Overview and clinical assessment of the complement system
- M Kathryn Liszewski, PhD
M Kathryn Liszewski, PhD
- Assistant Professor of Medicine
- Washington University School of Medicine
- John P Atkinson, MD
John P Atkinson, MD
- Professor of Medicine
- Washington University School of Medicine
- Section Editors
- E Richard Stiehm, MD
E Richard Stiehm, MD
- Editor-in-Chief — Allergy and Immunology
- Section Editor — Immunology and Immunodeficiency
- Distinguished Research Professor of Pediatrics
- David Geffen School of Medicine at UCLA
- Peter H Schur, MD
Peter H Schur, MD
- Editor-in-Chief — Rheumatology
- Section Editor — Basic Science
- Professor of Medicine
- Harvard Medical School
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".)
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- PATHWAYS AND ACTIVATING CONDITIONS
- FUNCTIONS OF THE COMPLEMENT SYSTEM
- Destruction of microbes
- Clearance of cellular debris and apoptotic cells
- Promotion of inflammation
- Other functions
- Detrimental functions
- COMPLEMENT MEASUREMENT
- - Low CH50
- Laboratory error
- - Cold activation
- - Elevated CH50
- Measurement of specific components
- - Serum C3 and C4 levels
- - Other complement tests
- Impact of age on complement pathways
- PATTERNS ASSOCIATED WITH ACTIVATION OF SPECIFIC PATHWAYS
- Classical pathway activation
- Alternative pathway activation
- COMPLEMENT-BASED THERAPIES