Although researchers have been studying AIDS for nearly three decades, until this year no one had ever witnessed HIV—or any other viral particles—forming inside a cell.
Researchers at Rockefeller University in New York City tweaked the genetic program of HIV so that an essential protein, a building block of the virus, would turn fluorescent. They then used an imaging technique that zeroes in on a thin layer of a specimen to examine the surface of an HIV-infected cell. Within six minutes the scientists observed glowing spheres that looked like virus particles.
Seeing the potential virus was the easy part, says cell biologist Sanford Simon of Rockefeller University. Demonstrating that the glowing spheres really were developing viruses proved more challenging. Using several molecular tricks, Simon and his colleagues showed that the spheres contained tightly packed molecules that grew to a certain size and then stopped. By using a kind of cellular litmus paper to track the movement of protons, the researchers could also see when the round particles had isolated themselves from the rest of the cell. Together, these results confirmed that Simon and his team were watching HIV in action [subscription required].
With this ability to follow viruses in real time, the Rockefeller scientists hope to tease out how HIV recruits proteins from human cells to do its dirty work; they also plan to look more broadly at how viruses develop. Simon says the convergence of better optics and better genetic and chemical tools is allowing rapid progress in answering these fundamental questions about infectious disease. “Many of us are feeling like kids in a toy shop,” he says.