Interleukin 4 induces changes in the chromatin structure of the γl switch region in resting B cells before switch recombination

Interleukin 4 (IL4) can induce the expression of IgG1 in sIgG- murine B cells stimulated with mitogens or through a cognate interaction with T helper (Th) cells. We have investigated the molecular basis for the IL-4-induced switch to IgG1 in lipopolysaccharide (LPS)-stimulated murine B cells and have previously shown that IL-4 induces transcription of the γl switch region before switch recombination. We now demonstrate that IL4 induces a DNase I hypersensitive site at the 5′ end of the γ1 switch region in resting B cells. LPS is not required, but it enhances induction. Hence, the interaction of IL-4 with its receptor results in increased accessibility of the yl switch region. The more open chromatin structure and increased transcriptional activity may be important in the selection of this region for switch recombination.