Newcastle disease virus: the effect of monoclonal antibody in the overlay on virus penetration and the immunoselection of variants.

Monoclonal antibody to the haemagglutinin-neuraminidase or the fusion glycoprotein of Newcastle disease virus blocked virus penetration which otherwise occurred within 90 s of the temperature being increased from 4 degrees C to 37 degrees C. These antibodies regularly immunoselected variant plaques only when incorporated into the agarose overlay. Variant viruses then formed plaques whereas the growth of non-neutralized normal virus was suppressed.