Identification of a poliovirus neutralization epitope through use of neutralizing antiserum raised against a purified viral structural protein.

VP4, one of the poliovirus structural proteins, was purified and used to prepare rabbit anti-VP4 serum. In addition to the anti-VP4 activity, this serum was also found to contain significant anti-VP3 and antivirion activities. The serum also effectively neutralized viral infectivity. The ease with which nonneutralizable variants were obtained indicated that neutralization was due to an antibody population which bound to a single virion epitope. Antigen saturation and immunoprecipitation experiments demonstrated that antibody to this epitope was also responsible for the serum's antivirion and anti-VP3 activities, as well as for a part of the anti-VP4 activity. The identification of a neutralization epitope most probably present on VP3, which cross-reacts with a site on denatured VP4, is the first report of such an epitope on a poliovirus structural protein other than VP1.