Absence of transcription factors at IgH regulatory regions in cHL cell lines. (A) Expression of Oct1, Oct2, and BOB.1/OBF.1 transcription factors in cHL cell lines. The proteins were detected by Western blot as described in “Materials and methods.” Equal loading was controlled for using antibodies specific for RelA (Rel family member p65). (B) ChIP experiments were performed as described in Figure 1B. Due to the switch recombination to IgG4 in Hodgkin cell lines, only the Cα2 3′ enhancer was assayed.