A Sensitive Neutralization Test for the Adeno-Associated Satellite Viruses

A highly sensitive neutralization test for the four satellite serotypes was developed by selecting particularly effective combinations of adenovirus helper and cell system. Neutralizing antibody titers were measured by inhibition of satellite replication as assayed in terms of complement-fixation-producing units (CFPU) of virus. Neutralizing antibody measured by this method was more type-specific, and the antibody titers were much higher than those obtained by the direct complement-fixing antibody test. Homotypic neutralizing antibody titers of 103 were common, and in some instances titers as high as 106 were observed. The neutralizing activity against satellite virus was found to reside in the λ globulin fraction of post-infection human and post-immunization rabbit sera. The frequency of individuals with neutralizing antibodies but without CF antibodies suggests that the CF antibody titer falls off more rapidly than the neutralizing titer. Both neutralization and CF tests revealed significant intertypic crossing, especially between types 2 and 3.