(A) Spleens from mice of the indicated genotypes were analyzed by flow cytometry for B cell subsets (n=3, *p<0.05 vs. WT). (B) Immature bone marrow B cells (B220+IgM+CD19+AA4.1+) were purified by FACS and the diversity of CDR3 region lengths was determined by spectratyping analysis (representative of 2 experiments). (C–E) WT (solid line) or apex2Y/− (grey dotted line) mice were immunized with sRBC (C,D; n=6 WT, 4 APE2) or NP-ficoll (E, n=4 each) and antibody titers were determined at the times indicated. n.d., no difference.