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 IFNgamma 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 IFNgamma(+) 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.