Complement proteins are normally present in the bloodstream, where - in the form of inactive precursors - they make up about 10% of globulins. Only in particular conditions (inflammation, infections or other pathologies), these precursors are activated; this gives rise to bioactive complexes responsible for the various biological effects, the most important of which is cell lysis.
The complement proteins are made active by a set of enzymatic chain reactions, in a way very similar to what happens for the coagulation cascade: each component activates the next in the series, in defense of the organism.
Some pathologies can determine defects in the quantity and activity of complement proteins or their regulatory systems. The laboratory evaluation of these components makes it possible to measure their concentration in the bloodstream, as well as to verify their functionality. , if there are deficiencies or anomalies of complement proteins or their activity, such as to favor the onset of infections or increase autoimmune reactions (ie wrongly directed against the organism itself).
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The fundamental purpose of this system is to protect the organism, through the removal of pathogens (especially bacteria), interacting with the immune complexes and / or facilitating their destruction by other biological, serum or cellular systems.
However, complement can also act in the absence of an antibody component. This system is activated, in fact, even in the presence of autoimmune diseases, in which antibodies are produced that react against organs and tissues belonging to the organism itself (autoantibodies).
