Abstract
The capability to detect Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection and identify immune responses among the population is crucial for managing the outbreak of the COVID-19 pandemic. Although PCR-based nucleic acid detection techniques are utilized to detect viral infection in people, alternative tests capable of distinguishing between exposure and infection are urgently needed beyond this restricted window of detectable viral replication. Antibodies are produced in human sera within a few days after viral infection, providing longer period for performing tests to acquire reliable database. Herewith, we provide the results of our in-house developed ELISA (Enzyme-Linked Immunosorbent Assay) that displays all of the properties necessary for high-throughput of human sera sample analysis. This test does not involve the handling of live viruses, although it detects a variety of antibody types in serum and plasma of human after exposure to the virus. For in-house development of the kit, the nucleocapsid (N) gene of SARS-CoV-2 virus was cloned in the prokaryotic expression vector pGEX-6P-1, and purified N protein was used to detect IgG antibodies in human sera samples. In total 76 human serum samples that were collected before novel coronavirus registry in Mongolia in March 2020, as well as 200 serum samples from patients who had been infected by SARS-CoV-2 virus, were used. Among 200 serum samples, 188 were positive and 12 were false negative, while in non-infected cases 69 were negative and 7 were false positive, suggesting 94 per cent sensitivity and 90.7 per cent specificity of the kit, with p-values of 0.02.
Highlights
The first case of atypical human pneumonia and its causative virus named as Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), which causes Coronavirus Disease 2019 (COVID-19), was reported in Wuhan, People’s Republic of China in December 2019 [1]
The S protein located on the surface of the viral particle is required for virus attachment to host cells, mediating the interaction with the angiotensin-converting enzyme 2 (ACE2) with the receptor binding domain of S protein [7]
It is in place to note that N protein was not separated from Glutathione S-transferase, since we did not observe any distinction in the absorbance of ELISA results between fusion protein and N protein after cleavage
Summary
The first case of atypical human pneumonia and its causative virus named as Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), which causes Coronavirus Disease 2019 (COVID-19), was reported in Wuhan, People’s Republic of China in December 2019 [1]. SARS-CoV-2 is a betacoronavirus and the seventh member of the Coronaviridae family of viruses [1] It is an enveloped virus with positive stranded RNA which contains ORF1a, ORF1b and genes of major structural proteins, such as envelope (E), spike (S), membrane (M) and nucleocapsid (N) [4]. As for N protein, it is the crucial structural protein of the virus and is functionally served in the expression of the virus RNA, packaging of virions [8] [9] as well as intervening with the host cell cycle processes [10]. Both S and N proteins are highly immunogenic and are profusely expressed during infection [11]
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