How to cite this article: Vet. Res. (2008) 39:21
DOI: 10.1051/vetres:2007062

Protection, systemic IFN, and antibody responses induced by an ISCOM-based vaccine against a recent equine influenza virus in its natural host

Romain Paillot¹, Humphrey Grimmett², Debra Elton¹ and Janet M. Daly<sup>1, 3

1</sup>  Animal Health Trust, Centre for Preventive Medicine, Lanwades Park, Newmarket, Suffolk, CB8 7UU, UK
²  Schering Plough, Animal Health, Breakspear Rd, South Harefield, Uxbridge, Middlesex, UB9 6LS, UK
³  Present address: Viral Brain Infections Group, University of Liverpool, Daulby Street, Liverpool L69 3GA, UK

(Received 31 August 2007; accepted 9 November 2007; published online 7 February 2008)

Abstract - In the horse, conventional inactivated or subunit vaccines against equine influenza virus (EIV) induce a short-lived antibody-based immunity to infection. Alternative strategies of vaccination have been subsequently developed to mimic the long-term protection induced by natural infection with the virus. One of these approaches is the use of immune-stimulating complex (ISCOM)-based vaccines. ISCOM vaccines induce a strong antibody response and protection against influenza in horses, humans, and a mouse model. Cell-mediated immunity (CMI) has been demonstrated in humans and mice after ISCOM vaccination, but rarely investigated in the horse. The aim of this study was to evaluate EIV-specific immune responses after intra-muscular vaccination with an ISCOM-EIV vaccine (EQUIP F) containing both equine influenza H7N7 (A/eq/Newmarket/77) and H3N8 (A/eq/Borlänge/91 and A/eq/Kentucky/98) strains. The antibody response was measured by single radial haemolysis (SRH) assay using different H3N8 EIV strains. Stimulation of type-1 immunity was evaluated with a recently developed method that measures EIV-specific IFN synthesis by peripheral blood lymphocytes (PBL). The protective efficacy of this ISCOM-based vaccine against challenge infection with a recent equine influenza (H3N8; A/eq/South Africa/4/03) strain was also evaluated. Vaccinated ponies developed elevated levels of EIV-specific SRH antibody and increased percentage of EIV-specific IFN PBL, whereas these responses were only detected after challenge infection in unvaccinated control ponies. Vaccinates showed minimal signs of disease and did not shed virus when challenged shortly after the second immunisation. In conclusion, evidence of type-1 immunity induced by an ISCOM-based vaccine is described for the first time in horses.

Key words: equine influenza virus / vaccine / ISCOM / equine IFN gamma / immunity

Corresponding author: romain.paillot@aht.org.uk

© INRA, EDP Sciences 2008