Treg and Th2 cell–associated cytokine production by stimulated T cells is increased by Notch1-activated mature B cells. (A) Cytokine production by WT CD3⁺CD4⁺ T cells cultured in vitro with or without CD19⁺RFP⁺ B cells from NICD1 mice and controls and stimulated with LPS and anti-CD3/anti-CD28 activators. An anti–IL-33 receptor ST2-blocking antibody was added as indicated. Cytokine concentration in the culture medium was measured in a bead-based immunoassay after 4.5 days of culture. (B) IFN-γ production by WT CD3⁺CD8⁺ T cells cultured in vitro with or without CD19⁺RFP⁺ B cells from NICD1 mice and controls and stimulated with LPS and anti-CD3/anti-CD28 activators. In panels A-B, data in the bar graphs are expressed as the mean and SEM from 3 independent experiments. *P < .05, **P < .01, and ***P < .001 (Tukey-Kramer test). (C) Percentages of Treg and Th2–cell subsets and IL-10–producing T cells within the splenic CD3⁺ CD4⁺ T-cell population from NICD1 mice and controls on the IL33^WT/WT, IL33^KO/WT, or IL33^KO/KO background, as determined by intracellular flow cytometric analysis. Data in the bar graphs are expressed as the mean and SEM from 3 to 4 individual mice. **P < .01 and ***P < .001 (Tukey-Kramer test).