Antibodies directed against a variable and neutralizable region of the HTLV-I envelope surface glycoprotein.

The majority of neutralizing antibodies of HTLV-I are directed against linear epitopes of the envelope surface glycoprotein (gp46) in the immunodominant region 175-199. Although gp46 presents a remarkable degree of conservation, the substitution of the proline at position 192 by a serine is described for 10 isolates among the 54 sequenced ones. This amino acid substitution is known to induce an important change in the orientation of the exposed residues of this region and has drastic consequences on the immunogenicity of the neutralizable epitopes located in this region. We developed monoclonal antibodies directed against epitopes located in this region containing a proline or a serine at position 192. The six monoclonal antibodies obtained recognize the gp46 at the surface of living HTLV-I producing cells, two of them are specific of a 190-197 epitope with a serine at position 192. This demonstrates that the antigenicity of this epitope differs depending on the presence of a proline or a serine at position 192. Altogether, these results demonstrate that the immunodominant neutralizable region 175-199 is antigenically variable.