COMPLEMENT - ACTIVATION, REGULATION OF ACTIVATION AND BIOLOGICAL ACTIVITY

The complement system (complement) involves over 30 circulating and membrane-fixed proteins with an effector role in the innate and humoral immunity. These proteins help the function of antibodies to protect the organism from foreign molecules (antigens) which the term complement comes from. Soluble proteins of the complement system made mainly in the liver and circulate in blood in an inactive form. The activation of complement may be initiated in three ways (classical, alternative and lecitin pathway), and it is realized by sequential proteolysis of complement proteins (proenzymes) which become emzymes with the proteolitic activity after cleavage. Products of the activatin of complement bind to the surface of microbes or to the antibodies bound to antigens. An activated complement shows a number of biological effects, such as lysis of an attached cell, opsonization, neutralization of viruses, inflammation, clearance of immune complexes etc. In contrast of microorganisms, human cells have a number of regulatory proteins which prevent the complement activation and in that way, they regulate its activity