Antigenic relationships among homologous structural polypeptides of porcine, feline, and canine coronaviruses.

Horzinek, M C; Lutz, H; Pedersen, N C

Transmissible gastroenteritis virus of swine (TGEV), feline infectious peritonitis virus (FIPV), and canine coronavirus were studied with respect to their serological cross-reactivity in homologous and heterologous virus neutralization, immune precipitation of radiolabeled TGEV, electroblotting, and enzyme-linked immunosorbent assay using individual virion polypeptides prepared by polyacrylamide gel electrophoresis. TGEV was neutralized by feline anti-FIPV serum, and the reaction was potentiated by complement; heterologous neutralization involved antibody reacting with the peplomer protein (P), the envelope protein (E), and cellular (glycolipid) components incorporated into the TGEV membrane. Electrophoretic analysis of immune precipitates containing [35S]methionine-labeled disrupted TGEV and feline anti-FIPV antibody confirmed the reaction with the P and E polypeptides and showed the nucleocapsid protein (N) in addition. Electroblotting, followed by incubation with antibody, 125I-labeled protein A, and fluorography, disclosed cross-reactions between the three viruses at the N and E levels and revealed differences in the apparent molecular weights of the latter. Enzyme immunoassays performed with standard amounts of immobilized P, N, and E polypeptides of the three viruses showed recognition of the antigens by homologous and heterologous antibody to comparable degrees. These results indicate a close antigenic relationship between TGEV, FIPV, and canine coronavirus due to common determinants on the three major virion proteins. The taxonomic implications of these findings are discussed.