The complement system

The complement system consists of 9 consecutively activated components and 3 inhibitors. This system plays an important role, especially with inflammation and the development of resistance to infectious agents. In order for lysis of a bacterial or other cell to occur, activation from C3 to C9 of the components of the complement system should be activated along the classical or alternative pathway. The complement system is of great importance not only in the processes of cytolysis, but also in the amplification of phagocytosis, neutralization of viruses, and also in immune adhesion, through which antigen-antibody complexes are attached to certain cells, including B-lymphocytes.

Defects in the complement system are accompanied by a decrease in the anti-infective resistance of the organism.

Simultaneous determination of 3 indices - C3, C4 components and the titre of complementary activity allows to evaluate the state of both classical and alternative ways of activation. The consumption of complement by the classical pathway (immune complexes) is accompanied by a decrease in all three indices. When complement is activated on an alternative pathway (for example, with glomerulonephritis), C3 and the titre of complementary activity are reduced, and C4 (a component of the classical cascade) remains normal. The determination of the complementary activity titer is a good method of screening for complement deficiency (characterizes the presence of all components of the complement activation pathway). A reduced or undetectable level of the titer of complementary activity indicates a hereditary deficiency of the complement system.