Enhanced sensitivity to neutralizing antibodies in a variant of equine infectious anemia virus is linked to amino acid substitutions in the surface unit envelope glycoprotein

Infectious molecular clones have been isolated from two maedi-visna virus (MVV) strains, one of which (KV1772kv72/67) is an antigenic escape mutant of the other (LV1-1KS1). To map the type-specific neutralization epitope, we constructed viruses containing chimeric envelope genes by using KV1772kv72/67 as a backbone and replacing various parts of the envelope gene with equivalent sequences from LV1-1KS1. The neutralization phenotype was found to map to a region in the envelope gene containing two deletions and four amino acid changes within 39 amino acids (positions 559 to 597 of Env). Serum obtained from a lamb infected with a chimeric virus, VR1, containing only the 39 amino acids from LV1-1KS1 in the KV1772kv72/67 backbone neutralized LV1-1KS1 but not KV1772kv72/67. The region in the envelope gene that we had thus shown to be involved in escape from neutralization was cloned into pGEX-3X expression vectors, and the resulting fusion peptides from both molecular clones were tested in immunoblots for reactivity with the KV1772kv72/67 and VR1 type-specific antisera. The type-specific KV1772kv72/67 antiserum reacted only with the fusion peptide from KV1772kv72/67 and not with that from LV1-1KS1, and the type-specific VR1 antiserum reacted only with the fusion peptide from LV1-1KS1 and not with that from KV1772kv72/67. Pepscan analysis showed that the region contained two linear epitopes, one of which was specific to each of the molecularly cloned viruses. This linear epitope was not bound by all type-specific neutralizing antisera, however, which indicates that it is not by itself the neutralization epitope but may be a part of it. These findings show that mutations within amino acids 559 to 597 in the envelope gene of MVV virus result in escape from neutralization. Furthermore, the region contains one or more parts of a discontinuous neutralization epitope.

Section: Discussionmentioning

confidence: 99%

Naturally Occurring Mutations within 39 Amino Acids in the Envelope Glycoprotein of Maedi-Visna Virus Alter the Neutralization Phenotype

Skraban

Matthíasdóttir

Torsteinsdóttir

et al. 1999

“…The structural changes in the envelope that mediated this adaptation created viruses that were abnormally sensitive to neutralization and thus were unrepresentative of the more resistant primary (or field) isolates (5,16,38,42,50,56,70). Precisely why primary isolates are resistant to neutralization is uncertain, but it is clear that this phenomenon is not unique to HIV-1 and may be a general property of lentiviruses (3,8,11,41,74).…”

mentioning

confidence: 99%

Neutralization of the human immunodeficiency virus type 1 primary isolate JR-FL by human monoclonal antibodies correlates with antibody binding to the oligomeric form of the envelope glycoprotein complex

Fouts

Binley

Trkola

et al. 1997

216

To test whether antibodies that are neutralizing or nonneutralizing for human immunodeficiency virus type 1 (HIV-1) primary isolates can be distinguished by their affinities for the oligomeric envelope glycoproteins, we selected HIV-1 JR-FL as a model primary virus and a panel of 13 human monoclonal antibodies (MAbs) and evaluated three parameters: (i) half-maximal binding to recombinant monomeric envelope, gp120 JR-FL ; (ii) half-maximal binding to oligomeric envelope of HIV-1 JR-FL expressed on the surface of transfected 293 cells; and (iii) neutralization of HIV-1 JR-FL in a peripheral blood mononuclear cell-based neutralization assay. Two conclusions can be drawn from these experiments. First, we confirm that antibody interactions with monomeric gp120 do not predict primary virus neutralization. Second, we show that neutralization correlates qualitatively with the relative affinity of an antibody for the oligomeric envelope glycoproteins, at least for HIV-1 JR-FL .

“…Although the role of neutralizing antibodies in the clearing of HIV-1 infections, in the abrogation of acute-infection viremia, and in curbing disease progression is uncertain (34), the neutralization insensitivity of PI has influenced the decision to interrupt clinical vaccine trials, which were monitored in part by testing for neutralizing antibodies (34). Other lentiviruses, such as simian immunodeficiency virus (SIV), feline immunodeficiency virus, and equine infectious anemia virus, have also been reported to lose their natural neutralization resistance upon serial passage in cell lines (5,8,34): a general explanation may be required.…”

mentioning

confidence: 99%

Quantitative model of antibody- and soluble CD4-mediated neutralization of primary isolates and T-cell line-adapted strains of human immunodeficiency virus type 1

Klasse

Moore

1996

Primary isolates (PI) of human immunodeficiency virus type 1 (HIV-1) are considerably less sensitive than T-cell line-adapted strains to neutralization by soluble CD4 and by most cross-reactive monoclonal antibodies to the viral envelope (Env) glycoprotein, as well as by postinfection and postvaccination sera (J. P. Moore and D. D. Ho, AIDS 9 [suppl. A]:5117-5136, 1995). We developed a quantitative model to explain the neutralization resistance of PI. The factors incorporated into the model are the dissociation constants for the binding of the neutralizing agent to native Env oligomers, the number of outer Env molecules on the viral surface (which decreases by shedding), and the minimum number of Env molecules required for attachment and fusion. We conclude that modest differences in all these factors can, when combined, explain a relative neutralization resistance of PI versus T-cell line-adapted strains that sometimes amounts to several orders of magnitude. The hypothesis that neutralization of HIV is due to the reduction below a minimum number of the Env molecules on a virion available for attachment and fusion is at odds with single-and few-hit neutralization theories. Our analysis of these ideas favors the hypothesis that neutralization of HIV is instead a competitive blocking of interactions with cellular factors, including adsorption receptors.