Study Examines How HIV Progresses To AIDS
HIV Progresses To AIDS
Long-held theories on how HIV progresses to AIDS might beincorrect, according to a study published in the July 31 issue of the Proceedings of the Royal Society B, HealthDay News/Washington Postreports. The common belief among most scientists has been that variousstrains of HIV "battle a silent war within the body over time" untilthe fittest strain -- defined as the one that replicates itself themost -- "wins," according to HealthDay/Post. This strain"goes on to overwhelm" the immune system's cells and destroy theHIV-positive person's "defenses against disease," according to thetheory, HealthDay/Post reports.
To test the theory, David Levy of New York University and Dominik Wodarz, associate professor of biology at the University of California-Irvine,used a mathematical model that considered how quickly various strainsof HIV replicate, how fast they destroy cells and how immune systemsrespond to the virus.
They found that HIV progresses to AIDS when a "less-fit" variety of the virus succeeds over another strain, HealthDay News/Postreports. According to the researchers, that less-fit version thenbegins killing immune system cells extensively and rapidly while alsorestricting the number of times it replicates. The virus "basicallykills its own habitat, its house," Wodarz said. He added that becausethis form of HIV is efficient at quickly killing large numbers ofimmune cells, "once these less-fit strains emerge, they can plunge thepatient into AIDS."
According to Wodarz, two or more strainsof the virus can co-infect the same immune cell, and if a fast-killingstrain is among them, it will kill the cell before slower, butbetter-replicating forms can destroy the cell. "But without thisganging up on the same cell," HIV would "go extinct because evolutionwould select against it -- because it is less fit and replicates less,"Wodarz said. Therefore, one method of delaying the progression of HIVto AIDS would be to allow one type of HIV to enter a cell at any giventime, Wodarz said.
The study "throwsinto question a lot of the notions that have been accepted about theevolution" of the virus within a typical HIV-positive person, Wodarzsaid. Benigno Rodriguez, an assistant professor of medicine at Case Western Reserve Universityand a specialist in the evolution of HIV, said the study is an"interesting concept" but that it contains some flaws. According toRodriguez, most available data show that HIV becomes more efficient atreplicating as AIDS progresses. He also questioned the importance ofseveral HIV strains infecting the same cell. "The data that we alreadyhave in hand shows that multiple infection is relatively infrequent,"Rodriguez said. The scientists also did not consider that most AIDSpatients' immune systems are not destroyed directly by the disease butby "bystander" mechanisms that accompany AIDS, according to Rodriguez."In an individual with advanced disease, if you look at the number ofcells that are actually infected [with HIV], we are talking less than1%," Rodriguez said, adding, "But, in reality, that individual may havelost 20, 30, 50% of his immune cells." He also said the mathematicalmodel should be tested outside laboratory settings. Wodarz said thatexperiment verification is needed, but he added that "mathematicalmodels have led to great progress before" in HIV/AIDS research(Mundell, HealthDay News/Washington Post, 8/3).
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