Mousa Komai-Koma, Damo Xu, Charles McSharry, Mariola Kurowska-Stolarska, Dong-Dong Li, Li-Li Zhang, Majid S. Jabir, Foo Y. Liew, Anne-Gaelle Besnard, Rodrigo Guabiraba, Gerard J. Graham, Li, Dong, Guabiraba, Rodrigo, McSharry, Charles, Xu, Damo, Institute of Infection, Immunity and Inflammation, University of Glasgow, Infectiologie et Santé Publique (UMR ISP), Institut National de la Recherche Agronomique (INRA)-Université de Tours (UT), Umm Al-Qura University, University of Technology, Institute of Laboratory Animal Science, Chinese Academy of Medical Sciences and Peking Union Medical College, King Abdulaziz University, Supported by Arthritis Research UK (AR UK 18912 to D.X.), the Medical Research Council UK, and the Wellcome Trust (to F.Y.L.), and Institut National de la Recherche Agronomique (INRA)-Université de Tours
Background The initiation and regulation of pulmonary fibrosis are not well understood. IL-33, an important cytokine for respiratory diseases, is overexpressed in the lungs of patients with idiopathic pulmonary fibrosis. Objectives We aimed to determine the effects and mechanism of IL-33 on the development and severity of pulmonary fibrosis in murine bleomycin-induced fibrosis. Methods Lung fibrosis was induced by bleomycin in wild-type or Il33r ( St2 ) −/− C57BL/6 mice treated with the recombinant mature form of IL-33 or anti–IL-33 antibody or transferred with type 2 innate lymphoid cells (ILC2s). The development and severity of fibrosis was evaluated based on lung histology, collagen levels, and lavage cytology. Cytokine and chemokine levels were quantified by using quantitative PCR, ELISA, and cytometry. Results IL-33 is constitutively expressed in lung epithelial cells but is induced in macrophages by bleomycin. Bleomycin enhanced the production of the mature but reduced full-length form of IL-33 in lung tissue. ST2 deficiency, anti–IL-33 antibody treatment, or alveolar macrophage depletion attenuated and exogenous IL-33 or adoptive transfer of ILC2s enhanced bleomycin-induced lung inflammation and fibrosis. These pathologic changes were accompanied, respectively, by reduced or increased IL-33, IL-13, TGF-β1, and inflammatory chemokine production in the lung. Furthermore, IL-33 polarized M2 macrophages to produce IL-13 and TGF-β1 and induced the expansion of ILC2s to produce IL-13 in vitro and in vivo . Conclusions IL-33 is a novel profibrogenic cytokine that signals through ST2 to promote the initiation and progression of pulmonary fibrosis by recruiting and directing inflammatory cell function and enhancing profibrogenic cytokine production in an ST2- and macrophage-dependent manner.