Comparative Analysis of Antigen-Specific Anti–SARS-CoV-2 Antibody Isotypes in COVID-19 Patients

Abstract

Serological tests for detection of anti–severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Abs in blood are expected to identify individuals who have acquired immunity against SARS-CoV-2 and indication of seroprevalence of SARS-CoV-2 infection. Many serological tests have been developed to detect Abs against SARS-CoV-2. However, these tests have considerable variations in their specificity and sensitivity, and whether they can predict levels of neutralizing activity is yet to be determined. This study aimed to investigate the kinetics and neutralizing activity of various Ag-specific Ab isotypes against SARS-CoV-2 in serum of coronavirus disease 2019 (COVID-19) patients confirmed via PCR test. We developed IgG, IgM, and IgA measurement assays for each Ag, including receptor-binding domain (RBD) of spike (S) protein, S1 domain, full-length S protein, S trimer, and nucleocapsid (N) domain, based on ELISA. The assays of the S protein for all isotypes showed high specificity, whereas the assays for all isotypes against N protein showed lower specificity. The sensitivity of all Ag-specific Ab isotypes depended on the timing of the serum collection and all of them, except for IgM against N protein, reached more than 90% at 15–21 d postsymptom onset. The best correlation with virus-neutralizing activity was found for IgG against RBD, and levels of IgG against RBD in sera from four patients with severe COVID-19 increased concordantly with neutralizing activity. Our results provide valuable information regarding the selection of serological test for seroprevalence and vaccine evaluation studies.

Antibody responses to BNT162b2 vaccination in Japan: Monitoring vaccine efficacy by measuring IgG antibodies against the receptor binding domain of SARS-CoV-2

“…The levels of RBD-IgG in serum after the second vaccination showed a higher correlation with the virus-neutralizing activity compared with that of the other isotypes. A previous study which used COVID-19 patient serum showed that the levels of RBD-IgG were useful markers for diagnosing SARS-CoV-2 infection and neutralizing activity (16). These data indicate that the second dose vaccination potentiates neutralizing activity against COVID-19.…”

“…All procedures were performed in accordance with the manufacturer's instructions. IgM and IgA in serum samples were measured using ELISA assays that were developed in the previous study (16). Briefly, 96-well plates (Thermo Fisher Scientific) were coated with 250 ng of recombinant RBD protein (Acro Biosystems) and used for ELISA assays.…”

“…The neutralizing assay was conducted according to the method described in a previous report with minor modifications (16,17). Briefly, serum samples were heat-inactivated at 56°C for 30 min and then serially diluted with Dulbecco's Modified Eagle medium (FUJIFILM Wako Pure Chemical) supplemented with 2% fetal bovine serum (Biowest), 100 U/mL penicillin and 100 mg/mL streptomycin (Thermo Fisher Scientific).…”

“…Also, to monitor the efficacy of a vaccine by measuring antibodies against SARS-CoV-2 in the clinical laboratory, it is necessary to measure antibodies that are highly correlated with the serum neutralizing activity. A previous study from our group determined the kinetics and neutralizing activity of various antigen-specific antibody isotypes against SARS-CoV-2 in the serum of patients with COVID-19 (16). This study used enzyme-linked immunosorbent assay (ELISA) to measure IgG, IgM, and IgA for various antigens, including the full-length S, S1, receptor binding domain (RBD), and nucleocapsid (N) proteins.…”

12-month SARS-CoV-2 antibody persistency in a Tyrolean COVID-19 cohort

“…In contrast to the above antigens, antibodies against RBD showed a stable development over 12 months after infection and correlated strongest with NAb titres. The fact that this assay not only determines IgG but also IgA and IgM might explain this observation apart from RBD seeming to be the strongest driver of humoral immunity [ 17 ]. Although IgG is the most long-lasting subclass some people also develop persistent IgM and IgA [ 10 ].…”