The serum protein system existing in vertebrate blood or freshly prepared serum is composed of more than 30 glycoproteins such as plasma complement components, soluble and membrane type complement regulatory proteins, complement receptors, etc. It is a protein reaction system with precise regulation mechanism, or a multi molecular system, including soluble proteins, membrane binding proteins and complement receptors, so it is called Complement system 。 According to the biological function of each component of the complement system, it can be divided into intrinsic component of complement, regulatory component of complement and complement receptor (CR). The complement system can be activated through three relatively independent and interrelated pathways, so as to play a variety of biological effects such as regulating phagocytosis, splitting cells, mediating inflammation, immune regulation and clearing immune complexes, including enhancing phagocytosis and enhancing the chemotaxis of phagocytes; Increase vascular permeability; Neutralizing virus; Cytolysis; The regulation of immune response.
The content of complement C3 (C3) and complement C4 (C4) in serum is higher than that of other complement molecules. They play a very important role in completing multiple functions of the complement system. Laboratory measurement plays an important role in the diagnosis, treatment and etiology of diseases. The normal reference value of C3 is 0.9~1.8 g/L. The increase of C3 is common in various infectious diseases, acute inflammation and tissue damage, acute nephritis, liver cancer, etc. The patients with rheumatoid arthritis are normal or slightly increased. C3 reduction is common in: proliferative chronic glomerulonephritis (MPGN), acute streptococcal glomerulonephritis (AGN), lupus nephritis, recurrent infection, rash, hepatitis, cirrhosis and other serious liver diseases and joint pain caused by immune complexes. The normal reference value of C4 is 0.1~0.4 g/L. Elevated C4 is common in various infectious diseases, acute nephritis, tissue damage, multiple myeloma, etc. C4 reduction is common in nephritis, systemic lupus erythematosus, viral infection, lupus syndrome, cirrhosis, hepatitis, etc. caused by immune complexes.
