Background: Successful treatment of IgE mediated allergies by allergen-specific immunotherapy (AIT) usually correlates with the induction of allergen-specific IgG4. However, it is not clear whether IgG4 prevents the allergic reaction more efficiently than other IgG subclasses. Here we aimed to compare allergen-specific monoclonal IgG1 and IgG4 antibodies in their capacity to inhibit type I allergic reactions by engaging FcγRIIb. Methods: Three monoclonal antibodies (F127, A044 and G078) against Fel d 1, the major cat allergen in humans, recognizing three non-overlapping epitopes of Fel d 1 were tested for their capacity to block human basophils activation in vitro. The affinity of the three monoclonal antibodies in IgG1 and IgG4 formats to FcgRIIb were investigated by Biolayer Interferometry. Results: We found that IgG1, which is the dominant subclass induced by viruses, binds with a similar affinity to the FcγRIIb as IgG4 and is comparable at blocking human basophil activation from allergic patients; both by neutralizing the allergen as well as engaging the inhibitory receptor FcγRIIb. Conclusion: Hence, the IgG subclass plays a limited role for the protective efficacy of AIT even if IgG4 is considered the best correlate of protection because it is the dominant subclass induced by classical AITs.

Type I hypersensitivity, also known as classical allergy, is mediated via allergen-specific IgE antibodies bound to type I FcR (FcεRI) on the surface of mast cells and basophils upon cross-linking by allergens. This IgE-mediated cellular activation may be blocked by allergen-specific IgG through multiple mechanisms, including direct neutralization of the allergen or engagement of the inhibitory receptor FcγRIIb which blocks IgE signal transduction. In addition, co-engagement of FceRI and FcγRIIb by IgE-IgG-allergen immune-complexes causes down-regulation of receptor bound IgE, resulting in desensitization of the cells. Both, activation of FceRI by allergen-specific IgE and engagement of FcγRIIb by allergen-specific IgG are driven by allergen-binding. Here we delineate the distinct roles of antibody affinity versus avidity in driving these processes and discuss the role of IgG subclasses in inhibiting basophil and mast cell activation.

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.

Background: Several new variants of SARS-CoV-2 have emerged since fall 2020 which have multiple mutations in the receptor binding domain (RBD) of the spike protein. It is unclear which mutations affect receptor affinity versus immune recognition. Methods: We produced RBD with single mutations (E484K, K417N or N501Y) or with all three mutations combined and tested their binding to ACE2 by biolayer interferometry (BLI). The ability of convalescent sera to recognize RBDs and block their interaction with ACE2 was tested as well. Results: We demonstrated that single mutation N501Y increased binding affinity to ACE2 but did not significantly affect its recognition by convalescent sera. In contrast, single mutation E484K had almost no impact on the binding kinetics, but essentially abolished recognition of RBD by convalescent sera. Interestingly, combining mutations E484K, K417N and N501Y resulted in a RBD with both features: enhanced receptor binding and abolished immune recognition. Conclusion: Our data demonstrate that single mutations either affect receptor affinity or immune recognition while triple mutant RBDs combine both features.