Antibody responses to DNA vaccination of horses using the influenza virus hemagglutinin gene

Equine influenza virus infection remains one of the most important infectio us diseases of the horse, yet current vaccines offer only limited protectio n. The equine immune response to natural influenza virus infection results in long-term protective immunity, and is characterized by mucosal IgA and s erum IgGa and IgGb antibody responses. DNA vaccination offers a radical alt ernative to conventional vaccines, with the potential to generate the same protective immune responses seen following viral infection. Antigen-specifi c antibody isotype responses in serum and mucosal secretions were studied i n ponies following particle-mediated delivery of hemagglutinin (HA)-DNA vac cination on three occasions at approximately 63-day intervals. One group of four ponies were vaccinated at skin and mucosal sites and the another grou p were vaccinated at skill sites only. All ponies were subjected to a chall enge infection 30 days after the third vaccination. Skin and mucosal vaccination provided complete protection from clinical sig ns of infection. while skin vaccination provided partial protection: DNA va ccination provided partial protection from viral shedding. DNA vaccination generated only IgGa and IgGb antibody responses, which occurred with a high er frequency in the skin and mucosa vaccinated ponies. No mucosal IEA respo nse was generated prior to challenge infection and IgA responses were only detected in those ponies which shed virus postchallenge. These results demo nstrate that HA-DNA vaccination induces IgG(a) and IgG(b) antibody response s which are associated with protection in the absence of mucosal IgA respon ses. In addition, additional DNA vaccinations of mucosal sites increased pr otection and the frequency of seroconversion in ponies. (C) 1999 Elsevier S cience Ltd. All rights reserved.