Advanced in vitro models for pneumonia research

Epithelial cells serve as the initial defense barrier against invading pathogens. To comprehend the primary defense mechanisms towards pulmonary pathogenic insults, it is essential to work with intact differentiated epithelial layers that emulate in vivo phenotypes. Therefore, we established a human lung organoid model derived from primary alveolar epithelial cells. Apart from discovering that alveolar progenitors can regenerate not only alveolar cells but also bronchiolar type cells, we found that infection of the bronchioalveolar organoids with Influenza A virus recapitulates tissue responses with a strong inflammatory and robust interferon signaling as revealed by single-cell transcriptomic analysis. Despite the considerable stress response, organoids survived the acute infection and preserved epithelial integrity, while infected cells were shed into the lumen. On the other hand, to study lung barrier function upon infection, we used electrical-cell substrate impedance sensing (ECIS) as well as a human lung-on-a-chip model that integrates physiological functions, including breathing motion and perfusion. Doing so we revealed that modulating the alveolar glycocalyx by treatment with Heparinase led to break-down of the epithelial barrier. Besides, treatment of alveolar epithelial cells with Heparinase or hyaluronidase resulted in an enhanced barrier failure upon infection with Streptococcus pneumoniae, which reflects findings of in vivo studies. Together our results show that the advanced human cell models, which complement animal experiments with the advantage of avoiding species particularities, are valuable tools for studying mechanistics of pneumonia in vitro.