Nebulized Mycobacterium vaccae protects against asthma by attenuating the imbalance of IRF4/IRF8 expression in dendritic cells

Objective: To assess the effects of nebulized inhaled Mycobacterium vaccae on allergic airway inflammation, airway hyperresponsiveness, and Th1/Th2 cell imbalance in mice with ovalbumin (OVA)-induced asthma. Methods: Mice received OVA sensitization and challenge for establishment of the asthmatic model. For intervention, mice received Mycobacterium vaccae nebulization once every other day from the first day of sensitization to the day before challenge. After challenge, pulmonary histological analysis and airway responsiveness measurement were performed. In addition, Th1/Th2 cytokines and OVA-specific IgE levels in bronchoalveolar lavage fluid were measured by ELISA. Th1/Th2 subset ratios and the expression of interferon-regulatory factor 4 (IRF4), IRF8 and Toll-like receptor 4 (TLR4) in dendritic cells were evaluated by flow cytometry. Results: Severe inflammatory infiltration and airway hyperresponsiveness were observed in OVA-induced asthmatic mice. Asthmatic mice showed higher Th2 cytokine concentration and increased percentage of Th2 cells, along with lower Th1 cytokine concentration and reduced percentage of Th1 cells compared with the normal control. Moreover, an imbalance of IRF4+ and IRF8+ in dendritic cells was found in asthmatic mice. Nebulized inhaled Mycobacterium vaccae reduced airway hyperresponsiveness and inflammation in OVA-induced asthmatic mice. In addition, nebulized inhaled Mycobacterium vaccae enhanced TLR4 and IRF8 expression, and alleviated the imbalance of Th1/Th2 as well as IRF4+ and IRF8+ in dendritic cells. Conclusions: Nebulized inhaled Mycobacterium vaccae protects against asthma by alleviating the imbalance of Th1/Th2 and IRF4/ IRF8 in OVA-induced asthmatic mice.