A hypothesis accounting for the effect of the host cell on neutralization-resistant virus.

Evidence is presented showing that a monkey anti-enterovirus 71 immune serum contains several antibody populations which differ in their mode of function. One population reduces infectivity, although inefficiently, by interactions at exposed antigenic sites and can be detected by measuring residual virus infectivity after mixtures of virus and antibody have been allowed to interact. Another antibody population, which is unaffected by the immunosorbent Staphylococcus aureus (Cowan I strain), appears to attach to its antigenic site(s) only after interactions between enterovirus 71 and host cells have already begun. In view of the transience of (presumed) conformational changes in the invading viruses, demonstration of this type of antibody activity requires a particular host cell system. This second type of antibody neutralization could be detected on RD cells but not on green monkey kidney cells.