Analysis of the Newly Identified Neutralization Epitopes on VP7 of Human Rotavirus Serotype 1

Neutralizing monoclonal antibodies (MAbs) directed to the VP7 protein and neutralization-resistant mutants were used to analyse the antigenic structure of VP7 of human rotavirus serotype 1. Cross-neutralization tests using the MAbs and the resistant mutants indicated the existence of two functionally independent neutralization epitope regions (S1 and S2) on VP7. Region S1 corresponds to a single epitope domain of VP7 which has been detected previously. Two MAbs prepared in this study recognized the S1 region, and the resistant mutants they selected had amino acid substitutions at positions 94 or 213. On the other hand, region S2 is considered to be a novel epitope. Single or double amino acid substitutions were detected in the variable regions (amino acid positions 145, 217 and 221) and in the constant regions (positions 104, 201 and 291) of the VP7 protein of mutants selected by MAbs directed to the S2 region. It was suggested that the variable region E (amino acids 208 to 221) includes two independent neutralization sites, and that amino acid substitutions in the constant region of VP7 also affect serotype-specific neutralization epitopes. Neutralization epitopes on VP7 are considered to be highly dependent on the conformation of VP7.