A porcine ex vivo lung perfusion model to investigate bacterial pathogenesis

The use of animal infection models is essential to understand microbial pathogenesis and to develop and test treatments. Insects, and 2D and 3D tissue models are increasingly being used as surrogate for mammalian models. However, there are concerns whether these models recapitulate the complexity of host-pathogen interactions. Here, we developed the ex vivo lung perfusion (EVLP) model of infection using porcine lungs to investigate Klebsiella pneumoniae-triggered pneumonia as model of respiratory infections. The porcine EVLP model recapitulates features of K. pneumoniae-induced pneumonia lung injury. This model is also useful to assess the pathogenic potential of K. pneumoniae as we observed that the attenuated Klebsiella capsule mutant strain caused less pathological tissue damage with a concomitant decrease in the bacterial burden compare to lungs infected with the wild type. The porcine EVLP model allows assessment of inflammatory responses following infection; similar to the mouse pneumonia model, we observed an increase of il-10 in the lungs infected with the wild type and an increase of ifn-{gamma} in lungs infected with the capsule mutant. This model also allows monitoring phenotypes at the single-cell level. Wild-type K. pneumoniae skews macrophages towards an M2-like state. In vitro experiments probing pig bone marrow-derived macrophages uncovered the role of the M2 transcriptional factor STAT6, and that Klebsiella-induced il10 expression is controlled by p38 and ERK. Klebsiella-induced macrophage polarization is dependent on the capsule. Altogether, this study support the utility of the EVLP model using pig lungs as platform to investigate the infection biology of respiratory pathogens.\n\nIMPORTANCEThe implementation of infection models that approximate human disease is essential to understand infections and for testing new therapies before they enter into clinical stages. Rodents are used in most of pre-clinical studies, although the differences between mouse and man have fuelled the conclusion that murine studies are unreliable predictors of human outcomes. Here, we have developed a whole lung porcine model of infection using the established ex vivo lung perfusion (EVLP) system established to re-condition human lungs for transplant. As a proof-of-principle, we provide evidence demonstrating that infection of the porcine EVLP with the human pathogen K. pneumoniae recapitulates the known features of Klebsiella-triggered pneumonia. Moreover, our data revealed the porcine EVLP model is useful to reveal features of the virulence of K. pneumoniae including the manipulation of immune cells. Altogether, this study supports the utility of the EVLP model using pig lungs as surrogate host for assessing respiratory infections.