IL-33 promotes cytokine production and enhances IgE receptor–induced mediator release as efficiently as IL-3. (A) Direct and synergistic induction of secretion of Th2 cytokines and IL-8 by IL-3 and IL-33. Freshly isolated basophils were cultured in medium alone or with IL-18 (50 ng/mL), IL-33 (50 ng/mL), IL-3 (10 ng/mL) or in combination of IL-3 + IL-33 for 8 hours. Cytokine secretion was measured in the cell supernatants. Means plus SEM of 8 independent experiments are shown. (B,C) IL-33 augments IL-4, IL-13, IL-8, and LTC4 production in basophils activated by IgE receptor crosslinking. (B) Cells were activated by a maximally effective concentration of anti-FcϵRIα mAb (anti-IgER; 100 ng/mL) alone or with IL-18 (50 ng/mL), IL-33 (50 ng/mL), IL-3 (10 ng/mL), or IL-33 + IL-3, and cytokines were measured in cell supernatants after culture for 8 hours. Mean plus SEM of 5 experiments with cells from different donors are shown. (C) Basophils were stimulated with increasing concentration of anti-IgER in the absence or presence of IL-3, IL-33, or IL-3 + IL-33 for 8 hours. Mean values plus or minus SEM of 2 independent experiments performed in duplicates are shown. Statistical analysis: The statistical significance of differences between the different experimental conditions (marked by lines for each pair of conditions) was analyzed using the Student t test (ns, not significant, *P < .05, **P < .01, ***P < .001).
