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Editorial

Nature Immunology 9, 471 (1 May 2008) | doi:10.1038/ni0508-471

Outside the box

First identified in 1975 by virtue of their ability to rapidly kill tumor cells without previous 'priming', NK cells have puzzled and dazzled—perhaps in equal measures—immunologists for more than 30 years. No longer considered simple 'killing machines', NK cells have gained recognition for their abilities to secrete cytokines that influence the differentiation of adaptive immune responses, to combat viral and parasitic infections, and to promote vascularization of implanting embryos during pregnancy.