The diagnosis of coronavirus infection relies on RT-PCR analysis of upper respiratory and nasopharyngeal specimens. The limited testing capacity and the wide variability of patients’ viral load have so far provided a narrow view of the pervasiveness of the infection among the population. A recently developed coronavirus antigen microarray represents a promising diagnostic and epidemiologic tool for an accurate estimate of the seroprevalence of COVID-19 antibodies. Furthermore, information about antigens’ cross-reactivity and antigenicity of the coronavirus proteins obtained in this study can be applied to vaccine and passive immune therapy development. In this study, 67 antigens across subtypes expressed in either baculovirus or HEK-293 cells were printed on ONCYTE nitrocellulose film slides. Coronavirus spike protein (S), separated receptor-binding (RBD), S1, and S2 domains or whole protein (S1+S2) and nucleocapsid protein (NP), from multiple coronaviruses including SARS-CoV-2, SARS-CoV, MERS-CoV, and the four common cold coronaviruses were among the antigens selected for the investigation. Differential reactivity for these antigens was evaluated with convalescent plasma from PCR-positive individuals (positive group) and sera collected before the COVID-19 pandemic from naïve individuals (negative group). Secondary detection was performed with human IgA and IgG conjugated to quantum dot fluorophores.
This study revealed that despite the high sequence homology of the SARS-CoV-2 nucleocapsid protein with other coronaviruses, very low cross-reactivity could be detected in the negative group. Thus, confirming that little or no immunity exists in the general population against SARS-CoV-2 and that the nucleocapsid protein is a potential target for vaccine development. Epitope characterization can help to further pinpoint antigenicity within the protein sequence. Learn more here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7217240/