Background: IgE antibodies are involved in type-1 hypersensitivity. Cross-linking IgE bound to the high-affinity IgE receptor, FceRI on effector cells with an allergen can cause anaphylaxis. Recent studies have shown that IgE glycosylation significantly impacts the ability of IgE to bind to its high-affinity receptor FceRI and exert effector functions 1,2. We have recently shown that immunization of mice with IgE in complex with an allergen leads to a protective, glycan-dependent anti-IgE response 3. However, to what extent the glycans on IgE determine the induction of those antibodies and how they facilitate serum clearance is unclear. We investigated the role of glycan-specific IgG anti-IgE autoantibodies in regulating serum IgE levels and preventing systemic anaphylaxis by passive immunization. Methods: Mice were immunized using glycosylated or deglycosylated IgE-allergen-immune complexes (ICs) to induce anti-IgE IgG antibodies. The anti-IgE IgG antibodies were purified and used for passive immunization. Results: Glycosylated IgE-ICs induced a significantly higher anti-IgE IgG response and more IgG secreting plasma cells than deglycosylated IgE-ICs. Passive immunization of IgE sensitized mice with purified anti-IgE IgG increased the clearance of IgE and prevented systemic anaphylaxis upon allergen challenge. Anti-IgE IgG purified from the serum of mice immunized with deglycosylated IgE-ICs, led to a significantly reduced elimination and protection, confirming that the IgE glycans themselves are the primary drivers of the protectivity induced by the IgE-immune complexes. Conclusion: IgE glycosylation is essential for a robust anti-IgE IgG response and might be an important regulator of serum IgE level.

IgE, the key molecule in atopy has been shown to bind two receptors, FcRI, the high affinity receptor and FcεRII (CD23), mostly found on B cells and that binds IgE with lower affinity. Whereas cross-linking of IgE on FcRI triggers allergic reaction, binding of IgE to CD23 is known to play an important role in both IgE synthesis and presentation. Thus, targeting IgE-immune complexes on B cells has shown to enhance antibody and T cell responses in mice and humans. However, the mechanisms that regulate the targeting of the two receptors and the respective function of the two pathways in inflammation or homeostasis are still matter of debate. Here, we discuss several mechanisms related to IgE and IgE binding to both receptors, as well as the influence of the antigen binding on different immune cells expressing the receptors. One recent paper has shown that free IgE preferentially binds to FcRI whereas IgE immune complexes (IgE-ICs) are preferentially captured by CD23. Binding of IgE-ICs to CD23 on B cells can on one hand regulate serum IgE and prevent effector cell activation and on the other hand facilitate the antigen presentation by delivering antigen to dendritic cells. The data suggest that CD23 play a multifunctional role in regulating the allergic response pathway.