B-cell receptor ligation selectively inhibits IgE class switch recombination.

Mechanisms that restrict class switch recombination (CSR) to IgE may limit the subsequent production of IgE antibodies in allergic diseases. A role for B-cell receptor (BCR) signaling in IgE regulation was revealed in mice and in cultured B cells with altered BCR signaling. While prior work has focused on BCR signaling in IgE-switched cells, BCR signaling also reportedly inhibits CSR. We sought to determine whether BCR signaling selectively inhibits IgE CSR. We assessed whether BCR signaling strength affected IgE responses in immunized mice. For mechanistic evaluation, primary mouse or human B cells were induced to switch to IgE in cell culture and were perturbed with antibodies or cognate antigen to ligate the BCR, pharmacologic inhibitors of signaling proteins, and/or additional cytokines. Primary readouts were flow cytometry and RNA analysis. In immunized mice, BCR signaling strength inversely correlated with the relative frequencies of IgE-switched germinal center B cells and plasma cells. In mouse B-cell cultures, BCR signaling selectively inhibited IgE CSR in a manner dependent on ligand concentration, affinity, and avidity. This inhibition required Syk, whereas blockade of the PI3K subunit p110δ increased IgE cell frequencies independently of BCR ligation. The cytokines IL-21 or TGF-β1, in combination with BCR ligation, cooperatively inhibited IgE CSR. Similar results were observed in cultures of human tonsillar B cells. IgE CSR is uniquely susceptible to inhibition by BCR signaling in mouse and human B cells, with important implications for the regulation and pathogenesis of allergic disease.