CD170, also known as Siglec-5, is a single pass transmembrane protein member of the immunoglobulin superfamily. On the cell surface, CD170 forms a 140 kD dimer. The cytoplasmic domain of Siglec-5 contains 2 ITIM motifs that recruit the tyrosine-phosphatases SHP-1 and SHP-2 after tyrosine-phosphorylation, which in turn results in the inhibition of cell signaling. Siglec-5 is expressed by granulocytes, monocytes/macrophages, subsets of lymphocytes, and a subset of activated dendritic cells. Siglec-5 binds alpha2,3- and alpha2,6-linked sialic acid as well as glycophorin A, and is involved in cell adhesion.