Mast cell tryptase induce alarmin release and secretion of pro-inflammatory cytokines from bronchial epithelial cells

Background: Increased mast cell (MC) densities in the airway epithelium is an important hallmark of asthma. Within the epithelium, MCs are ideally situated to react on harmful substances and to exert immunological responses. However, little is known regarding the direct effect of MC mediators on the epithelium. Objective: To investigate the density and phenotype of MCs in bronchial biopsies in patients with asthma and the effect of MC mediator tryptase on bronchial epithelial cells (BECs). Methods: Intraepithelial MCs were characterised in bronchial biopsies from patients with asthma and controls using immunohistochemistry for tryptase (MCT) and tryptase/chymase (MCTC). To study the effect of MC mediator tryptase on BECs, BEAS-2B and 16HBE cell lines were treated with tryptase (0.1 to 1nM) for 1, 3, 6 and 24h. Culture supernatants and cell lysates were evaluated for alarmin and inflammatory cytokine release and expression of tight-junction proteins. Results: Tryptase-positive MCTs, but not MCTCs, were increased in the bronchial epithelium in patients with difficult-to-control asthma compared to healthy controls. Furthermore, our data showed that tryptase induced release of the alarmin ATP from BECs after 1h stimulation. Also, tryptase induced inflammatory cytokine CXCL8 gene and protein release from BECs at 6 and 24h, respectively. Additionally, tryptase induced a downregulation of the tight junction proteins ZO-1 and E-cadherin mRNA. Conclusion: Our results suggest that tryptase released from MCs may play a direct role in inducing an inflammatory response and a damaged barrier function in BECs which may have an important role in the progression of asthma pathology.