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, are immunoglobulin superfamily members that recognize sialylated ligands. The common sialic acids of mammalian cells are N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc). The human Siglec-1 gene maps to chromosome 20p13 and encodes a 1,709 amino acid protein, also known as CD169. Alternative splicing of the Siglec-1 gene produces a variant, encoding a type I transmembrane protein isoform that is soluble rather than membrane-bound. Studies have shown human Siglec-1 has greater affinity for Neu5Ac over Neu5Gc. Siglec-1 is a sialic acid-binding receptor that is expressed in hemopoietic cells. It mediates local cell-cell interactions in lymphoid tissues and can be detected at contact points of macrophages with other macrophages, sinus-lining cells and reticulum cells.