SARS-CoV-2 IgG Antibody Detection Assay

The qualitative detection (IgG screening) and semi-quantitative (U/mL) detection of IgG class antibodies against SARS-CoV-2 were undertaken using the BioPlex 2200 SARS-CoV-2 IgG Panel (Bio-Rad Laboratories, Inc., Hercules, CA, USA). This device can screen and differentiate IgG antibodies to the receptor-binding domain (RBD) and the spike 1 (S1), spike 2 (S2), and nucleocapsid proteins (N) of the SARS-CoV-2 coronavirus [19 ,20 (link)]. The positive anti-SARS-CoV-2 N/RBD/S1/S2 IgG levels were set to ≥10 U/mL, particularly for levels that were above 100 U/mL, and the machine provided 1:16 dilutions of the anti-IgG levels. The machine’s upper limit of values obtained from the dilutions was set at 1600 U/mL. All of the calculations necessary to interpret the results were performed automatically by Plex^TM 2200 System Software (Bio-Rad, USA) [19 ,20 (link),21 (link)].