Development of Capture-ELISA Assays to Measure the Humoral Responses to SARS-CoV-2 Nucleocapsid and Spike Proteins

Abstract

Diagnosis of the newly emerged Sever Acute Respiratory Syndrome 2 (SARS-CoV-2) since the start of the pandemic in 2020 is heavily reliant on sequence amplification by the Polymerase Chain Reaction (PCR) technique. However, this technique has limitations. Besides the fact that it requires especially skilled operators and costly equipment, low viral load might mislead to a false-negative result. Other serological techniques are used to confirm SARS-CoV-2 infection by detecting anti- spike (S1) antibodies, presenting difficulties in differentiation between infected cases from individuals vaccinated with S1 and producing increasing levels of anti-S1 antibodies. We aimed to develop a capture-ELISA that targets and detects anti-nucleoprotein (NP) IgG and IgM to confirm natural infection of SARS-CoV-2. We were able to detect anti-NP IgG and IgM antibodies with a specificity of 100% and 89%, respectively. This assay has also showed a sensitivity of 83% to detecting anti-NP SARS-CoV-2 IgG antibodies and 90% to detecting IgM antibodies. We were looking to increase the understanding of the development of IgA antibodies to SARS-CoV-2, through designing a capture-ELISA. We detected anti-S1 IgA antibodies in serum of confirmed infected cases, with a specificity of 100% and 79% sensitivity. We found that those developed IgA antibodies increase early after symptoms appearance and decline a month later. Additionally, severe cases of SARS-CoV-2 infection seem to develop strong, high levels of anti-S1 IgA antibodies when compared to mild cases. The two capture-ELISAs developed in this research can be optimized in the future to confirm SARS-CoV-2 infection from simply on-site collected samples including, saliva and dried blood spots (DBS), as well as from serum. This is to further simplify investigating ongoing SARS-CoV-2 infection through detection of anti-NP IgG and IgM antibodies and anti-S1 IgA antibodies.