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Circulating immune complexes in the blood
Last reviewed: 05.07.2025
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The normal content of CIC in blood serum is 30-90 IU/ml.
Circulating immune complexes (CIC) are complexes consisting of antigens, antibodies and associated complement components C3, C4, C1q. Normally, immune complexes formed in the bloodstream are phagocytized and destroyed. With an increase in their size (with an excess of antigens and the presence of IgM, complement component C1q in their structure), the complexes can be deposited in the perivascular space and the renal cortex, causing activation of complement and inflammatory processes. Pathological reactions to immune complexes can be caused by an increase in the rate of their formation over the rate of elimination, a deficiency of one or more complement components, or functional defects of the phagocytic system. Determination of the content of immune complexes in the blood serum is important in the diagnosis of acute inflammatory processes and type III allergic reactions, in which the level of CIC increases, as well as in assessing the effectiveness of the treatment.
In autoimmune diseases, autoantibodies reacting with tissues appear, exerting a cytotoxic effect, but immune complexes exert an incomparably greater damaging effect. More than a hundred diseases have been described, mainly caused by the deposition of CIC in various organs, tissues or systems with subsequent activation of complement and lysosomes of cells, the development of an inflammatory reaction or tissue destruction under the influence of T-killers and macrophages.
An increase in the concentration of CIC in the blood is possible for the following diseases.
- Acute bacterial, fungal, parasitic and viral infections.
- Autoimmune diseases, collagenoses, rheumatism, glomerulonephritis, allergic alveolitis, vasculitis, Arthus phenomenon.
- Immune complex diseases, serum sickness.
- Allergic reactions of type III.
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