The MBC 78.2 monoclonal antibody recognizes CD31 which is also known as, Platelet endothelial cell adhesion molecule (PECAM-1), platelet GPIIa, or EndoCAM. CD31 is a ~130 kDa type I transmembrane glycoprotein that belongs to the Ig gene superfamily. CD31 is comprised of an extracellular region with six IgC-like domains, a transmembrane region, and a cytoplasmic domain that contains two immunoreceptor tyrosine-based inhibitory motifs (ITIMs). The MBC 78.2 antibody specifically binds to an epitope located on membrane-proximal, extracellular Ig-like domain 6 of CD31. This epitope remains expressed by activated T cells after enzymatic cleavage and shedding of a soluble extracellular CD31 fragment comprised of Ig-like domains 1 to 5 from cells. In contrast to the MBC 78.2 antibody, the WM59 monoclonal antibody reportedly binds to the extracellular Ig-like domain 2 of CD31. WM59 can thus bind to cells that express intact CD31 but not to cells that express a truncated form CD31 that lacks at least the membrane distal Ig-like domains 1 and 2 of CD31. CD31 has wide tissue distribution and is expressed on platelets, monocytes, granulocytes, some T cell subsets, and at high levels on endothelial cells. This cell adhesion molecule has been implicated in a number of cellular phenomena, including vascular wound healing. angiogenesis, transendothelial migration of leucocytes, and the regulation of T cell responses.
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.