Studies on the Interaction of the Large and Small Hemagglutinating Components of Newcastle Disease Virus with Red Cells

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Abstract
Summary: Partially purified preparations of the L and S components of Newcastle disease virus were obtained from infected allantoic fluid and membrane suspensions, respectively, by differential centrifugation. The L component could be separated also from the infected tissues but S could be detected in allantoic fluid only in relatively low concentrations. The S component was found to be partially sedimentable by centrifugal forces far in excess of those needed for removal of L. Suspension of the L component revealed ID50/HA ratios of the order of 106. In contrast, S preparations gave ratios as low as 100.6 and generally below 102. Whereas L was readily absorbed onto red cells in the cold, only relatively small amounts of S appeared to combine with these cells under the same conditions. No inhibitor of adsorption could be detected in S preparations. The data presented suggest that the S component either possesses greater eluting activity than L or that an elution-promoting factor is present in such preparations. The L component readily causes hemolysis whereas S according to all indications lacks this property. When red cells were exposed to S and subsequently washed they resisted hemolysis by the L component. Heated S or control material had no such effect. Only the L component showed the phenomenon of extension of titers in hemagglutinin assays upon repeated resuspension and settling of the red cells at 37°C. Only red cells previously exposed to L at 37°C until stabilized could be agglutinated by dilute NDV-immune serum or were capable of agglutinating normal red cells. These properties, according to Burnet, are closely linked with the hemolytic activity. The facts that S failed to reveal these reactions and was found to be non-hemolytic appear to be in agreement with this suggestion. Under carefully graded conditions S precedes the L component in the receptor gradient. Various problems concerning the mechanisms of interaction of these components with red cells have been discussed.