Scientists in the United States said on Monday they could help
explain why women infected with the human immunodeficiency virus
(HIV) advance faster to Aids than men.
One of the enigmas about the Aids pandemic is why women, after
infection with HIV-1, seem better able to combat the virus in its
early stages but then advance faster to Aids compared to men
infected with a similar level of the virus.
The answer lies in the response of a key component in their
immune system, and hormonal differences may account for it,
according to a paper published online by the journal Nature
If right, it throws up new possibilities for drugs that would
hinder the process, its authors added.
How the study was done
The study focuses on plasmacytoid dendritic cells (pDCs), which
are "first responders" in the immune system. They detect a
microbial intruder and then alert other defenders.
The pDCs recognise the Aids virus through a little docking point
called Toll-like receptor 7, or TLR7. Once their TLR7 is switched
on, the pDCs call up an important immune-system molecule called
Researchers at the Ragon Institute of the Massachusetts General
Hospital were intrigued by lab-dish tests that showed higher levels
of the female hormone progesterone intensified pDC activation.
The team then linked interferon alpha to the activation of one
of the heavy artillery of the immune system - CD8 cells.
Previous research has already spotted an intriguing phenomenon.
The more CD8 cells that are stimulated, the faster a patient
progresses to acquired immune deficiency syndrome (AIDS), the stage
whereby the immune system is so devastated that the body becomes
prey to opportunistic disease. Why this is so is unclear, though.
What the study showed
Ragon Institute investigator Marcus Altfeld said that the
results suggest men and women may differ in an important way in how
their immune systems respond to HIV.
In the early stages of infection, a stronger activation of their
immune system could be beneficial to women, he said.
But in the long run, the persistent viral replication and
chronic activation of the immune system - as indicated by the CD8
cells - can lead to faster progression to Aids.
Altfeld said the study raised new questions about how sex
hormones modulate the molecular cascade to HIV infection. One
interesting idea, he added, could be a drug that stops or slows the
TLR7 alarm system.
"Focussing on immune activation separately from viral
replication might give us new therapeutic approaches" to tackling
the virus, he said. – (Sapa, July 2009)
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