ABSTRACT
The complement system is a well-orchestrated, highly complex, and tightly controlled biological system, which constitutes a major part of both the innate and adaptive immune systems 0-3). Its primary function is to recognize and destroy pathogenic micro-organisms, and in this capacity, therefore, it has evolved a sophisticated mechanism of discrimination between self and nonself. There are situations however, in which complement can turn against the self, thereby causing tissue damage and destruction. Comprised of three independent activation pathways, the complement system consists of more than 30 serum and cell surface proteins, which, together with an intricate array of modulators and regula tors, form one of the proteolytic cascade systems of blood plasma (4). In the classic sense, complement is activated primarily when antigenantibody complexes are formed in either plasma or tissues and, as a consequence, secondary activation peptides are generated that play an important role in many types of immunological reactions and inflammatory
processes. Activation of complement requires an initial contact with and recognition of an activator. This initial contact is thought to provide the subtle molecular signal necessary to trigger a series of protein-protein interactions involving, sequentially, the conversion of proteolytic zymogens to active proteinases and the assembly of functionally defined protein complexes on the surface of the activator particle. If the activating agent is a virus, a bacterium, or a tumor cell, activation of complement will lead to its destruction by causing irreversible structural and functional impairment of its membrane.
