Summary: Synthetic peptides were used to identify continuous antigenic sites on the external envelope glycoprotein gp125 of human immunodeficiency virus (HIV)-2. Initially, seven HIV-2-positive human serum samples were screened with 172 sequential nonapeptides containing a six-amino-acid overlap. This represents the entire gp125 molecule of HIV-2ISY. The antibody reactivity was found to be mainly restricted to 14 regions within gp125. Following these results, 33 longer peptides, 15-24 amino acids in length, were synthesized and tested against a larger number of samples. Eleven antigenic regions were thus identified. Two of these were detected within a region corresponding to the C1 region and four others within a region corresponding to the C2 region of HIV-1. The highest frequency of reactivity (90%) of 31 HIV-2 seropositive human serum samples was elicited by three peptides from a region corresponding to the V3 region of HIV-1. The C-terminal portion of this region was recognized by almost 80% of the samples. Reactive regions corresponding to the V4, V5, and N-terminal portion of V4 were also identified. A mouse monoclonal antibody reacting with gp125 was mapped to the N-terminal region of the molecule and was found to react with the sequence DVWNLFETS. The peptides were used to evaluate the antibody response of monkeys immunized with whole killed HIV-2 or simian immunodeficiency virus (SIV). The monkeys showed a pattern of reactivity similar to HIV-2-infected human serum samples. Postinfection samples from monkeys inoculated with HIV-2 or SIV reacted mainly to peptides from the V3 region. Two peptides were used to detect the seroconversion of two SIV-infected monkeys. Thus, we have demonstrated that human seroreactivity to HIV-2 gp125 occurs at a few distinct linear antigenic sites distributed at similar positions on the molecule as those in HIV-1 gp120.
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