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™ BUV563 which is part of the BD Horizon Brilliant™ Ultraviolet family of dyes. This dye is a tandem fluorochrome of BD Horizon BUV395 which has an Ex Max of 348 nm and an acceptor dye. The tandem has an Em Max at 563 nm. BD Horizon BUV563 can be excited by the 355 nm ultraviolet laser. On instruments with a 561 nm Yellow-Green laser, the recommended bandpass filter is 585/15 nm with a 535 nm long pass to minimize laser light leakage. When BD Horizon BUV563 is used with an instrument that does not have a 561 nm laser, a 560/40 nm filter with a 535 nm long pass may be more optimal. Due to the excitation and emission characteristics of the acceptor dye, there may be spillover into the PE and PE-CF594 detectors. However, the spillover can be corrected through compensation as with any other dye combination.