The serum and spleen were collected from approximately 20-week-old Bach2 KO mice and their WT littermates. Serum was assayed by ELISA to determine titers of total IgM and IgG a, anti-dsDNA IgM and IgG d, and anti-M3R IgM and IgG f. Spleens were examined by fluorescence confocal microscopy to detect GCs b, FACS to detect GC B cells c, and ELISPOT to count Ab-secreting cells e, g. Data are presented as the means ± SEMs in arbitrary units (AU) and Ab-secreting cells (ASCs) per indicated number of cells, pooled from three independent experiments. FACS profiles gated on B220+CD138- cells are representative of three independent experiments. Scale bar, 250 μm. *p < 0.05, **p < 0.01 and ***p < 0.001 by Student’s t-test.