Characteristic of HIV-1 in V3 loop region based on seroreactivity and amino acid sequences in Thailand.

The third variable (V3) domain of the envelop (env) protein has been used for determining genetic subtype and phenotypic characteristics of human immunodeficiency virus type 1 (HIV-1) isolates. Based on the seroreactivity of the HIV-1 subtype by V3 peptide binding enzyme immunoassay (EIA) of 351 samples obtained in 1998 from HIV-1 infected individuals and AIDS patients, we found that 283 (80.6%) were subtype E, 20 (5.7%) were subtype B, 28 (8.0%) were cross-reactive between both types and 20 (5.7%) were non-typeable. The degree of seroreactivity of HIV-1 subtype E decreased significantly when the amino acid at the crown of the V3 loop was substituted from a GPGQ motif to GPGR motif. Interestingly, AIDS patients who had V3 sequences of subtype E as GPGR motif had a stronger immunoreactivity to GPGQ motif peptides than to GPGR motif peptides, in contradiction for their proviral sequences. The results suggested that mutations in the V3 loop may lead to a changed immunoreactivity that makes HIV-1 mutants unrecognizable or allow escape from the primary immune response by means of neutralizing sensitivity. In connection with vaccine development, it should be pointed out that the combination of V3 sequencing and peptide EIA could provide a novel approach to obtain a primarily infected virus sequence as a target for a preventive AIDS vaccine.