Association of Lung Inflammatory Cells with Small Airways Function and Exhaled Breath Markers in Smokers – Is There a Specific Role for Mast Cells?

BACKGROUND: Smoking is associated with a mixed inflammatory infiltrate in the airways. We evaluated whether airway inflammation in smokers is related to lung function parameters and inflammatory markers in exhaled breath. METHODS: Thirty-seven smokers undergoing lung resection for primary lung cancer were assessed pre-operatively by lung function testing including single-breath-nitrogen washout test (sb-N2-test), measurement of fractional exhaled nitric oxide (FeNO) and pH/8-isoprostane in exhaled breath condensate (EBC). Lung tissue sections containing cancer-free large (LA) and small airways (SA) were stained for inflammatory cells. Mucosal (MC(T)) respectively connective tissue mast cells (MC(TC)) and interleukin-17A (IL-17A) expression by mast cells was analysed using a double-staining protocol. RESULTS: The median number of neutrophils, macrophages and mast cells infiltrating the lamina propria and adventitia of SA was higher than in LA. Both MCTC and MC(T) were higher in the lamina propria of SA compared to LA (MC(TC): 49 vs. 27.4 cells/mm(2); MC(T): 162.5 vs. 35.4 cells/mm(2); P<0.005 for both instances). IL-17A expression was predominantly detected in MC(TC) of LA. Significant correlations were found for the slope of phase III % pred. of the sb-N2-test (r(s)= -0.39), for the FEV(1)% pred. (r(s)= 0.37) and for FEV(1)/FVC ratio (r(s)=0.38) with MC(T) in SA (P<0.05 for all instances). 8-isoprostane concentration correlated with the mast cells in the SA (r(s)=0.44), there was no correlation for pH or FeNO with cellular distribution in SA. CONCLUSIONS: Neutrophils, macrophages and mast cells are more prominent in the SA indicating that these cells are involved in the development of small airway dysfunction in smokers. Among these cell types, the best correlation was found for mast cells with lung function parameters and inflammatory markers in exhaled breath. Furthermore, the observed predominant expression of IL-17A in mast cells warrants further investigation to elucidate their role in smoking-induced lung injury, despite the lack of correlation with lung function and exhaled breath parameters.