A killer in close up

摘要

Ebola is a simple virus, but also a subtle one. The stringy looking particles consist of a genome wrapped up in two layers of protein (see diagram). This long, thin package, along with a large protein called a polymerase, is packed into a membrane that is studded with a glycoproteins-that is, proteins with sugar stuck to them. When the virus infects a cell the polymerase makes copies of the genome and the cell is tricked into using these to make the proteins that the virus needs. These include two, called VP35 and VP24, which stymie interferons, a class of molecule that alerts the immune system to infection. VP35 prevents interferons from being made; VP24 stops their cries for help from being heard. The sugars on the virus's outside make it hard for other parts of the immune system to get to grips with; to confuse things more, the virus makes infected cells produce more glycoprotein than it needs for its coat, with the surplus simply secreted into the bloodstream. Antibodies which would otherwise attack the virus stick to this decoy protein instead.