Mistaken notions about natural killer cells

As natural killer (NK) cells were first described more than 30 years ago-a lifetime in recent immunological history-this is a good time to reflect on their transition from outcasts of mainstream immunology to prominent players in innate immunity. Whereas much of our existing knowledge about NK cells is taken as longstanding fact, it may be surprising to immunologists of a younger vintage, particularly those working on NK cells today, that some of this knowledge was, at least initially, unexpected. In this Perspective, I take an unconventional approach to discussing our progress in understanding NK cells.