Natural killer (NK) cells express a multitude of activating and inactivating cell surface receptors through which they recognise tumors and infected cells. Among the activating receptors, the family of Ig-like molecules is termed natural cytotoxicity receptors (NCRs). These NCRs include Natural cytotoxicity triggering receptor 1 (NCR1 also referred as NKp46 or LY94), Natural cytotoxicity triggering receptor 2 (NCR2 also referred as NKp44) and Natural cytotoxicity triggering receptor 3 (NCR3 also referred as NKp30 ) (Hecht et al. 2009). All three NCRs are involved in the elimination of both tumor and virus infected cells. NCRs are coupled to different signal transducing adaptor proteins, including CD3zeta, FCER1G, and KARAP/DAP12.
NCR1 (NKp46) is selectively expressed by all resting and activated human NK cells (Sivori et al. 1997). NCRI recognises and targets the direct killing of virus-infected cells. The antiviral activity is initiated by the interaction of NCR1 with hemagglutinin of influenza virus or Sendai virus (Mandelboim et al. 2001). Biochemical analysis revealed that NCR1 molecules are coupled with associated adaptor proteins CD3z and FCERIG that contain immune tyrosine-based activating motifs (ITAM) (Moretta et al. 2001).