Use of recombinant nucleocapsid proteins for serological diagnosis of feline coronavirus infection by three immunochromatographic tests

Three types of immunochromatographic assays (ICAs) were designed to detect anti-feline coronavirus (FCoV) antibodies. Recombinant FCoV nucleocapsid protein (rNP) was used as a conjugate or test line in all 3 ICA kits ((CJ)IgG/(T)NP, (CJ)NP/(T)NP, and (CJ)NP/(T)PA). All three ICA kits were capable of detecting anti-FCoV antibodies; however, non-specific positive reactions of anti-FCoV antibody-negative plasma samples with the test line were observed in 2 ICA kits ((CJ)IgG/(T)NP and (CJ)NP/(T)NP), in which rNP was used as the test line. On the other hand, the specific detection of anti-FCoV antibodies was possible in all plasma, serum, whole blood, and ascitic fluid samples using the ICA kit with protein A blotted as the test line ((CJ)NP/(T)PA). In addition, the specificity and sensitivity of ICA ((CJ)NP/(T)PA) were equivalent to those of the reference ELISA. The development of simple antibody test methods using the principle of ICA ((CJ)NP/(T)PA) for other coronavirus and feline viral infections is expected in the future.