Background: Knowledge of the factors which control IgE production is essential in order to understand the pathogenesis of immediate hypersensitivity reactions. We have studied the extent to which the route and frequency of antigen application as well as different antigen amounts may influence IgE synthesis. Methods: We established sensitisation protocols in BALB/c mice, in which various doses of ovalbumin (Ova) were applied via intranasal, epicutaneous or intraperitoneal routes. Ova-specific antibodies were measured by ELISA. After 6 weeks of sensitisation, anaphylactic shock was measured following intravenous challenge with Ova. In addition, bronchoalveolar lavages were performed in intranasally sensitised mice. Results: We were able to show that the most efficient IgE production was achieved by long-term antigen application via the airways, leading to local allergic airway pathology. The epicutaneous route of antigen application also induced very high IgE titres, while intraperitoneal sensitisation led to significantly lower IgE levels. After intraperitoneal sensitisation, IgE synthesis was best induced by increasing the frequency of antigen application, but not by increasing the amount of antigen. In all groups of mice, Ova-specific IgE antibodies were high enough to induce systemic allergic symptoms leading to anaphylactic shock. The severity of shock correlated with the amount of specific IgE. Conclusions: Taken together, our results demonstrate that antigen application via the airways or skin induces IgE synthesis more efficiently than via the intraperitoneal route. Few exposures with high-dose antigen are less efficient than multiple exposures with low doses. Our finding that both the route and the frequency of antigen application strongly influence IgE synthesis may help to understand how environmental antigens lead to allergic sensitisation.

In non-autoimmune mice, the 3H9 transgenic Ig heavy chain can pair with endogenous Iglambda1 light chains to generate B cells with specificity for DNA. These autoreactive cells are actively regulated in vivo, as indicated by the exclusion of lambda1 cells from the splenic B cell follicle and the absence of auto-antibody production. To study the role of Fcgamma receptor IIb (FcgammaRIIb) in peripheral B cell tolerance, FcgammaRIIb(-/-) mice were crossed with C57BL/6 mice bearing a site-directed knock-in of the 3H9 transgene. 3H9FcgammaRIIb(-/-) mice become autoreactive, lose the follicular exclusion of anti-DNA B cells and instead have lambda1 B cells located within splenic germinal centers. They have increased frequencies of splenic auto-antibody-producing cells and elevated titers of IgG anti-DNA auto-antibody. The data implicate an FcgammaRIIb-dependent checkpoint that can exclude autoreactive B cells from splenic follicles. By restricting their participation in germinal center reactions, this putative checkpoint helps attenuate the production of potentially pathogenic auto-antibodies. The data further suggest that this FcgammaRIIb-dependent regulation is B cell autonomous.

Background: IL-4 and IL-13 are key regulators in atopic disorders and both signal through the receptor chain IL-4Rα. IL-4 and IL-13 are also the only cytokines known to induce class switching to IgE. We sought to compare allergen-specific IgE responses and allergic reactivity of wild-type (wt) mice with IL-4^–/– and IL-4Rα^–/– mice, which lack both IL-4 and IL-13 functions. Methods: BALB/c wt, IL-4^–/– and IL-4Rα^–/– mice were immunized with ovalbumin intranasally or intraperitoneally and specific antibody titers were measured by ELISA. Bronchoalveolar lavage fluids and lung tissue were analyzed cytologically and histologically. Allergic reactivity was determined by active cutaneous anaphylaxis and anaphylactic shock. Results: wt mice immunized intranasally or intraperitoneally showed high titers of specific IgE 3 and 6 weeks after primary sensitization, resulting in cutaneous anaphylaxis and anaphylactic shock upon challenge. Intranasal sensitization resulted in airway eosinophilia and goblet cell metaplasia. In contrast, IL-4^–/– and IL-4Rα^–/– mice showed no specific IgE after 3 weeks, but produced high titers after 6 weeks. At this time cutaneous anaphylaxis and anaphylactic shock could be induced as in wt mice, but lung pathology was absent. Conclusions: We conclude that upon long-term allergen exposure, alternative switch mechanisms independent of IL-4 and IL-4Rα may induce IgE but not asthma-like lung pathology. This may be relevant for the development of allergic disease, since long-term allergen exposure is a frequent condition during allergic sensitization.

No abstract