Blockade of IL-6 trans signaling attenuates pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a lethal lung disease with progressive fibrosis and death within 2-3 y of diagnosis. IPF incidence and prevalence rates are increasing annually with few effective treatments available. Inhibition of IL-6 results in the attenuation of pulmonary fibrosis in mice. It is unclear whether this is due to blockade of classical signaling, mediated by membrane-bound IL-6Ra, or trans signaling, mediated by soluble IL-6Ra (sIL-6Ra). Our study assessed the role of sIL-6Ra in IPF. We demonstrated elevations of sIL-6Ra in IPF patients and in mice during the onset and progression of fibrosis. We demonstrated that protease-mediated cleavage from lung macrophages was important in production of sIL-6Ra. In vivo neutralization of sIL-6Ra attenuated pulmonary fibrosis in mice as seen by reductions in myofibroblasts, fibronectin, and collagen in the lung. In vitro activation of IL-6 trans signaling enhanced fibroblast proliferation and extracellular matrix protein production, effects relevant in the progression of pulmonary fibrosis. Taken together, these findings demonstrate that the production of sIL- 6Ra from macrophages in the diseased lung contributes to IL-6 trans signaling that in turn influences events crucial in pulmonary fibrosis.