The complement system is an important part of the immune system as it helps fight pathogens and antigens, helps clean up after the fight, and even assists in tissue repair following the battle. However, complement can be detrimental as well if elevations persist.
The most abundant complement is C3, a compound that triggers histamine release, smooth muscle contraction, vasodilation, inflammation, phagocytosis, and antibody delivery. Insufficient complement may result in incomplete cleanup after an immune response, leaving behind immune complexes and cellular debris that can trigger an autoimmune response. However, both overactivation and depletion of complement can contribute to autoimmunity.
Elevations in C3 may be caused by toxins in the environment, cigarette smoke, and other pollutants and can be seen in respiratory disorders such as asthma. High levels can also be seen with cardiometabolic disorders, kidney disease, gallbladder dysfunction, and rheumatoid arthritis.
Low levels of C3 can be seen with immune overactivation that leads to complement depletion, recurrent bacterial infections, and autoimmune disorders such as lupus.
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