Sialidase and protease activities of commercial RDE products used for the HI test of influenza viruses.

Hemagglutination inhibition (HI) test against influenza viruses is performed generally after the treatment of serum samples with receptor destroying enzyme (RDE) derived from Vibrio cholerae culture fluid. The RDE destroys receptors on the surface of erythrocytes to influenza viruses, as well as nonspecific HA-inhibitors contained in serum. Unless it is destroyed, the inhibitor inhibits the viral hemagglutination and makes a deleterious disturbance on the determination of specific antibodies in the serum. Therefore, RDE products are expected to abolish effectively the property of nonspecific HI subtances by splitting off the sialic acid portion of the molecule. Human serum samples