[Immunology] Protein Identified That Turns Off HIV-fighting T Cells

biospace via immuno%40net.bio.net (by biospace from noster-it.com)
Thu Jan 15 10:37:08 EST 2009

In HIV-infected patients the body's immune system is unable to fight
off the virus. A new study to be published online on November 10th in
the Journal of Experimental Medicine shows that T cells in HIV-
infected individuals express a protein called TIM-3, which inactivates
their virus killing capacity. Blocking this protein, the study
suggests, might one day help patients to eliminate HIV as well as
other chronic infections.
Large numbers of virus-fighting T cells can be found in the blood of
most chronically infected HIV patients. However these cells eventually
become exhausted and cannot function. To identify the cause of this
exhaustion, a team of researchers at the University of Toronto, lead
by Mario Ostrowski, compared blood from healthy individuals and HIV
patients. In the patients, TIM-3 was found on a large number of HIV-
specific T cells, and the number of TIM-3-positive cells increased
with the severity of infection.

Under normal circumstances, exposing T cells to bits of virus causes
the cells to replicate and produce virus-killing chemicals. Cells
expressing TIM-3, however, were unreactive and TIM-3 was to blame;
disrupting its signals restored the cells' virus-fighting functions.
TIM-3 normally gets expressed on T cells after they carry out their
normal function, perhaps as a way to turn the cells off and thus
prevent excessive inflammation. But during HIV infection, persistent
TIM-3 expression may help the virus avoid T cell attack.

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