Studies of hemagglutination-inhibition reactions of the antigenically related measles soluble (SDA) and envelope-integrated viral (HA) hemagglutinins have shown the following:

  1. Eighty units of SDA failed to compete with 4 units of HA for HI antibodies, although in the same experiment SDA required, unit for unit, an antibody concentration of the same magnitude for inhibition as that required by HA.

  2. A negative Danysz effect was demonstrated with SDA and a positive effect with viral HA, which indicates that SDA forms a less stable union with antibody than does HA. Reversibility of SDA-antibody combination was proposed as an explanation for the result above.

  3. The ratios of SDA inhibition titer to HI titer varied under different circumstances. Factors included time of serum collection relative to disease onset, class of immunoglobulin predominating, and average size and state of aggregation of the HA preparation used for the comparison.

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This work was supported by United States Public Health Service Grant AI-06864 from the National Institute of Allergy and Infectious Diseases.

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