ULBP-2 is a member of a family of cell-surface proteins that function as ligands for human NKG2D. ULBP-2 has also been described under the names RaeT1H (retinoic acid early transcript), NKG2DL2, and ALCAN-alpha. The name ULBP-2 derives from the original identification of three proteins, ULBP-1, -2, and -3, as ligands for the human cytomegalovirus glycoprotein UL16; they were designated UL16 binding proteins (ULBP). The gene for ULBP-2 resides in a cluster of ten related genes, six of which encode potentially functional glycoproteins. Amino acid sequence identity within this family ranges from 30 – 60%. These proteins are distantly related to MHC class I proteins, but they possess only the alpha 1 and alpha 2 Ig-like domains, and they have no capacity to bind peptide or interact with beta 2-microglobulin. Some family members, including ULBP-2, are anchored to the membrane via a GPI-linkage, whereas others have transmembrane domains. ULBP-2 and several other family members are known to bind to human NKG2D, an activating receptor expressed on NK cells, NKT cells, gamma δ T cells, and CD8⁺ alpha beta T cells. Engagement of NKG2D results in the activation of cytolytic activity and/or cytokine production by these effector cells. The ULBPs are expressed on some tumor cells and have been implicated in tumor surveillance.