507. Activation of Macrophages Enhances Susceptibility to SARS-CoV-2 Antibody-Dependent Enhancement and Promotes Damage to Downstream Epithelial Cells

Background The distinct shift in peripheral monocyte activation and infiltration of these cells into the respiratory tract observed in severe cases of COVID-19 suggests that like SARS-CoV-1, the acute respiratory distress syndrome (ARDs) observed in SARS-CoV-2 infections may result from damage to the respiratory epithelia by improperly activated macrophages (MPs). In this study, we examined the ability of non-neutralizing antibodies to sensitize MPs to killing by SARS-CoV-2, as well as the impact of these cells on downstream epithelial cells. Methods Raw 264.7 cells were seeded into 96-well plates at a density of 1x104/well and incubated overnight in the presence or absence of heat-inactivated LPS derived from either E. coli (EC) or S. enteritidis (Sal). Cells were then treated with non-neutralizing antibodies or vehicle control at the time of infection with SARS-CoV-2. Viability was assessed 48 hours post-infection by luminescence following the addition of CellTiter-Glo® (Promega). Results While no decrease in cell viability was observed with SARS-CoV-2 alone, the presence of non-neutralizing antibodies against either the nucleocapsid or spike protein of SARS-CoV-2 decreased cell survival to 35.98% and 53.67% of the cell control, respectively (p< 0.0001 and p=0.0003). Activation of MPs with Sal-derived LPS sensitized MPs to viral killing, even in the absence of non-neutralizing antibody (20.12% viability, p< 0.0001). This was not observed in MPs activated by EC LPS. MP activation by both Sal and EC LPS further enhanced viral killing in the presence of anti-nucleocapsid, reducing cell viability to 12.21% (0.0001) and 6.46% (p< 0.0001). Finally, supernatants collected from naïve MPs subjected to ADE markedly increased the susceptibility of Vero E6 cells to SARS-CoV-2 nearly 9.8-fold (p< 0.0001). Conclusion Here we demonstrate that naïve MPs, normally resistant to infection by SARS-CoV-2, are rendered susceptible to viral killing by activation and the presence of non-neutralizing antibodies to SARS-CoV-2. Furthermore, MPs secrete an as yet, unknown factor that enhances the susceptibility of Vero E6 to SARS-CoV-2. Taken together, these data suggest that MPs play an important role in determining the severity of SARS-CoV-2 infection. Disclosures All Authors: No reported disclosures