Dual Roles of IL-4 in Lung Injury and Fibrosis

Abstract

Increased lung IL-4 expression in pulmonary fibrosis suggests a potential pathogenetic role for this cytokine. To dissect this role, bleomycin-induced pulmonary inflammation and fibrosis were analyzed and compared in wild type (IL-4+/+) vs IL-4-deficient (IL-4−/−) mice. Lethal pulmonary injury after bleomycin treatment was higher in IL-4−/− vs IL-4+/+ mice. By administration of anti-CD3 Abs, we demonstrated that this early response was linked to the marked T lymphocyte lung infiltration and to the overproduction of the proinflammatory mediators such as TNF-α, IFN-γ, and NO in IL-4−/− mice. In contrast to this early anti-inflammatory/immunosuppressive role, during later stages of fibrosis, IL-4 played a profibrotic role since IL-4−/− mice developed significantly less pulmonary fibrosis relative to IL-4+/+ mice. However, IL-4 failed to directly stimulate proliferation, α-smooth muscle actin, and type I collagen expression in lung fibroblasts isolated from the wild-type mice. Upon appropriate stimulation with other known fibrogenic cytokines, fibroblasts from IL-4−/− mice were relatively deficient in the studied parameters in comparison to fibroblasts isolated from IL-4+/+ mice. Taken together, these data suggest dual effects of IL-4 in this model of lung fibrosis: 1) limiting early recruitment of T lymphocytes, and 2) stimulation of fibrosis chronically.