Background: The uptake of inhaled particulate matter by airway phagocytes is an important defense mechanism contributing to the clearance of potentially toxic substances, including aeroallergens, from the lung. Since airway monocytes and macrophages can also function as antigen presenting cells, their ability to engulf materials deposited on the airway surface is of particular interest in allergic asthmatics. To determine whether airway mononuclear phagocytes of allergic asthmatics might have enhanced phagocytic activity, we compared the in-vivo uptake of inhaled radiolabeled particles in mild allergic asthmatics (N=10) and healthy (non-allergic) individuals (N=8).
Methods: Phagocyte function was assessed by quantifying the proportion of radioactivity associated with cellular and supernatant fractions of induced sputum 2 hours after inhalation of radio-labeled sulfur colloid particles. All subjects were pre-treated with albuterol prior to sputum induction. A standardized breathing pattern was used to target aerosol deposition in the bronchial airways.
Results: In-vivo particle uptake by airway cells was significantly greater in asthmatic versus healthy volunteers (57.2% (46.5-67.9) vs. 22.3% (4.9-39.6), p<0.01) as was in-vitro phagocytosis of opsonized Zymosan-A bioparticles. There was also a significant correlation (r = 0.85, p<0.01) between the percentage of sputum mononuclear phagocytes and the % uptake of particles in the asthmatics, but not in the control subjects.
Conclusions: In-vivo particle uptake by airway macrophages is enhanced in persons with mild asthma. Enhanced uptake and processing of particulate antigens could contribute to the pathogenesis and progression of allergic airways disease and may contribute to the increased risk of disease exacerbation associated with particulate exposure.