Biological Activities of Monoclonal Antibodies to the Hemagglutinin-Neuraminidase (HN) Protein of Newcastle Disease Virus

Abstract

Eleven monoclonal antibodies to the HN protein of NDV strain Sato were established and used to elucidate the functions and antigenic structure of the HN molecule. Seven of these antibodies showed various patterns of inhibition against biological functions of the virus; whereas, 4 antibodies did not inhibit any viral function tested. The differences in the inhibition patterns of the antibodies were not apparently due to differences in avidity for viral antigen. One antibody inhibited viral neuraminidase but not hemagglutination, thus supporting the concept of spatially distinct active sites for hemagglutination and neuraminidase on the HN protein molecule of paramyxoviruses. This anti-neuraminidase antibody did not show neutralization activity unless it was reacted with virus before attachment of the virus to the cells, indicating that neuraminidase may play a role at the initial stage of infection. One antibody inhibited hemagglutination, neuraminidase and hemolysis but not infectivity of the virus; whereas, another antibody inhibited neither hemagglutination nor neuraminidase but inhibited hemolysis and infectivity. These findings may suggest possible differences in the cellular receptors or membrane structure between erythrocyte and host cell, or alternative mechanism of viral neutralization by anti-HN antibodies which may not involve inhibition of viral attachment or neuraminidase.