siglec-9 (HGMW-approved symbol SIGLEC9) a member of the sialic acid-binding Ig-like lectin (Siglec) family, which belongs to the immunoglobulin superfamily (IgSF). SIGLEC9 shows a high degree of homology to many members of the siglec family, including siglec-7 (80%), siglec-8 (72%), siglec-5 (65%), and CD33 (64%). This high degree of homology is also conserved in the extracellular Ig-like domains. They are characterized by an N-terminal Ig-like V-type domain which mediates sialic acid binding, followed by varying numbers of Ig-like C2-type domains。Siglec-9 with a hydrophobic signal peptide, an N-terminal Ig-likeV-type domain, two Ig-like C2-type domains, a transmembrane region and a cytoplasmic tail.