Complement Component 3 (C3), the most abundant serum complement component, is a disulfide-linked 185kDa 1,637 amino acid glycoprotein which supports the classical, alternative, and lectin pathways of complement activation. C3 is proteolytically activated by C3-convertase to the anaphylatoxin C3a and the opsonizing agent C3b. Serum concentrations of C3 are increased during acute and chronic inflammation such as rheumatoid arthritis, and are decreased due to increased consumption or autoimmune disorders such as systemic lupus erythematosus.
C3 is present in normal mouse plasma at average concentrations of 0.54-1.0 mg/ml. The assay measures total mouse C3 in the 0.1-100 ng/ml range. Samples giving mouse C3 levels above 100 ng/ml should be diluted in blocking buffer before use. For best results, dilute plasma and serum samples 1:100,000 to 1:1,000,000. Mouse C3 will bind to the capture antibody coated on the microtiter plate. After appropriate washing steps, HRP labeled anti-mouse C3 primary antibody binds to the captured protein. Following an additional washing step, TMB substrate is used for color development at 450nm. Color development is proportional to the concentration of C3 in the samples. A standard calibration curve is prepared using dilutions of purified C3 and is measured along with the test samples.