Live Mycobacterium bovis Bacille Calmette-Guérin (BCG) has a suppressive effect on asthma, but its use in clinical practice may be limited due to adverse reactions. To develop a product that is effective for suppressing asthma with minimal adverse reactions, we investigated whether the heat-killed body or culture supernatants of mycobacteria could also prevent asthma development.
Female BALB/c mice were treated with live BCG, the heat-killed body, or culture supernatants of BCG or Mycobacterium tuberculosis intraperitoneally, while sensitizing and provoking with ovalbumin. Then they underwent a methacholine bronchoprovocation test, and the peribronchial inflammatory cell numbers and cytokine levels in splenocyte culture supernatants were assessed.
The airway sensitivity to methacholine decreased significantly after treatment with not only live BCG (30.8 versus 10.0 mg/mL, P<0.001) but also with the culture supernatant (BCG, 23.0 mg/mL, P<0.05; M. tuberculosis, 20.5 mg/mL, P<0.05). In contrast, heat-killed mycobacteria did not effectively decrease airway sensitivity. The peribronchial eosinophil counts and the goblet cell proportions in total epithelial cells decreased significantly in most of the groups. The interferon-γ/interleukin-5 ratios increased significantly in most of the treatment groups except for the heat-killed groups, and were significantly related to airway sensitivity (r=0.312, P<0.01) and peribronchial eosinophil counts (r=-0.416, P<0.001). Interleukin-17A level was inversely related to airway sensitivity (r=-0.212, P<0.05) and was significantly lower in the live BCG group than in the control (137±20 versus 308±57 pg/mL, P<0.05).
BCG and mycobacteria culture supernatants may effectively prevent the development of asthma associated with altered Th1/Th2 cytokines and interleukin-17A levels.