Important note: Information in this article was accurate in 1998. The state of the art may have changed since the publication date.
The Associated Press; Thursday, September 10, 1998
Joseph B. Verrengia, AP Science Writer
New research by a nationwide team of scientists suggests that the human immunodeficiency virus eventually attacks a class of disease-fighting cells produced by the immune system that were thought to be impervious to attack by the virus.
The results, which have been limited so far to test-tube experiments, could provide drug makers with a new target for drugs designed to keep the virus in check, as well as vaccines aimed at preventing infection.
Researchers said the attack on this different group of immune cells, known as CD8 T cells, triggers an explosion of cell death that exhausts the immune system and leaves the body vulnerable to pneumonia and other secondary infections that typically kill most AIDS patients.
The new study was published in the latest issue of the journal Nature.
Exactly how AIDS affects the CD8 cells remains unclear, though. Researchers said one possibility is that the virus reduces the immune system's "social control" over its own powerful cells. The disruption to this precise chemical balance triggers a potentially fatal domino effect that not only leaves the body vulnerable to infection, but also may contribute to the loss of brain cells that causes AIDS-related dementia and other debilitating side effects.
"Because CD8 T cells are professional killers, they may do serious harm if they end up in the wrong place," said French AIDS researcher Jean Claude Ameisen of the Hospital Bichat in Paris.
For several years, scientists have known that HIV readily infects one type of immune cell known as the CD4, or helper T cell, by locking onto a protein on its surface and breaching its cell wall.
The CD8 cells were thought to have better protection. Yet in the latter stages of AIDS, CD8 cells start dwindling rapidly, too.
Researchers said their experiments show that a strain of HIV that usually evolves late in the course of infection latches onto a particular surface protein of the CD8 cell known as CXCR4.
But unlike in CD4 cells, the virus does not actually take over its cellular machinery.
Instead, they report, when the virus latches onto the CXCR4 protein the CD8 cell sees the change as a kind of a death signal and commits suicide.
The cell death process is complex, and quickly involves an array of other cell types that soon may subvert the entire immune system and lead to full-blown AIDS symptoms, said lead author Georges Herbein of the Picower Institute for Medical Research in Manhasset, N.Y.
"Because CD8 cells are thought to limit the spread of the infection, the failure of CD8 function could contribute to the development of AIDS," he said.
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