Figure 1.

Schematic representation of the cellular events and basic mechanisms in persistent pulmonary fibrosis and fibrosis resolution. Alveolar epithelial damage causes recruitment of fibroblasts, which is activated by TGF-β, leading to collagen deposition and organ fibrosis. Fibrosis can be persistent, or eventually resolve via wound healing and lung regeneration. With normal collagen clearance and fibroblast apoptosis, fibrosis lesion in the lung is possible to resolve spontaneously. On the contrary, abnormal epithelial hyperplasia, fibroblast apoptosis resistance and collagen clearance failure caused by aberrant wound healing and pulmonary vascular dysfunction may lead to persistent pulmonary fibrosis.