The loss of Blimp-1 rescues defect of CSR in Bach2−/− B cells. (A) Splenic B cells from mice of indicated genotypes were induced to undergo isotype switching to IgG3 or IgG1 in culture by stimulation with LPS or LPS plus IL-4, respectively. Surface expression of immunoglobulin isotypes on cultured B cells was analysed by FACS at indicated days. Average percentages from wild-type (n=4), Bach2−/− (n=6), Blimp-1−/− (n=4) and Bach2&Blimp-1 DD (n=4) mice are shown. (B, C) Sort-purified FO B cells (B220+, IgM+, CD21low and CD23+) were labelled with CFSE and stimulated with LPS plus IL-4 for 3 days. Cell division numbers were determined by FACS and average percentages from wild-type (open circle, n=3), Bach2−/− (closed triangle, n=4) and Bach2&Blimp-1 DD (closed box, n=1) mice are shown (B). Average cell numbers at day 3 are shown (C). WT, wild type; B2, Bach2−/−; DD, Bach2&Blimp-1 DD.