Gene variants
help stop HIV
Immune changes combat
virus in ‘elite controllers’
Body & Brain
Variations in an immune system gene
account for at least part of the uncanny
ability of some people to withstand an
HIV infection without developing AIDS,
researchers report online November 4
in Science. The study confirms past data
linking the gene, called HLA-B, to HIV
defense and narrows researchers’ focus
to molecular changes brought on by particular variations in the gene.
About one in 300 people with HIV
are “elite controllers.” Though infected
with the virus, their immune systems
somehow control the disease such that
it rarely progresses, even without medicine. Scientists have long thought that
By binding tightly to a fragment of the
virus (center), one form of the HLA-B
protein may help stymie HIV.
understanding this protection could help
to create drugs or a vaccine against HIV.
In the new study, a multinational con-
sortium of researchers identified more
than 1 million genetic variations in blood
samples from people with HIV, some elite
controllers and some not. The scientists
were able to spot more than 300 varia-
tions that differed substantially bet ween
the groups, says study coauthor Paul
de Bakker of Harvard Medical School
and Brigham and Women’s Hospital in
Boston. For example, a variant
called HLA-B*57:01 showed up
five times as often in controllers
as in the others.
MRIs able to pinpoint time of stroke
Prompt scans could expand usefulness of clot-busting drugs
By Nathan Seppa
MRI scans of stroke patients can indicate
when the stroke occurred, a revelation
that could allow more aggressive treatment to limit brain damage, researchers
report in the December Radiology.
When a clot obstructs an artery in the
brain, an estimated 2 million neurons
are lost each minute as tissue is starved
of blood and oxygen. A clot-busting drug
called tPA, or tissue plasminogen activator, can often dissolve the clot and free
up the vessel. But the drug is generally
considered safe to administer only in
the first three to 4. 5 hours after a stroke
begins (SN: 10/25/08, p. 16).
Stroke patients typically get a CT
scan when they show up at the hospital,
says neurologist Andrew Barreto of the
University of Texas Medical School at
Houston. But a CT scan cannot pin-
point when a stroke began. Neither can
many patients, either because they can’t
recall exactly when their symptoms first
appeared or because they woke up already
in the throes of a stroke. In such cases,
doctors hesitate to give tPA if too many
hours might have passed. Giving tPA too
late won’t help tissue that’s already dead
and risks causing bleeding in the brain.
the others were imaged three to 12 hours
after symptoms started.
The doctors examined the MRI scans
without knowing how long after the
stroke each had been performed. Applying three standard tests, the researchers
made measurements to assess the extent
of dead tissue in the brain resulting from
a clot. One measurement, called fluid-attenuated inversion recovery, clearly
distinguished between MRIs taken during the first three hours and those taken
later. That measurement was accurate in
about 90 percent of cases, whereas the
other tests were less exact.
“These data look provocative,” Barreto
says. “If a CT scan shows no bleeding but
subtle changes, you don’t always know
what to do with the patient. That’s where
an MRI is superior.” Although an MRI
can take 30 to 45 minutes to complete,
Baretto says, that delay might be worthwhile if the readings expand the group of
patients who could benefit from tPA.
P. DE BAKKER
www.sciencenews.org
