Anti-C1q autoantibodies are indicative for lupus nephritis, but can also be found in other conditions and inflammatory diseases.
Circulating immune complexes can be demonstrated in rheumatic, infectious, and neoplastic diseases, as well as most immunologically mediated illnesses (inflammatory bowel disease, thrombotic thrombocytopenic purpura). Complement is part of the innate immune system. Its major function is recognition and elimination of pathogens. Complement activity plays also an important role in the pathogenesis of systemic autoimmune diseases. It is activated amongst others by CIC in the blood stream. In the process of complement activation split products like C3d can be detected in patients suffering lupus nephritis or in patients with cutaneous systemic scleroderma. Patients with systemic autoimmune diseases might also develop antibodies targeting components of the complement cascades. One of the important components that is been targeted is C1q.
Why is this test important?
C1q can assist to monitor immune complex disease (ie, lupus, glomerulonephritis, serum hepatitis, arthritis, vasculitis) or to monitor progress of some malignancies.
Circulating immune complexes may be found without any evident pathology and positive results do not necessarily implicate the immune complex in a disease process.
References:
Siegert CE, Kazatchkine MD, Sjöholm A, Würzner R, Loos M, Daha MR. Autoantibodies against C1q: view on clinical relevance and pathogenic role. Clin Exp Immunol. 1999 Apr;116(1):4-8. doi: 10.1046/j.1365-2249.1999.00867.x. PMID: 10209498; PMCID: PMC1905233.
Immune Complexes, C1q Binding
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