Cystatin-SN is a member of family 2 of the Cystatin superfamily and a cysteine proteinase inhibitor found in saliva, tears, urine, and seminal fluid. Together with Cystatins S and SA, it is produced by the salivary gland and secreted largely in the submandibular/sublingual saliva. Cystatin-SN inhibits members of the Papain family including Cathepsins B, C, H and L.