Health News
2006-06-20
Genetic mutation
may have made HIV deadly
Mutations in a
single gene may have turned the AIDS virus from a fairly
benign infection of monkeys and apes into a global pandemic
Mutations in a
single gene may have turned the AIDS virus from a fairly
benign infection of monkeys and apes into a global pandemic
that has killed more than 25 million people in 25
years, researchers say. The virus in humans appears to
have lost a genetic characteristic that protected the
immune system in apes and monkeys, the researchers report
in this week's issue of the journal Cell.
"The observed
difference in Nef function may provide—for the first
time—a mechanism to explain why many monkey species
naturally infected with SIV do not develop disease,"
said Frank Kirchhoff of the University of Ulm in
Germany, who helped lead the study.
Beatrice Hahn of
the University of Alabama at Birmingham had earlier
shown that the human immune deficiency virus, or HIV,
descended from a chimpanzee virus called simian
immunodeficiency virus, or SIV.
Many species of
monkeys and chimps are infected with various strains of
SIV, and it almost never causes disease. But HIV destroys
the human immune system, leading to AIDS and usually
death. There is no cure or vaccine.
Working with
colleagues in Germany, Gabon, and elsewhere, Kirchhoff and
Hahn's team focused on a protein and a gene called nef,
found in all SIV and HIV strains. In SIV it helps
ratchet down the activation of T-cells. These immune
system cells are key to protection against disease, and HIV
selectively infects T-cells known as CD4 helper T-cells.
In HIV infection,
these T-cells destroy themselves in a process known as
programmed cell death or apoptosis. But the SIV version of
the virus seems to somehow shut off the death
function.
"The findings
suggest that the gene function was lost during viral
evolution in a lineage that gave rise to HIV-1 and may have
predisposed the simian precursor of HIV-1 for greater
pathogenicity in humans," the researchers wrote.
This finding
could open the door to new ways of treating HIV, they said.
"A strong immune
response can be good in the short term, but if
sustained for a long time as in those with HIV, it can
exhaust the immune system," Kirchhoff said. "If you
could somehow dampen the response, it might
effectively convert the condition to the more chronic,
asymptomatic infection seen in monkeys." (Reuters)
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