Mast cell subtypes in adults and children with severe asthma

Background: Adults´ and childrens´ severe asthma are considered as distinct phenotypes. A recent study has shown that mast cells are associated with exacerbations in children with severe asthma (Lezmi, G et al . ERJ 2016). Differences in mast cell number and spatial distribuition in the bronchial wall between adults and children with severe asthma have not been assessed yet. Aim: To analyze mast cell subtypes in the epithelial layer (EL), lamina propria (LP) and airway smooth muscle bundles (Asm) of bronchial biopsies taken from adults and children with severe asthma after optimal treatment. Methods: Using digitized images from immunohistochemistry, we quantified tryptase+ and chymase+ mast cells in the EL, LP and Asm of endobronchial biopsies from 35 adults (27 female/08 male, 44.11 + 10.05 years old) and 11 children (03 female/08 male, 13.18 + 02.52 years old), with uncontrolled severe asthma after a 12-week trial of optimal anti-inflammatory treatment. Results: Children had a higher total number of (tryptase+) mast cells in the bronchial epithelial layer than adults (02.36 + 04.47 vs 08.28 + 09.36 cells/mm basement membrane, p = 0.021). In the Asm, however, adults had more chymase+ mast cells than children (232.17 + 189.10 vs 51.27 + 49.72 cells/mm 2 , p Conclusions: Mast cells subtypes differ in their spatial distribution and density in the airway wall between adults and children with severe asthma. We hypothesize that these findings could be related to the different presentation of severe asthma in children and adults.