An evaluation of two antigen nonspecific assays for circulating immune complexes using a model system

Area of Science:

• Immunology
• Biochemistry

Background:

• Circulating immune complexes (CIC) play a role in various autoimmune diseases.
• Accurate detection of CIC is crucial for diagnosis and monitoring.
• Existing detection methods have limitations in sensitivity and specificity.

Purpose of the Study:

• To compare the efficacy of the Protein A-glass fiber filter assay (PA-GFF) and the polyethylene glycol (PEG) insolubilization assay for detecting CIC.
• To evaluate the suitability of the PEG assay for clinical applications.

Main Methods:

• Comparison of PA-GFF and PEG assay using a BSA/anti-BSA model system.
• Testing serum samples from rheumatoid arthritis patients and healthy individuals.
• Analysis of PEG-insolubilized complexes and assessment of interfering factors.

Main Results:

• The PEG assay accurately detected CIC across a range of antigen-antibody ratios, correlating well with the Farr Test.
• The PA-GFF assay failed to detect soluble CIC but could quantify aggregated globulins.
• The PEG assay showed elevated CIC levels in rheumatoid arthritis patients and lower levels in healthy individuals.
• Fasting serum is recommended for the PEG assay to avoid unpredictable results caused by postprandial samples or anticoagulants.

Conclusions:

• The PEG insolubilization assay is a sensitive, reproducible, and practical method for detecting and quantifying CIC in serum.
• The PEG assay is suitable for clinical use, particularly in diagnosing and monitoring immune complex-related diseases.
• The PEG assay offers advantages over the PA-GFF assay for soluble CIC detection.