Semen protein raises HIV infection risk

Scientists have identified a protein in human semen that increases the risk of HIV infection up to 100,000 fold. The discovery could provide new drug targets and strategies for combating the global AIDS epidemic.

The German team screened a library of peptides and discovered that fragments from prostatic acidic phosphatase (PAP), an enzyme abundant in semen, boosted the chances of cells becoming infected with the HIV virus. The enzyme forms tiny clumps of insoluble fibres - which the researchers named Semen-derived Enhancer of Virus Infection (SEVI) - that capture virus particles and ferry them straight into cells.

’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,’ said Frank Kirchoff, who led the research at the University Clinic of Ulm, Germany.

Jan M?nch, who also worked on the project, told Chemistry World: ’Agents blocking the generation or enhancing activity of SEVI, and related virus attachment factors, may offer new prospects for strategies preventing HIV transmission.’

The HIV virus, which is the causative agent of AIDS, has infected about 60 million people worldwide, the majority caused by unprotected sexual intercourse. However, despite its widespread nature, the sexual route of contraction is relatively inefficient - it has been estimated that the chance of HIV transmission via male-to-female sexual intercourse is about 1 in 200. 

This infection rate would be significantly reduced by blocking chemical enhancers like SEVI, and the researchers hope to identify the exact mechanisms involved in transmission and develop an inhibitor. Such inhibitors could potentially be combined with therapies such as microbicide gels in lubricants to improve protection and make them more available.

John Altman, an expert in HIV vaccine immunology at Emory University in Georgia, US, commented: ’Although it is unlikely that these findings will lead to novel therapies for treating already infected patients, I agree that this might enhance the potency of certain vaccine approaches.’

Lewis Brindley