Background: Live/Killed mycobacteria and their secretory proteins can suppress asthmatic reaction. This study investigated to determine the proper doses of BCG secretory protein MPB70 for treating asthma.
Methods: Female BALB/c mice with established airway hyperresponsiveness were administered intraperitoneally with live BCG (2 x 105 CFUs) or MPB70 (0.3, 1, 3, 10, and 30 μg). One week after the treatment, they underwent a methacholine challenge. Inflammatory cell numbers in bronchoalveolar lavage fluid (BAL) were assessed.
Results: Live BCG and MPB70 proteins significantly increased the airway sensitivity index as compared to the asthma control group (29.1 mg/mL [geometric mean] in BCG; 23.2, 34.1, 34.8, 32.4, and 20.6 mg/mL in 0.3, 1, 3, 10, 30 μg MPB70; 9.4 mg/mL in control). The fold increases in the index following treatment were significantly higher in all treatment groups than the asthma control group (1.63 for BCG; 1.40, 1.52, 1.57, 1.52, and 1.31 for MBP70; 0.99 for control). The proportion of eosinophils in BAL fluid was significantly decreased in all treatment groups than the asthma control group.
Conclusions: Not only live BCG but also BCG secretory protein MPB70 was effective against the established asthma. However, excessive dose of MPB70 might reduce therapeutic effects and thus an appropriate dose of the protein would be desirable for asthma treatment.