In the human tragedy of HIV infection, dendritic cells play a vicious double role analogous to an international cocaine trafficker who morphs into a street-level crack peddler. These antigen-presenting immune-system cells transport HIV from the mucosal membranes near which it enters the body to secondary lymphoid organs. There, the cells pass the virus over to the T lymphocytes that it will ultimately destroy.

Exactly how dendritic cells serve these functions is unknown, but two new studies appear to provide a crucial clue.1,2 It is a receptor on dendritic cells that binds to the HIV envelope glycoprotein gp120 and to an adhesion molecule on T cells known as ICAM-3. This receptor has been dubbed DC-SIGN (for "dendritic cell-specific ICAM-3 grabbing nonintegrin").

Dutch and American researchers applied tissue staining and diverse in vitro experiments to show how crucial DC-SIGN might be. HIV bound to cultured dendritic cells via DC-SIGN, which was...

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