Serum antibody responses to equine herpesvirus 1 glycoprotein D in horses, pregnant mares and young foals.

This study investigates the effectiveness of the envelope glycoprotein D (EHV-1 gD) of the equine herpesvirus 1 as a potential vaccine ingredient for horses, and how this affects the immune response in adult horses, pregnant mares, and young foals.

Overview of the Research

• The study is centered around the envelope glycoprotein D (EHV-1 gD) found in equine herpesvirus 1 (EHV-1). This gD has been demonstrated in previous laboratory animal studies to trigger protective immune responses against EHV-1, suggesting its potential as a vaccine antigen.
• The researchers explored the effects of intramuscular inoculation of EHV-1 gD (generated through a recombinant baculovirus and mixed with the adjuvant Iscomatrix), on adult mixed breed horses.

Immune Response in Adult Horses

• The results revealed that the aforementioned inoculation elicited virus-neutralizing antibodies and gD-specific ELISA antibodies in the serum of over 90% of adult horses, showing that EHV-1 gD incites a strong immune response.
• Interestingly, the immune response following inoculation was comparable to the response seen after inoculation with a commercially available killed EHV-1/4 whole virus vaccine. This further supports the perceived potential utility of EHV-1 gD as a vaccine ingredient.
• The researchers also explored an alternate delivery method, where the EHV-1 gD DNA, rather than the glycoprotein itself, was administered in a mammalian expression vector. This method, while inducing some antibody responses, was less effective compared to the direct use of EHV-1 gD protein as an immunogen.

Immune Response in Pregnant Horses and Young Foals

• Upon inoculation of pregnant mares with EHV-1 gD, their offspring demonstrated significantly higher levels of anti-gD antibodies passed through the colostrum, compared to foals born to non-inoculated mares.
• However, direct inoculation of neonatal foals with EHV-1 gD, administered at 12 hours post-birth and at 30 days of age, did not lead to a significant mean antibody response. This suggests that the immune system of neonatal foals might not be ready to effectively respond to such inoculation, regardless of the immune response of the mother.

Conclusion

• In conclusion, the comparable immune response elicited by EHV-1 gD and a whole virus vaccine establishes the former as a promising potential ingredient of subunit vaccines against EHV-1. This insight can guide future attempts at vaccine development against the equine herpesvirus.