Antibodies specific to SARS- CoV-2 proteins N, S and E in COVID-19 patients in the normal population and in historical samples

Severe acute respiratory syndrome coronavirus 2 (SARS- CoV- 2) has spread globally; recognition of immune responses to this virus will be crucial for coronavirus disease 2019 (COVID- 19) control, prevention and treatment. We comprehensively analysed IgG and IgA antibody responses to the SARS- CoV- 2 nucleocapsid protein (N), spike protein domain 1 (S1) and envelope protein (E) in: SARS- CoV- 2- infected patient, healthy, historical and pre- epidemic samples, including patients' medical, epidemiological and diagnostic data, virus- neutralizing capability and kinetics. N- specific IgG and IgA are the most reliable diagnostic targets for infection. Serum IgG levels correlate to IgA levels. Half a year after infection, anti- N and anti- S1 IgG decreased, but sera preserved virus- inhibitory potency; thus, testing for IgG may underestimate the protective potential of antibodies. Historical and pre- epidemic sera did not inhibit SARS- CoV- 2, thus its circulation before the pandemic and a protective role from antibodies pre- induced by other coronaviruses cannot be confirmed by this study