A Combination of N and S Antigens With IgA and IgG Measurement Strengthens the Accuracy of SARS-CoV-2 Serodiagnostics.

Pinja Jalkanen,Jukka Hytönen,Olli Ritvos,Pekka Kolehmainen,Kaisa Rantasärkkä,Krister Melén,Anu Haveri,Satu Kurkela,Moona Huttunen,Maija Lappalainen,Rickard Lundberg,Matti Waris,Pamela Österlund,Lav Tripathi,Laura Kakkola,Suvi Kuivanen,Sari Maljanen,Ilkka Julkunen,Arja Pasternack,Rauno Naves,Sisko Tauriainen,Tytti Vuorinen,Anne J Jääskeläinen ,Hira Khan ,Mikael A Ritvos

doi:10.1093/infdis/jiab222

Abstract

BackgroundPrimary diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is based on detection of virus RNA in nasopharyngeal swab samples. In addition, analysis of humoral immunity against SARS-CoV-2 has an important role in viral diagnostics and seroprevalence estimates.MethodsWe developed and optimized an enzyme immunoassays (EIA) using SARS-CoV-2 nucleoprotein (N), S1 and receptor binding domain (RBD) of the viral spike protein, and N proteins from SARS, Middle East respiratory syndrome (MERS), and 4 low-pathogenic human CoVs. Neutralizing antibody activity was compared with SARS-CoV-2 IgG, IgA, and IgM EIA results.ResultsThe sensitivity of EIA for detecting immune response in COVID-19 patients (n = 101) was 77% in the acute phase and 100% in the convalescent phase of SARS-CoV-2 infection when N and RBD were used as antigens in IgG and IgA specific EIAs. SARS-CoV-2 infection significantly increased humoral immune responses against the 229E and NL63 N proteins. S1 and RBD-based EIA results had a strong correlation with microneutralization test results.ConclusionsThe data indicate a combination of SARS-CoV-2 S1 or RBD and N proteins and analysis of IgG and IgA immunoglobulin classes in sera provide an excellent basis for specific and sensitive serological diagnostics of COVID-19.

Highlights

Primary diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is based on detection of virus RNA in nasopharyngeal swab samples
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causing coronavirus disease 2019 (COVID-19), emerged in December 2019 [1] and the outbreak was declared as a pandemic by the World Health Organization in March 2020 [2]
SARS-CoV-2 is closely related to 2 coronaviruses causing severe respiratory infections in humans, SARS-CoV and Middle East respiratory syndrome (MERS) CoV, of which SARS-CoV shares 79% sequence identity with SARS-CoV-2 [4]

Summary

Methods

We developed and optimized an enzyme immunoassays (EIA) using SARS-CoV-2 nucleoprotein (N), S1 and receptor binding domain (RBD) of the viral spike protein, and N proteins from SARS, Middle East respiratory syndrome (MERS), and 4 lowpathogenic human CoVs. COVID-19 patient serum samples (n = 119) were collected from 40 patients at Turku University Hospital (TYKS, Turku, Finland; data treated according to ethical permission HUS/1238/2020) and 61 patients at Helsinki University Hospital (HUS, Helsinki, Finland; data treated according to ethical permissions HUS/32/2018 and HUS/1238/2020). All patients were confirmed to be SARS-CoV-2 RNA-positive with RT-qPCR test from nasopharyngeal swab samples (at TYKS by Corman assay [14]; and at HUSLAB by either Cobas SARS-CoV-2 test on the Cobas 6800 system [Roche Diagnostics], Amplidiag COVID19 test [Mobidiag], or Corman assay). Selected control samples (n = 100) were collected in early 2019. A pool of COVID-19–negative control samples was selected from a child serum panel described previously [15] and used as a negative control in EIAs. Production and Purification of Recombinant Coronavirus Nucleoproteins

Results

Discussion

Conclusion