NK1.1, also known as KLRB1C and NKRP1C, is a type II integral membrane glycoprotein with a C-type lectin domain and belongs to the NKR-P1 family of cell surface receptors. It is expressed as a disulfide-linked homodimer on all NK and NKT cells in some strains of mice, particularly serving as a good marker for these cell types in the C57BL/6 genetic background. NK1.1 associates with the ITAM-bearing γ-chain adaptor molecule and does not engage ligands with an MHC class-I-like fold, but interacts with C-type lectin-like CLEC2 glycoproteins. Although crosslinking of the NK1.1 receptor using a specific mAb can induce NK cell-mediated cytotoxicity and effector cytokine secretion, the in vivo functions of NK1.1 and the identity of its ligand（s） are still not fully understood.