Humans might lack immunity to HIV in part because they carry a version of a protein that protected them against a long-extinct virus, according to a study published in Friday's issue of the journal Science, the Los Angeles Times reports. Research has shown that nonhuman primates carry an antiviral protein, called TRIM5, that makes them immune to HIV; however, the slightly altered human version of the protein is unable to defend against the virus (Dance, Los Angeles Times, 6/23).
For the study, researchers at the Fred Hutchison Cancer Research Center reproduced a mutated version of the extinct virus Pan troglodyte endogenous retrovirus, or PERV. They found that cells carrying the human version of TRIM5 could not be infected by PERV, while cells carrying the nonhuman primate version of TRIM5 were susceptible to the virus, the San Francisco Chronicle reports. According to study author Shari Kaiser, it is unclear why human TRIM5 is important in protecting against PERV (Russell, San Francisco Chronicle, 6/22). The researchers then manipulated the protein and found that a single mutation bolstered its ability to recognize HIV but hindered its ability to attack PERV. TRIM5 appears to be able to fight either PERV or HIV but not both, according to the researchers (Los Angeles Times, 6/23). They concluded that the version of the protein that evolved to protect humans against PERV might have weakened the immune system's natural defense against HIV. University of California-San Francisco virologist Jay Levy said that the study's findings are interesting but speculative, adding that they will "lead to further evaluation of this idea by other researchers in the field." Warner Greene, director of the Gladstone Institute for Virology and Immunology, said, "It is an absolutely fascinating story in evolutionary biology" (San Francisco Chronicle, 6/22).
The study abstract is available online.
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