Induction of IL-6 in activated B cells is dependent on Oct2 and OBF-1. (A and B) qPCR measurement of Il6 expression in sorted and LPS- or CpG-stimulated Gr1⁺, Mac1⁺ macrophages or BM-derived DCs from WT or Obf-1^−/− mice. (C) Western blot analysis of Oct2 and OBF-1 in mature resting or CpG- or LPS-stimulated B cells. Blots were probed with α–OBF-1, α-Oct2, or α-actin. (D and E) Il6 expression in sorted and activated splenic B220⁺ B cells from OBF-1–deficient or WT mice and Oct^+/+ or Oct^−/− B cells from fetal liver reconstituted mice. Bars and numbers show relative gene expression normalized to Hmbs expression ± SEM (n = 3). (F) In vitro generation of IL-21–producing cells. Co-culture of WT naive CD4⁺, CD62L⁺ T cells, activated with α-CD3/α-CD28, with different numbers of CpG-preactivated B cells from WT, Obf-1^−/−, Oct2^−/−, or IL-6–deficient mice. After 4 d of co-culture, the CD4⁺ T cells were sorted, and Il21 expression was determined by qPCR. (A and F) Error bars represent SDs of triplicate assays. (G) T cells stimulated with medium alone, with recombinant IL-6, or with B cells and recombinant IL-6. Il21 expression was determined by qPCR and normalized as described for D–E. Bars and numbers show relative gene expression normalized to Hmbs expression ± SEM (n = 3).