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How does the complement system help the body fight infection during inflammation?
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inflammation
The main function of complement proteins is to aid in the destruction of pathogens by piercing their outer membranes (cell lysis) or by making them more attractive to phagocytic cells such as macrophages (a process known as opsonization). Some complement components also promote inflammation by stimulating cells to release histamine and by attracting phagocytic cells to the site of infection.
The complement system aids the body in fighting infection during inflammation through a cascade of protein activations that target pathogens and recruit immune cells.12
When the system is activated, the pivotal protein C3 is cleaved into two functional fragments that drive the immune response:12
- Promoting Inflammation: The smaller fragment, C3a, acts as a potent pharmacological agent. It stimulates mast cells and basophils to release histamine, which increases blood vessel permeability, and attracts granulocytes and monocytes to the site of infection.2
- Direct Pathogen Destruction: The larger fragment, C3b, facilitates the formation of membrane attack complexes. These structures poke holes in the membranes of invading microorganisms, causing them to burst (lysis).12
- Enhancing Phagocytosis: C3b coats the surface of pathogens in a process called opsonization. This makes the microbes more attractive to macrophages and neutrophils, which recognize the C3b and ingest the invaders.12
These coordinated actions ensure that the immune response is localized and effective at eliminating foreign threats.2