Myofibroblasts are increased in the lung parenchyma in asthma

BACKGROUND: Increased airway smooth muscle is observed in large and small airways in asthma. Semi-quantitative estimates suggest that cells containing alpha smooth muscle actin (α-SMA) are also increased in the lung parenchyma. This study quantified and characterized α-SMA positive cells (α-SMA+) in the lung parenchyma of non-asthmatic and asthmatic individuals. METHODS: Post-mortem sections of peripheral lung from cases of fatal asthma (FA), persons with asthma dying of non-respiratory causes (NFA) and non-asthma control subjects (NAC) were stained for α-SMA, quantified using point-counting and normalised to alveolar basement membrane length and interstitial area. RESULTS: α-SMA+ fractional area was increased in alveolar parenchyma in both FA (14.7 ± 2.8% of tissue area) and NFA (13.0 ± 1.2%), compared with NAC (7.4 ± 2.4%), p < 0.05 The difference was greater in upper lobes compared with lower lobes (p < 0.01) in both asthma groups. Similar changes were observed in alveolar ducts and alveolar walls. The electron microscopic features of the α-SMA+ cells were characteristic of myofibroblasts. CONCLUSIONS: We conclude that in asthma there is a marked increase in α-SMA+ myofibroblasts in the lung parenchyma. The physiologic consequences of this increase are unknown.