The 7E9 antibody specifically recognizes CD21/CD35, an epitope shared by mouse Complement receptor 2 (CR2) and Complement receptor 1 (CR1), which are also known as CD21 and CD35, respectively. Mouse CD21 and CD35 are ~145-kDa and ~190-kDa single pass type I transmembrane glycoproteins, respectively. Unlike human CD21 and CD35 that are encoded by separate CR2 and CR1 genes, mouse CD21 and CD35 are encoded by a single Cr2 gene and are generated by alternative mRNA splicing. CD21 and CD35 are expressed on B cells and follicular dendritic cells (FCD) but not on thymocytes, T cells, erythrocytes, or platelets. CD35 is also expressed on macrophages and activated granulocytes. CD21 binds to cleaved C3b fragments, including C3d- and C3dg-bound to antigen, whereas CD35 binds to C3b-, iC3b-, and C4b-bound complexes. These receptors play many important roles including the transport, presentation, and retention of complement fragment-tagged antigens and immune complexes crucial for generating strong B cell antibody-producing responses. Complement-tagged antigen can bind to CD21, part of the B cell coreceptor complex and to the B cell receptor for antigen (BCR) which facilitates the antigen-driven activation of B cell responses. CD35 interacts with other regulatory factors to promote C3b and C4b degradation as well as playing roles in stimulating phagocytic functions in activated leucocytes. The 7E9 antibody recognizes an epitope on CD35 distinct from the epitope recognized by the mouse CD35-specific clone, 8C12, as well as the mouse CD21/CD35-specific clone, 7G6.
This antibody is conjugated to BD Horizon™ BV605 which is part of the BD Horizon Brilliant™ Violet family of dyes. With an Ex Max of 407-nm and Em Max of 602-nm, BD Horizon BV605 can be excited by a violet laser and detected with a standard 610/20-nm filter set. BD Horizon BV605 is a tandem fluorochrome of BD Horizon BV421 and an acceptor dye with an Em max at 605-nm. Due to the excitation of the acceptor dye by the green (532 nm) and yellow-green (561 nm) lasers, there will be significant spillover into the PE and BD Horizon PE-CF594 detectors off the green or yellow-green lasers. BD Horizon BV605 conjugates are very bright, often exhibiting brightness equivalent to PE conjugates and can be used as a third color off of the violet laser.