Pathotyping isolates of Newcastle disease virus using antipeptide antibodies to pathotype-specific regions of their fusion and hemagglutinin-neuraminidase proteins

Summary

Antipeptide antibodies have been evaluated for their abilities to predict the characteristics of the cleavage motifs of the fusion protein precursors (F₀) of 25 isolates of Newcastle disease virus (NDV) with a range of virulences, grouped into 12 sets according to their monoclonal antibody reactivities. A Western blot format was used to show that antisera to synthetic peptides representing sequences at the C-termini of the F₂-polypeptides of defined pathotypes of NDV usually distinguish between pathotypes on the basis of their Fo cleavage sequences. However, exceptions were found with three groups of virulent isolates. Protein sequencing and mass spectral analysis of the F₂-polypeptide of isolate Texas GB from one of these groups, identified an anomalous cleavage/activation process which removed the amino acids required for recognition by the antisera. This probably also explained the lack of reactivity of the Roakin isolate and low reactivity of the Komarov isolate from this group. The other exceptions involved isolates in groups with cleavage region variations from the usual motif of virulent isolates or isolates with undefined cleavage motifs. Antipeptide antisera were also raised to sections of the 45 residue C-terminal extension the hemagglutinin-neuraminidase precursor (HN₀) encoded by the genes of some avirulent isolates. Western blot analysis showed that positive reactions with antibodies to peptides based on sequences between residues 577 and 613 of the HN₀ was evidence for the presence of an avirulent isolate but did not exclude the presence of other pathotypes. Antisera designed to target residues 569–577 detected HN₀ extensions of 6 residues on isolates known to encode such extensions. These antisera also enabled differentiation of isolates with HN₀ extensions of 6 residues from those with no extension, however, it was not possible to determine the virulence of isolates based on reaction with these antisera.