Strike two

日期:2017-05-18 01:04:16 作者:车正楸玩 阅读:

By Bob Holmes SOME strains of HIV launch not one but two strikes at the immune system. This may help explain the sudden steep decline of some AIDS patients who have previously been stable and relatively disease-free. The second strike hits white blood cells known as CD8 cells. Unlike their sister CD4 cells, which are the ones actually invaded by HIV, CD8 cell counts do not decline steadily during the course of HIV infection. Instead, in nearly half of patients, the CD8 count begins to tail off a year or two before the patients take a turn for the worse. HIV causes this decline in CD8 cells through mistaken identity, according to Eric Verdin, a viral immunologist with the Gladstone Institute of Virology and Immunology at the University of California, San Francisco and his colleagues (Nature, vol 395, p 189). The surface of CD8 cells bears a receptor molecule called CXCR4, which is also found on CD4 cell surfaces. HIV sometimes uses CXCR4 to enter CD4 cells. Verdin’s experiments with white blood cell cultures show that when HIV interacts with this receptor on CD8 cells they undergo apoptosis or programmed cell death. Viral strains that target CXCR4, if they appear at all, do so relatively late in infection. To Verdin, this suggests that the shift to the new strain may cause the drop in CD8 cells. “It might be one of many mechanisms that could account for death of T cells,” says Michael Lenardo,