The outer capsid proteins VP4 and VP7 induce neutralizing antibody against rotavirus. We have investigated in a mouse model the protection mediated by immunization with VP8*, the amino-terminal tryptic fragment of VP4. BALB/c female mice immunized with simian rotavirus SA11 VP6 and VP8* proteins expressed in Escherichia coli were mated with seronegative males. Litters were orally challenged with the SA11 strain (P5B[2], G3) or with the murine rotavirus strain EDIM (P10[16], G3) to verify the degree of protection against diarrhea induced in the newborns. Only those pups born to dams immunized with VP8* did not develop diarrhea after having been orally challenged with the SA11 strain. Pups born to naive dams but foster nursed by VP8*-immunized dams did not develop diarrhea after having been orally infected with the SA11 strain, but they suffered diarrhea when challenged with the EDIM strain. These results support the concepts that (1) VP8* is a highly immunogenic polypeptide that induces effective homotypic protection against disease in pups born to dams immunized with this antigen and (2) in newborn mice the protection against disease is mediated by neutralizing secretory antibodies present in the milk rather than by serum antibodies transferred through the placenta to the offspring.

Rotavirus-specific cytotoxic T lymphocytes (CTL) play an important role in the resolution of rotavirus infection. The outer capsid glycoprotein, VP7, elicits a class I MHC-restricted CTL response. Vaccinia virus recombinants expressing the VP7 genes from simian rotavirus SA11 (serotype G3) and from the RF strain of bovine rotavirus (serotype G6) were used to analyze the CTL activity to this antigen in BALB/c (H-2(d)) and C57BL/6 (H-2(b)) mice neonatally infected with homologous and heterologous rotaviruses. A vaccinia virus recombinant expressing the first amino-terminal 88 amino acids of VP7 was constructed and used to search for cross-reactive CTL against this region of the protein. By using synthetic Kb, Db, and Kd motif-fitting peptides two overlapping CTL epitopes have been identified located in the first hydrophobic domain (H1) of VP7. Splenocytes obtained from rotavirus SA11-infected C57BL/6 mice induced the strongest CTL response against target cells sensitized with a peptide containing a Kb-restricted CTL epitope (amino acids 8-16). A second Kd-restricted epitope (residues 5-13) was recognized by splenocytes derived from rotavirus-infected BALB/c mice. These findings reveal the existence of CTL epitopes in the H1 signal sequence of the VP7 glycoprotein that coexist with a CTL epitope (residues 31-40) previously described within the H2 region.

Between September 1996 and May 1999, the incidence and distribution of the main human rotavirus G genotypes (VP7 associated: G1-G4) and P genotypes (VP4 associated: P[8], P[4], P[6] and P[9]) among children with rotavirus gastroenteritis were determined using reverse transcription and polymerase chain reaction (RT-PCR)-based genotyping methods. From a total of 145 rotavirus strains examined, we identified the G type in 131 (90.3%) and the P type in 127 (87.5%) of the samples. An overall predominance of genotypes P[8] G1 (42.7%) and P[8] G4 (32.4%) was found during the period of study, with much lower incidence of genotypes P[4] G2 (5.5%) and P[8] G3 (2%). P[6] and P[9] types were not detected, neither were unusual combinations of P and G types. A significant genotypic shift was observed: whereas P[8] G4 was the most prevalent genotype during the first year of the study (60%), the genotype P[8] G1 gradually increased to account for 62.3% of the strains analysed in the following winter season. Mixed G types revealing dual infections G1/G4 and G3/G4 were found at low frequency (2%).