Long-term exposure to low-dose Haemophilus influenzae during allergic airway disease drives a steroid-resistant neutrophilic inflammation and promotes airway remodeling

// Xu Yang 1 , Yijie Wang 1, 2 , Shengtao Zhao 1, 3 , Ran Wang 1 and Changzheng Wang 1 1 Institute of Respiratory Disease, Xinqiao Hospital, Third Military Medical University (Army Medical University), Chongqing, 400037, China 2 Department of Respiratory Medicine, The 305 Hospital of PLA, Beijing, 100017, China 3 Department of Respiratory Medicine, Kunming General Hospital of Chengdu Military Region, Kunming, 650032, China Correspondence to: Changzheng Wang, email: czwang@netease.com Keywords: allergic airway disease; Haemophilus influenzae; neutrophilic inflammation; airway remodeling; long-term effect; Immunology Received: December 21, 2017      Accepted: January 14, 2018      Published: May 18, 2018 ABSTRACT Growing evidences indicate that bacteria are associated with pathogenesis of neutrophilic asthma. However, the long-term effect of airway bacterial colonization remains unclear. We sought to establish a murine model to simulate the airway inflammation of long-term bacterial colonization, and to assess the effects of bacteria on allergic airway disease (AAD). BALB/c mice were sensitized twice and subsequently challenged with ovalbumin (OVA) and exposed to low-dose Haemophilus influenzae for approximately 2 months. Mice in treatment groups inhaled budesonide for consecutively 6 days in the last week. Airway inflammatory phenotype, immune response, phagocytic capacity, mucus production, airway remodeling and steroid sensitivity were assessed. Long-term exposure to low-dose H. influenzae during AAD did not cause serious infection but only a slightly increased airway inflammation, which resembled the colonization. Inflammatory phenotype was converted from a steroid-sensitive T helper (Th) 2-associated eosinophilic inflammation to a steroid-resistant Th17-associated neutrophilic inflammation. The increased neutrophilic inflammation was accompanied by defects in regulatory T cell (Treg)-associated immunosuppression and macrophage phagocytosis, and finally promoted mucus hypersecretion and airway remodeling. These features resembled those of refractory neutrophilic asthma in humans. These findings indicate that in asthmatic patients, airway bacterial colonization may be a potential therapeutic target. Minimizing the pathogen burden in airway, such as Haemophilus influenzae , may be beneficial.