Siglec-8. A novel eosinophil-specific member of the immunoglobulin superfamily

We describe the characterization of Siglec-8, a novel sialic acid-binding immunoglobulin-like lectin that is expressed specifically by eosinophils. A full-length cDNA encoding Siglec-8 was isolated from a human eosinophil cDNA library. Siglec-8 is predicted to contain three extracellular immunoglobulin-like domains, a transmembrane region, and a cytoplasmic tail of 47 Amino acids. The Siglec-8 gene mapped on chromosome 19q13.33-41, closely linked to genes encoding CD33 (siglec-3), Siglec-5, siglec-6, and siglec-7. When Siglec-8 was expressed on COS cells or as a recombinant protein fused to the Fc region of human IgG(1), it was able to mediate sialic acid-dependent binding to human erythrocytes and to soluble sialoglycoconjugates. Using specific monoclonal Antibodies, Siglec-8 could be detected only on eosinophils and hence appears to be the first example of an eosinophil-specific transmembrane receptor.