Biphasic lung injury during Streptococcus pneumoniae infection in a murine model.

OBJECTIVES: Streptococcus pneumoniae is the leading cause of community-acquired pneumonia. We aimed to analyze the epithelial response to S. pneumoniae-induced lung injury. METHODS: Using an in vitro model with 16HBE cells and experimental in vivo murine model of acute lung injury, we analyzed the epithelial response to S. pneumoniae. Lung epithelial cell monolayers were exposed to S. pneumoniae and permeability was assessed by transepithelial resistance (TER) measurement and organization and expression of junction proteins. Functional consequences were studied with an in vivo murine model measuring alveolar permeability, distal alveolar fluid clearance (DAFC), and the alveolar inflammatory response. RESULTS: In vitro, S. pneumoniae induced a dose-dependent decrease in transepithelial resistance, which was associated with significant modifications in the organization of junction proteins assessed by immunofluorescence staining and expression after 6hours of exposure. In vivo, S. pneumoniae induced a transient increase in alveolar permeability with an adequate increase in DAFC 6hours post infection. In a second phase, a permanent increased permeability was associated with a major decrease in DAFC. CONCLUSION: Overall, the epithelial response to S. pneumoniae followed a biphasic pattern with an initial reversible increase in permeability related to the alteration of tight and adherens junctions and a second phase associated with an epithelial injury with a major increase in permeability with a decreased DAFC reflecting an injured alveolar capillary barrier.