IL13 and pulmonary fibrosis: Although transgenic over-expression of IL-13 alone in the lung leads to the development of pulmonary fibrosis [6], [7], both IL-4 and IL-13 appear to contribute to the development of pulmonary fibrosis [8], [9], presumably due to their ability to act directly on pulmonary fibroblasts [10] and mononuclear cells/macrophages [11].