Respiratory tract dendritic cells in paediatric asthma.

Abstract

Airway dendritic cells (DC) are critical mediators of lung inflammation in asthma, but the characteristics of DC in the airways of healthy children, and children with asthma, are currently unknown. We sought to identify changes in DC subset distribution and activation profile in paediatric asthma using flow cytometry to analyse induced sputum samples obtained from healthy and asthmatic children. Lung function and atopic status were determined by spirometry and skin prick testing. Induced sputum samples were analysed using 7-colour flow cytometry to identify airway DC populations (lineage(-) HLA-DR(+) sputum cells expressing either CD11c as conventional DC or CD123 as plasmacytoid DC). Sputum samples containing lower airway plugs were obtained from 10 healthy children and 8 children with asthma. Lineage(-) HLA-DR(+) DC were successfully identified in all samples, and DC comprised a significantly higher proportion of sputum cells in children with asthma compared with age-matched healthy controls (1.29% vs. 0.67%, P=0.02). DC expression of the costimulatory marker CD86 was significantly reduced in asthmatic children (73.4% vs. 59.7%, P=0.04). Sputum DC also included numerous CD1c(+) cells (mean 57% of the total DC population) and low frequencies of cells expressing the subset markers CD141 or CD123, although the proportions of these did not differ between groups. Airway DC can be identified and characterized non-invasively using flow cytometry to analyse paediatric sputum samples. Our data reveal that children with steroid-treated asthma exhibit increased frequency of airway DC with reduced expression of the costimulatory marker CD86, suggesting altered trafficking and/or maturation of these cells either due to asthma or steroid therapies.