IgG subclass determination in human sera with commercially available reagents: comparison of different assay systems

IgG subclass determinations are of increasing importance for the diagnosis of humoral immunodeficiencies. The search for a method which is accurate, reliable and suitable for the clinical routine, while utilizing commercially available reagents, was the aim of this study. Different assay systems for determination of IgG subclasses were compared. Radial immunodiffusion with polyclonal antisera (RIDpoly) proved to be a reliable method for subclass determination in individual human sera. Sera deficient in one or several IgG subclasses as well as several myeloma proteins were readily and reliably detected. The RID method with monoclonal antibodies (RIDmono) yielded results comparable to those obtained with RIDpoly in the IgG1 and IgG2 determination. Differences between RIDpoly and RIDmono were observed, however, in the determination of IgG3 and IgG4. These discrepancies were shown to be due to differences in the calibration of the standards as given by the manufacturers, and not to different recognition of distinct allotypes. The results of an enzyme immunoassay (EIA) using commercially available IgG reagents without further purification did not compare satisfactorily with the results of the RIDpoly method. These discrepancies, however, were assay-inherent rather than monoclonal reagent-inherent.