Neutralizing antibodies (NA) against HIV-1MN and HIV-1IIIB, and antibodies binding to synthetic peptides (BA) derived from the gp120 envelope V3 region principal neutralizing determinants (PND) of the HIV-1MN, HIV-1IIIB, and HIV-1Z3 virus strains were assayed in HIV-1 antibody-positive sera from the United States, Haiti, Brazil, Zaire, and Zimbabwe. The ability of soluble PND peptide to block neutralization of the corresponding virus by representative sera was also tested. In each country, NA and BA titers were highest against the HIV-1MN strain, and compared with other countries, NA and BA titers against HIV-1MN were higher in sera from the United States and Haiti. When NA titers were compared with BA titers against either HIV-1MN or HIV-1IIIB, no correlation was found for the HIV-1IIIB strain, but there was a significant correlation for HIV-1MN. Addition of the HIV-1MN strain peptide to a neutralization assay for HIV-1MN resulted in a four- to tenfold reduction in NA titers in sera from the United States, Zaire, and Brazil. The results suggest that HIV-1MN and closely related variants are prevalent in many parts of the world, and that antibodies directed against the PND account for most of the neutralizing activity in sera of infected individuals.
PIP: Virologists assessed the extent of neutralizing antibody cross-reactivity to multiple virus strains in sera from 112 HIV-1 infected individuals from the US, Brazil, Haiti, Zaire, and Zimbabwe. They also looked at the association between virus neutralization and the level of antibody binding to synthetic peptides representing the HIV-1 gp120 V3 region principal neutralizing determinant (PND) sequences. The 3 strains observed included HIV-1 MN, HIV-1 Z3, and HIV-1 IIIB. Neutralizing antibodies (NA) and antibodies binding to synthetic peptides (BA) titers ranked highest against the PND sequence HIV-1 MN in all countries (p.01). These titers were higher in sera from the US and Haiti than sera from Brazil and Africa (p.05). A significant correlation existed between the NA and BA titers for HIV-1 MN (p.01), but not for HIV-1 IIIB. When the virologists added HIV-1 MN strain peptide to a neutralization assay for HIV-1 MN, NA titers in sera from the US, Zaire, and Brazil fell 4-10 fold. These findings intimated that HIV-1 MN and closely related variants are commonplace in several locations around the world, and that antibodies directed against HIV--1 gp120 V3 region PND sequences make up most of the neutralizing activity in sera of infected individuals. In conclusion, virologists need to conduct more studies that examine the true extent of strain variation worldwide. These studies could lay the groundwork for the development of an effective HIV-1 vaccine.