Epitope variation in the Newcastle disease virus HN gene under antibody immune selective pressure in cell culture.

The influence of antibody immune selective pressure on Newcastle disease virus (NDV) HN and F gene mutations was studied in cell cultures. NDV field strain TZ060107 was inoculated into chicken embryo fibroblast cells and continuously passaged with (group A) or without (group B) anti-NDV monospecific serum. Each group contained three independent passage series. HN and F genes were amplified and sequenced for the 10th, 20th, 30th, 40th and 50th generations of each serial passage, and compared with the original strain. The results demonstrated that increased HN gene mutations were observed in group A with the antibody than in group B without the antibody. The nonsynonymous (NS) to synonymous (S) mutations ratio was 6 for group A, significantly higher than 3.4 in group B. In group A with the antibody, there were five stable NS mutations in HN gene, three of which (related to aa#353, 521 and 568) were related to known epitopes. There were two stable NS mutations in F gene in group A, but no stable NS mutations in group B. The NS/S ratios of F gene were less than 2.5 for both groups A and B. Our results suggested that the antibody strongly influenced HN gene mutations, while the F gene was less influenced by the same antibody.