IL-25/IL-33/TSLP contributes to idiopathic pulmonary fibrosis: Do alveolar epithelial cells and (myo)fibroblasts matter?

Abstract

Idiopathic pulmonary fibrosis is a relentless fibrotic disease with largely unknown etiologies. Currently, the crosstalk between alveolar epithelial cells and lung-resident mesenchymal cells (especially [myo]fibroblasts) is considered to be the central pathogenesis to initiate and propagate the fibrotic process. Unfortunately, the master switch hidden in the profibrotic milieu that mediates pathogenic epithelial-mesenchymal interactions is still not well elucidated. Thus, the definite treatment target that can block and cure idiopathic pulmonary fibrosis is now lacking. Based on the previous studies, we proposed the notion that epithelium-derived triple type 2 cytokines, i.e. interleukin (IL)-25, IL-33, and thymic stromal lymphopoietin (TSLP) are important pro-fibrotic mediators in idiopathic pulmonary fibrosis via two possible mechanisms: (1) paracrine pathway: directly acting on (myo)fibroblast. There may exist a structural and functional axis of (IL-25/IL-33/TSLP)⁺alveolar epithelial cells-(IL-25R/IL-33R/TSLPR)⁺ (myo)fibroblasts in fibroblastic foci of idiopathic pulmonary fibrosis patients. The crosstalk between alveolar epithelium and the adjacent mesenchymal compartment is well established by the binding of IL-25/IL-33/TSLP expressed on alveolar epithelial cells with their corresponding receptors (i.e. IL-17BR/sT2L/TSLPR) expressed on (myo)fibroblasts; (2) autocrine pathway: directly acting on alveolar epithelial cells. Alveolar epithelial cells may act as both cellular sources and targets of IL-25/IL-33/TSLP. Autocrine IL-25/IL-33/TSLP causes salient injury and phenotypic changes of alveolar epithelial cells. Thus, epithelium-derived IL-25/IL-33/TSLP may be the novel promising treatment target for the cure of idiopathic pulmonary fibrosis.

Impact statement

We suggest a novel modality in terms of IL-25/IL-33/TSLP’s pro-fibrotic role in IPF. First, IL-25/IL-33/TSLP fully activates (myo)fibroblasts in fibroblastic foci (FF) in a paracrine-dependent manner. (IL-25/IL-33/TSLP)⁺alveolar epithelial cells-(IL-25R/IL-33R/TSLPR)⁺ (myo)fibroblasts axis may contribute greatly to the abnormal epithelial-mesenchymal crosstalk and lung fibrosis. Second, IL-25/IL-33/TSLP causes significant injury and phenotypic changes of alveolar epithelial cells in an autocrine-dependent manner. By acting directly on the two most important cells in the fibrotic process, i.e. alveolar epithelial cells and (myo)fibroblasts, we support the notion that biological therapies targeting IL-25/IL-33/TSLP will shed new light on the cure of IPF patients.