Pulmonary fibrosis often results from improper regeneration of the alveolar epithelium. The pathophysiology of fibrosis is due to many micro-injuries to the lung, leading to fibroblast recruitment and activation and eventually matrix accumulation. Diagnosis of pulmonary fibrosis involves elimination of other lung diseases, and finding decreased static lung volumes. The median survival of idiopathic pulmonary fibrosis is 3 years, and there are currently no good treatment options. Regeneration of the alveolar epithelium is thought to be due to type 2 alveolar epithelial cells (AEC2s), which are stem cells. Liang et all found that deletion of the innate immune receptor Toll-like receptor 4 (TLR4) or deletion of the extracellular matrix glycosaminoglycan hyaluronan (HA) synthase in AEC2s lead to severe fibrosis and mortality. In addition, Liang et al found that patient AEC2s have less cell surface HA and impaired colony forming abilities, which may lead to pulmonary fibrosis. Finally, Liang et al had previously shown that HA interaction with TLR4 may promote recover from acute lung injury. 

http://www.nature.com/nm/journal/v22/n11/full/nm.4192.html

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