SPN is a major sialoglycoprotein found on the surface of thymocytes, T lymphocytes, monocytes, granulocytes, and some B lymphocytes. It may be part of a physiologic ligand-receptor complex involved in T-cell activation. During T-cell activation, this protein is actively removed from the T-cell-APC (antigen-presenting cell) contact site, suggesting a negative regulatory role in adaptive immune response. Recombinant human SPN protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.