RESUMO
In the context of DNA vaccines the native equine infectious anemia virus (EIAV)-envelope gene has proven to be an extremely weak immunogen in horses probably because the RNA transcripts are poorly expressed owing to an unusual codon-usage bias, the possession of multiple RNA splice sites and potential adenosine-rich RNA instability elements. To overcome these problems a synthetic version of sequences encoding the EIAV surface unit (SU) envelope glycoprotein was produced (SYNSU) in which the codon-usage bias was modified to conform to that of highly expressed horse and human genes. In transfected COS-1 cell cultures, the steady state expression levels of SYNSU were at least 30-fold greater than equivalent native SU sequences. More importantly, EIAV-specific humoral and lymphocyte proliferation responses were induced in ponies immunized with a mammalian expression vector encoding SYNSU. However, these immunological responses were unable to confer protection against infection with a virulent EIAV strain.
Assuntos
Anemia Infecciosa Equina/prevenção & controle , Vírus da Anemia Infecciosa Equina/imunologia , Vacinas de DNA/imunologia , Proteínas do Envelope Viral/imunologia , Vacinas Virais/imunologia , Sequência de Aminoácidos , Animais , Anticorpos Antivirais/imunologia , Sequência de Bases , Proliferação de Células , Cavalos , Imunoglobulina G/sangue , Dados de Sequência Molecular , Proteínas Recombinantes/imunologia , Linfócitos T , Fatores de Tempo , Proteínas do Envelope Viral/químicaRESUMO
Pathogenicity was reportedly restored to an avirulent molecular clone of equine infectious anemia virus (EIAV) by substitution of 3' sequences from the pathogenic variant strain (EIAV(PV)). However, the incidence of disease in horses/ponies was found to be significantly lower (P = 0.016) with the chimeric clone (EIAV(UK)) than with EIAV(PV). This was attributable to 3' rather than 5' regions of the proviral genome, where EIAV(UK) differs from the consensus EIAV(PV) sequence by having a 68-bp duplication in the 3' LTR and arginine (R(103)) rather than tryptophan (W(103)) at position 103 in the second exon of rev. In EIAV(UK) recipients the duplication was rapidly eliminated and R(103) replaced by W(103) in the viral population. Furthermore, removal of the 3' variant sequences from EIAV(UK) (EIAV(UK3)) resulted in an equivalent (P = 0.013) disease potential in Equus caballus to EIAV(PV). The 68-bp duplication and/or R(103) may limit peak viral RNA accumulation during acute infection.
