IL-7 inhibits fibroblast TGF-β production and signaling in pulmonary fibrosis

IntroductionIdiopathic pulmonary fibrosis (IPF) is a devastating disease with less than a 50% five-year survival (1, 2).While steroids and other immunosuppressive agents serve as the standard treatment for IPF, these agents have proved inadequate (3).In most instances immunosuppressive agents do little to affect the course of the disease and have serious adverse side effects.Thus, novel therapeutic strategies are clearly needed.Recent published findings suggest novel treatment paradigms based on a more complete understanding of the pathogenesis of pulmonary fibrosis (3, 4).IL-7 is a 25-kDa glycoprotein originally isolated from bone marrow stroma cells (5).IL-7 was originally defined as a pre-B lymphocyte growth factor and was subsequently found to augment the growth of T lymphocytes (6-8).We (9) and others (10-13) have documented that IL-7 can potently enhance T cell function and IFN-γ production.IL-7 synergizes with IL-12 in the induction of T cell proliferation, cytotoxicity, and IFN-γ release (11).In agreement with these findings are studies indicating that IL-7 plays a role in cell-mediated immune responses characteristic of type 1 cytokines (10).We have found that IL-7 downregulates macrophage (14), fibrosarcoma, and melanoma (15, 16) production of TGF-β.IL-7 has the capacity to downregulate the transcriptional rate of the TGF-β gene in murine macrophages in an IFN-γindependent manner (14).TGF-β is a critical fibrogenic factor in the development of pulmonary fibrosis.Based on the importance of TGF-β in the pathogenesis of pulmonary fibrosis, we speculated that the most effective therapies would be those that decrease both the production and the cellular effects of TGF-β.In the current study we investigate the role of IL-7 in TGF-β production and signaling and the potential for IL-7 as a new antifibrotic agent in the treatment of interstitial pulmonary fibrosis. MethodsCell culture.Pulmonary fibrosis fibroblasts (PFFs) were isolated from lung resection specimens obtained from patients with IPF.Normal fibroblasts (NFs) were isolated from patients with nonfibrotic diseases.U4A, U3A, and U4A/JAK1 cell lines were generously provided by George R. Stark (Cleveland Clinic Foundation, Cleveland, Ohio, USA).The cells were maintained in 5% CO 2 in air as monolayers at 37°C in 75-cm 2 tissue culture flasks containing 20 ml of DMEM supplemented with 10% FBS, 100 units/ml penicillin, 0.1 mg/ml streptomycin, and 2 mM glutamine (JRH Biosciences, Lenexa, Kansas, USA). Cytokines and antibodies.Human activated recombinant TGF-β1 (3.2 × 10 4 units/µg), recombinant human IL-7