Dynamics of NK cell interactions in vivo.

Natural killer (NK) cells are innate lymphocytes endowed with the capacity to survey and eliminate infected and transformed cells. Like T cells and B cells, NK cells fulfill their task by responding to soluble factors and to signals exchanged during cell-cell contacts. In this respect, cellular interactions established by NK cells are critical at every stage of their life. They regulate their survival and tune their responsiveness in the periphery. They are also important during their activation and for the targeted delivery of their cytotoxic granules. With the help of two-photon imaging, the occurrence and dynamics of these interactions as they occur in vivo are being uncovered. Interestingly, several of these initial observations were not predicted by in vitro studies and revealed the transient nature of many NK cell interactions. We review here our recent understanding of NK cell interactions in vivo at steady state, during inflammation, and during tumor elimination, emphasizing the similarities and differences with T cells.