B-cell epitopes of the envelope glycoprotein of caprine arthritis-encephalitis virus and antibody response in infected goats

Goats infected with caprine arthritis-encephalitis virus (CAEV) develop hig h titres of antibodies to Env. Not only is no consistent neutralizing respo nse found but anti-Env antibodies have even been associated with disease in infected goats. To identify the continuous antigenic determinants involved in this atypical anti-Env response, we mapped CAEV-CO Env by screening an epitope expression library with infected goat sera. In addition to the four previously described epitopes, seven novel antigenic sites were identified , of which five were located on the surface (SU) and two in the transmembra ne (TM) subunits of Env. The SU antibody-binding domains located in the var iable regions of the C-terminal part of the molecule (SU3 to SU5) showed th e strongest reactivity and induced a rapid seroconversion in six experiment ally infected goats. However, the response to these immunodominant epitopes did not appear to be associated with any neutralizing activity. The patter n of serum reactivity of naturally infected goats with these epitopes was r estricted, suggesting a type-specific reaction. Interestingly, the reactivi ty of peptides representing SU5 sequences derived from CAEV field isolates varied with the geographical and/or breeding origin of the animals. This su ggests that peptides corresponding to the immunodominant SU epitopes may we ll be useful in the serotyping of CAEV isolates. Furthermore, the identific ation of the CAEV Env epitopes will permit us to functionally dissect the a ntibody response and to address the role of anti-Env antibodies either in t he protection from or in the pathogenesis of CAEV infection.