Association with FcRγ Is Essential for Activation Signal through NKR-P1 (CD161) in Natural Killer (NK) Cells and NK1.1+ T Cells

Natural killer (NK) cells exhibit cytotoxicity against variety of tumor cells and virus-infected cells without prior sensitization and represent unique lymphocytes involved in primary host defense. NKR-P1 is thought to be one of NK receptors mediating activation signals because cross-linking of NKR-P1 activates NK cells to exhibit cytotoxicity and IFN-gamma production. However, molecular mechanism of NK cell activation via NKR-P1 is not well elucidated. In this study, we analyzed the cell surface complex associated with NKR-P1 on NK cells and found that NKR-P1 associates with the FcRgamma chain which is an essential component of Fc receptors for IgG and IgE. The association between FcRgamma and NKR-P1 is independent of Fc receptor complexes. Furthermore, NK cells from FcRgamma-deficient mice did not show cytotoxicity or IFN-gamma production upon NKR-P1 cross-linking. Similarly, NK1.1+ T cells from FcRgamma-deficient mice did not produce IFN-gamma upon NKR-P1 crosslinking. These findings demonstrate that the FcRgamma chain plays an important role in activation of NK cells via the NKR-P1 molecule.