emen protein helps HIV infect cells: study
Researchers in Germany have discovered that a protein found in semen dramatically enhances the rate of HIV infection.
A study published in the medical journal Cell describes how this protein latches onto HIV particles and helps them attach to cells.
Worldwide there have been more than 60 million infections of HIV, with 80 per cent occurring during sexual intercourse.
But until now there has been little research on the impact semen has on infection.
But despite its dramatic spread through many parts of the world, most notably sub-Saharan Africa, the HIV virus is actually difficult to transmit.
Dr Dominic Dwyer is from the Australian Centre for HIV and Hepatitis Virology Research at Westmead Hospital in Sydney.
"Even though sexual transmission is the main way of transmitting the [HIV] virus around the world, it's still not that easy to do," he said.
"The reason is that the virus has got to get into the sexual secretions, then get across what we call the mucosal surfaces of the genital tract, into the cells underneath that mucosal surface, to infect them and then go and spread through the body."
In an attempt to prevent this transmission, researchers at the University Clinic of Ulm in Germany, searched for a chemical compound in semen that might act to block the HIV virus.
But what they found was a protein that actually increased HIV infections.
"There are some proteins that are present in semen that appear to facilitate the entry of the virus into the uninfected person," said Dr Dwyer.
"The virus essentially binds to these proteins and the proteins kind of drag the virus across the mucosal surface of the genital tract, to allow the virus then to come in to contact with cells that then carry the virus around the rest of the body."
'Exciting potential'
The research published in Cell describes how the protein forms tiny fibres known as amyloid fibrils that catch the virus and help it attach to cells.
Professor Sharon Lewin, the director of the Infectious Diseases Unit at Alfred Hospital in Melbourne, says it is the first time that semen has been analysed in this way.
"Previous studies have actually looked at semen, how infectious it is," she said.
"The semen itself is quite toxic to cells that you're trying to infect. So they used a very clever way of looking at bits of the semen, and which bits promoted infection.
"Once they identified that particular bit of the semen, they could then work out which part of the protein didn't.
"So they had to sort of break the semen up into components ... if you used more crude experiments by just infecting the cells in the presence of semen, you would generally kill the cells."
Professor Lewin says the protein was tested in various cultures to mimic different types of transmission.
"In the female genital tract, the environment [is] very different than in semen alone," she said.
"It's generally what's called an acidic environment, and this paper did try to mimic that.
"When they made conditions more acidic, like the conditions within the vagina, they still observed this effect of the protein enhancing infectivity."
The study found that the protein found in semen increases the rate of HIV infection by 100,000 times.
Professor Lewin says it is an important discovery that could lead to the development of medicines or localised gels that may prevent future infections.
"The exciting potential of these findings are that if you could inhibit that effect, you might make HIV really, really non-infectious," she said.
"It could be a very interesting and exciting way to interfere with transmission."
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