The detection of circulating immune complexes containing immunoglobulin G

Area of Science:

• Immunology
• Biochemistry
• Clinical Chemistry

Background:

• Circulating immune complexes (CICs) are implicated in various autoimmune and inflammatory diseases.
• Accurate detection and characterization of CICs are crucial for diagnosis and monitoring disease activity.
• Existing assays for CICs have limitations in sensitivity, specificity, or interference from certain factors.

Purpose of the Study:

• To describe and validate a novel assay for detecting human IgG-containing immune complexes.
• To evaluate the performance characteristics of the developed assay, including sensitivity to complex size and interference.
• To compare the novel assay with a standard method for CIC detection.

Main Methods:

• Development of a radioimmunoassay utilizing radiolabeled immunospecific antibodies against human IgG.
• Application of polyethylene glycol (PEG) precipitation to isolate immune complexes.
• Characterization of reactive material using aggregated immunoglobulins, in vitro-prepared immune complexes, patient sera, and normal serum.
• Analysis of immune complex size using sucrose density gradient ultracentrifugation.
• Comparative analysis with the C1q binding assay.

Main Results:

• The developed assay, termed the IgG-PEG assay, specifically detects large immune complexes (greater than 25 S).
• A highly significant positive correlation (p < 0.001) was observed between the IgG-PEG assay and the C1q binding assay.
• Rheumatoid factors were found to have no influence on the results obtained from the IgG-PEG assay.
• The assay demonstrated specificity for immune complexes containing IgG.

Conclusions:

• The IgG-PEG assay is a specific and reliable method for detecting IgG-containing immune complexes.
• The assay's ability to detect large CICs and its lack of interference from rheumatoid factors offer advantages over some existing methods.
• This assay holds potential for clinical applications in diagnosing and managing diseases associated with immune complex deposition.
• The methodology may be adaptable for detecting other components of circulating immune complexes.