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Overview and clinical assessment of the complement system

M Kathryn Liszewski, PhD
John P Atkinson, MD
Section Editors
E Richard Stiehm, MD
Peter H Schur, MD
Deputy Editor
Anna M Feldweg, MD


The complement system is a major component of innate immunity and a complement (from whence its name is derived) to antibody-triggered responses [1,2]. It consists of nearly 60 plasma and membrane proteins that form three distinct but overlapping activating pathways as well as a common terminal lytic cascade and a network of potent fluid-phase and cell surface regulators.

This topic review will discuss the functions of the complement system, the pathways involved, the measurement of complement activity, and the clinical significance of abnormally low or high complement tests. More detailed descriptions of the complement pathways, regulatory proteins, and clinical disorders of complement are found elsewhere:

(See "Complement pathways".)

(See "Regulators and receptors of the complement system".)

(See "Inherited disorders of the complement system".)

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Literature review current through: Oct 2017. | This topic last updated: May 10, 2016.
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