MBE Advance Access published online on April 23, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn099
Research Article |
Influence of the mutant spectrum in viral evolution: focused selection of antigenic variants in a reconstructed viral quasispecies
1 Centro de Biología Molecular "Severo Ochoa" (CSIC-UAM), C/ Nicolás Cabrera, 1 Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
* Correspondence to: Esteban Domingo e-mail: edomingo{at}cbm.uam.es, Tfno. 91 196 4540, Fax: 91 196 4420
Received for publication February 14, 2008. Revision received April 17, 2008. Accepted for publication April 19, 2008.
RNA viruses replicate as complex mutant distributions termed viral quasispecies. Despite this, studies on virus populations subjected to positive selection have generally been performed and analyzed as if the viral population consisted of a defined genomic nucleotide sequence; such a simplification may not reflect accurately the molecular events underlying the selection process. In the present study we have reconstructed a foot-and-mouth disease virus quasispecies with multiple, low frequency, genetically distinguishable mutants that can escape neutralization by a monoclonal antibody. Some of the mutants included an amino acid substitution that affected an integrin-recognition motif that overlaps with the antibody-binding site, while other mutants included an amino acid substitution that affected antibody binding but not integrin recognition. We have monitored consensus and clonal nucleotide sequences of populations passaged either in the absence or the presence of the neutralizing antibody. In both cases, the populations focused towards a specific mutant that was surrounded by a cloud of mutants with different antigenic and cell recognition specificities. In the absence of antibody selection, an antigenic variant that maintained integrin recognition became dominant, but the mutant cloud included as one of its minority components a variant with altered integrin recognition. Conversely, in the presence of antibody selection, a variant with altered integrin-recognition motif became dominant, but it was surrounded by a cloud of antigenic variants that maintained integrin recognition. The results have documented that a mutant spectrum can exert an influence on a viral population subjected to a sustained positive selection pressure, and have unveiled a mechanism of antigenic flexibility in viral populations, consisting in the presence in the selected quasispecies of mutants with different antigenic and cell recognition specificities.
Key Words: positive selection • antigenic heterogeneity • antibody-escape • virus infection