A battery of 19 synthetic peptides was used to characterize efficient neutralizing and helper T-celi epitopes on the bovine leukemia virus (BLV) external envelope glycoprotein gp5l. Four of the antipeptide antisera 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 neutralized vesicular stomatis virus-BLV pseudotypes. This study clearly demonstrates that neutralizing properties can be observed with antibodies raised to regions undescribed so far and induded in both the amino-terminal and central parts of the antigen. In addition, some helper T-cell determinants were defined from gpSl-immunized mice and from BLV-infected cattle. Although none of the peptides tested behaved as a universal helper T-celi 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. Further experiments performed with three peptides overlapping the 169-188 region (177-192, 179-192, 181-192) demonstrated the particular relevance of residue(s) P-177 and/or D-178 in the helper T-celi epitope. These data should assist in the design of an efficient subunit vaccine against BLV infection that contains peptides possessing both B-neutralizing and helper T-cell determinants.

Peripheral blood mononuclear cells (PBMCs) from bovine leukaemia virus (BLV) -seronegative cattle and from BLV-seropositive cows either with normal haematological values or persistent lymphocytosis were tested for their proliferative response to BLV antigens. Ceils from only BLV-infected cattle with normal lymphocyte counts were stimulated to a detectable level by the fetal lamb kidney cell supernatant ~containing BLV antigens. Proliferation assays performed with the purified major core protein p24 indicated that this protein has to be processed through a chloroquine-sensitive compartment before being recognized by CD4 + T lymphocytes. Fortyone 15-mer overlapping peptides spanning the entire p24 sequence were synthesized and analysed for their stimulating potential. It appeared that two regions included T cell epitopes recognized by PBMCs from three of five animals tested. These regions were represented by amino acids 31 to 55 (PGSQVWIQTL-RLAILQADPTPADLE) and 141 to 165 (AESYVE-FVNRLQISLADNLPDGVPK). The possible implication of this cell-mediated immune response in BLV pathogenesis and vaccine development is discussed.

No abstract

No abstract