Hierarchical suppression of asthma-like responses by mucosal tolerance

Background: Mucosal tolerance can be induced by oral or nasal administration of soluble proteins and results in the suppression of cellular and/or humoral immune responses to the specific antigen. Objective: To compare the effect of oral or nasal ovalbumin administration before, during or after immunization on the development of cellular and humoral immune responses by using a murine asthma model. Methods: To induce lung allergic inflammation, animals were immunized twice with ovalbumin/aluminum hydroxide gel and challenged twice with ovalbumin. To induce tolerance, BALB/c mice received ovalbumin by the oral or nasal routes for 3 consecutive days. The ovalbumin administration was initiated before (day -7), during (day 0), or after immunization (day 7). Results: Airway eosinophilia, airway hyperreactivity, mucus hypersecretion, and cytokine production were suppressed when oral or nasal ovalbumin administration was initiated before immunization. Oral but not nasal ovalbumin exposure suppressed ovalbumin-specific nonanaphylactic IgG(1) antibodies, whereas both routes suppressed the production of anaphylactic IgG(1) and IgE antibodies. Mucosal ovalbumin administration at day 0 inhibited all T(H)2-mediated allergic parameters but not nonanaphylactic IgG(1) antibodies. Finally, ovalbumin exposure 7 days after immunization was still effective in suppressing lung allergy but not ovalbumin-specific anaphylactic IgG(1) and IgE antibodies. Conclusion: We show that the effectiveness of mucosal tolerance depends on route and time and presents a hierarchical pattern of suppression in the following order: lung allergic responses > anaphylactic antibodies > ovalbumin-specific IgG(1).