Solid-phase radioimmunoassay as a method for evaluating antigenic differences in type A influenza viruses

An indirect solid-phase radioimmunoassay (RIA) procedure was developed to determine its usefulness in assessing antigenic variation in the surface antigens of type A influenza virus strains. The importance of several test variables was examined, and those having a significant effect on the binding ratios were identified. The reproducibility of the RIA procedure was investigated. Maximum variation of the mean binding ratios encountered in repetitive tests was found to be approximately 20%. The antigenic characteristics of the A/Aichi/68 virus strain were compared with several different type A virus strains. Utilizing anti-A/Aichi/68 immune serum together with specific anti-hemagglutinin and antineuraminidase immune sera, the RIA method was shown to quantitatively differentiate the surface antigens of the A/Aichi/68 virus strain from the surface antigens of the type A strains that preceded, as well as from those that succeeded, the introduction of the Aichi virus strain in 1968. Using antigen-specific serum, both the hemagglutinin and neuraminidase antigens can be independently characterized in one test system. This advantage, together with the ease and greater sensitivity of the RIA, should make it a useful serological test for evaluating antigenic variation of type A influenza viruses.