Neutralizing antibody response of gnotobiotic piglets after fetal infection and neonatal challenge with human rotavirus strains

Evidence that active protection following oral immunization of mice with live rotavirus is not dependent on neutralizing antibody

Studies were performed to determine whether active immunity against murine rotavirus (EDIM) infection of mice correlated with titers of neutralizing antibody to the challenge virus. Neonatal mice administered either murine or heterologous rotaviruses all developed diarrhea and high titers of serum rotavirus IgG. However, only mice given EDIM, the murine EB, or simian SA11-FEM strains were protected against EDIM infection when challenged 60 days later. Other serotype 3 strains (RRV, SA11-SEM), as well as strains belonging to serotypes 5 and 6 (OSU, NCDV, WC3), were not protective. Serum neutralizing antibody titers to EDIM were almost undetectable after rotavirus infection with any strain and could not, therefore, be correlated with protection. Likewise, intestinal neutralizing antibody titers were extremely low 21 days after EDIM infection, and by 60 days after inoculation, EDIM-infected mice had no greater intestinal neutralizing antibody titers than uninoculated controls. Mice inoculated with SA11-FEM as neonates had much higher serum rotavirus IgG responses than mice inoculated as adults, and only those infected with this virus as neonates were protected. Thus, although immunity to EDIM did not correlate with the presence of neutralizing antibody to EDIM, it did correlate with the overall magnitude of the immune response after inoculation with SA11-FEM.

Serologic and mucosal immune response to rotavirus infection in the rabbit model

We examined the humoral immune response to rotavirus infection in specific pathogen-free rabbits inoculated and challenged orally with rabbit Ala rotavirus (7.5 x 10(5) to 1 x 10(7) PFU). The humoral immune response in both serologic and mucosal samples was monitored by using total antibody enzyme-linked immunosorbent assays (ELISAs), isotype-specific ELISAs, and plaque reduction neutralization assays. Following a primary infection, all rabbits shed virus and serologic and mucosal antibody responses were initially detected by 1 week postinoculation. Intestinal immunoglobulin M was detected by 3 days postinoculation, and secretory immunoglobulin A was detected by 6 days postinoculation. Following challenge, rabbits were protected (no detectable virus shedding) from infection. An anamnestic immune response was observed only with mucosal neutralizing antibodies, and all serologic and mucosal immune responses persisted at high levels until at least 175 days postchallenge (204 days postinoculation). Detection of neutralization responses was influenced by the virus strain used in the neutralization assay; all inoculated rabbits developed detectable serum and intestinal neutralizing antibodies against the infecting (Ala) virus strain. Neutralization activity in both serum and mucosal samples was generally, but not exclusively, homotypic (VP7 serotype 3) after both primary and challenge inoculations with Ala virus. Heterotypic serum neutralization activity was observed with serotype 8 (9 of 12 rabbits) and 9 (12 of 12 rabbits) viruses and may be based on reactivity with the outer capsid protein VP4 or on a shared epitope in the C region of VP7. Comparisons of heterologous (serotype 3) and heterotypic neutralizing responses in mucosal and serologic samples revealed that 43% (21 of 49) of the responses were discordant. In 19 of 49 (39%) of these cases, a heterotypic serologic response was seen in the absence of a heterotypic mucosal response, but in 2 of 49 (4%) instances, a heterotypic mucosal response was seen in the absence of a concomitant serologic response. These results provide insight into factors which may affect detection of heterotypic responses.

DNA amplification-restricted transcription-translation: rapid analysis of rhesus rotavirus neutralization sites

DNA amplification-restricted transcription-translation (DARTT), is based on DNA amplification by the polymerase chain reaction (PCR) and uses PCR to truncate protein-encoding DNA while adding transcriptional and translational initiation signals to the segment. The amplified DNA segments are transcribed into RNA and translated into protein in vitro and the synthesized proteins are used to define functional sites. DARTT was applied to rhesus rotavirus gene segment 4 cDNA in order to create a series of carboxyl-terminal truncations and new amino termini in the encoded VP4 capsid protein. The truncated VP4 polypeptides were tested for reaction with 11 VP4-specific neutralizing monoclonal antibodies to identify the minimum polypeptides required for antibody recognition. Monoclonal antibodies 2G4, M2, and M7, which neutralize a number of serologically distinct rotaviruses, required amino acids 247-474 of VP4 for binding. DARTT is potentially applicable to the identification of discontinuous epitopes and functional domains on a variety of proteins.

Immunity to rotaviruses

A potent, multivalent, serotype-specific RV vaccine and improved tests for measuring vaccine potency would help eliminate the necessity to pretest for vaccine efficacy in every country selected for its deployment. Until then, the need will continue for vaccine trials in various countries because the pathogenesis and epidemiology of RV and RV serotypes differ between and within countries. Although RV vaccinology is complex, it has forged ahead of our knowledge of RV immunopathogenesis and epidemiology.