The 3E7 monoclonal antibody specifically recognizes multifunctional C3b and iC3b fragments of the ~190 kDa plasma glycoprotein, Complement component 3 (C3). C3 is a key component of the classical, alternative and lectin complement activation pathways which participate in innate and adaptive immune responses to eliminate pathogens, dying cells, and immune complexes from the body. C3 is produced by hepatocytes, mast cells, and leucocytes including some monocytes, macrophages, dendritic cells (DC), and T cells. As a result of complement activation, eg, initiated by an antigen-antibody immune complex in the classical pathway, biologically active C3b fragments can be cleaved from C3 by enzymatic C3 convertases. C3b can function as an opsonin by binding covalently via its reactive thioester to the surfaces of target cells, including microbes. C3b can also bind to antigen-antibody immune complexes. Macrophages and neutrophils can recognize and bind to C3b by their complement receptors, such as Complement Receptor 1 (CR1, CD35), which enhances their phagocytosis of C3b-bound target cells or immune complexes. Opsonization of target surfaces, including the cell surfaces of pathogenic organisms, infected or tumor cells, through C3b deposition is central to all three pathways of complement activation during innate or adaptive immune responses. C3b can also associate with other components of the complement system to form a C5 convertase. This complex cleaves C5 into the C5a anaphylatoxin and C5b which initiates formation of the of the cytolytic membrane attack complex (MAC) that can produce holes in target cell membranes. C3b can be further cleaved into iC3b by factor I protease and its cofactors. The iC3b fragment serves as a ligand for engaging lymphoid and phagocytic cells via various receptors including CR2 (CD21), CR3 (CD11b/CD18), CR4 (CD11c/CD18), and CRIg. The 3E7 antibody van reportedly block the activation of the alternative pathway of complement.
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.