Removal of bronchoalveolar cells augments the late eosinophilic response to segmental allergen challenge

Background: In patients with quiescent asthma, macrophages are the most prevalent cells recovered by bronchoalveolar lavage (BAL). Through activation via their FcεRII receptors or by acting as antigen-presenting cells, macrophages could, in theory, promote the late airway response to allergen. Objective: In order to investigate the importance of macrophages and other airway luminal cells in inducing the late airway response, a novel washout experiment was designed. Methods: Five patients with ragweed-allergic asthma underwent bronchoscopy and segmental bronchial challenge with either normal saline or short ragweed extract in two segments of one lung. In a third segment of the opposite lung, 12 successive BALs (25mL each) were performed, followed by challenge with an identical dose of short ragweed (washed-challenged segment). After 24 h, all three challenged segments underwent BAL. Results: Initially, in the washed-challenged segment, over 80% (mean 80.4%, range 68-88%) of the recoverable airway dwelling cells were removed. Unexpectedly, 24 h later these same washed-challenged segments contained more eosinophils in the BAL than the challenged segments from the opposite lung (P = 0.033). Conclusions: Removing the majority of airway luminal cells followed by allergen bronchoprovocation increased the number of eosinophils recovered 24 h after challenge. Our results suggest that in quiescent allergic asthma, the airway luminal cells are protective and attenuate the late eosinophilic response to allergen challenge.