SARS-CoV-2 enzyme-linked immunosorbent assays as proxies for plaque reduction neutralisation tests

Grant A Kay,David J Clark,Sanjeev Krishna,Daniela E Kirwan,Benedict M O Davies,Emanuele Giorgi,Nicholas M Eckersley,Grant L Hughes,Stefanie Menzies,Tim Planche,Sophie I Owen,Luis E Cuevas,Christopher T Williams,Henry M Staines,Edward I Patterson,Emily R Adams

doi:10.1038/s41598-022-07263-8

Abstract

Severe acute respiratory coronavirus 2 (SARS-CoV-2) has spread globally since its emergence in 2019. Most SARS-CoV-2 infections generate immune responses leading to rising levels of immunoglobulins (Ig) M, A and G which can be detected using diagnostic tests including enzyme-linked immunosorbent assays (ELISA). Whilst implying previous SARS-CoV-2 infection, the detection of Ig by ELISA does not guarantee the presence of neutralising antibodies (NAb) that can prevent the virus infecting cells. Plaque reduction neutralisation tests (PRNT) detect NAb, but are not amenable to mass testing as they take several days and require use of SARS-CoV-2 in high biocontainment laboratories. We evaluated the ability of IgG and IgM ELISAs targeting SARS-CoV-2 spike subunit 1 receptor binding domain (S1-RBD), and spike subunit 2 (S2) and nucleocapsid protein (NP), at predicting the presence and magnitude of NAb determined by PRNT. IgG S2 + NP ELISA was 96.8% [95% CI 83.8–99.9] sensitive and 88.9% [95% CI 51.8–99.7] specific at predicting the presence of NAbs (PRNT80 > 1:40). IgG and IgM S1-RBD ELISAs correlated with PRNT titre, with higher ELISA results increasing the likelihood of a robust neutralising response. The IgM S1-RBD assay can be used as a rapid, high throughput test to approximate the magnitude of NAb titre.

Highlights

Severe acute respiratory coronavirus 2 (SARS-CoV-2) has spread globally since its emergence in 2019
Our data show that the IgG subunit 2 (S2) + nucleocapsid protein (NP) enzyme-linked immunosorbent assays (ELISA) provides a sensitive (96.8%) and specific (88.9%) test to predict the presence of SARS-CoV-2 neutralising antibodies (PRNT80 ≥ 1:40)
NP-only IgG ELISAs have performed to those targeting only the S1 antigen in previous e valuations[18,19]. This suggests that anti-NP antibodies are raised as part of a broad immune response, and whilst not directly neutralising, are indicative of the presence of other neutralising immunoglobulins

Summary

Introduction

Severe acute respiratory coronavirus 2 (SARS-CoV-2) has spread globally since its emergence in 2019. Four samples that were only ELISA positive by the IgG S1-RBD assay, did not exhibit a neutralising response (PRNT ≥ 1:40). One sample was positive by both IgG S1-RBD, and IgG S2 + NP ELISA but did not show a neutralising response ( PRNT80 ≥ 1:40).

Results

Conclusion