Protective effects of combined Mycobacterium bovis BCG and interleukin-12 vaccination on airway inflammation in a murine model of allergic asthma

Abstract

Purpose. Allergic asthma is characterized by chronic airway inflammation and airway hyperresponsiveness driven by allergen-specific T helper (Th)2 cells. Mycobacterium bovis bacillus Calmette-Guérin (BCG) vaccination has been documented to suppress Th2 responses and allergic airway inflammation in animal models. Since interleukin (IL)-12 is capable of inhibiting Th2 responses, we sought to investigate whether IL-12 could function as an adjuvant to increase the efficacy of BCG vaccination against allergic asthma. Methods. BALB/c neonatal mice (24 mice, 48-72 h old) were randomly divided into 3 subgroups (n = 8 for each group) to be immunized with PBS (control) or BCG with or without DNA plasmid-expressing IL-12. All of the mice were then sensitized and provoked with ovalbumin (OVA) to establish a model of allergic asthma. Results. Mice vaccinated with BCG alone showed a significant reduction in airway inflammation, percentage of eosinophils in bronchoalveolar lavage (BAL) fluid, and serum OVA-specific immunoglobulin E (IgE) levels in comparison with control animals. The suppressive effects of BCG were substantially augmented by the combination with IL-12. Furthermore, a decreased IL-4 and increased interferon-gamma (IFN-γ) production in BAL fluid were observed in animals inoculated with BCG alone or with IL-12 relative to control animals. Conclusion. Our data indicate that the combined vaccination with BCG and IL-12 yields a favorable outcome in prevention of experimental allergic airway inflammation, which is likely mediated through triggering a shift from a Th2 response to a Th1 response.