5 upper panel, open histograms). Furthermore, part of CD127−ptCD56bright and NKIL-15 re-expressed CD127 (Fig. 5, lower panel). Hence, CD56bright, ptCD56bright and NKIL-15 are identical with respect to c-kit and CD127 expression once cytokines are withdrawn from their environment and differences in the expression of c-kit and CD127 on CD56bright NK cells appear to be more related to their activation state than to a difference in NK-cell subset. It is notable that although the presence and withdrawal of IL-15 were the key to the modulation of c-kit, CD127 and CCR7, it was not the only signal determining their level of expression. Upregulation

of c-kit and CD127 selleck screening library was fast (overnight) in AIM-V serum-free medium, whereas it was much slower (days) and less profound in the presence of FBS (data not shown). Conversely, downregulation of c-kit, CD127 and CCR7 by IL-15 was less pronounced in serum-free medium (data not shown). We also measured to what extent IL-2 or

IL-7 were able to downregulate c-kit, CD127 and CCR7 on CD56bright. We found that stimulation with IL-2 resulted in the same downregulation of receptors as IL-15. On the contrary, IL-7 downregulated only CD127 to the same extent as IL-2 and Selleckchem SB203580 IL-15 did but had a less profound effect on the expression of c-kit and CCR7 (Fig. 6). As was the case after stimulation with IL-15, withdrawal of the respective cytokines swiftly upregulated c-kit and CD127 to the levels of NKIL-15 after withdrawal of IL-15. Hence, the Morin Hydrate level of expression of c-kit, CD127 and CCR7 is affected by several cytokines as well as by other constituents of the cell’s external milieu and caution should be taken when interpreting their expression as a distinctive feature of an NK-cell maturation stage or subset. NK cells have originally been defined as large granular lymphocytes capable of killing tumor targets without priming by antigen. This definition now seems imprecise.

NK cells are very heterogeneous and the cytokine-producing CD56bright that lack cytotoxic capability largely outnumber NK cells exerting natural cytotoxicity 5, 6. During maturation, pre-NK cells and iNK express high levels of CD56 18, 19. Furthermore, CD56bright from SLO as well as from peripheral blood may acquire many features of CD56dim after stimulation with cytokines 5, 12, 20, 21. These observations have introduced the notion that CD56bright are immature and somewhat obscured the definitions of iNK, “less mature” NK cells, cytokine-producing CD56bright and “precursors of CD56dim”. It is not known what fraction of CD56bright mature into CD56dimin vivo. The bulk of CD56bright are probably end-stage effector cells with an important role in restricting infections through monokine-induced cytokine production that guide the adaptive immune response 6.