Mild COVID-19 elicits early functional plasmablasts and longterm memory B cells while sustaining neutralizing antibody titers

Aim: Evaluate the kinetics of antibody, plasmablasts (PB) and memory B cells (MBCs) from day 7 up to 8 months following mild COVID-19 Methods: This observational study enrolled 31 RT-PCR confirmed acute mild COVID-19 patients longitudinal followed ups at six visits: 0, +7, +14 +28, +56 and +200 days post onset of symptoms (dpos). Antibodies against S1 domain of the spike and N (nucleocapside) proteins of SARSCoV- 2 were evaluated using ELISA, while neutralization was quantified by a commercially available surrogate (sVNT) assay. Specific PB and MBC were assessed by ELISPOT Results: During mild COVID-19, anti-S1, anti-N as well as neutralizing antibodies were elicited during the first 3 weeks pos, reached a peak between 20-30 dpos and decayed slowly, however 80% of patients had detectable neutralizing antibodies at +200 dpos. S1-specific IgA and IgM PB reached their peak around +14 days while IgG slow increased. All patients developed anti-S1 IgG MBCs by one month that peaked at 49 dpos and remained stable up to 245dpos;anti-N IgG MBCs kinetics was similar but their magnitude was reduced. We next correlated humoral with cellular immune responses and found that anti-S1 IgG and IgA titers at visits +14 and +28 days correlated with plasmablast, while there was a poor correlation between antibody titers and MBCs at visit +56 days that was lost at visit +200 days Conclusion: Mild COVID-19 elicits early and long lasting neutralizing antibodies Antigen-specific PB correlated with early antibody titers, while specific MBCs frequencies were stable and independent of antibody titers up to 245 dpos.