Introduction
Complement Factor B (FB) is a component of the alternative pathway of complement activation. The zymogen circulates in the blood as a 93 kDa single chain glycoprotein with 739 amino acids (1 - 3). In the presence of C3b, it is cleaved by factor D into a 30 kDa N terminal noncatalytic Ba fragment and a 63 kDa C terminal catalytic Bb fragment. The active subunit Bb associates with C3b to form the alternative pathway C3 convertase. Human FB plays a major role in the initiation of the alternative pathway and in amplification of C3 cleavage. The polymorphism of FB influences C3 convertase formation, and is associated with age-related macular degeneration and polypoidal choroidal vasculopathy (4 - 5).

Principle of the Assay
The AssayMax Human Complement Factor B ELISA kit is designed for detection of human FB in plasma, serum, saliva, milk, and cell culture samples. This assay employs a quantitative sandwich enzyme immunoassay technique that measures FB in less than 4 hours. A monoclonal antibody specific for human FB has been pre-coated onto a 96-well microplate with removable strips. Human FB in standards and samples is sandwiched by the immobilized antibody and the biotinylated polyclonal antibody specific for FB, 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.