NK1.1/CD161, also known as KLRB1, is a receptor protein expressed on the surface of natural killer (NK) cells and certain T cells. In mice, NK1.1 belongs to the NKRP1 receptor family and interacts with C-type lectin-related molecules, playing a role in immune recognition and regulation. In humans, CD161 on NK cells interacts with ligands such as LLT1, and this interaction is inhibitory, helping to regulate NK cell function. Additionally, CD161 is involved in intracellular signaling pathways, such as the AKT pathway, which influences NK cell activity. This protein is also a marker for different subsets of NK cells, with high expression in certain mature and cytotoxic NK cell populations.