IL‐17A deficiency mitigates bleomycin‐induced complement activation during lung fibrosis

Abstract

Interleukin 17A (IL-17A) and complement (C') activation have each been implicated in the pathogenesis of idiopathic pulmonary fibrosis (IPF). We have reported that IL-17A induces epithelial injury <i>via</i> TGF-β in murine bronchiolitis obliterans; that TGF-β and the C' cascade present signaling interactions in mediating epithelial injury; and that the blockade of C' receptors mitigates lung fibrosis. In the present study, we investigated the role of IL-17A in regulating C' in lung fibrosis. Microarray analyses of mRNA isolated from primary normal human small airway epithelial cells indicated that IL-17A (100 ng/ml; 24 h; <i>n</i> = 5 donor lungs) induces C' components (C' factor B, <i>C3</i>, and GPCR kinase isoform 5), cytokines (<i>IL8</i>, <i>-6</i>, and <i>-1B</i>), and cytokine ligands (<i>CXCL1</i>, <i>-2</i>, <i>-3</i>, <i>-5</i>, <i>-6</i>, and <i>-16</i>). IL-17A induces protein and mRNA regulation of C' components and the synthesis of active C' 3a (C3a) in normal primary human alveolar type II epithelial cells (AECs). Wild-type mice subjected to IL-17A neutralization and IL-17A knockout (<i>il17a^-/-</i> ) mice were protected against bleomycin (BLEO)-induced fibrosis and collagen deposition. Further, BLEO-injured <i>il17a^-/-</i> mice had diminished levels of circulating Krebs Von Den Lungen 6 (alveolar epithelial injury marker), local caspase-3/7, and local endoplasmic reticular stress-related genes. BLEO-induced local C' activation [C3a, C5a, and terminal C' complex (C5b-9)] was attenuated in <i>il17a^-/-</i> mice, and IL-17A neutralization prevented the loss of epithelial C' inhibitors (C' receptor-1 related isoform Y and decay accelerating factor), and an increase in local TUNEL levels. RNAi-mediated gene silencing of <i>il17a</i> in fibrotic mice arrested the progression of lung fibrosis, attenuated cellular apoptosis (caspase-3/7) and lung deposition of collagen and C' (C5b-9). Compared to normals, plasma from IPF patients showed significantly higher hemolytic activity. Our findings demonstrate that limiting complement activation by neutralizing IL-17A is a potential mechanism in ameliorating lung fibrosis.-Cipolla, E., Fisher, A. J., Gu, H., Mickler, E. A., Agarwal, M., Wilke, C. A., Kim, K. K., Moore, B. B., Vittal, R. IL-17A deficiency mitigates bleomycin-induced complement activation during lung fibrosis.