Determinants for the syncytium-inducing phenotype of HIV-1 subtype F isolates are located in the V3 region.

The HIV-1 syncytium-inducing phenotype is determined by virus replication and the presence of cytopathic effects in MT-2 cells. There is a strong correlation between the syncytium-inducing/MT-2-tropic phenotype and positively charged amino acids at positions 306 and 320 in the V3 loop for HIV-1 subtypes A, B, D, and E. In contrast, a lack of correlation between signature amino acids and syncytium formation in MT-2 cells for subtype F viruses from Romania has been reported. Virus phenotype and V3 loop amino acid sequences from Romanian HIV-1 subtype F isolates were further investigated in the present study. While the determinants of MT-2 tropism are clearly harbored in the V3 loop of subtype F isolates from Romania, the induction of syncytium formation occurs in the presence or absence of positively charged amino acids at positions 306, 320, and/or 324. However, the net positive charge of V3 loop sequences derived from syncytium-inducing viruses was higher than that of the nonsyncytium-inducing isolate.

HIV-1 diversity in Romania.

OBJECTIVES: To evaluate the prevalence and the dynamics of HIV-1 subtypes in Romanian adults and children, and to investigate the origins of the nosocomial epidemic. DESIGN: A total of 1000 serum and plasma samples, from adults (n = 579) and children (n = 421) who were diagnosed as being HIV-1-infected during 1990-1997 in 39 of the 41 Romanian districts, were serotyped. Viral DNA was isolated from blood samples of 84 patients and the viruses were genotyped. METHODS: Serotyping was performed with a peptide subtype-specific enzyme immunoassay (SSEIA), based on in vitro competition for antibody binding between the representative V3 peptides of the different clades (A-F). Proviral HIV-1 DNA was genotyped by heteroduplex mobility assay or by sequence analysis of the C2-V3 env region. RESULTS: SSEIA showed that 93% of the samples from horizontally infected children were serotype F, 1% were serotype B, and the remaining 6% were uninterpretable. In vertically infected children, 74% of strains were serotype F, 10% were serotype A, 3% were serotype B, and 3% were serotype E. Serotype F was also the dominant subtype in adults (68%), but serotypes A, B, C, D and E were also detected. SSEIA gave indeterminate results in 7% of cases. A strong correlation (90%) between serotyping and genotyping for subtype F was found. Analysis of the relative incidence of the different serotypes over a 7-year period (1990-1997) showed a stable distribution. CONCLUSIONS: Subtype F largely dominates the epidemiology of HIV-1 infection in both children and adults in Romania, although other major subtypes are present. The predominance of subtype F in Romania may be a future potential source of HIV-1 variability in Europe.

Characterization of HIV type 1 from Romanian children: lack of correlation between V3 loop amino acid sequence and syncytium formation in MT-2 cells.

The biological properties and amino acid sequences of the third variable domain (V3 loop and flanking regions) of the env region of 34 HIV-1 isolates obtained from Romanian children were analyzed. Unambiguous nucleic acid sequences were obtained from 31 isolates. The derived V3 amino acid sequences were highly homologous (93-100%) and clustered with the HIV-1 subtype F Romanian consensus. Five of the 31 isolates presented a syncytium-inducing phenotype in MT-2 cells and established continuous viral replication in various CD4+ cell lines (rapid/high phenotype). The V3 sequence from one of these isolates showed a slightly lesser degree of homology with the consensus sequence. The presence of positively charged amino acids at positions 306 and 320 has been strongly associated with the ability to induce syncytia in MT-2 cells, whereas negatively or uncharged amino acids at these positions are present in non-syncytium-inducing isolates (slow/low phenotype). There was, however, no correlation between phenotype and amino acid sequence in the five syncytium-inducing isolates; negatively or uncharged amino acids were conserved at positions 306 and 320 for all 31 isolates in sequences obtained from PBMCs. A tendency toward a more positive net charge in the V3 loop of syncytium-inducing isolates was noted. These data confirm the recent observations that HIV-1 isolates from Romania not only cluster in subtype F, but also show a high degree of interpatient homogeneity in the V3 region.(ABSTRACT TRUNCATED AT 250 WORDS)