OCIL/CLEC2D, also known as lectin-like transcript-1 (LLT-1), is a type II transmembrane protein belonging to the natural killer cell receptor group of the C-type lectin superfamily. It is found on hematopoietic cells, osteoblasts, and chondrocytes. Human OCIL preferentially binds high molecular weight sulfated glycosaminoglycans and is a ligand for the single human NKR-P1A receptor (CD161). Human OCIL blocks osteoclast differentiation. Engagement of OCIL with CD161 on NK cells also inhibits NK cell-mediated cytotoxicity and IFN-gamma secretion.