Abstract
There have been considerable advances in characterization of the complexities of natural killer (NK) cell ligand recognition, activation, subsets and effector functions. The nature of the transcription factors that act to define distinctive functional programmes of NK cell subsets are now starting to be clarified as a consequence of studies in knockouts. Importantly, this is being extended to improved understanding of the nature of NK cell memory. As NK cell biology offers increasing resonance with analogous pathways in CD8 biology, some have made the case that immunology may sometimes benefit from a little less conceptual 'splitting' and a little more conceptual 'lumping.'