Antibodies neutralizing a broad range of primary isolates (PI) are very difficult to induce by vaccination. These antibodies can however sometimes be detected in sera from HIV-infected individuals. The aim of this study is to characterize the neutralizing antibodies induced in HIV-infected individuals and to determine the epitope they recognize. Large volume of sera and plasma have been collected and screened for neutralization of both autologous and heterologous PI on PBMC. Eleven out of the 25 sera tested neutralized at least one of four heterologous PI with neutralizing titer higher than 25, and two neutralized the four ones. The IgA and IgG fractions were purified by using Jacalin and Protein A affinity chromatography respectively. For most of the sera, neutralization was retained in the IgG-contaming fraction. However, flowthrough fractions from 4 of them displayed neutralizing activity and for the two that neutralize the 4 PI, the neutralizing activity was entirely recovered in the flowthrough fraction. Dialysis experiments showed that this inhibition was not due to immunoglobulins, demonstrating the necessity to use purified Ig instead of whole serum for the study of neutralizing antibodies.In order to identify the epitopes recognized by neutralizing antibodies, we investigated their accessibility on the native virions. No correlation was found between neutralization and binding of antibodies to purified virions. Depletion of the immune complexes formed after incubation of antibodies with native PI did not decrease the neutralizing activity. These results suggest that antibodies directed against epitopes accessible on native virus did not substantially contribute to the neutralizing activity. The role of antibodies directed against epitopes exposed after conformational changes is under evaluation.The information about the nature of epitopes involved will provide essential data for the development of a vaccine designed to induce neutralizing antibodies.
Keywords: AEGIS, HIV-1, HIV Antibodies, HIV Infections, Antibodies, Epitopes, HIV Seropositivity, Virion, Antibodies, Monoclonal, Chromatography, Affinity, Immune Sera, analysis, immunology, AIDS 000709
LbPeA7021
