Complement system facts for kids

The classical and alternative complement pathways

The complement system helps or “complements” the ability of antibodies and phagocytic cells to clear pathogens from an organism. It is part of the innate immune system.

The complement system consists of a number of small proteins found in the blood, made by the liver. Normally they circulate as inactive precursors ("pro-proteins"). When stimulated by a trigger, proteases split specific proteins to release active cytokines. This starts a series (a cascade) of further cleavages which release more cytokines. This amplifies (makes bigger) the response. So, if the original stimulus was an invading bacterium, the cytokines disrupt the phospholipid bilayer cell membrane of the target, which kills it.

Images for kids

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  Membrane Attack Complex (Terminal Complement Complex C5b-9)

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  Reaction Cascade of the Complement System: Classical, Alternative and Lectin Pathway, Amplification Loop, Terminal Pathway, and Membrane Attack Complex.

See also

In Spanish: Sistema del complemento para niños