Anti-V3 and anti-IgG antibodies of healthy individuals share complementarity structures

It was recently shown that antibodies reactive with a peptide from the tip of the HIV-1(NY5) gp120 V3 loop (V3 peptide) are present not only in sera o f HIV-positive patients but also in sera of healthy HIV-negative individual s. In the present study, we show that V3 peptide reactive antibodies are pr edominantly IgM in sera of HIV negative individuals and that a fraction of the IgG anti-V3 antibodies exhibit features of autoantibodies. These antibo dies were purified by chromatography on IgG-sepharose columns from sera as well as from purified IgG anti-V3 antibodies. A higher IgG anti-V3 reactivi ty was detected in autoantibody preparations from HIV-positive sera as comp ared with the reactivity of sera and purified antibodies from HIV-negative individuals. This was confirmed by solid phase binding of IgG anti-V3 antib odies both to V3 and to human IgG F(ab')(2) antigens. The autoantibodies di d not bind to peptides that share sequence similarity with V3 peptide indic ating a high epitope specificity. The detection of antibodies against HIV e pitopes in HIV-negative individuals may suggest that anti-V3 antibodies aft er HIV infection represent at least in part a secondary immune response.