Antigen production and development of an indirect ELISA based on the nucleocapsid protein to detect human SARS-CoV-2 seroconversion

Conzentino, M. d. S.; Forchhammer, K.; Souza, E. M.; Pedrosa, F. d. O.; Nogueira, M. B.; Raboni, S. M.; Rego, F. G. M.; Zanette, D. L.; Aoki, M. N.; Nardin, J. M.; Fornazari, B.; Morales, H. M. P.; Celedon, P. A. F.; Lima, C. V. P.; Mattar, S. B.; Lin, V. H.; Morello, L. G.; Marchini, F. K.; Bueno, L. B.; Reis, R. A.; Huergo, L.

Serological assays are important tools to identify previous exposure to SARS-CoV-2, helping to track COVID-19 cases and determine the level of humoral response to SARS-CoV-2 infections and/or immunization to future vaccines. Here the SARS-CoV-2 nucleocapsid protein was expressed in Escherichia coli and purified to homogeneity and high yield using a single chromatography step. The purified SARS-CoV-2 nucleocapsid protein was used to develop an indirect enzyme-linked immunosorbent assay for the identification of human SARS-CoV-2 seroconverts. The assay sensitivity and specificity were determined analyzing sera from 140 PCR-confirmed COVID-19 cases and 210 pre-pandemic controls. The assay operated with 90% sensitivity and 98% specificity; identical accuracies were obtained in head-to-head comparison with a commercial ELISA kit. Antigen coated plates were stable for up to 3 months at 4oC). The ELISA method described is ready to mass production and will be an additional toll to track COVID-19 cases.