HIV's Surprise Entrance

The way HIV enters cells—by fusing to cell membranes and directly injecting its genetic contents—seemed to have been settled long ago. But researchers at the University of Maryland School of Medicine realized that evidence for that mechanism was merely circumstantial. They now report the surprising observation that the virus instead infects cells by endocytosis, a process of cell-membrane invagination that produces endosome vesicles, which bud off from the membrane and then release the virus's contents (Cell 2009, 137, 433). Gregory B. Melikyan and coworkers used live-cell microscopy to watch individual virus particles entering cells and a fluorescence technique to measure viral content delivery. "The findings suggest new potential targets for HIV antivirals and new avenues for studying HIV entry and identifying cellular factors involved in fusion and infection," comments NIH membrane biologist Leonid V. Chernomordik.