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Strain-specific neutralizing determinant in the transmembrane protein of simian immunodeficiency virus
T Kodama1, D P Burns, D P Silva
1New England Regional Primate Research Center, Harvard Medical School, Southborough, Massachusetts 01772.
Abstract:
Monoclonal antibody SF8/5E11, which recognizes the transmembrane protein (TMP) of simian immunodeficiency virus of macaque monkeys (SIVmac), displayed strict strain specificity. It reacted with cloned and uncloned SIVmac251 but not with cloned SIVmac142 and SIVmac239 on immunoblots. This monoclonal antibody neutralized infection by cloned, cell-free SIVmac251 and inhibited formation of syncytia by cloned SIVmac251-infected cells; these activities were specific to cloned SIVmac251 and did not occur with the other viruses. Site-specific mutagenesis was used to show that TMP amino acids 106 to 110 (Asp-Trp-Asn-Asn-Asp) determined the strain specificity of the monoclonal antibody. This strain-specific neutralizing determinant is located within a variable region of SIVmac and human immunodeficiency virus type 2 (HIV-2) which includes conserved, clustered sites for N-linked glycosylation. The determinant corresponds exactly to a variable, weak neutralizing epitope in HIV-1 TMP which also includes conserved, clustered sites for N-linked glycosylation. Thus, the location of at least one neutralizing epitope appears to be common to both SIVmac and HIV-1. Our results suggest a role for this determinant in the viral entry process. Genetic variation was observed in this neutralizing determinant following infection of a rhesus monkey with molecularly cloned SIVmac239; variant forms of the strain-specific, neutralizing determinant accumulated during persistent infection in vivo. Selective pressure from the host immune response in vivo may result in sequence variation in this neutralizing determinant.
Insights
A specific monoclonal antibody targeting the simian immunodeficiency virus transmembrane protein (TMP) shows strain-specific neutralization. This study identifies a key amino acid region in TMP responsible for this specificity and its potential role in viral entry.
Area of Science:
- Virology
- Immunology
- Molecular Biology
Background:
- Monoclonal antibody SF8/5E11 targets the simian immunodeficiency virus of macaque monkeys (SIVmac) transmembrane protein (TMP).
- Previous studies indicated strain-specific reactivity of SF8/5E11 with SIVmac isolates.
Purpose of the Study:
- To characterize the strain specificity of monoclonal antibody SF8/5E11 against SIVmac TMP.
- To identify the specific amino acid residues within SIVmac TMP responsible for antibody recognition and neutralization.
- To investigate the conservation and potential role of this epitope in viral entry and evolution.
Main Methods:
- Immunoblotting to assess antibody reactivity with different SIVmac strains.
- Neutralization assays to evaluate the antibody's ability to block viral infection and cell fusion.
- Site-specific mutagenesis of SIVmac TMP to pinpoint critical amino acids for antibody binding.
- Sequence analysis of TMP in SIVmac and related viruses (HIV-2, HIV-1).
- In vivo infection model using rhesus monkeys to observe viral evolution.
Main Results:
- Monoclonal antibody SF8/5E11 demonstrated strict strain specificity, reacting only with SIVmac251 and not SIVmac142 or SIVmac239.
- The antibody effectively neutralized SIVmac251 infection and inhibited syncytia formation, with activity limited to the SIVmac251 strain.
- Site-specific mutagenesis identified amino acids 106-110 (Asp-Trp-Asn-Asn-Asp) in TMP as the determinant for strain specificity.
- This determinant is located in a variable region of SIVmac TMP, conserved in HIV-2 and analogous to a neutralizing epitope in HIV-1 TMP.
- Genetic variation in this determinant was observed during persistent SIVmac239 infection in vivo, suggesting immune pressure.
Conclusions:
- The identified amino acid region (106-110) in SIVmac TMP is crucial for the strain-specific recognition and neutralization by antibody SF8/5E11.
- This epitope is shared across SIVmac and HIV-1, suggesting a common functional role in viral entry.
- In vivo viral evolution indicates that this neutralizing determinant is subject to host immune selection pressure, leading to sequence variation during persistent infection.