Kinetics of SARS-CoV-2 Antibody Avidity Maturation and Association with Disease Severity

Luo, Y. R.; Chakraborty, I.; Yun, C.; Wu, A. H. B.; Lynch, K. L.

The kinetics of immunoglobulin G (IgG) avidity maturation during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was studied. The IgG avidity assay used a novel label-free immunoassay technology to test IgG against the virus spike protein receptor-binding domain (RBD). The technology, thin-film interferometry (TFI), is able to sense the formation of immune complex on a sensing probe without attaching a reporter (enzyme, fluorophore, etc.). It was found that there was a strong correlation between IgG antibody avidity and days since symptom onset (p < 0.0001). In addition, peak readings were significantly higher for specimens from ICU than non-ICU patients for the first month after symptom onset (1-4 weeks) and thereafter (p<0.0001). The findings are consistent for what has been reported for SARS-CoV. Given that SARS-CoV-2 specific IgG avidity is strong in ICU patients after 1 month, this suggests that antibody-mediated immune enhancement triggered by suboptimal antibodies may not play a role in COVID-19 disease progression and severity.