Intranasal application of purified protein derivative suppresses the initiation but not the exacerbation of allergic rhinitis in mice

Background: Several epidemiological and experimental studies have demonstrated that exposure to pathogens such as those from the genus Mycobacterium leads to the suppression of allergic sensitization and inflammation. However, little is known as to whether pathogen-derived soluble antigens have the potential to modulate the pathogenesis of allergic rhinitis. Objective: We sought to determine whether application of purified protein derivative (PPD) from Mycobacterium tuberculosis can suppress the initiation and/or exacerbation of allergic rhinitis using a recently developed murine model. Methods: First, we investigated whether a single intranasal application of PPD could elicit cytokine production in the nose by RT-PCR. BALB/c mice were repeatedly sensitized with Schistosoma mansoni egg antigen (SEA) intranasally without an adjuvant. PPD was applied through different routes either before or after sensitization. The production of SEA-specific antibodies, nasal eosinophilia and cytokines by nasal lymphocytes was compared among mice that had or had not received PPD treatment. Results: IFN-γ, but not IL-4, was detected in the nasal tissue 12 to 48 h after a single intranasal application of 10 μg PPD. Repeated intranasal application of PPD prior to and during sensitization with SEA significantly inhibited the production of both SEA-specific IgE/IgG1 and nasal eosinophilia. Moreover, it partially inhibited the production of IL-4 by nasal lymphocytes in response to SEA. Conversely, this treatment led to a significant increase in IFN-γ production. On the other hand, PPD applied through the footpad had no effect over the same period. Repeated intranasal application of PPD after sensitization with SEA had no exacerbative effect on allergic inflammation. Conclusion: These results indicate that the local application of PPD, and the subsequent induction of IFN-γ, inhibits the initiation, but not the exacerbation, of allergic rhinitis in mice. This suggests that pathogen-derived antigens have potential for use in the prevention and prophylaxis of allergic rhinitis.