Scientists Discover 'Natural Barrier' to HIV

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When HIV comes in contact with genital mucosa, its ultimate target -- the cells it seeks to hijack and destroy -- are immune system T-cells. But T-cells are relatively far away (in lymph tissues), so HIV uses nearby Langerhans cells as "vehicles" to migrate to T-cells.

For decades, the common wisdom was that HIV easily enters and infects Langerhans cells. Geijtenbeek's team has now cast doubt on that notion.

Looking closely at the interaction of HIV and Langerhans cells, they found that the cells "do not become infected by HIV-1, because the cells have the protein Langerin on their cell surface," Geijtenbeek said. "Langerin 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, Geijtenbeek said, "Langerhans cells act more like a virus vacuum cleaner."

Only in certain circumstances -- such as when levels of invading HIV are very high, or if Langerin activity is particularly weak -- are Langerhans cells overwhelmed by the virus and infected.

The finding is exciting for many reasons, not the least of which is its potential for HIV prevention, Geijtenbeek said.

"We are currently investigating whether we can enhance Langerin function by increasing the amount of Langerin on the cell surface of Langerhans cells," he said. "This might be a real possibility, but it will take time. I am also confident that other researchers will now also start exploring this possibility."

The discovery might also help explain differences in vulnerability to HIV infection among people.

"It is known that the Langerin gene is different in some individuals," Geijtenbeek noted. "These differences could affect the function of Langerin. Thus, Langerhans cells with a less functional Langerin might be more susceptible to HIV-1, and these individuals are more prone to infection. We are currently investigating this."

The finding should also impact the race to find topical microbicides that might protect women against HIV infection. Choosing compounds that allow Langerin to continue to work its magic will enhance any candidate microbicide's effectiveness, the Dutch researcher said.

Laurence did offer one note of caution, however.

"In the test tube, this is a very important finding," he said. "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."

More information

For more on the fight against HIV/AIDS, head to the Foundation for AIDS Research.