Anticomplementary activity of IVIG concentrates – important assay parameters and impact of IgG polymers

Background and Objectives  A high concentration of large size polymers in intravenous immunoglobulin preparations was always correlated with high anticomplementary activity (ACA). In former days, high ACA was also linked to adverse reactions in patients. The goal of this study was to scrutinize critical parameters of the ACA assay and the influence of different polymer variants of IgG on the complement consumption. Materials and Methods  Critical reagents as the complement and the preparation of erythrocytes were investigated. The influence of molecular integrity of IgG on the ACA was tested by subjecting IgG solutions ranging from pH 4·5 to 7·0 to heat treatment at 60°C. Results  The different complement batches had a significant impact on the test result of the ACA assay. It was demonstrated that polymers, provoked by heat treatment at pH values above 5·5, consumed complement almost completely whereas a polymer content up to 12% formed under acidic conditions did not lead to an increase in ACA. Conclusion  It was shown that suitable complement batches have to be identified in a screening procedure. Furthermore, it could be demonstrated that IgG polymers formed in the neutral pH range during heat treatment were potential ACA inducing compounds. Manufacturing the IVIG preparations under acidic conditions may help to avoid the formation of those ACA active polymers. Thus, intensive analysis of ACA during process development and validation is recommended.