a Signal intensity (absorbance) sorted by IgG (blue). b Thresholding of seropositivity in small-scale test cohort for SARS-CoV-2 IgG, black = archival negative controls, red = known PCR-diagnosed positive controls, green = test cohort. c Signal intensity (absorbance) sorted by IgM (orange). d Thresholding of seropositivity in small-scale test cohort for SARS-CoV-2 IgM. e Relation between IgM expression and IgG expression of spike and RBD antigens. f Seropositivity in non-symptomatic individuals who have not tested (PCR) positive for SARS-CoV-2 infection show robust IgG expression in absence of symptoms. n = 68 symptomatic donors, n = 6 non-symptomatic donors, IgG = blue, IgM = yellow, IgA = green. Source data are provided as a Source Data file.