Patients Suffering From Post‐ <scp>COVID</scp> ‐19 Syndrome Feature Enhanced Antibody Reactivity Towards Specific Linear Epitopes Within <scp>EBV EBNA1</scp>

Post-COVID-19 syndrome (PCS; also known as post-acute sequelae of COVID-19, PASC and Long COVID) manifests with various clinical symptoms of unclear aetiology that persist or develop months after acute infection with SARS-CoV-2. Potential triggers for PCS include reactivation of latent viruses and autoimmune reactions. In our retrospective cross-sectional and explorative study we compared 48 PCS patients with 48 individuals that recovered fully from COVID-19 (convalescents, CC). We focused on characterising humoral immunity by recording IgG antibody reactivity patterns against Epstein-Barr virus (EBV) EBNA1 antigen using peptide microarray and ELISA methodology as well as determining the presence of autoantibodies. The overall binding landscape of IgG antibodies for the EBV EBNA1 protein was similar for the patients with sequelae versus the convalescents. However, the PCS patients displayed stronger reactivity for epitopes contained within the glycine-alanine repeat region of EBNA1, in particular residues 90-325, and within the central part, amino acids 393-420. Intriguingly, in the latter case, the EBNA1 peptide (residues 405-419) that discriminated the PCS and CC cohorts was localised in a different segment C-terminal from the sequence proposed to be mechanistically associated with multiple sclerosis. The screening for autoantibodies against nuclear/cytoplasmic antigens in HEp-2 cells and against CRYAB, cardiolipin, beta-2-glycoprotein I, IFN-alpha2, IFN-omega, and IL-15 antigens did neither reveal higher prevalence nor increased reactivity in the PCS patients compared to the convalescents. In conclusion, elevated antibody levels against linear peptides derived from residues 90-325 and 405-419 of EBV EBNA1 were the most distinctive characteristics in our cohort of post-COVID-19 syndrome patients.