Bacterium guards against HIV.It's not just the stuff of bad cheese anymore. Two years ago, investigators identified the bacterium Listeria Listeria /Lis·te·ria/ (lis-ter´e-ah) a genus of gram-negative bacteria (family Corynebacterium); L. monocyto´genes causes listeriosis. Lis·te·ri·a n. monocytogenes, which had fouled soft cheeses, as the cause of many cases of a flu-like illness in several states. Now, researchers at the University of Pennsylvania School of Medicine The University of Pennsylvania's School of Medicine, presently located in the University City section of Philadelphia, Pennsylvania, was the United States's first school of medicine, founded at the College of Philadelphia, as the University was then called. in Philadelphia are trying to transform this troublesome bug into a vaccine for 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. , the AIDS virus AIDS virus n. See HIV. . Yvonne Paterson and her team began their experiment by inserting a specific HIV gene into the chromosomes of L. monocytogenes. They found that, when grown in culture, these genetically engineered genetically engineered adjective Recombinant, see there bacteria use the information encoded by the HIV gene to manufacture one of the virus' protein products. Paterson's team decided to immunize im·mu·nize v. 1. To render immune. 2. To produce immunity in, as by inoculation. im mice with the newly transformed bacterium suspended in a solution. After giving the animals an intramuscular injection of this vaccine, the researchers found several encouraging signs of protection. White cells called T lymphocytes taken from the mice secreted large amounts of gamma interferon, a substance thought to keep HIV at bay, the scientists discovered. In addition, they found, such mice showed long-term evidence of killer T cells directed against HIV. Once L. monocytogenes has set up shop inside a cell, the researchers believe, the altered bacterium starts to produce the HIV protein. The cell's machinery recognizes that viral protein as foreign and escorts it to the surface of the cell -- where it flags the attention of killer T cells. The researchers hope that such a process will yield protective immunity against HIV. In the event HIV does get into the bloodstream of an immunized animal, the 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. will be primed to attack, Paterson says. L. monocytogenes can cause illness in people with impaired immune systems who eat contaminated food. Yet people with HIV appear relatively resistant to this bug. "You'd expect AIDS patients to be full of Listeria, but they're not," Paterson says. Still, the safety and efficacy of this approach remains to be proved, she adds. |
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