ULBP-4/RAET1E: Luminex Assays

ULBP-4 (UL16 binding protein 4; also NKG2D Ligand 4, Latel and RAET1E) is a 30-40 kDa glycoprotein member of the MHC Class I family of molecules. It has widespread tissue expression, and is particularly prominent on tumor cells. ULBP4 is a monomeric, non-antigen presenting MHC molecule that does not interact with beta₂-microglobulin. It is a ligand for both TCR gamma/delta and homodimeric NKG2D, the latter which appears on NK, CD8⁺ and gamma delta T cells. NKG2D ligation induces cellular cytotoxicity and cytokine secretion. Mature human ULBP4 is a 234 amino acid (aa) type I transmembrane protein. It contains a 196 aa extracellular region (aa 30-225), and a short 15 aa cytoplasmic domain. Multiple splice variants exist. One shows a five aa substitution for aa 208-263, a second shows a deletion of aa 28-63, a third shows a two aa substitution for aa 208-263, while a fourth possesses an 18 aa substitution for Gly30. Soluble ULBP4 is described to be 35 kDa in size. There is no reported rodent counterpart to ULBP4.