Complement refers to a set of serum proteins that cooperates with both the innate and the adaptive immune systems to eliminate blood and tissue pathogen.
The complement system is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promotes inflammation, and attacks the pathogen’s plasma membrane.
Properties of Complement
Complement shows the following properties:
- It is present in sera of all mammals including humans and in lower animals including birds, amphibians, and fishes.
- These are heat-labile substances that are inactivated by heating serum at 56°C for 30 minutes.
- These are glycoproteins and are synthesized primarily by liver cells and to a very less extent by macrophages and many other cell types. The rate of synthesis of the various complement glycoproteins increase when complement is activated and consumed.
- The complement usually does not bind to the antigen or antibody but only to antigen–antibody complex.
- The importance of the complement lies in the fact that it contributes to both the acquired and innate immunity of an individual.
Effects of Complement
There are four main effects of complement:
- It causes lysis of cells (such as bacteria, viruses, allografts, and tumor cells).
- It generates mediators that participate in triggering specific cell functions, inflammation, and secretion of immune-regulatory molecules.
- It facilitates opsonization, (process by which bacteria are more readily and more efficiently engulfed by phagocytes).
- It causes immune clearance, (immune complexes from the circulation are removed and are transported to spleen and liver).
Complement takes part in both specific and non-specific resistance and generates a number of products of biological and pathophysiological significance.
Imbalance of complement proteins can lead to disorders. There have been cases of genetic deficiencies of complement components (most individual C component). C3 deficiency is most fatal or serious one. Deficiency of complement can also occur during acute and chronic bacterial, parasitic and viral infections as well as immune diseases.
Functions of complements
- Phagocytosis/ Opsonization of foreign particles.
- Membrae attack- Rupturing of the cell wall.
- Inflammation- Attracts macrophages and neutralization.
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