Cross-neutralization and antigenic characterization of simian and equine group A rotaviruses.

Overview

• This research investigates how different strains of rotavirus A from horses and simians cross-neutralize each other, focusing on the roles of viral proteins VP7 (G genotype) and VP4 (P genotype) in eliciting immune protection.
• The study aims to better understand immune responses to inform vaccine design against equine rotavirus infections by analyzing antibody reactions from different species and identifying key viral epitopes responsible for cross-neutralization.

Background

• Rotaviral diarrhea in foals is mainly caused by two genotypes: G3P[12] and G14P[12] of equine rotavirus A (ERVA).
• Foals gain protection through antibodies obtained from the colostrum of vaccinated mares, specifically those vaccinated with an inactivated G3P[12] monovalent vaccine.
• Simian rotavirus SA11 G3P[2] is also included in ERVA vaccines to help protect foals, despite being a different species’ strain.

Research Objectives

• Characterize cross-neutralization and protection among three distinct rotaviruses with either matching or differing G (VP7 protein) and P (VP4 protein) genotypes.
• Use rabbit and equine monospecific antisera to evaluate cross-neutralization capacity.
• Combine serological assays with structural and computational analyses of viral epitopes to understand molecular determinants of cross-protection.

Key Findings

• Cross-neutralization between rSA11 G3P[2] and equine G3P[12]:
  • Rabbit antisera showed strong cross-neutralization between these two strains.
  • However, both had less cross-neutralization ability against equine G14P[12].
• Asymmetrical cross-protection:
  • Rabbit antisera raised against equine G14P[12] provided stronger cross-protection against simian rSA11 G3P[2] than the other way round.
• Role of VP8* domain in VP4:
  • Despite only minor amino acid differences between VP8* domains of the two equine viruses, antisera to VP8* from equine G3P[12] moderately neutralized G14P[12].
  • These antisera showed potent neutralization against simian rSA11 G3P[2], indicating cross-reactive epitopes.
• Differences in species-specific responses:
  • Equine antisera exhibited broader and stronger cross-neutralization among the three viruses compared to rabbit antisera.
  • This underscores how antibody response varies depending on the host species.
• Identification of novel epitopes:
  • Structural analyses revealed multiple amino acid residues that are highly exposed on VP7 and VP8* proteins and conserved across the three viruses.
  • These regions likely function as new B cell epitopes facilitating cross-neutralization.

Implications for Vaccine Design

• Importance of the G genotype (VP7):
  • The study suggests that the VP7-defined G genotype plays a more crucial role in determining cross-neutralization specificity than the P genotype (VP4).
  • Incorporating diverse G genotypes in vaccines might improve breadth of protective immunity against different rotavirus strains.
• Limited role of P genotype (VP4) alone:
  • Variability in cross-neutralization by the P genotype indicates it may not be sufficient as the sole target for broad protection.
• Novel epitopes as vaccine targets:
  • Newly identified conserved B cell epitopes in VP7 and VP8* could be promising components for designing vaccines that elicit cross-protective antibodies.
• Need for species-relevant vaccine evaluation:
  • Differences in cross-neutralization efficacy between horse and rabbit antisera highlight the importance of assessing vaccines in the target species or relevant animal models.
  • This approach ensures vaccines confer broad and effective protection in natural hosts.

Conclusions

• Cross-neutralizing antibody responses among equine and simian rotaviruses are complex and influenced by viral protein genotype combinations as well as species-specific immune responses.
• VP7-defined G genotypes exert a dominant influence on the breadth of neutralization, and vaccines incorporating multiple G types may offer enhanced protection.
• The identification of conserved solvent-exposed amino acids as novel epitopes could guide future vaccine antigen design aimed at broad cross-protection.
• This study emphasizes the necessity to include diverse viral genotypes and consider host species differences in developing effective rotavirus vaccines for horses.