Introduction
Human Complement Component 5 (C5) is the fifth component of the complement system. C5 has a molecular weight of about 195 kDa and matures into heterodimers with α- and β-chains of 120 kDa and 75 kDa, respectively (1). Upon complement activation, C5 is cleaved into a small C5a and larger C5b polypeptides by C5 convertase. The potent pro-inflammatory anaphylatoxin C5a binds to receptors C5aR and C5L2 to initiate acute inflammatory responses (2 - 3). The C5a-mediated early pro-inflammatory responses include sepsis, systemic lupus erythamatosis, and cerebral malaria (4 - 6). The larger C5b interact with complement components C6, C7, C8, and C9 to form a membrane attack complex C5b-9 which is involved in cell apoptosis, cell activation, and production of proinflammatory mediators (7). C5 deficiency is associated with severe infantile dermatitis Leiner's disease (8).

Principle of the Assay The AssayMax Human Complement C5 ELISA kit is designed for detection of C5 in human plasma, serum, saliva, milk, and cell culture supernatants. This assay employs a quantitative sandwich enzyme immunoassay technique that measures C5 in less than 4 hours. A polyclonal antibody specific for C5 has been pre-coated onto a microplate. C5 in standards and samples is sandwiched by the immobilized antibody and a biotinylated polyclonal antibody specific for C5, which is recognized by a streptavidin-peroxidase conjugate. All unbound material is then washed away and a peroxidase enzyme substrate is added. The color development is stopped and the intensity of the color is measured.