Rapid induction of transcription of unrearranged S gamma 1 switch regions in activated murine B cells by interleukin 4.

The distribution of immunoglobulin isotypes in activated B lymphocytes can be modulated by interleukin 4 (IL4), which enhances IgG1 and suppresses IgG3. We show here that IL4 induces transcription of the region 5' adjacent to the s gamma 1 switch region within hours after onset of activation of B cells by bacterial lipopolysaccharide (LPS). Transcripts of 1.7 and 3.2 kb size containing sequences of the region 5' of s gamma 1 are detected. This transcription precedes class switch recombination between s mu and s gamma 1 and reflects the rapid opening of the s gamma 1 region as induced by IL4. This suggests that IL4 directs class switching to IgG1 by opening the s gamma 1 switch region, thus making it accessible for switch recombination.