- SAN FRANCISCO (Reuters) - The AIDS virus may trick some of the body's immune
cells into a kind of mass suicide, suddenly stripping patients of key immune
defenses after years of relative good health, according to a new study
released Wednesday.
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- U.S. researchers reported in the journal
Nature that their study could provide new clues as to why AIDS patients
rapidly sicken and die years after infection, and what types of therapy
might stop the precipitous decline.
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- The study focused on the interaction
between HIV and the CD8 T-cells -- known as "killer T-cells"
because of their role in fighting off infection.
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- Unlike CD4 T-cells, the "helper"
T-cells which doctors measure as a standard marker for the progress of
HIV infection in the body, CD8 T-cells lack the receptor, or chemical doorway,
that HIV uses to get into a cell. This makes them immune to HIV infection.
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- While the number of CD4 T-cells in an
infected person's body drops over time, levels of CD8 T-cells can remain
stable for years before suddenly plunging -- a sharp drop which gives HIV
the chance to multiply even faster.
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- Researchers Eric Verdin of the University
of California San Francisco and Georges Herbein of the Picower Institute
for Medical Research at North Shore University Hospital in New York found
evidence that a particular strain of HIV that appears in the late stages
of HIV disease may prompt the "killer" T-cells to commit suicide.
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- "Once patients lose their CD8 T-cells,
growth of the virus in CD4 helper cells is probably boosted, and more cells
will be killed," Herbein said. "So you will have an accelerated
decline in overall immune function, until the immune system is exhausted."
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- Such cell suicide, also known as apoptosis,
is usually a normal function. It helps the body get rid of damaged or cancerous
cells.
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- Herbein and Verdin said a type of AIDS
virus known as the "syncytium inducing", or SI strain common
in the later stages of HIV disease, gets rid of the CD8 T-cells by bringing
in another immune cell, the macrophage.
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- The SI strain binds itself to a molecule
known as CXCR4 found both on the CD8 T-cell and on macrophages. When both
CD8 T-cells and macrophages are present, the CD8 cells commit suicide.
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- Verdin and Herbein said the "suicide"
of the CD8 T-cells occurred only when macrophages were present, and only
when a syncytium-inducing strain of HIV was used.
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- They said both kinds of immune cells
produced a chemical known as tumor necrosis factor, which is supposed to
trigger apoptosis.
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- "It is a surprise that different
HIV strains would affect CD8 cells differently, since the virus doesn't
infect those cells," Herbein said. "This is a totally new idea."
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- The researchers said that their results
could indicate a new treatment path focused on preventing HIV from binding
with CXCR4. This, at least in some cases, could theoretically prevent patients
from seeing their condition progress to advanced AIDS.
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- "Right now, everyone's focused on
finding ways to block CCR5," a molecule that allows a cell to become
infected by early strains of HIV, Verdin said. "Our research shows
that it may be just as important to find ways to stop viruses that bind
to CXCR4."
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