Siglecs (sialic acid binding Ig-like lectins) are I-type (Ig-type) lectins belonging to the Ig superfamily. 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. Eleven human Siglecs have been cloned and characterized. To date, no Siglec has been shown to recognized any cell surface ligand other than sialic acids, suggesting that interactions with glycans containing this carbohydrate are important in mediating the biological functions of Siglecs. Human Siglec-7 encodes a 467 amino acid (aa) polypeptide with a hydrophobic signal peptide, an N-terminal Ig-like V-type domain, two Ig-like C2-type domains, a transmembrane region and a cytoplasmic tail. Siglec-7 exists as a monomer on the cell surface and is expressed on natural killer cells, CD8+ T cells and monocytes. It binds equally well to both alpha 2,3- and alpha 2,6-linked sialic acid.