SARS-CoV-2 nucleocapsid induces hyperinflammation and vascular leakage through the Toll-like receptor signaling axis in macrophages.

Tens of thousands of severe COVID-19 cases are hospitalized weekly in the U.S., often driven by an imbalance between antiviral responses and inflammatory signaling, leading to uncontrolled cytokine secretion. The SARS-CoV-2 nucleocapsid (N) protein is a known immune antagonist, but its role in macrophage-driven cytokine storms is unclear. We demonstrate that N functions in a pathway-specific manner, specifically amplifying nuclear factor κB-related transcripts upon Toll-like receptor 7/8 stimulation. Moreover, we show that this is a conserved feature of pathogenic coronaviruses, with the delta variant N being the most pro-inflammatory. Our interaction networks suggest the delta variant N drives inflammation through interactions with several stress granule-related proteins. Profiling of secreted cytokines revealed that supernatants from the delta variant N-expressing macrophages disrupt brain and heart endothelial barriers, implicating N in COVID-19-associated cognitive and cardiac complications. Our findings highlight N-mediated immune imbalance as a driver of severe COVID-19 and identify N as a promising therapeutic target to mitigate hyperinflammation.