Natural HIV Barrier Snares AIDS Virus

Protein in Specialized Skin Cells Traps and Destroys HIV

By
Daniel DeNoon

WebMD Health News

Reviewed By
Louise Chang, MD

March 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.

SOURCES: De Witte, L. Nature Medicine, advance online publication, downloaded March 5, 2007. WebMD Medical Reference from Medscape: “Microbicides: ‘Cause Celebre’ in HIV Prevention.”

© 2007 WebMD Inc. All rights reserved.

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