Antigenic relationships among human rotaviruses as determined by outer capsid protein VP4

cDNA clones representing the VP4 gene of symptomatic human rotavirus strain KU (VP7 serotype 1) or DS-1 (VP7 serotype 2) or asymptomatic human rotavirus strain 1076 (VP7 serotype 2) were constructed and inserted into a baculovirus expression vector under the control of the polyhedrin promoter. The resulting recombinants expressed the appropriate authentic VP4 rotavirus outer capsid protein. Guinea pigs immunized with these VP4 proteins developed antibodies that neutralized infectivity of the rotavirus from which the immunizing VP4 was derived. These antisera were then used in neutralization tests to define the extent and distribution of VP4 antigenic polymorphism among human rotaviruses. Three distinct serotypes and one subtype of the VP4 outer capsid protein were identified among 17 human rotavirus strains that had previously been assigned to five distinct VP7 serotypes. For the most part, VP4 serotype segregated independently of VP7 serotype. Ten strains of human rotavirus that were associated with symptomatic infection and that exhibited VP7 serotype 1, 3, 4, or 9 specificity, each possessed a VP4 of the same serotype and subtype, designated VP4 serotype 1A. Both symptomatic human rotavirus strains with VP7 serotype 2 specificity were related by neutralization to the VP4 serotype 1A strains and were classified as a subtype of VP4 serotype 1--i.e., serotype 1B--since viruses of serotype 1A appeared to be prime strains. Four human rotavirus strains that were recovered from healthy infants in newborn nurseries in which virus transmission persisted over a long interval, belonged to VP7 serotype 1, 2, 3, or 4, but each strain possessed the same VP4 antigenic specificity that was designated VP4 serotype 2. Finally, a single strain of symptomatic human rotavirus of VP7 serotype 1 specificity possessed a unique VP4 that was provisionally classified as VP4 serotype 3 but this remains to be confirmed because neutralization tests were performed in only one direction. Among the 10 rotavirus strains whose VP4 gene was previously sequenced, there was complete concordance between assignment of VP4 serotype by neutralization and classification according to VP4 amino acid homology. Thus, rotaviruses that exhibited a VP4 amino acid homology of 89% or greater belonged to the same VP4 serotype and subtype as determined by neutralization. Finally, evidence was obtained that the serotype-specific domain is located on the VP8 subunit of VP4.