How do viruses travel through and escape from cells they’ve infected? Some viruses, it turns out, use the cell’s own skeleton to propel themselves. Protein chemist Michael Way, cell biologist Sally Cudmore, and their colleagues at the European Molecular Biology Laboratory in Heidelberg and at the Pasteur Institute in Paris have found that vaccinia--a virus used in smallpox vaccines--surfs through cells on piles of actin, one of the basic structural proteins in the cellular skeleton. The virus somehow gets actin in the cell to assemble behind it. It’s a bit like someone standing on a stack of something, and they want to get higher, so they insert a new block underneath them, and up they go, says Way. This image shows vaccinia viruses (the green dots) erupting from the surface of a human cell on long red actin plumes. The plumes can even penetrate a neighboring cell, thereby giving the virus a free ride into uninfected territory. It’s actually a big advantage to go from the inside of one cell directly to the inside of another cell, says Way, because the host never sees you. You never raise antibodies, and you don’t get an immune response.