Control of equine infectious anemia virus is not dependent on ADCC mediating antibodies

Horses infected with equine infectious anemia virus (EIAV) have recurrent episodes of viremia which are eventually controlled, but the immune mechanisms have not been identified. Antibodies were detected to the surface of EIAV-infected cells within 1 month postinfection and remained for at least 3.5 years postinfection. These antibodies recognized cell surface-exposed envelope (Env) glycoproteins, but could not mediate antibody dependent cellular cytotoxicity (ADCC) using EIAV-WSU5-infected equine kidney (EK) cells as targets and peripheral blood mononuclear cells (PBMC) or polymorphonuclear cells (PMN) as effector cells. Furthermore, purified IgG antibodies from horses infected with either EIAV-WSU5 or EIAV-Wyo did not mediate ADCC of infected target cells. Armed effector cells could not be detected in infected horse blood nor could effector cells be prearmed by incubation with serum antibodies to cell surface antigens. The use of EIAV-WSU5-infected equine macrophages as target cells did not result in ADCC. In contrast, serum antibody from EHV-1 vaccinated horses and PBMC or PMN as effector cells caused ADCC of EHV-1-infected EK cells. These results indicate that ADCC is not involved in the control of EIAV in carrier horses.