MAPPING OF B-NEUTRALIZING AND T-HELPER CELL EPITOPES ON THE BOVINE LEUKEMIA-VIRUS EXTERNAL GLYCOPROTEIN GP51

A battery of 19 synthetic peptides was used to characterize efficient neutralizing and helper T-cell epitopes on the bovine leukemia virus ( BLV) external envelope glycoprotein gp51. Four of the antipeptide anti sera raised in rabbits inhibited the formation of BLV-induced syncytia ; these antisera are directed against peptides 64-73, 98-117, and 177- 192. Only antisera directed against the 177-192 region also neutralize d vesicular stomatis virus-BLV pseudotypes. This study clearly demonst rates that neutralizing properties can be observed with antibodies rai sed to regions undescribed so far and included in both the amino-termi nal and central parts of the antigen. In addition, some helper T-cell determinants were defined from gp51-immunized mice and from BLV-infect ed cattle. Although none of the peptides tested behaved as a universal helper T-cell epitope, peptide 98-117 stimulated T-cell proliferation from BALB/c mice and from three infected cows, while peptide 169-188 strongly stimulated T-cell proliferation from one infected cow. Furthe r experiments performed with three peptides overlapping the 169-188 re gion (177-192, 179-192, 181-192) demonstrated the particular relevance of residue(s) P-177 and/or D-178 in the helper T-cell epitope. These data should assist in the design of an efficient subunit vaccine again st BLV infection that contains peptides possessing both B-neutralizing and helper T-cell determinants.