[Circulating immune complexes: optimization and characteristics of the C1q(I125) fixation test]

Area of Science:

• Immunology
• Biochemistry

Context:

• Circulating immune complexes (CICs) are implicated in various autoimmune diseases.
• Accurate detection of CICs is crucial for diagnosis and monitoring disease activity.

Purpose:

• To optimize a liquid-phase [125I] C1q binding assay for the sensitive and reproducible detection of CICs.
• To establish optimal conditions for serum collection, storage, and assay performance.

Summary:

• The optimized assay requires blood collection without anticoagulant, allowing for standard serum storage and transport.
• A 90-minute incubation period is necessary to achieve reaction equilibrium.
• Polyethylene glycol (2.5% final concentration) is used to precipitate the [125I] C1q-CIC complex.

Impact:

• The simplified and reproducible assay can be readily implemented in clinical laboratories.
• This assay is particularly valuable for monitoring patients undergoing plasmapheresis treatment.
• Facilitates improved diagnosis and management of conditions associated with CICs.