Humoral response and antiviral cytokine expression following vaccination of thoroughbred weanlings--a blinded comparison of commercially available vaccines.

Previous studies in experimental ponies using interferon gamma (IFN-γ) as a marker for cell mediated immune (CMI) response demonstrated an increase in IFN-γ gene expression following vaccination with an ISCOM subunit, a canarypox recombinant and more recently, an inactivated whole virus vaccine. The objective of this study was to carry out an independent comparison of both humoral antibody and CMI responses elicited following vaccination with all these vaccine presentation systems. Antibody response of 44 Thoroughbred weanlings was monitored for three weeks following the second dose of primary vaccination (V2) by single radial haemolysis (SRH). The pattern of antibody response was similar for all vaccines. The antibody response of horses vaccinated with the inactivated whole virus vaccine (Duvaxyn IE-T Plus) was superior to that of the horses vaccinated with the ISCOM-matrix subunit (Equilis Prequenza Te) and canarypox recombinant (ProteqFlu-Te) vaccine. In this study 39% of weanlings failed to seroconvert following their first dose of primary vaccination (V1). Poor response to vaccination (H3N8) was observed among weanlings vaccinated with Equilis Prequenza Te and ProteqFlu-Te but not among those vaccinated with Duvaxyn IE-T Plus. PAXgene bloods were collected on days 0, 2, 7 and 14 following V1. Gene expression levels of IFN-γ, IL-1β (proinflammatory cytokine) and IL-4 (B cell stimulating cytokine) were measured using RT-PCR. Mean gene expression levels of IL-1β and IL-4 peaked on day 14 post vaccination. The increase in IL-4 gene expression by horses vaccinated with Equilis Prequenza Te was significantly greater to those vaccinated with the other two products. Vaccination with all three vaccines resulted in a significant increase in IFN-γ gene expression which peaked at 7 days post V1. Overall, there was no significant difference in IFN-γ gene expression by the horses vaccinated with the whole inactivated, the subunit and the canarypox recombinant vaccines included in this study.