Recombinant SARS-CoV-2 Nucleocapsid Protein (a.a.1-419) [His]

Author summary The world is facing an unprecedented challenge with communities and economies affected by the growing pandemic of coronavirus disease 2019 (COVID-19). Currently, there is no vaccine or effective drugs have been approved to treat or prevent COVID-19. The development of antibody response to SARS-CoV-2, the virus that causes COVID-19, started to be reported but remained largely elusive. Understanding the adaptive responses where the body makes antibodies that specifically bind to the SARS-CoV-2 among COVID-19 patients provides fundamental information for developing effective treatment and preventive vaccine. In this study, we not only successively analyzed the specificity and magnitude of antibody responses using four SARS-CoV-2 related antigens, but also monitored the neutralization potency of the convalescent sera from COVID-19 patients at the time point of hospital discharge and follow-up visit. Our results indicated that most patients generated humoral responses against nucleoprotein and three spike protein-related antigens with their distinct kinetics profiles. Additionally, most convalescent sera had the varying extents of neutralization activities against SARS-CoV-2. Of note, we identified that IgA antibody responses specific to S1 and ECD were strongly correlated with neutralization activities in non-severe patients, but not in severe patients. Furthermore, we identified a significant reduction of neutralizing activities of the convalescent sera within one month. Our data provide a collective basis of serological testing, antibody-based intervention, and vaccine design of COVID-19. There is an urgent need for effective treatment and preventive vaccine to contain this devastating global pandemic, which requires a comprehensive understanding of humoral responses specific to SARS-CoV-2 during the disease progression and convalescent phase of COVID-19 patients. We continuously monitored the serum IgM and IgG responses specific to four SARS-CoV-2 related antigens, including the nucleoprotein (NP), receptor binding domain (RBD), S1 protein, and ectodomain (ECD) of the spike protein among non-severe and severe COVID-19 patients for seven weeks since disease onset. Most patients generated humoral responses against NP and spike protein-related antigens but with their distinct kinetics profiles. Combined detection of NP and ECD antigens as detecting antigen synergistically improved the sensitivity of the serological assay, compared to that of using NP or RBD as detection antigen. 80.7% of convalescent sera from COVID-19 patients revealed that the varying extents of neutralization activities against SARS-CoV-2. S1-specific and ECD-specific IgA responses were strongly correlated with the neutralization activities in non-severe patients, but not in severe patients. Moreover, the neutralizing activities of the convalescent sera were shown to significantly decline during the period between 21 days to 28 days after hospital discharge, accompanied by a substantial drop in RBD-specific IgA response. Our data provide evidence that are crucial for serological testing, antibody-based intervention, and vaccine design of COVID-19.

Objectives: In the context of the coronavirus disease 2019 (COVID-19) pandemic, the development and validation of rapid and easy-to-perform diagnostic methods are of high priority. This study was performed to evaluate a novel rapid antigen detection test (RDT) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in respiratory samples. Methods: The fluorescence immunochromatographic SARS-CoV-2 antigen test (Bioeasy Biotechnology Co., Shenzhen, China) was evaluated using universal transport medium with nasopharyngeal (NP) and oropharyngeal (OP) swabs from suspected COVID-19 cases. Diagnostic accuracy was determined in comparison to SARS-CoV-2 real-time (RT)-PCR. Results: A total of 127 samples were included; 82 were RT-PCR-positive. The median patient age was 38 years, 53.5% were male, and 93.7% were from the first week after symptom onset. Overall sensitivity and specificity were 93.9% (95% confidence interval 86.5-97.4%) and 100% (95% confidence interval 92.1-100%), respectively, with a diagnostic accuracy of 96.1% and Kappa coefficient of 0.9. Sensitivity was significantly higher in samples with high viral loads. Conclusions: The RDT evaluated in this study showed a high sensitivity and specificity in samples mainly obtained during the first week of symptoms and with high viral loads, despite the use of a non-validated sample material. The assay has the potential to become an important tool for early diagnosis of SARS-CoV-2, particularly in situations with limited access to molecular methods. (C) 2020 The Authors. Published by Elsevier Ltd on behalf of International Society for Infectious Diseases.