Natural HIV barrier snares AIDS virus

Source: WebMD

Protein in Specialized Skin Cells Traps and Destroys HIV
By Daniel J. DeNoon
WebMD Medical NewsReviewed by Louise Chang, MDMarch 5, 2007 -- A natural barrier to HIV snares and destroys the AIDS virus, Dutch researchers report.

The newly discovered barrier is a powerful first line of defense against HIV infection. But at least one new strategy for preventing HIV transmission may breach this barrier, inadvertently opening the door to infection.

HIV targets T cells, a type of immune cell. It gets to T cells via a type of skin cell called a dendritic cell. Dendritic cells are supposed to warn T cells about foreign invaders. But HIV subverts this line of communication and uses dendritic cells to carry an infectious virus to the T cells.

That doesn't happen if HIV first encounters a specialized kind of dendritic cell called a Langerhans cell. It's hard for HIV to infect Langerhans cells -- and now scientists know why. It's because the cells carry a special molecule, dubbed Langerin.

Langerin grabs HIV and throws it in a kind of garbage disposal within the Langerhans cell, find Lot de Witte of Vrije University, Amsterdam, and colleagues. When the researchers disabled the Langerin molecule, HIV easily infected Langerhans cells.

"Thus Langerin is a natural barrier to HIV infection," de Witte and colleagues conclude.

HIV Prevention Method Has Flaw
As the AIDS epidemic rages on, researchers are looking for ways to prevent HIV infection. One powerful method would be a vaginal microbicide -- an easy-to-apply gel that would block HIV and protect women from being infected by their sex partners.

Because dendritic cells carry HIV to T cells, one promising vaginal-gel ingredient is a molecule called mannan. Mannan breaks the tether that dendritic cells use to haul HIV across mucous membranes.

But de Witte and colleagues find that mannan also disables Langerin, breaching this natural barrier to HIV.

"Inhibitors such as mannan have an unwanted and completely counteractive effect on Langerhans cells -- namely, they negate the protective function of Langerhans cells and enable [HIV] transmission by dendritic cells," they warn.

Instead, the researchers suggest using another molecule that keeps dendritic cells from latching on to HIV without affecting Langerhans cells.

De Witte and colleagues report their findings in the advance online issue of the journal Nature Medicine.