Involvement Of Purine Metabolites In Dsrnainduced Il-33 Expression In Human Bronchial Smooth Muscle Cells

Rationale: Rhinovirus (RV) infections are main triggers of asthma exacerbations and along with tissue damage cause release of exogenous and endogenous danger signals. Considered such an alarmin, IL-33 has emerged as a potent inducer of Th2-type immunity and is implicated in asthma pathogenesis. Bronchial smooth muscle cells (BSMC) from severe asthmatics have previously been shown to overexpress IL-33. Here, we aimed to explore the effect of viral stimuli and purine metabolites on IL-33 in BSMC. Methods: Primary human BSMC from three healthy donors were infected with RV1B (0.1-0.5MOI) or stimulated with the RV replication intermediate dsRNA (0.1-10μg/ml), ATP-γ-S or adenosine (10-500μM) for 3 or 24h. The NF-κB inhibitor PS1145 (1-10μM) or the purinergic receptor antagonist suramin (10-100μM) were added 1h prior to stimulation. Samples were analyzed by RT-qPCR, western blot and ELISA. Results: IL-33 expression was dose-dependently increased in BSMC after 24h RV1B infection (p<0.01) and secreted IL-33 was detected in supernatants from RV-infected cells. dsRNA upregulated both mRNA and protein levels of IL-33 at 24h (p<0.001), but did not cause IL-33 release. IL-33 mRNA was also increased at 3 and 24h by ATP-γ-S and adenosine (p<0.01). Suramin, but not PS1145, abolished IL-33 expression induced by both purine metabolites and dsRNA (p<0.01). Conclusions: Viral stimuli and purine metabolites triggered human BSMC expression of IL-33, implicating airway smooth muscle as a potential source of IL-33 in virus-infected or inflamed airways. The inhibitory effect of suramin on IL-33 responses also suggests a role for purine metabolites in mediating dsRNA-inducible IL-33 expression.