V3 Loop Sequences Variability of HIV-1 Proviral of Thai Asymptomatic Carriers Whose Plasma Antibody to HIV-1 V3-Ioop Peptide are Non-detectable

The peptide enzymeimmuno assay (PEIA) has been applied for determination the subtype of HIV-1 by detection of antibody to HIV-1 V3 specific peptide. It was useful for monitoring a wide distribution of HIV-1 subtype in Thailand. However some samples cannot be identified the subtype due to non-reactive or inconclusive PEIA results. To investigate any possible factors affected the results of HIV-1 subtype by PEIA, we analyzed the nucleotide and amino acid sequence variability of V3 region of HIV-1 proviral from asymptomatic carriers whose plasma antibody to HIV-1 V3-loop peptide were non-detectable or inconclusive comparing with the reactive samples in each subtype of HIV-1. Genetic variability of V3 sequence was analysed by nested PCR and direct DNA sequencing. No significant difference of V3 intrasubtype genetic divergence between the samples with PEIA reactive and non-reactive in either subtype E and B. There was a distinct change of amino acid sequence found around the tip of V3-loop in some genotype E sequences but V3-PEIA was non-reactive. This may be one of the factors that cause undetectable EPIA. Dual infections of HIV-1 subtype B and F was found in one patient and causes a discordant result of peptide EIA and DNA sequences. Low level of antibody to V3-specific peptide during the time of infection was found in sequential plasma samples from the same patient. Keywords: HIV-1, genotype, peptide, EIA