Sepsis-induced
inflammation of the lung leads to
acute respiratory distress syndrome (ARDS), which may trigger persistent
fibrosis. The pathology of ARDS is complex and poorly understood, and the therapeutic approaches are limited. We used a baboon model of Escherichia coli
sepsis that mimics the complexity of human disease to study the pathophysiology of ARDS. We performed extensive biochemical, histological, and functional analyses to characterize the
disease progression and the long-term effects of
sepsis on the lung structure and function. Similar to humans,
sepsis-induced ARDS in baboons displays an early inflammatory exudative phase, with extensive
necrosis. This is followed by a regenerative phase dominated by proliferation of type 2 epithelial cells, expression of epithelial-to-mesenchymal transition markers, myofibroblast migration and proliferation, and
collagen synthesis. Baboons that survived
sepsis showed persistent
inflammation and
collagen deposition 6-27 months after the acute episodes. Long-term survivors had almost double the amount of
collagen in the lung as compared with age-matched control animals. Immunostaining for procollagens showed persistent active
collagen synthesis within the fibroblastic foci and interalveolar septa. Fibroblasts expressed markers of
transforming growth factor-β and
platelet-derived growth factor signaling, suggesting their potential role as mediators of myofibroblast migration and proliferation, and
collagen deposition. In parallel, up-regulation of the inhibitors of extracellular
proteases supports a deregulated matrix remodeling that may contribute to
fibrosis. The primate model of
sepsis-induced ARDS mimics the
disease progression in humans, including chronic
inflammation and long-lasting
fibrosis. This model helps our understanding of the pathophysiology of
fibrosis and the testing of new
therapies.