The 6C9 monoclonal antibody specifically recognizes human and mouse Complement component 3 (C3) and its multifunctional C3b and iC3b fragments. C3 is a ~190 kDa plasma glycoprotein that functions as a key component of the classical, alternative and lectin complement activation pathways. Active C3 fragments participate in innate and adaptive immune responses that 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 form holes in target cell membranes leading to cell lysis. 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 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.