NKp46 + NK frequency varied among the subjects, implying that viral-antigen experience in the host influenced NKp46 expression. Influenza infection may therefore alter the NKp46 + NK cell repertoire and imprint memory unto NK cells; alternatively, influenza virus entry and infection of NK cells may impair and inhibit NK cells. Thus, induction of one of two different pathways downstream of NKp46 may tip the balance Torin 1 toward either activating or inhibiting NK cell function. The changes in NKp46 occur gradually over months in our model, and this observation differs from previous studies pointing to a quick, transient drop in NKp46+ NK cells. In particular, our study likely differed from the 2004 Hanna J et al. study because they observed the more immediate rapid responses after stimulation than we evaluated here ; additionally, their internalization assays were performed in vitro, which might have elicited quick responses, whereas the internalization process that we observed might have more complex kinetics after being exposed to many different in vivo external LY2157299 factors that could regulate this expression after vaccination. In another study by Jost S et al. in 2011, the data showed a very early transient decrease in the proportion of NKp46+ NK cells. We speculate that their observed transient differences in NKp46 expression on CD56dim cells may represent an initial, direct effect of influenza vaccination on these NK cells due to only the HA��NKp46 interaction, whereas the differences that we observe here at the much later time points post-vaccination may be the result of a myriad of in vivo factors released during the ensuing immune response to vaccination��such as the effect of cytokines or other mediators produced by other cells after vaccination on CD56dim cells��that coordinate to cause a second wave of NKp46 downregulation. How surface NKp46 receptor internalizes into the cell and how NK cells interact with influenza during the recall phase remains to be established. TheW32R mutation within the natural cytotoxicity receptor gene in No�� mice abolished surface NKp46 expression but induced hyperresponsive NK cells, and silencing the Helios transcription factor gene regulated NKp46 expression and IFN-�� responses during NK cell development. Accordingly, identifying pathways promoting the development of NKp46 + NK cells will be important for understanding the molecular mechanisms underlying the generation of memory NK cells and developing NK cell��based vaccines. Since previous studies by the Greenberg and the Riley groups showed that IL-2 from influenza A��stimulated T cells was required to elicit IFN-�� from NK cells, we tested whether IL-2 was necessary for IFN-�� production. We treated the FluaRIX vaccine��stimulated PBMCs or purified NK cell cultures with an IL-2�Cneutralizing antibody and showed that neutralizing IL-2 did not significantly inhibit IFN-�� production from the purified NK cells in response to the recall antigen.