The neuraminidase of Newcastle disease virus inhibited in the elution-inhibition reaction.

The neuraminidase (NA) on strain 575 of Newcastle disease virus (NDV) was inhibited with elution-inhibition (EI) antibodies causing permanent agglutination patterns of red blood cells (RBC). Detection of EI antibody was unaffected by passage through sephadex, centrifugation or plaque purification of NDV. The haemagglutination-inhibition (HI) and EI reactions as well as the NA inhibition test all showed an increase in titre as immunization progressed. Fluorescent-stained IgG on RBC from the EI reaction appeared as foci but as a halo if NDV was disrupted with ether suggesting NDV aggregation. The haemagglutinin (HA) on "sensitized' RBC from the EI reaction was not neutralized and agglutinated newly added RBC. The NA cleaved fetuin at 49 to 88% of the maximum values while bound to RBC by EI antibody. Added NA substrates failed to block the EI reaction. The order of inactivation at 53 or 56 degrees C but not 50 degrees C was: the putative EI antibody determinant > NA > HA. The term elution inhibition is suggested for the antibody responsible for the EI reaction.