Antibody F1-4 recognizes a unique epitope that exists only on human complement C3c. The complement system mediates many basic biological functions and participates in the host's resistance to infection, the initiation of inflammatory responses, the processing and clearance of immune complexes, and the regulation of immune responses. There are three pathways for complement activation: the classical pathway is initiated by immune complexes, the lectin pathway is initiated by surface-bound mannan-bound lectins, and the alternative pathway is initiated by all surfaces that are not specifically protected. Each complement pathway produces C3 convertase, which is a serine protease that cleaves the central complement protein C3, and produces the major cleavage fragment C3b. C3b is an opsonin, a part of one of the main invertases that drive the complement cascade. In the presence of complement, the regulatory molecule C3b can be further degraded into iC3b, C3c, C3dg and C3d. The disadvantage of most complement biomarkers is their short half-life, making it difficult to collect and measure reliable samples. Unlike other C3 fragments, C3c does not bind to other structures, such as pathogens, cell surface (receptors) and other plasma proteins. Therefore, C3c is a stable complement biomarker and only appears in the liquid phase without interfering with other C3-based products. The measurement of C3c provides evidence of (uncontrolled) complement activation and can be used as an indicator of the inflammatory state. Complement is a key element of the innate immune system. The proper activation is pathological and causes for example. For various autoimmune diseases, such as HUS. There are also signs that C3 is related to the cardiovascular system and Parkinson's disease, making C3c a reliable and useful biomarker. Antibody F1-4 only reacts with C3c and will not cross-react with other C3 fragments. The antibody can be used in ELISA, Western blot and immunoprecipitation.