Antigenic and immunogenic investigation of the virulence motif of the Newcastle disease virus fusion protein

acid sequence (virulence motif) such as RRQKRF at the cleavage site of the precusor fusion (F0) protein. The antigenic and immunogenic characteristics of the virulence motif 112RRQKRF117 in the F0 protein of virulent NDVs were investigated. Epitope mapping analysis revealed that a RRQKRF-specific monoclonal antibody 4G2 recognized the KRF section of the motif. A synthetic peptide bearing the RRQKRF motif reacted strongly with sera from virulent NDV (with RRQKRF motif)-infected chickens. These sera also showed reactivity to peptides bearing other virulence motifs (112KRQKRF117, 112RRQRRF117 and 112RRRKRF117) but not an avirulence motif (112GRQGRL117) by ELISA. The synthetic bearing RRQKRF motif reacted with 60% to 91% of sera taken from surviving chickens on ND outbreak farms but not with sera from vaccinated birds, even though most of the sera had antibody to NDV due to vaccination. This indicates that the virulence motif has the potential to differentiate virulent NDV infected birds from vaccinated birds.