Recombinant soluble form of the high-affinity IgE receptor α subunit and anti-IgE antibody inhibit IgE synthesis by IgE-expressing B cells through distinct pathways

Background: Both a recombinant soluble form of the high-affinity IgE receptor α subunit (rsFcεRIα) and anti-IgE antibody have been shown to be involved in the regulation of IgE synthesis. However, the mechanisms of IgE regulation by two such IgE-binding agents remain unclear. In the present study, we investigated whether rsFcεRIα and anti-IgE antibody modulated IgE synthesis in an identical or different manner. Methods: Normal human B cells stimulated with interleukin (IL)-4 plus anti-CD40 antibody were analyzed for the regulatory effects of rsFcεRIα and anti-IgE antibody on the expression of Cε transcipts, the autocrine production of IL-6 and the induction of apoptosis. Results: Both rsFcεRIα and anti-IgE antibody inhibited mature Cε transcription, without affecting germline Cε transcription. In addition, rsFcεRIα was effective in decreasing IL-6 production at a later stage when IgE-expressing B cells were generated, whereas F(ab′)2, but not the Fab fragment, of anti-IgE antibody induced apoptosis in the cells. Although these three agents almost equally recognized IgE expressed on B cells, rsFcεRIα was unable to induce apoptotic cell death and the Fab fragment was similarly ineffective in the regulation of IL-6 production. The addition of IL-6 to cultures containing rsFcεRIα significantly restored its suppressive effect on IgE synthesis. Conclusions: These results indicate that regulation of IgE synthesis by rsFcεRIα differs from that by anti-IgE antibody