<p>The complement system (complement) involves over 30 circulating and membrane-fixed proteins with an effector<br />role in the innate and humoral immunity. These proteins help the function of antibodies to protect the organism from foreign<br />molecules (antigens) which the term complement comes from. Soluble proteins of the complement system made mainly in<br />the liver and circulate in blood in an inactive form. The activation of complement may be initiated in three ways (classical,<br />alternative and lecitin pathway), and it is realized by sequential proteolysis of complement proteins (proenzymes) which<br />become emzymes with the proteolitic activity after cleavage. Products of the activatin of complement bind to the surface of<br />microbes or to the antibodies bound to antigens. An activated complement shows a number of biological effects, such as<br />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</p>