5A). HLA-E+ target cells. Importantly, after IL-12 + IL-18 activation, reacquisition of NKG2A strongly correlates with IFN- production in CD56dimNKG2ANK cells. == Conclusions/Significance == With each other, these findings call for the reclassification of adult human NK cells into unique subsets and support a new model, in which the NK cell differentiation and practical fate are based on a stepwise decrease of NKG2A and acquisition of KIRs. == Intro == NK cells are one component of the innate immune system, able to recognise numerous targets without specific sensitisation. They constitute a first line of defence and may destroy infected and tumour cells. Mature NK cells are heterogeneous and differ in their proliferative potential, homing characteristics, practical capacities and responses to a wide range of cytokines[1],[2]. The complexity of the NK cell compartment is attributable to the vast network of receptors that are indicated on NK cell surfaces, which allow them to recognise target cells. These receptors can be either inhibitory or activating, and it is the balance between these opposing signals that dictates the practical status of the cells[3]. Around 10% of the NK cells in peripheral blood are CD56bright; this immunoregulatory subset generates a wide range of cytokines and chemokines after monokine activation, but its ability to destroy target cells spontaneously is usually poor. In contrast, the remaining 90% of the NK cells, the CD56dimcytotoxic NK cell subset, produces relatively lower cytokine levels, but possesses an abundance of cytolytic granules and may spontaneously lyse vulnerable target cells[4]. The precise relationship between these two major NK cell subsets, CD56brightand CD56dim, has long been debated. Several recent reports possess finally demonstrated quite convincingly that CD56brightNK cells are very probably precursors of the CD56dimsubset: the shorter telomeres of the second option, in both peripheral blood and lymph nodes, imply that they are more than the former[5],[6]. In addition, Romagnaniet alhave shownin vivothat efferent lymph nodes contain a considerable proportion of CD56dimKIR+NK cells[6]. Very LY-2940094 recently, Yuet alreinforced the concept of a transition from CD56brightto CD56dimcells, proposing CD94 like a developmental intermediary between these LY-2940094 NK cell subsets[7]. Along with others, we have exhibited that NK cells are the 1st lymphocytes appearing in patients recovering from hematopoietic stem cell transplantation (HSCT) and that these cells are constituted primarily from CD56brightNK cells[8],[9],[10],[11]. Additional and we have shown that CD56dimNK cells from patients who have recently experienced hematopoietic transplantations transiently overexpress NKG2A, compared with cells from healthy donors[8],[10],[11]. In addition, CD56dimNK cells from cord blood highly over-expressed NKG2A[12]. Completely, these data suggest that the modulation of NKG2A manifestation among CD56dimcells may define a crucial step of their differentiation. NKG2A is an inhibitory NK receptor that has been reported to form disulfide-linked heterodimers with invariant CD94. The NKG2A ligand has been identified as HLA-E, a non-classical MHC class-Ib molecule that is widely distributed among numerous tissues, exhibits relatively low surface manifestation, and Rabbit polyclonal to HLX1 offers limited polymorphism[13]. The cross-linking of NKG2A by target cells bearing HLA-E results in NK cells inhibition through the phosphorylation of the LY-2940094 two immunoreceptor Tyr-based inhibitory motifs (ITIMs) present in the intracellular tail of NKG2A[14]. Although it is well established that KIRs, in conjunction with NKG2A, perform a major part in the NK cell education that determines whether cells will end up proficient or hyporesponsive, the mechanisms fundamental this education are still debated[15]. One hypothesis proposes the engagement of self-MHC-specific inhibitory receptors directly renders NK cells practical, licensing them, so to speak. The disarming model, on the other hand, suggests that the hyporesponsiveness of NK cells missing self-MHC-specific inhibitory receptors is usually a consequence of the persistent activation of previously proficient cells. More recently a new rheostat model argues the responsiveness of each NK cell is tuned from the input of inhibitory receptors[16],[17],[18]. Here we used a combination of complementary methods that assess the kinetics of the appearance of each subset during development to examine the terminal phases of differentiation in the light of these hypotheses and to develop a detailed model that integrates our new insights with recent findings by others. All the observations from this study support the previous hypothesis that CD56dimcells derive from the CD56brightNK cell subset. Furthermore, this study provides the 1st phenotypic and practical analysis of adult CD56dimsubsets that focuses on the progressive decrease in NKG2A manifestation and the sequential acquisition of KIRs. We therefore put forward a.
