A new publication in the advance online version of Science journal reports on variable susceptibility to HIV infection among individuals depending on the number of copies of the CCL3L1 gene [Gonzalez E et al. Science 2005: 1101160]. The CCL3L1 protein blocks HIV infection by interacting with the cellular receptor CCR5, a major receptor for viral entry to target human blood cells. Researchers at the US National Institutes of Health (NIH) analysed blood from over 4300 African-Americans, Europeans and Hispanic-Americans, both HIV-positive and HIV-negative, and determined the average number of copies of the CCL3L1 gene for each group. These were four, two and three respectively for HIV-negative individuals. Individuals with fewer than the average number of CCL3L1 genes for their ethnic group were found to be more susceptible to HIV infection, and at an increased risk of between 39% and 260% of rapid progression to AIDS following infection. Individuals with more than the average number of CCL3L1 copies were reportedly less susceptible; each additional gene copy was said to be associated with a 4.5-10.5% reduction in the probability of HIV infection. Researchers also looked at CCR5 gene variants known to be associated with different rates of AIDS progression, and found that individuals who possessed both disease-accelerating CCR5 variants and lower than average CCL3L1 copy numbers had an even higher risk of infection and disease progression.

Dr Anthony Fauci, director of National Institute of Allergy and Infectious Diseases (NIAID), commented: "This important study identifies genetic factors of particular groups that either mitigate or enhance one's susceptibility to infection and disease onset" whilst Dr Carl Dieffenbach of the NIAID said: this study further emphasizes the significance of defining all existing types of genetic variation and the impact that these variations may have on human susceptibility to infectious diseases (see press release). The researchers reportedly hope that their findings could lead to a screening test to determine someone's susceptibility to HIV/AIDS, which might have an application in the treatment of the disease (see BBC news report).
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