Figure 3.

SARS-CoV-2-specific memory B cells in recovered COVID-19 patients. The frequency and isotype distribution of antibody secreting B cells (ASC) was measured in the unexposed subjects (“Unexposed”, n=28) prior to pandemic and in patients (“COVID-19”, n=18) up to 5 months of recovery from mild COVID-19. The memory B cells in PBMCs were polyclonally stimulated before measuring the frequency of SARS-CoV-2 Spike glycoprotein- and Nucleoprotein-specific IgG, IgM and IgA antibody secreting cells in Fluorospot assay. (A) Representative images of IgG, IgM and IgA secreting B cells in Unexposed subject and recovered COVID-19 patient. Graphs depicting the magnitude of antibody secreting B cells specific to the SARS-CoV-2 Spike glycoprotein and Nucleoprotein (expressed as spot forming cells (SFC) in 10⁶ PBMCs) for (B) IgG-ASC (C) IgM-ASC and (D) IgA-ASC, in Unexposed subjects (grey circle) and COVID-19 patients (red circle). For log scale, the spot count of less than one is depicted as 1. Black bars indicate the geometric mean. Statistical comparisons were performed by two-tail Mann-Whitney test. ns: non-significant.