Quercetin dose-response evaluated by assaying histamine release with an ELISA commercial kit. Histamine is expressed as ng/ml of the vasoactive amine. Basophils were pre-treated 10 min at 37°C with increasing doses of quercetin and subsequently stimulated for further 30 min at 37°C with 4 μg/ml anti-IgE (A), 100 nM fMLP (B), 0.5 μM calcium ionophore A23187 (C) or 50 nM PMA (D). Values are mean ± S.E.M. of 3 different triplicate assays. Negative control: cells which did not undergo any treatment with quercetin and the agonist (resting cells); positive control: cells treated with the agonist but not treated with quercetin. One way global ANOVA for activated samples series: A) p < 0.0001; B) p < 0.001; C) p = 0.034; D) p = 0.65. Post-hoc (LSD) analysis of each dose as compared to positive control is indicated above the respective bar chart as: (**) p < 0.01; (***) p < 0.001.