Purity ≥ 90% by SDSPAGE under reducing conditions and visualized by silver stain. Siglecs are sialic acid specific It ype lectins that belong to the immunoglobulin superfamily. Structurally, they are transmembrane proteins with an Nterminal Ig like Vset domain followed by varying numbers of Iglike C2set domains (1, 2). Mouse Siglec1, also known as sialoadhesin and CD169, is a 175 185kD glycoprotein that consists of a 1619 amino acid (aa) extracellular domain (ECD) with one Iglike Vset domain and 16 Iglike C2set domains, a 21 aa transmembrane segment , and a 35 aa cytoplasmic domain (3, 4). Within the ECD, mouse Siglec1 shares 73% and 83% aa sequence identity with human and rat Siglec1, respectively. Alternate splicing generates a soluble form of the ECD and a soluble isoform that is truncated following the first three Iglike domains (3). Siglec1 expression is restricted to lymphnode and spleen macrophages and some tissue macrophages (4). The adhesive function of Siglec