We describe here a detailed analysis of the
antigenic determinants of the surface unit
glycoprotein (gp90) of equine infectious anemia virus (EIAV), using a comprehensive panel of synthetic
peptides in
enzyme-linked
immunosorbent assays with immune serum from naturally and experimentally infected horses and with a panel of gp90-specific neutralizing and nonneutralizing
monoclonal antibodies. The results of these studies identify immunoreactive segments throughout the conserved and variable domains of gp90 but localize immunodominant (100% reactivity) determinants to the amino and carboxyl termini of the
glycoprotein molecule. Analysis of
peptide reactivities with longitudinal serum samples taken from experimentally infected ponies revealed that antibody responses to conserved B-cell determinants appeared earlier and at higher titers than do
antibodies specific for determinants contained in the variable domain of gp90. These observations suggest an evolution of antibody responses in EIAV-infected ponies that may correspond to the establishment of immunological control of virus replication and disease routinely observed in EIAV
infections. In addition, the mapping of
monoclonal antibody epitopes to
peptides of 9 to 12
amino acids demonstrated that all of the neutralizing
epitopes are located in the variable domain of gp90. The arrangement of neutralizing
epitopes and critical structural considerations suggest that
EIAV gp90 contains a principal neutralizing domain similar to the V3 loop of human immunodeficiency virus type 1. These antigenic analyses provide an important foundation for further analyzing the protective immune response generated during persistent EIAV
infections and also provide potential
peptide substrates for diagnostic assays and for
vaccine strategies.