Serum reactivity to HIV-1 accessory gene products distinguishes East African from West African HIV strains as infecting agent

The antibody response to the HIV-1 specific "out" (vpu) protein: identification of an immunodominant epitope and correlation of antibody detectability to clinical stages

Overlapping decapeptides based on the sequences of two human immunodeficiency virus type 1 (HIV-1) strains (HXB2 and ELI) were used to identify an immunodominant epitope of the nonstructural protein "out" (vpu) of the human immunodeficiency virus type 1. Of 29 HIV-1 antibody-positive sera, 6 reacted with decapeptides corresponding to the C-terminal amino acid sequence VEMGVEMGHHAPWDVDDL of the "out" (vpu) protein. This oligopeptide was synthesized by the solid phase method and used to develop an enzyme-linked immunosorbent assay (ELISA) for screening of 243 HIV-1-seropositive and 75 HIV-1-seronegative sera. It was found that 26% of the HIV-1 antibody-positive sera were reactive in the "out" (vpu) peptide ELISA, whereas none of the HIV-1-negative sera reacted with the oligopeptide. Correlation of reactivity of sera with the Walter Reed (WR) staging classification demonstrated that individuals classified WR 1 (36%) and WR 2 (42%) were more often reactive than patients classified WR 3-6 (11%).

Serum capacity to inhibit reverse transcriptase in vitro distinguishes HIV-1 infection from HIV-2 or SIV infection

The inhibition of HIV-1 and SIV reverse transcriptase by human and rhesus macaque serum positive for HIV-1 or HIV-2/SIV antibodies was studied. The domain to which reverse transcriptase-inhibiting antibodies were elicited appeared to be highly antigenic. A total of 67% (48 of 72) of individuals had HIV-1 reverse transcriptase-inhibiting (RTI) antibodies 1 year after seroconversion for HIV-1, 90% (9 of 10) of HIV-2 antibody positive persons had SIV RTI antibodies, and all four experimentally SIV-infected rhesus macaques developed SIV RTI antibodies. Low cross-reactivity between HIV-1 and HIV-2/SIV RTI antibodies was observed. Of 10 HIV-1 RTI sera, 2 reduced SIV RT activity by more than 50% (mean reduction 85 versus 24%). Only 1 of 9 SIV RTI human sera reduced HIV-1 RT (mean reduction 74 versus 25%). This serum, however, showed a shared reactivity against both HIV-1 and HIV-2. These results indicate that the HIV-1 domain inducing RTI antibodies is antigenically different from the HIV-2/SIV domain.

Antibody recognition of amino acid divergence within an HIV-1 neutralization epitope

Antibodies elicited by HIV-1 strains, and which neutralize such strains in vitro, bind to synthetic peptides of 5-8 amino acids in length. These amino acids, although variable, have a fixed location between two cysteines in the carboxyl terminus of the HIV-1 external envelope. Nine peptides of 9 amino acids corresponding to the gp120 domains of European and American (LAV-1, NY5, CDC4, SF2), Haitian (RF) and African (ELI, MAL, Z3, Z6) HIV-1 strains, were synthesized using LAV-1 and RF neutralization epitopes as models. Serum of chimpanzees infected with LAV-1, HTLV-IIIB or HTLV-IIIRF reacted predominantly with the homologous peptide, although cross-reactivity with heterologous peptides occurred: 8 out of 11 human sera with HTLV-IIIB-neutralizing activity bound the LAV-1/HTLV-IIIB peptide, and 6 out of 7 sera with HTLV-IIIRF-neutralizing activity bound the RF peptide. African sera reacted most frequently with the Z3 peptide (78%) while only 35% (p = 0.0001) of European and 20% (p less than 0.0001) of American sera recognized it. Recognition patterns of children from the USA and Europe were different. Although multiple reactivities were observed, blocking experiments favoured cross-reactivity as the explanation. Based on the antibody profiles of nonapeptide recognition, peptides LAV-1, RF and SF2 were clustered, as were NY5 and CDC4, and so were Z6, MAL and ELI. This antigenic relatedness of HIV-1 strains could not entirely be explained by the physico-chemical characteristics of the nonamers per se. Resemblance was observed with the clustering of HIV-1 strains based on the divergence of the nucleotide sequence of entire HIV-1 envelopes. This implies a role of peripheral envelope residues, in the context of infectious particles or infected cells, in determining the specificity of antibodies reactive to the V3 domain. Therefore, the neutralization domain in this variable region may be considered part of a conformational structure involving several envelope regions which appear distinct from each other in the primary sequence.