The Impact of the Route and Frequency of Antigen Exposure on the IgE Response in Allergy

<i>Background:</i> 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. <i>Methods:</i> 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. <i>Results:</i> 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. <i>Conclusions:</i> 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.