Antibody and IFN-y Responses Induced by a Recombinant Canarypox Vaccine and Challenge Infection With Equine Influenza Virus

摘要

Equine-influenza virus (EIV) is a leading cause of respiratory disease in horses. Conventional inactivated vaccines induce a short-lived immune response. By comparison, natural infection confers a long-term immunity to reinfection. One target of new equine-influenza vaccines is to more closely mimic natural infection to achieve a better protective immunity. A new live recombinant vaccine has been developed using the canarypox virus vector expressing hemagglutinin genes of EIV (subtype H3N8). Stimulation of the immune system was studied after intramuscular immunizations with this canarypox-based vaccine and challenge infection by exposure to a nebulized aerosol of EIV. The humoral immune response was evaluated by measuring serum antibody levels usingthe single radial haemolysis (SRH) assay. The cellular im-mune response was assessed by the measurement of ElV-specific interferon gamma (IFN-y) synthesis in peripheral blood mononuclear cells (PBMC). Clinical signs of the disease (temperature, coughing, nasal discharge, dyspnea, depression, and anorexia) and virus excretion were monitored after challenge infection. Clinical signs and virus shedding were significantly reduced in vaccinates compared with unvaccinated controls. ElV-specific immunity wasstimulated by vaccination with the recombinant vaccine; serological responses were detected after immunization. This study also provided the first evidence for an increase in ElV-specific IFN-y+-se-creting PBMC in vaccinated ponies after challenge infection with EIV compared with control ponies.