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™ BUV661 which is part of the BD Horizon Brilliant™ Ultraviolet family of dyes. This dye is a tandem fluorochrome of BD Horizon BUV395 with an Ex Max of 348-nm and an acceptor dye with an Em Max at 661-nm. BD Horizon Brilliant BUV661 can be excited by the ultraviolet laser (355 nm) and detected with a 670/25 filter and a 630 nm LP. Due to cross laser excitation of this dye, there may be significant spillover into channels detecting APC-like emissions (eg, 670/25-nm filter).
Due to spectral differences between labeled cells and beads, using BD™ CompBeads can result in incorrect spillover values when used with BD Horizon BUV661 reagents. Therefore, the use of BD CompBeads or BD CompBeads Plus to determine spillover values for these reagents is not recommended. Different BUV661 reagents (eg, CD4 vs. CD45) can have slightly different fluorescence spillover therefore, it may also be necessary to use clone-specific compensation controls when using these reagents.