Binding of complement components C1q, C3, C4 and C5 to a model immune complex in ELISA

Area of Science:

• Immunology
• Clinical Chemistry

Background:

• The complement system plays a crucial role in immune responses and is implicated in various autoimmune diseases.
• Assessing complement component binding can provide insights into disease pathogenesis and diagnostic markers.

Purpose of the Study:

• To investigate the binding patterns of complement components (C1q, C3, C4, C5) to IgG in patients with Systemic Lupus Erythematosus (SLE) and Rheumatoid Arthritis (RA).
• To compare the diagnostic utility of these binding assays with traditional methods like radial immunodiffusion and the CH50 assay.

Main Methods:

• MicroELISA plates coated with monomeric or aggregated IgG were incubated with normal human serum.
• Bound complement components were detected using specific chicken antibodies against C1q, C3, C4, and C5.
• Results were compared with radial immunodiffusion and CH50 assay data.

Main Results:

• Patients with SLE showed significantly increased C1q binding and decreased C3 and C4 binding.
• Patients with RA exhibited decreased C3 binding but normal C1q binding.
• The decreases in C3 and C4 binding in SLE were more pronounced than those measured by radial immunodiffusion; CH50 assay showed moderate correlation with C3 binding but no correlation with C1q, C4, or C5 binding.

Conclusions:

• Complement component binding assays, particularly for C1q and C3, can differentiate between SLE and RA.
• These assays offer a potentially valuable tool for diagnosing and monitoring autoimmune conditions.
• The findings highlight the complex involvement of the complement system in the pathophysiology of SLE and RA.