Abstract
BackgroundThe 2019 novel coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 virus (SARS-CoV-2) is a current worldwide threat for which the immunological features after infection need to be investigated. The aim of this study was to establish a highly sensitive and quantitative detection method for SARS-CoV-2 IgG antibody and to compare the antibody reaction difference in patients with different disease severity.ResultsRecombinant SARS-CoV-2 nucleocapsid protein was expressed in Escherichia coli and purified to establish an indirect IgG ELISA detection system. The sensitivity of the ELISA was 100% with a specificity of 96.8% and a 98.3% concordance when compared to a colloidal gold kit, in addition, the sensitivity of the ELISA was 100% with a specificity of 98.9% and a 99.4% concordance when compared to a SARS-CoV-2 spike S1 protein IgG antibody ELISA kit. The increased sensitivity resulted in a higher rate of IgG antibody detection for COVID-19 patients. Moreover, the quantitative detection can be conducted with a much higher serum dilution (1:400 vs 1:10, 1:400 vs 1:100). The antibody titers of 88 patients with differing COVID-19 severity at their early convalescence ranged from 800 to 102,400, and the geometric mean titer for severe and critical cases, moderate cases, asymptomatic and mild cases was 51,203, 20,912, and 9590 respectively.ConclusionThe development of a highly sensitive ELISA system for the detection of SARS-CoV-2 IgG antibodies is described herein. This system enabled a quantitative study of rSARS-CoV-2-N IgG antibody titers in COVID-19 patients, the occurrence of higher IgG antibody titers were found to be correlated with more severe cases.
Highlights
The 2019 novel coronavirus disease represents a worldwide health challenge
The identity of the rSARS-CoV-2-N protein was further confirmed via western blotting using with SARSCoV-2-immunized mouse serum and COVID-19 patient serum (Fig. 2)
Optimization of rSARS‐CoV‐2‐N based Immunoglobulin G (IgG) Enzyme linked immunosorbent assay (ELISA) To determine the amount of rSARS-CoV-2-N protein for coating and the dilutions of serum samples for the indirect IgG ELISA, checker board titration was performed by coating 2-fold serially diluted rSARS-CoV-2-N protein from 200 ng/well to 12.5 ng/well and serum 2-fold serially diluted from 1:100 to 1:800
Summary
The 2019 novel coronavirus disease (named COVID-19 by the World Health Organization) represents a worldwide health challenge. As of July, 2003, 8096 SARS cases and 774 deaths in 29 countries were reported, with a total fatality rate of 9.6% [3]. MERS is still not under control, to date, it has caused 2494 confirmed cases and 858 deaths in 27 countries, with a case fatality rate of 34.4% [4]. The mortality rate of COVID-19 is not as high as SARS and MERS, it has become a major threat to global public health due to the large number of cases. A total of 125 million COVID-19 cases were reported to have occurred globally by the end of March 2021. The 2019 novel coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 virus (SARS-CoV-2) is a current worldwide threat for which the immunological features after infection need to be investigated. The aim of this study was to establish a highly sensitive and quantitative detection method for SARSCoV-2 IgG antibody and to compare the antibody reaction difference in patients with different disease severity
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