The complement system: Pathways of activations and functions

Abstract

The complement system plays an important role in host defense. It is composed of series of plasma proteins which, when activated in a sequential reaction, unleashes a powerful destructive activity towards invading pathogens. Three major pathways exist in the activation of complement: the classical pathway, which is initiated by antibody-antigen binding, the alternative pathway, which is activated by a susceptible foreign surface, and the lectin pathways, which can be triggered by manann-binding lectins. The complement system consists of serum and cell surface proteins that interact with one another and with other molecules of the immune system in a highly regulated manner. Complement proteins are plasma proteins that are normally inactive and they are activated only under particular conditions to generate products that mediate various effector functions of the complement.

Sistem komplementa ima značajnu ulogu u odbrani domaćina od patogena. Sastoji se od niza proteina plazme koji se aktiviraju u kaskadnom procesu, dovodeći do oštećenja patogena. Opisana su tri puta aktivacije sistema komplementa: klasičan (aktivira se vezivanjem C1q komponente komplementa za kompleks antigen-antitelo), alternativni (aktivira se direktnim vezivanjem C3b komponente komplementa za površinske molekule mikroorganizama) i lektinski (indukovan je vezivanjem manoza vezućeg proteina za manozne rezidue na površini mikroorganizama). Najvažnija uloga sistema komplementa u urođenom i specifičnom imunitetu je stimulisanje fagocitoze, liza mikroorganizama i pospešivanje inflamacije. Komplement ima ključnu ulogu i u uklanjanju imunskih kompleksa.