The specific detection of IgG, IgA and the complement components C3 and C4 in circulating immune complexes

Area of Science:

• Immunology
• Biochemistry
• Clinical Chemistry

Background:

• Immune complexes play a role in various diseases.
• Accurate detection of immune complexes is crucial for diagnosis and monitoring.
• Existing assays may have limitations in sensitivity or specificity.

Purpose of the Study:

• To describe four novel polyethylene glycol (PEG) assays for detecting immune complexes.
• To characterize the size-selectivity of the IgA-PEG assay.
• To evaluate the utility of these assays in detecting immune complexes in patient sera.

Main Methods:

• Development of four radio-labelled antibody-based PEG assays targeting IgG, IgA, C3, and C4.
• Comparison of the IgA-PEG assay with an existing alpha-IgA-InhBA assay.
• Sucrose density gradient ultracentrifugation to determine the size of immune complexes.
• Analysis of patient sera for the presence of immune complexes.

Main Results:

• The IgA-PEG assay specifically detects large-sized immune complexes (>25 S).
• Ultracentrifugation confirmed the size-selectivity of PEG assays for IgA, C3, and C4 aggregates.
• All four PEG assays could detect their respective constituents (IgG, IgA, C3, C4) in mixed aggregates.
• Immune complexes containing these constituents were detected in sera from patients with various disorders.

Conclusions:

• The developed PEG assays are capable of detecting specific immune complex constituents.
• The IgA-PEG assay demonstrates size-selectivity, detecting larger immune complexes.
• These assays show potential for detecting immune complexes in diverse patient populations.
• Further research is required to determine if detected constituents reside in the same or different immune complexes.