Transfer of SARS-CoV-2 nucleocapsid protein to uninfected epithelial cells induces antibody-mediated complement deposition
2Biochemistry, Institute for Medical Research Israel-Canada, the Hebrew University-Hadassah Medical School, the Hebrew University of Jerusalem
3The Kuvin Center for the Study of Infectious and Tropical Diseases, The Hebrew University-Hadassah Medical School, The Hebrew University of Jerusalem
4Institute of Pulmonary Medicine, Hadassah Medical Center, Affiliated to the Faculty of Medicine, Hebrew University Jerusalem
5Department of Internal Medicine D, Hadassah Medical Center, Affiliated to the Faculty of Medicine, Hebrew University Jerusalem
6Barry Skolnick Biosafety Level 3 (BSL3) Unit, Core Research Facility, Faculty of Medicine, Hebrew University of Jerusalem
7Clinical Virology Unit, Hadassah Hebrew University Medical Center, Jerusalem, Israel Hadassah Hebrew University Medical Center
8Lautenberg Centre for Immunology and Cancer Research, The Institute for Medical Research Israel-Canada (IMRIC), Faculty of Medicine, Hebrew University of Jerusalem
SARS-CoV-2 infection triggers strong antibody response toward Nucleocapsid-Protein (NP), suggesting extracellular presence beyond its intra-virion RNA binding. Interestingly, NP was found to decorate infected and proximal uninfected cell surfaces. Here, we propose a new mechanism through which extracellular NP on uninfected cells contributes to COVID-19 pathogenicity. We show that NP binds to cell surface sulfated linear-glycosaminoglycans by spatial rearrangement of its RNA-binding sites facilitated by the flexible, positively charged, linker. Coating of uninfected lung-derived cells with purified NP attracted anti-NP-IgG from lung fluids and sera collected from COVID-19 patients. The magnitude of this immune recognition was significantly elevated in moderate compared to mild COVID-19 cases. Importantly, binding of anti-NP-IgG present in sera generated clusters that triggered C3b deposition by the classical complement pathway on SARS-CoV-2 non-susceptible cells, grown in proximity to infected cells. Heparin analog enoxaparin outcompeted NP-binding, rescuing cells from anti-NP IgG-mediated complement deposition. Our findings unveil how extracellular NP may exacerbate COVID-19 tissue damage, and suggest leads for preventative therapy.