Anti-SARS-CoV-2 Nucleoprotein Antibodies Derived from Pig Serum with a Controlled Specificity

Antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleoprotein (NP) were purified from pig serum through two steps: (1) isolation of anti-NP IgG antibodies using magnetic beads with immobilized human SARS-CoV-2 NP and (2) filtration of anti-spike protein (SP) IgG antibodies using magnetic beads with immobilized human SARS-CoV SP. The enhanced specificity of the purified antibodies to the NP of SARS-CoV-2 was demonstrated using an immunoassay with anti-NP IgG antibodies after the isolation and filtration steps. The binding constants (Kd) of the purified anti-NP IgG antibodies to the NP of SARS-CoV-2 and the SP of SARS-CoV were estimated using a surface plasmon resonance biosensor (SPR). A competitive assay using the two-step purified anti-NP IgG antibodies from pig serum demonstrated (a) the detection of SARS-CoV-2 in viral fluid and (b) the discrimination of SARS-CoV-2 from SARS-CoV, MERS-CoV, and CoV strain 229E in viral fluids.