Serological studies of infectious bronchitis vaccines against Japanese field isolates of homologous and heterologous genotypes.

The genetic diversity of the partial S1 gene involving the hyper variable region for infectious bronchitis (IB) vaccine strains in Japan were compared with those of IB virus isolated from the field in Japan. Field isolates have mainly been classified into three major genotypes, JP-I, JP-II and JP-III, since 2003; however, the 4/91 genotype was detected from recent field isolates in Japan. The virus neutralization (VN) activity with vaccine immunized serum was investigated to evaluate the protective effects of vaccines against Japanese field isolates. In the results of the VN test, antiserum immunized with the GN and C78 (JP-I), TM-86w and Miyazaki (JP-II) and 4/91 (793B) vaccine strains could neutralize a high rate of field isolates of homologous genotype (75% of field isolates of JP-I, 100% of that of JP-II and 100% of that of 793B, respectively). For field isolates of JP-III, even though there are no homologous genotype vaccine strain, some strains of JP-III were neutralized with immune serum from vaccine strains of the heterologous genotype. In this study, a correlation between serological property and genotype was found for JP-I, JP-II and 793B. Our results suggested that an effective vaccine could be predicted in accordance with the genotype of field isolates.