A microassay for measurement of Fc function of human immunoglobulin preparations by using tetanus toxoid as antigen

In order to minimize possible adverse reactions, the functional integrity of proteins in products derived from human plasma has to be unaffected by methods of preparation and storage conditions. Numerous biologically relevant functions of IgG, a major component of immunoglobulin for intravenous use preparations (IVIG), rely on the integrity of Fc fragments. Manufacturers are obliged to prove that Fc-mediated functions are maintained in IVIG preparations. The European Pharmacopoeia's monograph proposes a Rubella antigen-based test for Fc function of immunoglobulins. We present a modification of the proposed method achieved by using more convenient and readily available tetanus toxoid as an alternative antigen target and by adapting the procedure for the use on microtitre plates, thus greatly enhancing its feasibility and sample throughput. The test conditions were optimized so that batch-to-batch variability in tetanus antibody content did not influence the result. The precision of the test was within ± 5%. By using this test, we compared Fc functionality of 9 commercial IVIG-7S preparations, which were prepared by using different virus inactivation/removal approaches. No significant differences between them have been found.