Transient suppression of equine immune responses by equine infectious anemia virus (EIAV)

Suppression of the immune system is a common aspect of the disease pathogenesis associated with retroviral infections in both man and animals. We have measured transient suppression of the equine immune system as a loss or decrease in antigen-specific and polyclonal lymphocyte proliferation following experimental infection of ponies with three variants of equine infectious anemia virus (EIAV) with difference virulence characteristics. The transient suppression of proliferative responses was temporally associated with recurrent febrile episodes, which are the hallmark symptom of EIAV-induced disease. Decreased proliferative responses occurred at all times when EIAV viremia was identified, based on the detection of an infectious virus in plasma or viral proteins on peripheral blood mononuclear cells. The immunosuppression was observed most frequently in ponies infected with virulent variants of EIAV which suggested that this effect may contribute to disease pathogenesis. Suppression of polyclonal proliferative responses was induced in vitro by the addition of either infectious or heat-inactivated EIAV to cultures, demonstrating that the viral structural proteins were immunosuppressive in the absence of infection. These studies indicated that EIAV is similar to other retroviruses in that it has the ability to suppress the immune system.