ANALYSIS OF ENVELOPE GLYCOPROTEIN-SPECIFIC ANTIBODIES FROM SIV-INFECTED AND GP110-IMMUNIZED MONKEYS IN ACC AND ADCC ASSAYS

Sera collected from SIV-infected or recombinant glycoprotein-immunized monkeys were characterized for antibodies participating in antibody-c omplement-mediated cytolysis (ACC) and antibody-dependent cellular cyt olysis (ADCC) in terms of their IgG subclass and epitope specificity, In a competitive inhibition ELISA, gp110-specific antibody reactivity with nondenatured rgp110 was blocked completely by soluble homologous rgp110 and partially inhibited by heterologous rgp110, suggesting cros s-reactivity between viral strains, However, only partial inhibition w as observed with denatured recombinant gp140 (rgpl40) in selected monk eys, indicating that the majority of gp110-specific antibodies recogni zed conformational epitopes, ACC activity against recombinant vaccinia -infected, envelope-expressing targets was found in sera from both inf ected and immunized monkeys, whereas ADCC activity was observed only i n sera from infected monkeys, ACC was blocked with denatured rgpl40 as well as nondenatured rgp110, indicating that ACC-mediating antibodies recognized mainly linear epitopes, In contrast, rgpl40 did not compet e as effectively as rgp110 in the ADCC assay, indicating that the majo rity of ADCC antibodies recognized conformational epitopes, Competitiv e inhibition using three peptide fragments of gp110 indicated that epi topes recognized by ACC antibodies lie within amino acid residues 214- 471, a region that spans V3, whereas ADCC-reactive epitopes lie betwee n amino acid residues 52 and 214 at the N-terminal end of gp110, Colum n chromatography of rhesus IgG resulted in three subclass-enriched fra ctions, designated IgG-I, IgG-II, and IgG-III. IgG-I, but not IgG-II o r IgG-III, from both infected and immunized monkeys mediated ACC, wher eas IgG-I and IgG-II from infected monkeys mediated ADCC, The results of this study may be helpful in designing future immunization protocol s to induce membrane-reactive antibody effector mechanisms in controll ing HIV infection and/or disease progression.