Fibers in Semen Help HIV Penetrate Cells

THURSDAY Dec. 13, 2007 -- In a discovery that perplexes HIV experts, an international team reports that tiny fibers commonly found in semen drastically enhance the ability of the virus to do its damage.

According to a study in the Dec. 14 issue of Cell, the fibers capture the virus and then ferry it to target cells, increasing its ability to infect someone by more than 50 times in some cases and more than 100,000 times in others.

The findings could help scientists better understand how AIDS is transmitted. But Rowena Johnston, director of research with the Foundation for AIDS Research (amfAR), noted that the value of the research is limited, because it doesn't "necessarily reflect transmission in the 'real world.' "

"This is intriguing, and it's worth further investigation," said Johnston. "But there's nothing yet that makes me have a 'Eureka' moment."

While scientists have long known about the basics of AIDS transmission, it's not clear why the virus travels more easily through some routes than others.

For example, male-to-female sexual transmission is usually more common than the other way around but not always. And it's also not clear why the virus has become so prevalent even though it has a tiny presence in blood.

In the new study, led by a German team, scientists tried to figure out if components of human semen might affect transmission of the AIDS virus.

"We were not expecting to find an enhancer and were even more surprised about the strength," study author Dr. Frank Kirchhoff, of the University Clinic of Ulm, said in a statement. "Most enhancers have maybe a two- or threefold 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."

Dr. Jeffrey Laurence, a professor of medicine and director of the Laboratory for AIDS Virus Research at Weill Medical College of Cornell University, said there could be something similar at play in cervical fluid that affects transmission. "In a lot of situations in the real world, women transmit HIV quite easily...," Laurence said.

He added that many other factors affect transmission of HIV, from bodily abrasions to menstrual cycles and use of oral contraceptives.

Could this latest finding bring scientists closer to an AIDS vaccine? Laurence, who thinks a vaccine is decades off, is doubtful. Prevention, however, might be another matter.

Laurence said it might be possible to develop an "antidote" for the virus-boosting powers of semen and put it in a microbicide that people could use before sex.

Posted: December 2007


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