Suicidal cells give clue to HIV puzzle

The HIV virus overworks the cells of the immune system so much that they commit suicide, immunologists learned last week at a Biochemical Society conference in Edinburgh.

New research on T-cell suicide, presented by Marie-Lise Gougeon of the Pasteur Institute in Paris, shows that chronic over-stimulation rather than direct attack causes the immune systems of Aids patients to collapse.

All cells have a built-in suicide programme and can self-destruct if necessary. Controlled cell suicide is a useful regulatory lever for the immune system, removing surplus cells after an infection has been defeated and helping to prevent autoimmune disease. But the HIV virus seems to make the suicide programme go haywire, causing T-cells to kill themselves en masse.

The suicide programme is controlled by two genes. One makes a protein called Bcl-2, a kind of cellular Prozac that suppresses the cell's suicidal tendencies. The other makes a protein called Fas which is a component of the cell's self-destruct button.

Dr Gougeon's team has shown that persistent activation of the immune system by HIV turns Bcl-2 production down and Fas production up, making the T-cells suicidal. The virus then pushes them over the edge by inducing them to make a molecule called Fas Ligand, which binds to Fas and sets the suicide programme in motion.