Cell Surface SARS-CoV-2 Nucleocapsid Protein Modulates Innate and Adaptive Host Immunity
Despite the unprecedent global response to SARS-CoV-2, which has generated over 250,000 publications in 2 years, critical aspects of SARS-CoV-2 biology, pathogenesis and immunomodulation remain uncertain, including mechanisms underlying the cytokine storm and coagulation dyscrasias. Nucleocapsid (N) protein, the most abundant viral protein expressed during infection, induces strong antibody and T cell responses. N is considered to be strictly localized intracellularly. However, cell surface expression of viral nucleoproteins is the rule, not the exception, among RNA viruses including influenza A, vesicular stomatitis, measles and respiratory syncytial viruses. Cell surface viral nucleoproteins have been reported to induce immunosuppression, but also to serve as antibody targets.
We find that N is expressed on the cell surface of live cells in high copy numbers. It binds to infected and non-infected neighboring cells by electrostatically associating with glycosaminoglycans. Using biolayer interferometry (BLI), we found that N binds specifically to heparan sulfate/heparin with high affinity, but not to others glycosaminoglycans on the cell surface. BLI screening between SARS-CoV-2 structural and accessory proteins and 64 human cytokines, revealed high affinity interaction between N and a set of 11 human chemokines, including CXCL12b. Importantly, N inhibited CXCL12b-mediated leukocyte migration in chemotaxis assays, as did SARS-CoV-1 and MERS-CoV nucleoproteins. We also found that anti-N antibodies bound to the surface of infected cells can activate Fc receptor expressing cells.
These data indicate that cell surface N may play an important role in host adaptive immunity to SARS-CoV-2 and in manipulating innate immunity at the early stages of infection.
Alberto D. Lopez-Munoz, Ph.D., M.Sc. is a molecular virologist, passionate about understanding how viruses are able to mimic and modulate the human immune system. He received his PhD and MSc from the Universidad Autónoma de Madrid (Spain) where he studied immunomodulation and evolutionary mechanisms of human herpes simplex viruses. During his predoctoral training, he performed two research internships, at Imperial College London (UK) and at the US National Institute of Allergy and Infectious Diseases (NIAID, USA).
He is currently a postdoctoral fellow at the Laboratory of Viral Diseases within the NIAID (National Institutes of Health, NIH), investigating alternatives roles of human coronaviruses proteins in host immunomodulation.
His desire to improve the visibility of Spanish scientists and interconnect the Spanish and American scientific communities have motivated him to lead the ECUSA Washington DC chapter and to participate in the E-Visibility program.
