A r t i c l e Figure 6. H3K9me3 and KAP1 mark the donor switch region (S) before and during CSR. (A–D) ChIP analysis performed on chromatin prepared from resting or LPS-stimulated (48 h) and LPS + IL-4–stimulated (48 h) B cells obtained from CD19Cre/+Kap1F/+ mice using antibodies specific for H3K9/ K14Ac (A), H3K9me3 (B), KAP1 (C), and HP1- (D). Real-time quantitative PCR was performed by using primer pairs specific for JH4, I, S, C, I3, S3, C3, I1, S1, and C1. Regions surrounding the Mest promoter (10 kb and 0.5 kb) were used as negative and positive controls, respectively (Riclet et al., 2009). Fold change over control IgG is expressed as a percentage of input. Mean (+SD) of triplicate samples is shown. P-values were determined by the one-tailed Student’s t test (H3K9me3, LPS: *, P = 0.0003; **, P < 0.0001; ***, P < 0.0001; ****, P < 0.0001; H3K9me3, LPS + IL-4: *, P < 0.0001; **, P = 0.0001; ***, P = 0.0004; ****, P < 0.0001; KAP1, LPS: *, P = 0.0040; **, P = 0.0065; ***, P = 0.0289; KAP1, LPS + IL-4: *, P = 0.0134; **, P = 0.0170; ***, P = 0.0346). See Tables S2 and S5 for detailed statistical analysis and primer sequences, respectively. Data are representative of four independent experiments (see Fig. S7 for an additional experiment). JEM Vol. 208, No. 8 1655