What is the complement system?
The complement system refers to a series of >20 proteins, circulating in the blood and tissue fluids.
Most of the proteins are normally inactive, but in response to the recognition of molecular components of microorganisms they become sequentially activated in an enzyme cascade – the activation of one protein enzymatically cleaves and activates the next protein in the cascade.
- The complement system is a group of proteins that move freely through your bloodstream.
- It plays a critical role in inflammation and defense against certain bacterial infections.
- Is also activated during reactions against incompatible blood transfusions, and during the damaging immune responses that accompany autoimmune disease.
- Deficiencies of individual complement components or inhibitors of the system can lead to a variety of diseases.
What is the Complement C4 test?
The complement C4 test is one of the most frequently used complement component tests. Your doctor may order a complement C4 test if you’re experiencing symptoms that indicate an autoimmune disease. These symptoms may include:
- extreme fatigue
- muscle pain
- joint pain
- sudden, unexpected weight loss
- muscle weakness
- muscle paralysis
The complement C4 test is also sometimes used to monitor protein levels in people who have already been diagnosed with an autoimmune disease.
Sources:
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- Hawlisch H, Wills-Karp M, Karp CL, Köhl J. The anaphylatoxins bridge innate and adaptive immune responses in allergic asthma. Mol Immunol. 2004 Jun; 41(2-3):123-131. PubMed 15159057
- Gasque P. Complement: A unique innate immune sensor for danger signals. Mol Immunol. 2004 Nov; 41(11):1089-1098. PubMed 15476920
- Peng Q, Li K, Sacks SH, Zhou W. The role of anaphylatoxins C3a and C5a in regulating innate and adaptive immune responses. Inflamm Allergy Drug Targets. 2009 Jul; 8(3):236-246. PubMed 19601884
- Wills-Karp M. Complement activation pathways: A bridge between innate and adaptive immune responses in asthma. Proc Am Thorac Soc. 2007 Jul; 4(3):247-251. PubMed 17607007
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