Description: The 6D4 monoclonal antibody reacts with the human major histocompatibility complex (MHC) class I chain-related (MIC), MICA and MICB proteins. MICA and MICB are related proteins of 83% amino acid similarity, and show homology with classical human leukocyte antigen (HLA) molecules. The structure of MICA and MICB are similar to classical HLA class I chains, however they do not bind β2 microglobulin or bind peptide typical of HLA class I. MICA and MICB are expressed on the cell surface of endothelial cells, fibroblasts, gastric epithelium and PHA-stimulated T cells, and act as a ligand for NKGD2 expressed on the surface of NK cells, γδ T cells and αβ CD8+ T cells. There is evidence to suggest that human cytomegalovirus (HCMV) subverts NK cell detection by inhibiting the function of MICB. Furthermore, MICA and MICB expression has been detected in several epithelial tumours isolated from breast, lung, ovary, prostate, colon and kidney.