That's the image scientists have offered of a chemokine receptor that is like a molecular snake traversing in and out of the cell's membrane. Everywhere a loop sticks out, the virus can grab onto. Metaphors aside, chemokines are molecules released by immune system cells that act like chemical messengers and allow immune cells to communicate. When a chemokine latches onto a specific receptor on a cell surface, it sends a message to that cell. The list has since been expanded as new co-receptors have been discovered.
Some cell types carry both co-receptors.
The Language of Genes Enter genes into the picture. Certain genetic mutations may cause these chemokine receptors to be absent from the cell's surface or to be present in some altered form so that the virus can't easily latch onto the cell and sneak inside. In a remarkable piece of molecular detective work, scientists led by Stephen O'Brien of the National Cancer Institute have tracked down pieces of the genetic code relevant to the chemokine receptors CCR-5 and CXCR4. They called this mutation Delta 32, based on its location on the genome. The effect of this mutation, like that of other genetic changes, depends on whether it's inherited from one parent or both.