Isolation and characterization of monoclonal antibodyresistant mutants of Newcastle disease virus

Neutralizing monoclonal antibodies incorporated into plaque assay overlay medium were used to select antibody-resistant (Ab ~) mutants of both the Herts (using anti-fusion protein monoclonal 481) and Beaudette C (using anti-haemagglutinin-neuraminidase protein monoclonal 445) strains of Newcastle disease virus at the permissive temperature of 34 °C. Certain of the Herts, but none of the Beaudette C, Ab R mutants were also temperature-sensitive (ts-) and failed to form plaques at the non-permissive t mperature of 41.5 °C. pS]Methionine-labelled proteins from chick embryo fibroblasts infected with wild-type, ts ÷ Ab R and ts- Ab R virus when separated by two-dimensional polyacrylamide g l electrophoresis revealed a variety of changes in the isoelectric point of the fusion protein F (using monoclonal 481) and the haemagglutinin-neuraminidase protein HN (using monoclonal 445). The ts ÷ 'rever-tants ' of ts- Ab R mutants remained Ab R and also showed changed isoelectric points in the F protein. Monoclonal antibodies raised against viruses are of value in identifying virus antigens in virus-infected cells, in aiding purification of virus proteins by affinity chromatograph