Semen chemical promotes HIV infection


By Michael Day HIV’s ability to infect human cells may be vastly enhanced by the presence of a chemical that occurs naturally in semen, research suggests. The discovery could offer a new target for preventing the spread of AIDS, for example, by incorporating potential inhibitors of the semen chemical into the powerful new microbicides currently being developed to halt the spread of the virus. While searching for chemicals in semen that could block HIV transmission, an international team led by Frank Kirchhoff at the University Clinic of Ulm in Germany, was instead surprised to find that the naturally occurring chemical prostatic acidic phosphatase (PAP) promoted HIV infection. Closer inspection revealed that PAP formed tiny fibres known as amyloid fibrils that were able to “ferry” the virus into the immune cells that it preys upon. “Most enhancers have maybe a two or three-fold effect, but here the effect was amazing – more than 50-fold and, under certain conditions, more than 100,000-fold,” says Kirchhoff. “At first, I didn’t believe it, but we ran the experiment over and over, always with the same result.” “The fibrils act like a ferry. They pick the viruses up and then bring them to the cell,” adds fellow researcher Wolf-Georg Forssmann at the Hannover Medical School, also in Germany. Significantly, their laboratory tests showed that the fibrils’ ability to assist infection was greatest when the levels of infectious virus were low – resembling the conditions in which sexual HIV-1 transmission usually occurs. HIV-1, the most common and virulent form of the virus that causes AIDS, has infected about 60 million people and caused over 20 million deaths. Globally, most infections result from genital exposure to the semen of HIV-positive men. Women who acquire HIV-1 through vaginal intercourse constitute almost 60% of new infections in Africa. Therefore the latest findings could have enormous clinical and public health implications, particularly for regions such as Sub-Saharan Africa where AIDS has caused devastation. Kirchhoff says he hoped that agents that blocked PAP might be developed and added to vaginal microbicides that women could use to protect themselves from infection. He also believes the discovery could have important implications for researchers hunting an elusive HIV vaccine. Jonathan Weber, an eminent HIV researcher at Imperial College London, UK, was positive about the findings. “Kirchhoff is a great scientist and this is meticulous work,” he says. But Weber says there is much work to be done before new microbicides could be produced as a result of the findings. He notes, too, that the ability of HIV-positive women to infect men suggested that the presence of seminal PAP fibrils was not always required for infection to occur. He adds, however: “This work is exciting because it opens up whole new avenues of prevention. It really does suggest entirely new directions of research, and like many of the really important discoveries it was completely unexpected.” Journal reference: Cell (DOI: 10.1016/j.cell.2007.10.014) HIV and AIDS – Learn more about the worst pandemic in human history in our continuously updated special report. More on these topics:
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