Antiviral, Anti-glycoprotein and Neutralizing Antibodies in Foals with Equine Infectious Anaemia Virus

Equine infectious anaemia virus is related by genome sequence homology to human immunodeficiency virus, caprine arthritis-encephalitis virus and visna virus. Failure of the host to mount a strong neutralizing response detectable in vitro or to eliminate persistent infection in vivo characterizes lentivirus infections in the natural host. In this study the specificities and neutralizing activity of antibodies induced during experimental infection with equine infectious anaemia virus were investigated using antiviral ELISA, radioimmunoprecipitation and neutralization assays. ELISA antibody titres of 105 to 106 were demonstrated in samples collected 30 and 60 days after infection. Immunoprecipitation titrations demonstrated that antibody titres to the glycoproteins gp90 and gp45 were 10 to 100 times higher than titres to the internal structural protein, p24. Low levels of neutralizing antibody appeared at 23 to 46 days post-infection. The presence of low levels of neutralizing activity in the presence of high levels of anti-glycoprotein activity suggests that the major immunogenic sites on the viral surface are not sensitive to neutralization.