Figure. Antibody reactivity to coronavirus (CoV) nucleocapsid (N) protein fragments by ELISA. A set of recombinant protein fragments covering the N protein sequence of human CoV (HCoV)–OC43, HCoV-229E, and severe acute respiratory syndrome (SARS)–CoV were used as antigen; the serum (1:400 dilution) from the participant was tested by ELISA. The fragments include the following HCoVs: HCoV-OC43 N1 (aa 1–119), HCoV-OC43 N2 (aa 120–332), HCoV-OC43 N3 (aa 333–448), HCoV-229E N1 (aa 1–74), HCoV-229E N2 (aa 75–311), HCoV-229E N3 (aa 312–389), SARS-CoV N1 (aa 1–105), SARS-CoV N2 (aa 106–324), and SARS-CoV N3 (aa 325–422). The HCoV-OC43, HCoV-229E, and SARS-CoV fragments were coated at 4 × 10–7 M, 2.5 × 10–3 M, and 8 × 10–8 M, respectively. The N-terminal of the N protein contains a highly conserved motif (FYYLGTGP) found in all CoVs (7). This conserved motif is found in HCoV-OC43 N2, HCoV-229E N2, and SARS-CoV N2 recombinant protein fragments. The sizes of the expressed protein fragments used in this study were confirmed by sodium dodecyl sulfate–polyacrylamide gel electrophoresis. In addition, the reactivity of each protein fragment was confirmed by using Western blot with the anti-His antibody and the respective convalescent-phase serum. The mean optical density (OD) of absorbance at 405 nm (490-nm reference) of duplicate wells is shown. Error bars represent the standard deviation of duplicate wells.