Endothelial Cell-Activating Antibodies in COVID-19.

Objective: While endothelial dysfunction has been implicated in the widespread thromboinflammatory complications of COVID-19, the upstream mediators of endotheliopathy remain, for the most part, unknown. This study was undertaken to identify circulating factors contributing to endothelial cell activation and dysfunction in COVID-19.

Methods: Human endothelial cells were cultured in the presence of serum or plasma from 244 patients hospitalized with COVID-19 and plasma from 100 patients with non-COVID-19-related sepsis. Cell adhesion molecules (E-selectin, vascular cell adhesion molecule 1, and intercellular adhesion molecule 1 [ICAM-1]) were quantified using in-cell enzyme-linked immunosorbent assay.

Results: Serum and plasma from COVID-19 patients increased surface expression of cell adhesion molecules. Furthermore, levels of soluble ICAM-1 and E-selectin were elevated in patient serum and correlated with disease severity. The presence of circulating antiphospholipid antibodies was a strong marker of the ability of COVID-19 serum to activate endothelium. Depletion of total IgG from antiphospholipid antibody-positive serum markedly reduced the up-regulation of cell adhesion molecules. Conversely, supplementation of control serum with patient IgG was sufficient to trigger endothelial activation.

Conclusion: These data are the first to indicate that some COVID-19 patients have potentially diverse antibodies that drive endotheliopathy, providing important context regarding thromboinflammatory effects of autoantibodies in severe COVID-19.