Antibodies Against SARS-CoV-2 Nucleocapsid Protein Possess Autoimmune Properties

Area of Science:

• Immunology
• Virology
• Vaccine Development

Background:

• Despite the COVID-19 pandemic's official end, SARS-CoV-2 continues to cause illness and long-term post-COVID conditions, potentially due to autoimmune reactions.
• The conserved and immunogenic nucleocapsid (N) protein of SARS-CoV-2 is a target for vaccine development, but its role in antibody-induced autoimmunity requires further study.
• Understanding cross-reactivity between anti-N antibodies and human antigens is essential for predicting and mitigating autoimmune risks associated with natural infection or N-based vaccines.

Purpose of the Study:

• To identify potential structural or sequence homologies between the SARS-CoV-2 N protein and human antigens.
• To investigate the cross-reactivity of hyperimmune sera against the N protein with human self-antigens.
• To assess the immunogenicity and potential autoimmune implications of anti-N antibodies.

Main Methods:

• Western blot analysis of human cell line lysates to detect antibody cross-reactivity.
• Mass spectrometric identification of human self-antigens recognized by anti-N antibodies.
• Comparison of anti-N antibody responses in mice, rabbits, and hamsters.

Main Results:

• Anti-N antibodies from mice and rabbits showed significant cross-reactivity with human proteins, including heat shock proteins (HSP90-beta, HSP70, HSP60, HSPA8), histones (H2B, H3.1-3), and metabolic enzymes (G6PD, GP3, PKM).
• Anti-N immunoglobulins from hamsters did not exhibit cross-reactivity with human or hamster proteomic extracts, indicating a lack of autoreactivity in this model.
• Mass spectrometry identified specific autoantigenic targets, primarily heat shock proteins and histones.

Conclusions:

• Humoral immune responses to the SARS-CoV-2 N protein differ significantly between species, notably between humans and the Syrian hamster model.
• The identified cross-reactive antigens provide a basis for predicting potential autoimmune consequences in COVID-19 convalescents.
• These findings are critical for the rational design of future N protein-based vaccines offering cross-protection against novel coronaviruses.