Specificity of antipeptide antibodies produced against V2 and V3 regions of the external envelope of human immunodeficiency virus type 2

The V2 region of simian immunodeficiency virus (SIV) and V3 region of human immunodeficiency virus type 1 (HIV-1) have been reported to be neutralization epitopes. We analysed the corresponding regions in HIV-2. Synthetic peptides modeling the V2 (aa 149–168) and V3 (CV3: aa 298–315 and NV3: aa 306–324) regions of the HIV-2 external envelope glycoprotein were coupled to KLH and used as immunogens in rabbits. We characterized the resulting antiV2 and antiV3 antibodies for their ability to recognize native and deglycosylated HIV-2 envelope glycoprotein, to block gp-CD4 interaction and to inhibit syncytium formation in vitro. The three synthetic peptides induced antibodies able to recognize specifically the native HIV-2 envelope glycoprotein with a significant avidity (K0.5 between 6 × 10−7 and 8 × 10−9). Interestingly, the reactivity of antibodies produced against the V2 peptide, which contains two potential sites of N-glycosylation, was higher against the fully deglycosylated than glycosylated HIV-2 external envelope glycoprotein (gp105). The antipeptide antibodies were used to investigate the topography of these regions in the preformed gp-CD4 complex in indirect immunofluorescence assays. The V2 and V3 regions in the complex remained accessible to their respective antibodies. Moreover, preincubation of gp105 with anti V2 or anti V3 antibodies did not prevent gp-CD4 interaction. Thus the V2 and V3 regions are not directly involved in the gp105 binding site for the CD4 receptor. Finally, in contrast with results obtained with antibodies produced against the V3 region of HIV-1 gp120 and monoclonal antibodies produced against the V2 of SIV, antibodies produced against V2 and V3 of HIV-2 were unable to inhibit syncytium formation induced by HIV-2 in vitro.