Rhinovirus-induced IL-33 is overexpressed in asthmatic bronchial smooth muscle cells via TLR3 and activation of TAK1

Background: Asthma exacerbation is mainly associated with rhinovirus (RV) infection. Interleukin-33 (IL-33) plays a major role during exacerbation by enhancing Th2 inflammation. We have recently shown that RV infects bronchial smooth muscle cells (BSMCs) leading to production of interferons and IL-33. In this study, we compared levels of RV-induced IL-33 in asthmatics and healthy BSMCs and explored the involvement of pattern-recognition receptors and downstream signalling pathways in IL-33 expression. Method: BSMCs from 5 healthy, 6 severe (SA) and 7 non-severe asthmatics (NSA) were infected with RV1B for 24h. Knockdown of TLR3, RIG-I and MDA5 was performed and inhibitors targeting TBK1, NF?B and TAK1 were used. Further, BSMCs were stimulated with conditioned media (CM) from RV1B-infected primary human bronchial epithelial cells (BECs). Samples were analysed by RT-qPCR and western blot. Results: RV induced IL-33 gene and protein expression in BSMCs. NSA had higher IL-33 and lower IFNs expression compared to SA and healthy at 24h post infection. Further, CM from RV-infected BECs induced higher IL-33 expression in asthmatic than healthy BSMCs. RV induced IL-33 expression in BSMCs from healthy and asthmatics was attenuated by knockdown of TLR3, but not RIG-I or MDA5. Inhibition of TAK1 reduced RV-induced IL-33, while blocking NF?B and TBK1 had no effect. Conclusion: RV triggered IL-33 expression in BSMCs and this induction was higher in NSA. Our data suggest that RV-induced IL-33 expression is mainly regulated by TLR3 and downstream via TAK1. Our results support the view that these signalling molecules are potentially therapeutic targets for treating asthma exacerbations.