Airway smooth muscle proliferation and inflammation in asthma.

In asthma, it is unclear if the airway smooth muscle cells proliferate more or are increased at the onset of asthma and remain stable. This study aimed to compare smooth muscle cell proliferation in individuals with and without asthma and correlate proliferation rates with cell size and number and with granulocytic airway inflammation. Post-mortem airway sections were labelled with proliferating cell nuclear antigen (PCNA) and percent positive muscle cells calculated. On the same sections, smooth muscle cell size and number, and the number of eosinophils and neutrophils were estimated and compared in cases of nonfatal (n=15) and fatal (n=15) asthma, and control subjects (n=15). The %PCNA+ muscle cells was not significantly different in fatal (29.4 ± 7.7%, mean ± SD), nonfatal asthma (28.6 ± 8.3%) or control subjects (24.6 ± 6.7%) and not related to mean muscle cell size (r=0.09), number (r=0.36), thickness of the muscle layer (r=0.05) or eosinophil numbers (r=0.04) in the asthma cases. These data support the hypothesis that in asthma the increased thickness of the smooth muscle layer may be present before or at the onset of asthma and independent of concurrent granulocytic inflammation or exacerbation.