ULBP1 is ligand for the NKG2D receptor, together with at least ULBP2 and ULBP3. ULBPs activate multiple signaling pathways in primary NK cells, resulting in the production of cytokines and chemokines. In CMV infected cells, ULBP1 interacts with soluble CMV glycoprotein UL16. The interaction with UL16 blocked the interaction with the NKG2D receptor, providing a mechanism by which CMV infected cells might escape the immune system. UL16 also causes ULBP1 to be retained in the ER and cis-Golgi apparatus so that it does not reach the cell surface. Recombinant human ULBP1 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.