CD169, also known as Siglec-1 and Sialoadhesin (Sn), is a 210 kD type I single membrane-spanning glycoprotein. It is the largest member of the Siglec family, consisting of 1709 amino acids and belonging to the immunoglobulin superfamily. CD169 is expressed by macrophages and dendritic cells. By its affinity to alpha2,3-linked sialic acid, it is involved in macrophage binding to different cell types such as granulocytes, monocytes, NK, B and T cells. Several CD169 counter receptors, such as CD227 on human breast cancer cells, CD43 on T cells and CD206 on macrophages, have been reported.