THE NETHERLANDS — Although HIV has become an international scourge, especially on the African and Indian continents, having killed an estimated 22 million people globally during the 25 years in which it has been identified as a disease, the virus is surprisingly inefficient at infecting humans, when compared to other pathogens.Compared to the human papillomavirus (HPV), which has a nearly 100-percent exposure to infection rate, penile-vaginal intercourse with an HIV-positive partner runs a much lower one in 100 or one in 200 rate of transmission. Given the severity of the disease, this is a mercy, but it’s also a mercy that has researchers wondering why.

A study published on the March 4th online version of Nature Magazine reports that researchers may have a clue about how the human body protects itself against HIV infection, keeping the transmission rate as low as it is.

According to the article, researchers found that cells in the mucosal lining of human genitals produce an HIV eating protein called “Langerin” that could be integral to developing ways to decrease the transmission of the virus that leads to AIDS.

Lead researcher Teunis Geijtenbeek, an immunologist researcher at Vrije University Medical Center in Amsterdam, explains that the team “observed that Langerin is able to scavage viruses from the surrounding environment, thereby preventing infection.”

The discovery is good news for many reasons, including the fact that “generally all tissues on the outside of our bodies have Langerhans cells,” as Geijtenbeek points out, meaning that “the human body is equipped with an antiviral defense mechanism, destroying incoming viruses.”

As optimistic as these findings are, experts including Dr. Jeffrey Laurence, director of the Laboratory for AIDS Virus Research at the Weill Cornell Medical College in New York City urges caution. While he admits that the finding “is very interesting and unexpected,” he also reminds those following anti-HIV/AIDS research to remember that “In the test tube, this is a very important finding. But there are many things in the test tube that don’t occur when you get into an animal or a human. Having said that, though, this is a very intriguing finding.”

One reason that the discovery is so “intriguing” is that previously, many believed that HIV easily enters and infects Langerhans cells. Geitjtenbeek conjectures that while such is the case when HIV counts are high or Langerin activity is low, in previously uncompromised cells, they “do not become infected by HIV-1.” Instead, the protein “captures HIV-1 very efficiently, and this Langerin-bound HIV-1 is taken up (a bit like eating) by the Langerhans cells and destroyed.”

In essence, Geitjtenbeek says that “Langerhans cells act more like a virus vacuum cleaner.”

Since it is known that the Langerin gene differs between individuals, it’s possible that those with more protective cells have a lower risk of infection compared to those with fewer protective cells. Armed with this knowledge, Geitjtenbeek expects his own studies and those of others to focus on finding ways to boost Langerin production. The pursuit of a topical microbicide capable of protecting women against HIV infection will also likely experience a boost thanks to the discovery.