Identification of SAF-2, a novel siglec expressed on eosinophils, mast cells, and basophils

Background: Eosinophils, basophils, and mast cells are believed to be the c entral tenet cells in allergic conditions including allergic rhinitis, asth ma, and eczema. The molecular mechanisms underlying the recruitment of thes e cells to sites of allergic inflammation are poorly understood. Objectives: Our aim was to identify a common adhesion molecule that could p otentially be responsible for mediating the recruitment of the allergic cel l types to the lungs and other sites of allergy. Methods: We have cloned a sialoadhesin molecule from a human eosinophil lib rary with the use of expressed sequence tag technology and characterized it s expression on allergic cells by the use of flow cytometry and specific mA bs. Results: With the use of expressed sequence tag sequencing, we have identif ied a novel siglec molecule, SAF-2. SAF-2 has homology with other sialoadhe sin family members (CD33 and siglec-5) and belongs to a subgroup of the Ig superfamily. SAF-2 is a 431-amino acid protein composed of 3 Ig domains wit h a 358-amino acid extracellular domain and a 47-amino acid tail. SAF-2 is highly restricted to eosinophils, basophils, and mast cells. Antibodies to SAF-2 do not modulate Ca++ mobilization or chemotaxis of human eosinophils induced by eotaxin. Conclusion: SAF-2 is a highly restricted sialoadhesin molecule, which may b e useful in the detection and/or modulation of allergic cells.