C4, Human, mAb BSI1306

The monoclonal C4 antibody BSI1306 (HM2444) recognizes an epitope on the α-chain of C4. The C4 glycoprotein is a large key molecule in the activation of the classical and lectin pathway. The formed proteolytic complexes of both pathways lead to cleavage of C4 thereby releasing the anaphylotoxin C4a and the pathway activating C4b. Binding of C4b to the cell surface leads to the formation of the C5 convertases, which is the start of the terminal pathway of complement. C4 functions as an acute phase protein and has a concentration of 150-600 μg/ml in healthy individuals. The majority of the protein is synthesized in the liver but also locally by among others monocytes, macrophages, lung, spleen, kidney and intestinal epithelial cells. After activation of C4 the nascent C4b is quickly inactivated by its reaction with water. Only surface bound C4b forms the basis of formation of the CP/LP convertases. Total C4 concentration reflects potential to activate the complement system via the classical or lectin pathway.