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. 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. The gene encoding Siglec-7 was mapped to chromosome 19q13.3.