FIP200 promotes plasma differentiation by balancing ROS and heme metabolism. (A) Naïve, GC, memory, and plasma B cells FACSorted from WT and B-Fip200^−/− mice immunized with 50 μg NP₂₉-KLH with Imject Alum at day 11. UMAP showing 13 B cell clusters and phenotypic identities in WT (left) and Fip200^−/− (right) groups. Representative of one experiment, n = 5 pooled B-Fip200^−/− mice and n = 4 pooled WT mice. (B) Venn diagram shows common genes upregulated in Fip200^−/− cells in clusters 2, 6, and 7 (major plasma populations), and genes upregulated in all three clusters compared with their WT control. (C) Subset and reclustering of B cells from plasma clusters 2, 6, 7, and 12 in A, colored by cluster. (D) Scatterplots showing average signature score, calculated in VISION, for curated KEGG pathways on a cluster-by-cluster basis in Fip200^−/− versus WT plasma cells for ROS (left) and heme metabolism (right). FDR, false discovery rate; UMAP, Uniform Manifold Approximation and Projection.