German researchers say that a plentiful ingredient found in human semen drastically enhances the ability of HIV to cause infection. The findings, reported in the journal Cell, will help scientists further understand the sexual transmission of HIV and hopefully lead to novel new treatments.
The researchers found that naturally occurring fragments of so-called prostatic acidic phosphatase (PAP) in human semen form tiny fibers known as amyloid fibrils. Those fibrils "capture" HIV particles and help them to penetrate target cells, thereby enhancing the infection rate by several orders of magnitude.
"We were not expecting to find an enhancer, and were even more surprised about the strength," said researcher Frank Kirchhoff, of the University Clinic of Ulm. "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.
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," added co-researcher Wolf-Georg Forssmann. "They pick the viruses up and then bring them to the cell."
While the peptide that conglomerates into fibrils is always present in large quantities in semen, they don't yet know if the absolute levels vary from man to man. "We also plan to further explore how exactly the fibrils allow the virus to enter cells and to search for compounds, with our technology, that might block the process," Forssmann explained. If such inhibitors can be found, they might be added to microbicide gels now under development for HIV prevention.
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Source: Cell Press