TD is an early source of IL-4 production (by basophils and mast cells in TD) that leads to alternatively activated macrophages (M2) [26, 28]. M2 can release IL-10, which can conversely activate M2, and transforming growth factor, TGF-β . While IL-10 is a potent anti-inflammatory cytokine that down-regulates almost all important proinflammatory and TD-related processes, TGF-β is a multi-functional growth factor. In small airways, TGF-β is a potent inducer for extracellular matrix target genes such as collagens, and fibroblast proliferation and activation which both are key events in the fibrogenic process . However, in the lung parenchyma, TGF-β down-regulates tissue damage through inhibition of MMP-12 and MMP-9 .