Abstract

Background: Mucus plugging of the airways is invariably seen in cases of fatal asthma, mucus production is associated with asthma attacks, and the area of submucosal glands is increased in asthma. Mediators secreted from mast cells and neutrophils can stimulate mucous gland secretion. A study was undertaken to count the mast cells and neutrophils in submucosal glands and to relate cell numbers to the presence of mucus in the airway lumen.

Methods: Cartilaginous airways obtained at necropsy from cases of fatal asthma (n=8), non-fatal asthma (n=8), and control cases (n=8) were examined. Contiguous transverse sections were stained for mast cell tryptase and neutrophil elastase, and with Periodic Acid Schiff solution to identify mucus. Mucous gland area, lumen area, and the percentage of the relaxed lumen area occupied by mucus (mucus occupying ratio, MOR) were measured. Mast cells (intact and degranulated) and neutrophils per area of submucosal gland were calculated.

Results: Compared with controls, the cases of fatal asthma had increased mucous gland area, MOR, percentage of degranulated mast cells, and numbers of neutrophils in the submucosal glands (p<0.05). In cases of non-fatal asthma the MOR and the numbers of mast cells and neutrophils in the submucosal glands were increased (p<0.05). When all cases were pooled together, the MOR correlated with the total number of mast cells (r=0.55, p=0.005) and with the number of degranulated mast cells in the submucosal glands (r=0.51, p=0.013), but not with the number of neutrophils (r=0.21, p=0.121).

Conclusion: These results show that mucous gland area, MOR, and mucous gland inflammation are increased in asthma and that degranulation of mast cells may contribute to secretion of mucus into the lumen in cases of fatal asthma.