SARS-CoV-2 nucleocapsid protein-specific monoclonal antibodies as tools for studying its antigenic structure and interaction with host cells

Diagnostics and prevention of COVID-19 are essential for controlling the spread of the virus and reducing mortality rates. As SARS-CoV-2 surface proteins are susceptible to mutations, the nucleocapsid protein (NP) with its highly conserved gene sequence is an attractive target for studying virus-host interactions. NP plays a key role in the coronavirus life cycle, modulating viral RNA packaging, transcription, and assembly. In addition, its abundant expression during infection makes it a valuable diagnostic marker. NP is involved in modulating the host's innate immunity; however, the cellular mechanisms of its pathogenicity are not yet fully understood. This study developed and characterized murine monoclonal antibodies (MAbs) specific to the SARS-CoV-2 NP to investigate its antigenic regions and utilize the MAbs in virus-detecting systems or cellular NP blocking assays. The MAbs showed cross-reactivity with Omicron NP, recognizing epitopes within functionally active domains. They also identified NP in SARS-CoV-2-infected cells, supporting their feasibility in future immunoassays. Additionally, the ability to inhibit NP-cell interaction was assessed, with MAbs 4B3, 7F10, 16D9, and 18A8 found to reduce NP internalization. Overall, this study provides well-characterized tools for investigating SARS-CoV-2 antigenicity and pathogenicity and demonstrates the functional potential of the generated MAbs in studying NP-mediated host cell interactions.