Detection and differentiation of immune complexes and IgG aggregates by a complement consumption assay

Area of Science:

• Immunology
• Biochemistry

Background:

• The complement consumption assay is a tool for detecting immune complexes and IgG aggregates in serum.
• Background anticomplementarity (AC) can interfere with accurate assay results.
• IgG aggregates are a common cause of background AC.

Purpose of the Study:

• To evaluate the utility of a complement consumption assay for detecting IgG aggregates and immune complexes.
• To investigate methods for reducing background anticomplementarity in serum samples.

Main Methods:

• Detection of heavy (≥19S) and intermediate (11-17S) IgG aggregates.
• Quantification of Bovine Serum Albumin (BSA) anti-BSA complexes.
• Assessment of anticomplementarity in stored Normal Human Serum (NHS).
• Evaluation of heat treatment (56°C for 50 min) on AC and C1q fixation.

Main Results:

• The assay detected IgG aggregates with a sensitivity of ≥10 µg/ml.
• BSA anti-BSA complexes were detected at 200 ng/ml.
• Stored NHS developed significant AC, which was reduced by heat treatment.
• Heat treatment reduced AC and C1q fixation in aggregated IgG and stored NHS, but not in preformed antigen-antibody complexes.

Conclusions:

• The complement consumption assay is effective for detecting IgG aggregates and immune complexes.
• Heat treatment at 56°C for 50 minutes can mitigate background AC in serum due to IgG aggregates.
• This heat treatment does not affect the anticomplementary activity of preformed antigen-antibody complexes.