ABSTRACT
Background: About 10% of individuals with mild infection with SARS-CoV-2 suffer from Long COVID-19, defined as signs and symptoms developed during or following COVID-19 that continue for more than twelve weeks and cannot be explained by an alternative diagnosis. In this study, we analyzed the ADCC response and the reactivation of CMV and EBV in Long COVID-19 syndrome, in comparison with patients who completely recovered from mild COVID-19 Methods: 30 patients with Long COVID-19 (Long COVID-19) and 20 individuals who suffered mild COVID-19 and were completely recovered (Recovered) were recruited for this study. Specific anti-SARS-CoV-2 IgG titers were analyzed by direct ELISA and their neutralizing capability was measured by using pseudovirus neutralization assay. Phenotype of CD4+ and CD8+ T cells, NK, NKT, and B cells in peripheral blood was analyzed by flow cytometry. ADCC activity was analyzed using rituximab-coated Raji cells as target. EBV and CMV reactivation in plasma was analyzed by qPCR. Results: 1) 86.6% and 55.50% participants were female in Long COVID-19 and Recovered cohorts, respectively. Median age at COVID-19 diagnosis was 42y(IQR 37-46) and 45y (IQR 28-57), respectively. 2) Similar levels of CD4+ T cells were observed in both groups. However, Tregs were increased 2.8-fold in Long COVID-19 participants (p=0.0007). 3) CD8+ T cells, CD8+TCRγδ and CD8+TCRγδ were increased 1.3-(p=0.0005), 2.0-(p=0.049), and 2.5-fold (p=0.005) in Long COVID-19 individuals. 4) Expression of CD56 in NK cells and CD3-CD56+CD16+ cells were increased 1.7-(p=0.0005) and 1.7-fold (p=0.032) in Long COVID-19, respectively. 5) Specific anti-SARS-CoV-2 IgG titers were increased 2.3-fold in Long COVID-19 individuals (p=0.02) and their neutralizing capacity was increased 4.2-fold (p=0.034) in this cohort. However, ADCC activity was decreased 1.4-fold (p=0.0044). 6) Resting memory B cells were increased 2.3-fold during Long COVID-19, whereas plasmablasts were reduced 3.1-fold. 7) EBV was reactivated in 33.3% of Long COVID-19 individuals (p<0.0001), whereas CMV was not reactivated in any individual. Conclusion: Despite high levels of neutralizing antibodies and cytotoxic immune populations, an impaired antibody-dependent cytotoxic activity was observed in PBMCs from individuals with Long COVID-19. This defective cytotoxic immune response may impede viral clearance, which may also contribute to EBV reactivation observed in these individuals, thereby influencing on the persistent COVID-19 symptoms.