Backgroud: Idiopathic pulmonary fibrosis is a devastating disorder for which there is no effective treatment. Transforming growth factor (TGF)-β plays a critical role in provoking fibrosis. Interleukin (IL)-10 is a potent immunosuppressive cytokine but its effect on the fibrosing process is unclear. A study was undertaken to examine whether IL-10 affects the production and activation of TGF-β and thus can attenuate the fibrosis.

Methods: Mice were given an intratracheal injection of bleomycin. On day 1 or 14, IL-10 gene was delivered by rapid intravenous injection of Ringer’s solution containing plasmid. Two weeks after the plasmid injection the mice were examined for fibrosis. The effect of IL-10 on TGF-β production by alveolar macrophages was assessed.

Results: Even when delivered during the fibrosing phase, IL-10 gene significantly suppressed the pathological findings, hydroxyproline content, and production of both active and total forms of TGF-β₁ in the lung. Immunohistochemical analyses showed that alveolar macrophages were one of the major sources of TGF-β₁ and IL-10 diminished the intensity of the staining. IL-10 also suppressed the expression of α_Vβ₆ integrin, a molecule that plays an important role in TGF-β activation, on lung epithelial cells. Alveolar macrophages from bleomycin injected mice produced TGF-β₁ spontaneously ex vivo, which was significantly suppressed by treatment of the mice in vivo or by treatment of the explanted macrophages ex vivo with IL-10.

Conclusion: IL-10 suppresses the production and activation of TGF-β in the lung and thus attenuates pulmonary fibrosis, even when delivered in the chronic phase.