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.
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 (25 mL 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.