Endogenously expressed IL-13Ralpha2 attenuates IL-13- mediated responses but does not activate signaling in human lung fibroblasts

IL-13 can bind to two distinct receptors: a heterodimer of IL-13Ralpha1/IL-4Ra and IL-13Ralpha2. Whereas IL-13Ralpha1/IL-4Ralpha engagement by IL-13 leads to the activation of STAT6, the molecular events triggered by IL-13 binding to IL-13Ralpha2 remain incompletely understood. IL-4 can bind to and signal through the IL-13Ralpha1/IL-4Ralpha complex but does not interact with IL-13Ralpha2. Idiopathic pulmonary fibrosis is a progressive and generally fatal parenchymal lung disease of unknown etiology with no current pharmacologic treatment options that substantially prolong survival. Preclinical models of fibrotic diseases have implicated IL-13 activity on multiple cell types, including macrophages and fibroblasts, in initiating and perpetuating pathological fibrosis. In this study, we show that IL-13, IL-4, IL-13Ralpha2, and IL-13-inducible target genes are expressed at significantly elevated levels in lung tissue from patients with idiopathic pulmonary fibrosis compared with control lung tissue. IL-4 and IL-13 induce virtually identical transcriptional responses in human monocytes, macrophages, and lung fibroblasts. IL-13Ralpha2 expression can be induced in lung fibroblasts by IL-4 or IL-13 via a STAT6-dependent mechanism, or by TNF-alpha via a STAT6-independent mechanism. Endogenously expressed IL-13Ralpha2 decreases, but does not abolish, sensitivity of lung fibroblasts to IL-13 and does not affect sensitivity to IL-4. Genome-wide transcriptional analyses of lung fibroblasts stimulated with IL-13 in the presence of Abs that selectively block interactions of IL-13 with IL-13Ralpha1/IL-4Ralpha or IL-13Ralpha2 show that endogenously expressed IL-13Ralpha2 does not activate any unique IL-13-mediated gene expression patterns, confirming its role as a decoy receptor for IL-13 signaling. Copyright 2014 by The American Association of Immunologists, Inc. All rights reserve