The 6D4 monoclonal antibody specifically binds to the human MHC class I polypeptide-related sequence A (MICA, aka PERB11.1) and B (MICB. aka PERB11.2) proteins. These ~70 kDa transmembrane glycoproteins are homologs of the major histocompatibility complex class I molecules although they lack association with β2 microglobulin. The MHC class I-related MICA and MICB chains are expressed by some gut epithelial cells in vivo. MICA and MICB expression by other epithelial cells and cell types, including fibroblasts and endothelial cells, is induced by stress, eg, stress caused by bacterial and viral infections, autoimmunity or cellular transformation. Epithelial cell expression of MICA and MICB has also been detected in transplanted kidneys and pancreas that show histological signs of rejection and or cellular injury. This suggests their potential role in transplant immunopathology. MICA and MICB are ligands for NKG2D (CD314), an activating receptor expressed by natural killer (NK) cells, γδ T cells, CD8+ and some CD4+ αβ T cells. The 6D4 antibody reportedly blocks NKG2D-positive NK cell- and T cell-mediated cytotoxicity against MICA/B-positive target cells.
The antibody was conjugated to BD Horizon™ BV650 which is part of the BD Horizon Brilliant™ Violet family of dyes. This dye is a tandem fluorochrome of BD Horizon BV421 with an Ex Max of 405-nm and an acceptor dye with an Em Max at 650-nm. BD Horizon BV650 can be excited by the violet laser and detected in a filter used to detect APC-like dyes (eg, 660/20-nm filter). Due to the excitation and emission characteristics of the acceptor dye, there will be spillover into the APC and Alexa Fluor® 700 detectors. However, the spillover can be corrected through compensation as with any other dye combination.