CD161 is a 30 kD type II transmembrane C-type lectin, expressed as a homodimer. Rat NKR-P1 receptors are primarily expressed on NK cells, a subset of T cells, dendritic cells, and activated monocytes. There are three different types of NKR-P in rat, namely NKR-P1a, KNR-P1b and NKR-P1c. NKR-P1a does not contain an ITIM structure and is an activating receptor, while NKR-P1b contains an ITIM and displays inhibitory function. LLT-1 (ligand lectin like transcript 1) is the ligand, while KLR (killer cell lectin like) functions as a receptor.