) or 1 (f) independent experiments (n = 3–5). *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001. OD, optical density.