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™ BUV496 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 496-nm. BD Horizon BUV496 can be excited by the ultraviolet laser (355 nm) and detected with a 515/30 nm filter with a 450LP. Due to the excitation of the acceptor dye by other laser lines, there may be significant spillover into the channel detecting BD Horizon V500 or BV510 (eg, 525/40-nm filter). However, the spillover can be corrected through compensation as with any other dye combination.