Cutting edge: Salivary gland NK cells develop independently of Nfil3 in steady-state.

Nfil3 is viewed as an obligate transcription factor for NK cell development. However, mouse CMV (MCMV) infection recently was shown to bypass the requirement for Nfil3 by inducing the appearance of NK cells that express the MCMV-specific receptor Ly49H. Thus, signals transmitted by Ly49H and proinflammatory cytokines are sufficient to promote NK cell differentiation in the absence of Nfil3. In this study, we report that salivary gland (SG) NK cells develop in an Nfil3-independent fashion in the steady-state in the absence of MCMV or any infection. Moreover, we show that SG NK cells have an integrin profile reminiscent of tissue-resident lymphocytes and express TRAIL for killing target cells. These results demonstrate that SG NK cells, although related to conventional NK cells, are a distinct subset of innate lymphoid cells that deviates from the conventional developmental pathway, perhaps under the influence of tissue-specific factors.