A solid-phase anti-C3 assay for detection of immune complexes in six distinguished forms

Area of Science:

• Immunology
• Clinical Chemistry
• Renal Medicine

Background:

• Immune complexes (ICs) are crucial in autoimmune and renal diseases.
• Detecting specific C3 fragment-associated ICs can improve diagnostic accuracy.
• Current methods may not fully characterize the diverse forms of ICs.

Purpose of the Study:

• To develop and validate a novel solid-phase assay for detecting distinct forms of C3 fragment-associated immune complexes.
• To investigate the prevalence of different IC types in patients with systemic lupus erythematosus (SLE) and IgA-nephritis.
• To assess the diagnostic utility of IgA-type ICs in autoimmune and renal diseases.

Main Methods:

• Development of a solid-phase assay using two monoclonal antibodies targeting C3 fragments (C3b, C3c, C3i, C3dg, iC3b).
• Enzyme-linked immunosorbent assay (ELISA) combined with class-specific anti-immunoglobulin antibodies to detect six distinct IC forms (e.g., C3b-IgG-IC, iC3b/C3dg-IgA-IC).
• Analysis of plasma samples from patients with active SLE and IgA-nephritis.

Main Results:

• The assay successfully detected six distinct types of C3 fragment-associated immune complexes.
• Approximately 75% of plasma samples from patients with active SLE or IgA-nephritis tested positive for one or more IC types.
• IgA-type ICs were frequently detected in patients suffering from autoimmune or renal diseases.

Conclusions:

• The described solid-phase anti-C3 assay is effective in identifying various immune complexes linked to C3 fragments.
• The high prevalence of IgA-type ICs in patients with autoimmune and renal conditions suggests their potential as diagnostic biomarkers.
• This assay offers a valuable tool for the diagnosis and understanding of immune-mediated diseases.