HIV may spare cells - for a short time.While the AIDS virus AIDS virus n. See HIV. is best known for destroying the body's immune system immune system Cells, cell products, organs, and structures of the body involved in the detection and destruction of foreign invaders, such as bacteria, viruses, and cancer cells. Immunity is based on the system's ability to launch a defense against such invaders. by killing its cells, HIV HIV (Human Immunodeficiency Virus), either of two closely related retroviruses that invade T-helper lymphocytes and are responsible for AIDS. There are two types of HIV: HIV-1 and HIV-2. HIV-1 is responsible for the vast majority of AIDS in the United States. may also deliberately delay the death of immune cells, according to a new report. Like all viruses, HIV depends on host cells to make its offspring. If it kills infected cells too quickly, HIV may not have time to replicate. Indeed, part of the body's defensive strategy may be to sacrifice infected cells. "We have billions of T cells T cells A type of white blood cell produced in the thymus gland. T cells are an important part of the immune system. Infants born with an underdeveloped or absent thymus do not have a normal level of T cells in their blood. [the cells targeted by HIV]. Losing a few hundred thousand doesn't mean too much," says David Kaplan of Case Western Reserve University in Cleveland. Kaplan suspects that HIV can buy itself some time, however. The body has a system for regularly ridding itself of unwanted immune cells: When Fas, a protein found on the surface of immune cells, binds to Fas ligand (FasL), another cell surface protein, the Fas-bearing cell commits suicide. It's as if FasL were the finger pushing a cell's self-destruct button. Kaplan's group has found that immune cells from the blood of HIV-infected people have a FasL deficiency, compared to similar cells from uninfected people. Indeed, cells from three of six HIV-positive individuals showed no FasL activity at all in a test-tube study, the team reports in the May 27 Proceedings of the National Academy of Sciences The Proceedings of the National Academy of Sciences of the United States of America, usually referred to as PNAS, is the official journal of the United States National Academy of Sciences. . This was a surprise. Earlier studies had shown that Fas was made more abundantly by HIV-infected people, leading some scientists to speculate that HIV killed immune cells via the Fas-FasL system. Instead, HIV seems to interfere with this cell suicide mechanism, presumably pre·sum·a·ble adj. That can be presumed or taken for granted; reasonable as a supposition: presumable causes of the disaster. to keep infected cells alive long enough for the virus to replicate, says Kaplan. In studies of immune cells from HIV-positive people, antibodies that trigger Fas-induced suicide decreased HIV replication by 90 percent, the scientists report. Compounds similar to FasL might therefore prove medically useful, though Kaplan and other researchers caution that such drugs could also damage non-immune Fas-bearing cells, such as those in the liver. "This approach has some distant therapeutic potential, but nothing immediate," says Warner Greene of the Gladstone Institute of Virology virology, study of viruses and their role in disease. Many viruses, such as animal RNA viruses and viruses that infect bacteria, or bacteriophages, have become useful laboratory tools in genetic studies and in work on the cellular metabolic control of gene expression and Immunology in San Francisco. |
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