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J. Virol., Nov 1997, 8340-8346, Vol 71, No. 11
R Khanna, RW Slade, L Poulsen, DJ Moss, SR Burrows, J Nicholls and JM Burrows
The question whether immune pressure exerted by cytotoxic T lymphocytes
(CTLs) can influence the long-term evolution of genetically stable viruses
such as Epstein-Barr virus (EBV) has generated considerable scientific
interest, primarily due to its important implications for the overall
biology of the virus. While arguing for a role of CTLs in the evolution of
viruses, it is important to differentiate between genetic variation in
virus and immune recognition of these variant virus by CTLs. To assess the
role of genetic selection in the long-term evolution of EBV, we have
analyzed a large panel of type 1 EBV isolates from African, Southeast
Asian, Papua-New Guinean (PNG), and Australian Caucasian individuals. Seven
different regions of the EBV genome, which include nine CTL epitopes
restricted through a range of HLA class I alleles, were sequenced and
compared. Although numerous nucleotide changes were identified within these
isolates, comparison of synonymous and nonsynonymous substitutions in the
CTL epitope indicated that the genetic variation was generated mostly
independently of immune selection pressure. Surprisingly, an inverse
correlation between genetic variation within certain CTL epitopes and the
frequency distribution of HLA alleles that present the CTL epitopes was
seen, suggesting that the evolutionary pressures on the CTL epitopes of the
virus may be toward their conservation rather than their inactivation.
Furthermore, molecular evolutionary genetic analysis of nucleotide
sequences revealed that viral isolates from PNG are evolving as a lineage
distinct from isolates from African, Southeast Asian, and Australian
Caucasian individuals.
Copyright © 1997, American Society for Microbiology
Evolutionary dynamics of genetic variation in Epstein-Barr virus isolates of diverse geographical origins: evidence for immune pressure- independent genetic drift
Queensland Institute of Medical Research, Bancroft Centre, Brisbane, Australia. rajivK@qimr.edu.au
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