Synthetic peptides approach to identification of epitopes on bovine leukemia virus envelope glycoprotein gp51

Peptides corresponding to residues 21-28, 39-48, 57-67, 59-69, 78-92, 144-155, 144-157, 195-205, 255-268, and 260-268 of envelope glycoprotein gp51 of bovine leukemia virus (BLV) were chemically synthesized and coupled to keyhole limpet hemocyanin or tetanus toxoid. All peptides were immunogenic in rabbits and induced production of antipeptide antibodies. Enzyme-linked immunosorbent assays using Tween 80-purified gp51 or BLV particles showed that antibodies against peptides 78-92, 255-268, and to a lesser extent 39-48 and 144-157 were able to react with the parent glycoprotein, purified or as an integer part of BLV particles. Antisera against peptides 39-48, 78-92, and 144-157 neutralized VSV (BLV) pseudotypes in vitro, the highest neutralization titer being obtained with the 78-92 cyclized peptide. These observations confirm that the NH2 moiety of gp51 carries epitopes involved in virus infectivity.