Abstract
The bovine enteric caliciviruses Bo/Jena/1980/DE and Bo/Newbury2/1976/UK represent two distinct genotypes within a new genogroup, genogroup III, in the genus Norovirus of the family Caliciviridae. In the present study, the antigenic relatedness of these two genotypes was determined for the first time to enable the development of tests to detect and differentiate between both genotypes. Two approaches were used. First, cross-reactivity was examined by enzyme-linked immunosorbent assay (ELISA) using recombinant virus-like particles (VLPs) and convalescent-phase sera from calves infected with either Jena (genotype 1) or Newbury2 (genotype 2). Second, cross-reactivity was examined between the two genotypes with a monoclonal antibody, CM39, derived using Jena VLPs. The two genotypes, Jena and Newbury2, were antigenically distinct with little or no cross-reactivity by ELISA to the heterologous VLPs using convalescent calf sera that had homologous immunoglobulin G titers of log10 3.1 to 3.3. CM39 reacted with both Jena and heterologous Newbury2 VLPs. The CM39 epitope was mapped to nine amino acids (31PTAGAQIAA39) in the Jena capsid protein, which was not fully conserved for Newbury2 (31PTAGAPVAA39). Molecular modeling showed that the CM39 epitope was located within the NH2-terminal arm inside the virus capsid. Surprisingly, CM39 also reacted with VLPs from two genogroup II/3 human noroviruses by ELISA and Western blotting. Thus, although the bovine noroviruses Jena and Newbury2 corresponded to two distinct antigenic types or serotypes, they shared at least one cross-reactive epitope. These findings have relevance for epidemiological studies to determine the prevalence of bovine norovirus serotypes and to develop vaccines to bovine noroviruses.