it could finally be possible to prevent common cold, say researchers who claim to have figured out the molecular "handshake" that lets the cold viruses sneak into human cells. About 70 per cent of colds are caused by rhinoviruses. These invade cells in the respiratory tract after binding to a molecule called icam-1 on the cell's surfaces.

Two groups of researchers, one at Purdue University in Indiana, usa, led by Michael Rossmann, and the other headed by Tim Springer of Harvard Medical School, have figured out the precise structure of the region of icam-1 to which rhinoviruses attach themselves. Their results show that icam-1 has finger-like projections that slot into deep crevices on the outer coat of a rhinovirus (Proceedings of the National Academy of Sciences, Vol 95, p 4134-40).

icam-1 allows white blood cells to stick to cells under attack from invading pathogens. Fortunately, the site involved in this process is distinct from that used by rhinoviruses. So it may be possible to find drugs that shut rhinoviruses out of cells without disrupting normal immune responses. "This unlocks the potential for a rational drug design," says David Evans, a virologist at the University of Reading.