Genetic ablation of Foxp1 increases the propensity for activated B cells to switch to IgG1 and IgE. (A) Schematic for tamoxifen (TAM)-induced deletion and culturing of Foxp1-WT and Foxp1-KO B cells. D0–D3, days 0–3; D5, day 5; D9, day 9. (B) Representative flow cytometry plots of B cells from Foxp1-WT and Foxp1-KO mice after stimulation with supplemental IL-4 pregated on live CD19⁺ singlets. (C) Normalized frequency of IgG1 and IgE surface expression. Each data point represents an individual biological replicate pooled from three independent experiments that were normalized to mean WT Ig frequency (of 1) within each experiment. Statistics were generated by two-tailed Student’s t test. ***, P < 0.001.