Two families of mammalian lectin-like adhesion molecules, the selectins and the sialoadhesins, bind glycoconjugate ligands in a sialic acid-dependent manner. The sialic acid-binding immunoglobulin superfamily lectins, designated Siglecs or sialoadhesins, recognize sialylated ligands and play a key role in mediating sialic-acid dependent binding to cells. Siglec-15 (sialic acid binding Ig-like lectin 15), also known as CD33L3, is a 328 amino acid single-pass type I membrane protein that contains one Ig-like C2-type domain and one Ig-like V-type domain. Expressed in dendritic and macrophage cells, Sinlec-15 interacts with DAP10 and DAP12 and binds to sialylated glycoproteins. The gene encoding Siglec-15 maps to human chromosome 18, which houses over 300 protein-coding genes and contains nearly 76 million bases.