Pathogenicity of antigenic variants of Newcastle disease virus Italian strain selected with monoclonal antibodies.

: Antigenic variants of the Italian strain of NDV were selected using monoclonal antibodies directed against the HN and F proteins of Italian virus. Antigenic mapping of the HN and F proteins using variant viruses in cross neutralization tests revealed the presence of at least two different epitopes on HN and four epitopes on F protein. Immunoselected variant viruses were demonstrated to have different intravenous pathogenicity index than the parental Italian virus.