IL33 contributes to diesel pollution-mediated increase in experimental asthma severity.

BACKGROUND: Exposure to traffic pollution, notably diesel exhaust particles (DEP), increases risk for asthma and asthma exacerbations. The contribution of cytokines generated by stressed lung epithelial cells (IL25, IL33, TSLP) to DEP-induced asthma severity remains poorly understood.
METHODS: BALB/c mice were exposed intratracheally once to DEP or 9 times over 3-weeks to either saline, DEP, and/or house dust mite extract (HDM). Airway hyper-responsiveness (AHR), pulmonary inflammation, and T-cell subsets were assessed 24 hours after the last exposure in mice sufficient and deficient for the IL33 receptor ST2.
RESULTS: DEP exposure induces oxidative stress, IL6, neutrophils and pulmonary accumulation of IL33, but not IL25 or TSLP or other features of allergic disease. When mice are co-exposed to DEP and low doses of HDM, DEP increases IL33 lung levels and Th2 responses. ST2 deficiency partially protected mice from HDM + DEP induced AHR in association with decreased type 2 inflammation and lung levels of IL5+ IL17A+ co-producing T-cells. Upon in vitro HDM challenge of lung cells from HDM ± DEP exposed ST2-/- mice, secretion of IL5, IL13, IL6 and IL17A was abrogated by a mechanism involving IL33 signaling in both dendritic cells and T-cells. HDM + DEP exposed bone marrow derived dendritic cells and IL33 pulsed BMDC promote a mixed Th2/Th17 response that was dependent on ST2 expression by CD4+ T-cells.
CONCLUSION: IL33 contributes to DEP mediated increase in allergen-induced Th2 inflammation and AHR in a mouse model of severe steroid resistant asthma, potentially through the accumulation of pathogenic IL5+ IL17A+ CD4+ effector T-cells.