Essential role of Id2 in negative regulation of IgE class switching

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Abstract
Serum concentrations of immunoglobulin E (IgE) in normal circumstances are kept much lower than those of other Ig isotypes to avoid allergic reactions. B cells lacking Id2 have increased E2A activity, which leads to specific enhancement of germline transcription of the immunoglobulin ε locus. As a consequence, Id2-deficient B cells undergo class switch recombination (CSR) to IgE at a much higher frequency than wild-type B cells. In contrast, Id2 is induced in wild-type B cells by transforming growth factor-β1 (TGF-β1) and suppresses IgE CSR. Our results provide evidence for the inhibitory and selective role of Id2 in IgE CSR in response to TGF-β1. Id2 might act as molecular safeguard to suppress IgE CSR to prevent serious complications such as allergic hypersensitivity during the normal course of immune responses.