Figure 2.

Binding, neutralization, and avidity profiles of antibodies from individuals in the “convalescent” group. A, Analysis of different antibody isotypes (immunoglobulin [Ig] G, IgM, and IgA) against wild-type (WT) spike measured using our in-house enzyme-linked immunosorbent assay (ELISA; n = 40). Abbreviation: AUC, area under the curve. B, IgG levels measured using the SeroKlir commercial ELISA from Kantaro Biosciences (n = 40). Abbreviation: AU, arbitrary units. C, Neutralization titers against USA-WA1/2020 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), expressed as the inhibitory dilution 50% (ID₅₀; n = 40). D, Antibody avidity, expressed as avidity index (AI), against the spike, the receptor-binding domain (RBD), and the nucleoprotein (NP) (n = 40). In D, samples with AIs <35, indicated by the dotted lines, are considered to have low avidity. WT refers to the sequence of the original Wuhan-Hu-1 SARS-CoV-2 isolate. Samples were stratified based on their initial IgG anti-spike antibody response measured in a Mount Sinai Clinical Laboratory Improvement Amendments–certified laboratory and categorized as low (+; titer, 1:80 or 1:160), moderate (++; titer, 1:320), or high (+++; titer, 1:960 or ≥1:2880). Each symbol represents a single participant. A Mann-Whitney U test for comparisons among different groups was performed. In A–C, the limit of detection is indicated by the horizontal dotted line. *P < .03; **P < .002; ***P < .001. Bars represent geometric means; error bars, geometric standard deviations.