CD21 is a 145 kDa transmembrane glycoprotein that is expressed on mature B cells, follicular dendritic cells, a subset of immature thymocytes and on some epithelial cells. CD21 is also known as the C3d Receptor, Complement Receptor 2 (CR2), and the Epstein-Barr Virus receptor, (EBV-R). CD21 is part of a large signal-transduction complex that also includes CD19, CD81 and Leu13. CR2 serves as a receptor for the activation fragments of complement component C3, i.e. C3d, iC3d, and C3dg and C3d-bound antigens and plays a central role in the immune response by amplifying B-cell activation and proliferation. CR2 is also the receptor for EBV by binding its surface glycoprotein gp350/220. Anti-human CR2 hybridomas were generated from Cr2-/-mice (lacking the cr2 gene, that encodes CR2 and CR1 in mice) immunized with the recombinant protein representing the first two amino-terminal short consensus repeats (SRC) of human CR2, SCR1-2. Both the C3d and EBV binding sites of hu CR2 were localized to these sites. Clone 1048 has been reported to specifically react with CR2-expressing cells and to inhibit CR2 interactions with C3 fragments or the EBV surface protein, gp350/220.
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.