Natural killer cell surface protein P1A (NKRP1A or KLRB1 or CD161) receptor is a lectin like surface molecule expressed as a type II disulphide-linked homodimer on natural killer (NK) cells and subsets of T cells (Lknair et al. 1994, Mesci et al. 2006). Its expression is upregulated on mature NK cells by interleukin-12 (Poggi et al. 2007). It is thought to be involved in the regulation of NK and NKT cell function. Lectin-like transcript-1 molecule (LLT1) (also referred to as CLEC2D) a member of the KLR (killer cell lectin-like receptor) family has been identified as a ligand for the human NKRP1A (Aldemir et al. 2005, Rosen et al. 2005).