Abstract
Monoclonal antibodies to the haemagglutininneuraminidase (HN), fusion (F), polymerase and nucleocapsid polypeptides of Newcastle disease virus were prepared. Two epitopes were recognized on the HN polypeptide: one was associated with inhibition of haemagglutination and poor neutralization and the other with good neutralization and no inhibition of haemagglutination. The most effective neutralizing antibody was that produced against the F polypeptide. The poorer neutralization associated with the antibody against the HN epitope was augmented by antiglobulin or complement. The monoclonal antibodies that inhibited haemagglutination also inhibited neuraminidase activity when fetuin but not neuraminyl lactose was the substrate.