C1q binding and Raji immune complex assays: a comparison using defined immunoglobulin aggregates

Area of Science:

• Immunology
• Biochemistry

Background:

• Aggregated immunoglobulin G (IgG) is crucial for measuring immune complexes.
• Standardized aggregated IgG is needed for accurate immune complex quantification.

Purpose of the Study:

• To compare heat and alkali denaturation methods for creating aggregated IgG standards.
• To evaluate the performance of C1q binding and Raji cell assays in detecting immune complexes of varying sizes.

Main Methods:

• Human IgG was aggregated using heat or alkali denaturation.
• Aggregates were fractionated by size using LKB AcA 22 Ultrogel column chromatography.
• Fractionated aggregates were tested for C1q binding and in a Raji radioimmunoassay.

Main Results:

• Heat aggregation produced more monomeric IgG (47%) than alkali treatment (6.3%).
• Both methods yielded large aggregates (≥19 S); alkali produced smaller aggregates.
• C1q binding assay detected smaller aggregates more efficiently than the Raji cell assay.
• Neither assay detected monomeric IgG.

Conclusions:

• Both C1q binding and Raji cell assays effectively measure large immune complexes (≥19 S).
• The C1q binding assay shows superior sensitivity for smaller immune complexes.
• Combined use of both assays allows for the measurement of a broader range of immune complex sizes.