Inflammatory Cytokines and Alveolar Epithelium
The bronchial epithelium is a primary target for respiratory viruses28. Alveolar epithelium plays an important role in promoting cell barrier functions and strengthening cell-cell junctions against virus-induced disruption of tight junctions. However, virus infected epithelial cells express cytokines that primarily attract macrophages. Once recruited, the activated macrophages promote activation of adjacent endothelial cells. Infiltrating macrophages produce reactive oxygen species and nitric oxide30 that serve to damage the barrier31. Macrophages also promote epithelial-cell apoptosis epithelial cells and mediate phagocytosis of apoptotic cells31, 32, 33.