AhR antagonizes PCD ex vivo via Blimp-1 repression. (A) Representative flow cytometry plot of WT and AhR^−/− splenic (top) and LN (bottom) B cells stimulated with anti-CD40 + IL-4 (CI) for 96 h, showing CD138⁺ plasma cells. (B) Quantification summary of percent CD138⁺ splenic and LN B cells from WT and AhR^−/− mice. A representative of three experiments with three mice per group is shown. (C) Percentage of CD138⁺ cells at 96 h after CI stimulation of WT and AhR^−/− B cells treated with DMSO or TCDD. (D) Relative mRNA expression of prdm1 (normalized to β actin) at 48 h CI stimulation between WT and AhR^−/− splenic B cells. (E) Relative cyp1a1 mRNA levels (normalized to β actin) as a measure of AhR activation in 48-h CI-treated WT B cells infected with pMIG in the presence of DMSO or TCDD. (F) Relative mRNA expression of prdm1 (normalized to β actin) in CI-stimulated WT B cells infected with pMIG (48 h) in the presence of DMSO or TCDD. (G) Western blot showing Blimp-1 and tubulin (Tub; loading control) expression in CI-stimulated WT B cells infected with empty vector (pMIG) or pMIG–Blimp-1 for 48 h in the presence of DMSO or TCDD. Endogenous Blimp-1 was not detectable using the Blimp-1 antibody. A representative of two experiments is shown. (H) Percent GFP⁺ in pMIG- or pMIG–Blimp-1–infected (96 h after infection) WT B cells stimulated with CI in the presence of DMSO or TCDD. (I) Percent CD138⁺ cells at 96 h after infection with empty vector or pMIG–Blimp-1 in WT B cells stimulated with CI in the presence of DMSO or TCDD. (J) ChIP using anti-AhR antibody. Binding of AhR to the bach2 promoter or region encoding the 3′ untranslated region (3′-UTR) was examined. DNA in ChIP samples was quantified by quantitative PCR and normalized to 5% of input. (K) Relative mRNA expression of bach2 (normalized to β actin) at 48 h CI stimulation between WT and AhR^−/− splenic B cells. (C–F and H–K) n = 3. Mean ± SD is shown. *, P < 0.05; **, P < 0.005 (Student’s t test).