Inoculation route-dependent and allergen-specific suppressive effects of bacille Calmette-Guérin vaccination on asthmatic reactions in BALB/c mice

Intranasal bacille Calmette-Guérin (BCG) vaccination causes greater suppression of ovalbumin-induced airway eosinophilia in mice than does subcutaneous vaccination. Coadministration of ovalbumin with interleukin (IL)-18 induces an ovalbumin-specific Th1 immune reaction. The purpose of this study was to examine whether the suppressive effect of BCG is dependent on the inoculation method, using various murine asthma models. Female BALB/c mice (n = 7 per group) were immunized with BCG subcutaneously or intranasally, then sensitized with ovalbumin or Dermatophagoides farinae either immediately or one week later. After provocation with one of the allergens, the mice were tested by methacholine bronchial challenge, and analyses of the inflammatory cell numbers in the airways and cytokine levels in the supernatant of concanavalin A-stimulated splenocytes were conducted. Overall, the airway responses to the allergens were significantly lower and the interferon (IFN)-gamma level was significantly higher in BCG-treated mice than in untreated mice, and the number of airway eosinophils was significantly related to the IFN-gamma/IL-5 ratio (r = -0.444, p < 0.001). Subcutaneous BCG inoculation tended to have a greater suppressive effect on the development of airway hyperresponsiveness and eosinophilia than did intranasal inoculation. Concurrent BCG vaccination and D. farinae sensitization one week before ovalbumin sensitization tended to have a greater suppressive effect on airway responsiveness to methacholine induced by D. farinae aerosols than did that induced by ovalbumin aerosols. Subcutaneous BCG inoculation suppressed asthmatic reactions more remarkably than did intranasal inoculation, and concurrent BCG vaccination and allergen sensitization induced allergen-specific suppression of asthmatic reactions.