Figure 9.8. Isotype switching is preceded by transcriptional activation of heavy-chain C-region genes.

Figure 9.8Isotype switching is preceded by transcriptional activation of heavy-chain C-region genes

Resting naive B cells transcribe the μ and δ genes at a low rate, giving rise to surface IgM and IgD. Bacterial lipopolysaccharide (LPS), which can activate B cells independently of antigen, induces IgM secretion. In the presence of IL-4, however, Cγ1 and Cε are transcribed at a low rate, presaging switches to IgG1 and IgE production. The transcripts originate before the 5′ end of the region to which switching occurs, and do not code for protein. Similarly, TGF-β gives rise to Cγ2b and Cα transcripts and drives switching to IgG2b and IgA. It is not known what determines which of the two trans-criptionally activated heavy-chain C genes undergoes switching. Arrows indicate transcription. The figure shows isotype switching in the mouse.

From: B-cell activation by armed helper T cells

Cover of Immunobiology
Immunobiology: The Immune System in Health and Disease. 5th edition.
Janeway CA Jr, Travers P, Walport M, et al.
New York: Garland Science; 2001.
Copyright © 2001, Garland Science.

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.