Characterization of a New Mouse Model of Empyema and the Mechanisms of Pleural Invasion by Streptococcus pneumoniae

Abstract

Although empyema affects more than 65,000 people each year in the United States and in the United Kingdom, there are limited data on the pathogenesis of pleural infection. We investigated the pathogenesis of empyema using animal and cell culture models of Streptococcus pneumoniae infection. The pathological processes during the development of empyema associated with murine pneumonia due to S. pneumoniae (strain D39) were investigated. Lungs were examined using histology, and pleural fluid and blood bacterial colony-forming units, cytokine levels, and cellular infiltrate were determined over time. Bacterial migration across mesothelial monolayers was investigated using cell culture techniques, flow cytometry, and confocal microscopy. After intranasal inoculation with 10 7 S. pneumoniae D39 strain, mice developed pneumonia associated with rapid bacterial invasion of the pleural space; raised intrapleural IL-8, VEGF, MCP-1, and TNF-a levels; and caused significant intrapleural neutrophilia followed by the development of fibrinous pleural adhesions. Bacterial clearance from the pleural space was poor, and in vitro assays demonstrated that S. pneumoniae crossed mesothelial layers by translocation through cells rather than by a paracellular route. This study describes key events during the development of S. pneumoniae empyema using a novel murine model of pneumonia-associated empyema that closely mimics human disease. The model allows for future assessment of molecular mechanisms involved in the development of empyema and evaluation of potential new therapies. The data suggest that transmigration of bacteria through mesothelial cells could be important in empyema development. Furthermore, upon entry the pleural cavity offers a protected compartment for the bacteria.Keywords: Streptoccocus pneumoniae; empyema; animal models; translocation; mesothelial cells Pleural infection is a global problem that affects over 65,000 patients each year in the United States and in the United Kingdom and is associated with significant morbidity and mortality (1-5). Empyema is defined by the presence of bacteria or pus in the pleural cavity and usually develops as a complication of pneumonia. Important questions regarding the disease pathogenesis remain unanswered, which may in part account for the lack of recent therapeutic advances. A key limiting factor in this area of research is that there is no suitable preclinical animal model of empyema. Studying the evolution of pleuropulmonary infection ideally involves repeated sampling of the lung and pleural cavity, which is not feasible in patients with pneumonia, and the animal models used to date have significant limitations (6). Published in vivo models rely on intrapleural delivery of bacteria to create localized pleural infection without concurrent pneumonia and many use species-specific microorganisms, such as Pasteurella multocida (7-9), with limited relevance to humans. These models require concomitant administration of systemic antibiotics to control infection and fatalities (8), ...

Development of Primary Invasive Pneumococcal Disease Caused by Serotype 1 Pneumococci Is Driven by Early Increased Type I Interferon Response in the Lung

“…We have demonstrated that for invasive strain 1861, invasion of the pleural cavity as early as 6 h postchallenge consistently precedes detection of bacteria in the bloodstream. This supports the notion that the pleural cavity may act as a conduit for bacteria to travel from the lung to the blood (8) and highlights this niche as an important site for investigation of hostpathogen interaction in pneumococcal disease.…”

“…1C). These data suggest that invasion of the blood leading to bacteremia is preceded by invasion of the pleural cavity, as has been previously proposed (8), and that invasion of the normally sterile pleural cavity may be used as an early marker of invasion. The data also show that whereas pleural cavity invasion by strain 1861 had commenced at 6 h, this was not due to a difference in bacterial numbers in the lung from those determined for strain 1 but was likely due to a difference in the interactions between the host and the two bacterial strains within the lung.…”

“…However, the role of the host innate immune response in the translocation of the pneumococcus from the lungs to the blood has yet to be elucidated. In addition, the role of the pleural cavity in the development of IPD is unknown, but it has recently been suggested to act as the conduit through which pneumococci pass from the lungs to the blood (8). In this study, we investigated which elements of the early immune response might influence the progression of the pneumococcus from the lung to the blood as well as potential involvement of the pleural cavity.…”

Dose dependency of outcomes of intrapleural fibrinolytic therapy in new rabbit empyema models

“…While murine EMP models (41) are attractive due to the availability of animals with different genetic backgrounds, they possess inherent limitations for studies of fibrinolysis (9). Murine PAI-1 (12), fibrin (33), and urokinase receptor, uPAR (22), structurally and functionally differ from those of the human proteins.…”

Pulmonary cytokine composition differs in the setting of alcohol use disorders and cigarette smoking

“…cigarette smoking could be a factor in the development of complicated pneumococcal infections, such as empyema (66). Through potential effects on alveolar epithelial permeability, alterations in pulmonary VEGF could also play a role in the development of the acute respiratory distress syndrome (ARDS) that may complicate pneumococcal pneumonia.…”