LINEAR AND CYCLIC-PEPTIDES MIMICKING THE DISULFIDE LOOPS IN HIV-2 ENVELOPE GLYCOPROTEIN INDUCED ANTIBODIES WITH DIFFERENT SPECIFICITY

The aim of this study was to compare the immunogenicity and antigenici ty of cyclic and linear peptides that mimic the disulfide loops in HIV -2ROD gp125. Based on the hypothetical assignment of intrachain disulf ide bonds in HIV-2 envelope glycoprotein, peptides expected to mimic a ll 11 disulfide-bonded domains were synthesized, oxidized or cysteine- alkylated; they were then purified and characterized. Rabbits were imm unized with either linear cysteine-alkylated peptides (LI-LII) or cycl ic oxidized peptides (C1-C11). All peptides except 7L elicited antibod ies with titers between 10(3) and 5 x 10(6). Anti-peptide C (2, 3, 4, 7, 8, 9, 11) and anti-peptide L (2, 3, 8, 9, 11) antibodies recognized the native HIV-2 gp125. Moreover, we found that cyclization of the pe ptides significantly increased the level of anti-peptide antibodies re acting with the intact antigen protein. Deglycosylation increased the level of protein reactivity of anti-peptide antibodies and rendered th e epitopes in peptides 5, 6, 10 accessible, which were masked in the n ative protein. Peptide 1 induced antibodies reacting only with the den atured reduced gp125 HIV-2. In addition, while anti-peptide L antibodi es reacted better with L peptide (called ''linear'' structural specifi city), anti-peptide C antibodies reacted similarly with L and C peptid es (called ''broad'' structural specificity). Interestingly, the ''bro ad'' structural specificity of antibodies correlated with reactivity a gainst native gp125. Although none of these anti-peptide antisera disp layed neutralizing activity against HIV-2ROD, these results support th e hypothesis that the structural restriction of peptides have a major influence upon the generation of more specific antibodies for recogniz ing the intact protein. (C) 1997 Elsevier Science Ltd. All rights rese rved.