IL-21 inhibits IL-4–induced IgE production at single cell levels.

Purified splenic B cells from BALB/c mice or Stat6^−/−mice were labeled with CFSE and then stimulated with LPS (10 μg/mL) in the presence of IL-4 (50 ng/mL) or IL-21 (0-20 ng/mL) or both for 6 days. Where indicated, sIL-21R (20 μg/mL) was added to the culture. mIgE⁺ cells (A) and mIgG1⁺ cells (B) with the intensity of CFSE were detected by anti-IgE antibody and anti-IgG1 antibody, respectively. Shown are representative FACS profiles from 5 independent experiments and the numbers in the top right-hand corner indicate the percentage of mIgE⁺ cells and mIgG1⁺ cells.