Antigenic characterization of the internal proteins of Newcastle disease virus by monoclonal antibodies.

We have prepared and characterized monoclonal antibodies against the three internal structural proteins, M, P and NP, of Newcastle disease virus. At least two non-overlapping antigenic sites were delineated on the M protein, four on the P, and two on the NP by competitive binding assay. One of the two non-overlapping antigenic sites on the M protein was found to be a cluster of at least three distinct epitopes. Enhancement of antibody binding by the binding of a second antibody was observed with the M protein. The reactivity of these monoclonal antibodies with heterologous strains was studied by enzyme-linked immunosorbent assay. The results indicated that there are both highly conserved antigenic sites and those subject to remarkable change on both M and P proteins. On the other hand, NP appeared to be antigenically more stable.