Development of a high-sensitivity ELISA detecting IgG, IgA and IgM antibodies to the SARS-CoV-2 spike glycoprotein in serum and saliva.

Sian Faustini ,Alex Cook ,Carrie R Willcox ,Sian Jossi ,Margaret Goodall ,Maddy L Newby ,Max Crispin ,Joel D Allen ,Stephen Jolles ,Gabriella L Morley ,Aarnoud Huissoon ,Mark T Drayson ,Adam F Cunningham ,Barbara Torlińska ,Tonny Veenith ,Adrian Shields ,David C Wraith ,Edith Marcial‐Juárez ,Benjamin E Willcox ,Mahboob Salim ,Marisol Pérez-Toledo ,Jennifer Heaney ,Tim Plant ,Yasunori Watanabe ,Matthew K O’shea ,Stephen Harding ,Mark Ponsford ,Alex Richter

doi:10.1111/imm.13349

Abstract

Detecting antibody responses during and after SARS‐CoV‐2 infection is essential in determining the seroepidemiology of the virus and the potential role of antibody in disease. Scalable, sensitive and specific serological assays are essential to this process. The detection of antibody in hospitalized patients with severe disease has proven relatively straightforward; detecting responses in subjects with mild disease and asymptomatic infections has proven less reliable. We hypothesized that the suboptimal sensitivity of antibody assays and the compartmentalization of the antibody response may contribute to this effect. We systematically developed an ELISA, optimizing different antigens and amplification steps, in serum and saliva from non‐hospitalized SARS‐CoV‐2‐infected subjects. Using trimeric spike glycoprotein, rather than nucleocapsid, enabled detection of responses in individuals with low antibody responses. IgG1 and IgG3 predominate to both antigens, but more anti‐spike IgG1 than IgG3 was detectable. All antigens were effective for detecting responses in hospitalized patients. Anti‐spike IgG, IgA and IgM antibody responses were readily detectable in saliva from a minority of RT‐PCR confirmed, non‐hospitalized symptomatic individuals, and these were mostly subjects who had the highest levels of anti‐spike serum antibodies. Therefore, detecting antibody responses in both saliva and serum can contribute to determining virus exposure and understanding immune responses after SARS‐CoV‐2 infection.

Highlights

COVID-1 9, caused by SARS-C oV-2, has resulted in millions of cases and more than 400 000 deaths around the world [1]
There were three groups of subjects analysed: hospitalized subjects (HS, N = 14), which included individuals who were admitted to the hospital and had confirmed SARS-C oV-2 infection by PCR; non-h ospitalized convalescent (NHC, N = 39) subjects, who were patients with confirmed SARS-C oV-2 infection by PCR but were not hospitalized; and asymptomatic non-hospitalized convalescent patients (AS, N = 6), who were individuals without reported symptoms who gave a positive result for SARS-C oV-2 infection by PCR
If post-infection complications arise from COVID-19, the availability of high-quality assays to detect prior infection will be of obvious benefit

Summary

Introduction

COVID-1 9, caused by SARS-C oV-2, has resulted in millions of cases and more than 400 000 deaths around the world [1]. The development of novel antibody tests requires a comprehensive understanding of the humoral response to a specific pathogen across the spectrum of disease caused by that pathogen. An important factor is the variable clinical presentation of infection that can influence the concentration of antibody induced within a subject. Understanding antibody responses in individuals with the lowest symptomatology will be of major importance for monitoring viral transmission within this SARS-CoV-2 pandemic [2]. Antigen choice and purity are other elements that can influence performance of the assay, not least by detecting cross-reactive antibodies induced by previous infection to other coronaviruses.[4] the development of assays to detect low levels of antiviral antibodies need to consider multiple variables in order to be of use in seroepidemiological studies

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Conclusion