A Trigger of Natural (and Other) Killers

New work may help clarify how natural killer (NK) cells distinguish their targets--a variety of infected or cancerous cells. On page 727, a team reports that it has identified a molecular trigger that sets off some NK cells, as well as the receptor that recognizes that molecule, a protein called MICA that appears to be switched on in cancer cells or in cells under stress, as may happen when they are infected by a virus. And in a second report, on page 730, a team identifies the internal signaling pathway through which the MICA receptor tells NK cells to activate their killing machinery--information that may be useful to researchers hoping to develop drugs to beef up NK activity.