The monoclonal antibody 1C11 recognizes complement factor I (CFI). CFI is a protein of the complement system (serine protease), also known as C3b/C4f inactivator, and is a protein encoded by the CFI gene located on chromosome 4. CFI regulates complement activation by lysing cell binding or liquid phase C3b and C3b. C4b. CFI is mainly synthesized in the liver and is initially secreted as a single 88 kDa gene product. Then, the precursor protein is cleaved by furin to produce a mature CFI protein, which is the two residues of the heavy chain (residues 19-335, 51 kDa) and the light chain (residues 340-583, 37 kDa). Sulfur-linked dimer. Only mature proteins are active. Genetic polymorphisms in CFI have been observed (variants R201S, R406H, R502L). CFI deficiency can lead to uncontrolled activation of the complement alternative pathway, resulting in a decrease in the level of complement component 3 (C3) in plasma, and is associated with repeated bacterial infections in children; recently, mutations in the CFI gene have been shown to be associated with the development of hemolytic uremic syndrome Hemolytic uremic syndrome is also a kidney disease caused by uncontrolled complement activation. Monoclonal antibodies can be used to detect CFI levels in serum and plasma.