Fig. 2
Antibody reactivity to SARS-CoV-2 proteins in cats in Japan. Antibody reactivity was measured by an ELISA using protein-A/G conjugated with horseradish peroxidase (protein-A/G-based ELISA). The absorbance at 492 mm (A492) was normalized to that for positive control rabbit sera. Samples with a value higher than the cut-off were considered positive. The circles indicate individual tested samples. The star indicates a sample showing SARS-CoV-2 neutralizing activity in a neutralizing antibody assay. a Antibody reactivity to the S1 protein among 1,969 samples. The mean A492 ± SD of 145 negative control samples was 0.133 ± 0.111 A492, and the cut-off value (mean + 3 SDs) was 0.469 A492, shown as a dotted line. b Antibody reactivity to the RBD protein in 9 samples that were positive for anti-S1-protein antibody. The mean A492 ± SD of 28 negative control samples without specific selection was 0.231 ± 0.267 A492, and the cut-off (mean + 3 SDs) was 1.033 A492, shown as the dotted line. We screened 75 samples, namely, 9 positive samples and 66 negative samples in the protein-A/G-based ELISA, detecting anti-S1-protein antibody. c Comparison of antibody reactivities with those to the S1 protein, as measured by protein-A/G-based ELISA. Among the 9 samples positive in the protein-A/G-based ELISA detecting anti-S1-protein antibodies, 4 cats showed antibody reactivity to the RBD protein