Natural Killer Cells: Biology, Physiology and Medicine – Part 1

In this issue, as well as in the next issue of the Journal of Innate Immunity, a series of review articles on NK cells is published, summarizing some of the recent research activities within this growing field of research. Several leading scientists have made seminal contributions to the two issues. In the first issue (Vol. 3, Issue 3, 2011), a series of reviews relating to the molecular specificity of NK cells, including studies of their receptors and receptor signaling, is presented. These are followed by a series of reviews that discuss NK cell interactions with other immune cells and NK cell responses to infections. In the second issue (Vol. 3, Issue 4, 2011), we will publish reviews relating to the life span of NK cells, their development, differentiation and senescence. NK cell interactions with tumor cells will also be reviewed, as well as new insights into hematopoietic stem cell transplantations where NK cells may contribute to tumor eradication. Finally, two reviews will cover the role of NK cells in organ transplant rejection and in an inflammatory disease setting. The first review in this series of articles is an update on the molecular mechanisms for NK cell activation. With an array of activating and inhibitory receptors, Bryceson et al. [11] describe how NK cells upon target cell engagement can specifically get activated to eradicate infected and transformed cells. Likewise, it is described how similar receptors control the production of chemokines and cytokines, fulfilling important tasks in conIn the beginning of the 1970s, a number of groups observed unexpected spontaneous cytotoxic activities among lymphocytes. While at first considered as ‘annoying’ background phenomena, subsequent studies led to the realization that a new subpopulation of lymphocytes could be linked to this activity [1, 2] . The cells were termed ‘natural killer’ or, briefly, ‘NK’ cells [2] . Studies of these cells initially engaged a rather small community of scientists, who often had to fight for their existence among other fellow immunologist, many of whom were studying the more ‘sophisticated’ adaptive immune cells – the T cells and B cells. However, growing insights into the molecular specificity of NK cells [3–5] , and insights into their role in controlling virus and intracellular bacteria infections, certain tumors and their ability to regulate other immune cells, hence affecting complex diseases such as autoimmune and hypersensitivity conditions, have put NK cells in the front seat of modern immunology [6] . New insights are rapidly attributing new features to the cells, e.g. a possible role in controlling T-cell and macrophage homeostasis [7] and possibilities to use them in therapeutic settings of cancer [8] . Furthermore, the recent identification of adaptive immune cell features of NK cells is a ‘hot topic’ at the moment [9] . Studies of NK cells now engage a large community of scientists, working in diverse areas of NK cell research, in experimental model systems as well as in humans [10] . Published online: March 29, 2011 Journal of Innate Immunity