SIALOADHESIN, A MACROPHAGE SIALIC-ACID BINDING-RECEPTOR FOR HEMATOPOIETIC-CELLS WITH 17 IMMUNOGLOBULIN-LIKE DOMAINS

Sialoadhesin is a macrophage-restricted adhesion molecule of 185 kDa t hat mediates sialic acid-dependent binding to cells. It is expressed s trongly by macrophages in lymphoid and haemopoietic tissues where it i s likely to mediate cell-cell interactions. Here we report the molecul ar cloning of murine sialoadhesin and show that it is a new member of the immunoglobulin (Ig) superfamily with 17 Ig-like domains. COS cells transfected with a cDNA encoding full-length sialoadhesin bound mouse bone marrow cells in a sialic acid-dependent manner. Alternatively sp liced cDNAs, predicting soluble forms of sialoadhesin containing the f irst three or 16 Ig-like domains of sialoadhesin, were expressed in CO S cells and the respective proteins purified. When immobilized on plas tic, the 16-domain form bound cells in a sialic acid-dependent manner, suggesting that sialoadhesin can function in both secreted and membra ne-bound forms. The most similar proteins in the database were CD22, m yelin-associated glycoprotein, Schwann cell myelin protein and CD33. L ike sialoadhesin, CD22 mediates sialic acid-dependent cell adhesion. T he sequence similarity of sialoadhesin to CD22 and related members of the Ig superfamily indicates the existence of a novel family of sialic acid binding proteins involved in cell-cell interactions.