Complement C1q

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In medicine and immunology, complement C1qis a "subcomponent of complement C1, composed of six copies of three polypeptide chains (A, B, and C), each encoded by a separate gene (C1QA; C1QB; C1QC). This complex is arranged in nine subunits (six disulfide-linked dimers of A and B, and three disulfide-linked homodimers of C). C1q has binding sites for antibodies (the heavy chain of immunoglobulin G or immunoglobulin M). The interaction of C1q and immunoglobulin activates the two proenzymes complement C1r and complement C1s, thus initiating the cascade of complement activation via the classical complement pathway".[1]

The C1q level is low in acquired C1 esterase inhibitor deficiency (acquired angioedema).


  1. Anonymous (2015), Complement C1q (English). Medical Subject Headings. U.S. National Library of Medicine.