CD19^cre/+ PRDM1^flox/flox mice are a poor model for B-1–specific knockouts. (A–D) FACS analysis of the spleens and BM of wild-type (C57BL/6), CD19^cre/+, CD19^cre/+ PRDM1^flox/flox, and PRDM-1^ΔEx1A mice (n = 4–5). Results are representative of two independent experiments. (A) Frequencies ± SD of B-1a among B-1 cells and (B) the number ± SD of B-1a cells and total B-1 cells. (C) Frequencies ± SD of B-1PCs among live cells and of (D) follicular and marginal zone B-1 cells among B cells in the spleen. All statistics were done using an unpaired Student’s t test (*, P < 0.05; **, P < 0.005; ***, P < 0.0005).