Ancient interspecies viral battle may have left humans vulnerable to HIV
- From: Florida <demeter547opine@xxxxxxxxx>
- Date: Fri, 22 Jun 2007 04:29:48 -0700
Yahoo! News
http://news.yahoo.com/s/nm/20070621/hl_nm/aids_retrovirus_dc
Ancient viral battle left people vulnerable to HIV
By Will Dunham Thu Jun 21, 3:24 PM ET
A battle won by human ancestors against a virus that infected
chimpanzees and other primates millions of years ago may have left
people today more vulnerable to the AIDS virus, scientists said on
Thursday.
That ancient battle helped humans evolve and rely on a gene that may
not protect so well against a modern retrovirus, the human
immunodeficiency virus or HIV, the researchers said.
They focused on an ancient virus, known as Pan troglodytes endogenous
retrovirus, or PtERV1, to find clues as to why HIV has exacted such a
high toll on humanity.
"Events that happened millions of years ago have shaped human
evolution, in particular susceptibility to modern human infectious
diseases," Michael Emerman of the Fred Hutchinson Cancer Research
Center in Seattle, Washington, who led the study, said in a telephone
interview.
There is genetic evidence that the PtERV1 virus infected chimpanzees,
gorillas and old-world monkeys about 4 million years ago, but no
evidence it infected humans. The virus is believed to have gone
extinct perhaps 2 million years ago.
Emerman's team was able to resurrect a small portion of the PtERV1 by
using DNA remnants of the virus lodged in the genome of chimpanzees.
Working with cells in a laboratory, they found that an old virus-
fighting gene present in people, known as TRIM5a, succeeded in
neutralizing PtERV1.
The gene makes a protein that binds to and destroys the virus before
it can replicate within the body, they report in the journal Science.
"However, while TRIM5a may have served humans well millions of years
ago, the antiviral protein does not seem to be good at defending
against any of the retroviruses that currently infect humans, such as
HIV-1," Emerman said in a statement.
VIRAL INFILTRATION
Small mutations may account for this. TRIM5a taken from baboons and
African green monkeys carried mutations that helped it reduce HIV in
lab dishes but it was almost useless against PtERV1.
When TRIM5a worked well against PtERV1, as in humans, it was
ineffective against HIV.
"In the end, this drove human evolution to be more susceptible to
HIV," Emerman said.
Retroviruses have been infiltrating the genomes of human ancestors and
other animals for millions of years. These viruses go into the
chromosomes and DNA of the cells they infect and can get passed on
from generation to generation.
In fact, such vestiges of primitive infections comprise 8 percent of
the human genome, Emerman said.
Other researchers found remnants of the PtERV1 retrovirus in the
genomes of chimpanzees, gorillas and some other primates in Africa,
but not humans or another great ape, the orangutan.
When the chimpanzee genome was mapped, a major difference compared to
the human genome was the presence of about 130 copies of PtERV1 in
chimpanzees and zero in people, the researchers. The retrovirus is so
mutated in living chimps that it is inactivated, the researchers said.
While the study sheds light on the historical human susceptibility to
pathogens, Emerman said, it does not appear to provide immediate clues
as to how to beat HIV.
© 2007 Reuters Limited
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