Macrophage-Epithelial Interactions Modulate Epithelial Cell Injury During Airway Reopening.

During the acute respiratory distress syndrome (ARDS), bacterial/viral infections, including COVID-19, lead to significant pulmonary edema and severe hypoxia. Although ARDS patients often require mechanical ventilation (MV), the biophysical forces generated during MV are known to exacerbate lung injury resulting in ventilation-induced lung injury (VILI). During VILI, the complex biomechanical forces generated during the reopening of fluid-occluded airway/alveoli (atelectrauma) causes plasma membrane rupture and epithelial cell death. However, it is not known how the interaction of immune cells, including alveolar macrophages, with epithelial cells alters the degree of atelectrauma. We used in-vitro modeling techniques to investigate how co-culture of both monocyte derived macrophages and primary human alveolar macrophages with lung epithelial cells alter the degree of cell injury during airway reopening. Co-culture of epithelial cells with macrophages led to a significant increase in epithelial cell death/plasma membrane rupture during airway reopening and this increased injury was not due to soluble factors secreted by macrophages. Inhibiting macrophage-epithelial gap junction interactions decreased epithelial cell injury during airway reopening. Morphological and cell biomechanical measurements indicate that epithelial cells in co-culture with macrophages have a lower height-to-width aspect ratio, a lower instantaneous elastic modulus, and a lower power-law exponent. Since lower aspect ratios have been associate with reduced atelectrauma, our data indicate that the reduced stiffness (lower elastic modulus) and increased elasticity (lower power-law exponent) is the biomechanical mechanism by which macrophages exacerbate epithelial cell injury during airway reopening.