A Three-Layer Immunoradiometric Assay for Determination of IgG Subclass Antibodies in Human Sera ("IgG Subclass RAST")

We report the development of a three-layer immunoradiometric assay (TIRA) for measurement of IgG antibodies of all four subclasses in human sera. The first layer consists of diluted human serum, the second layer is monoclonal mouse antibodies to human IgG subclasses., and the third layer is ¹²⁵I-labelled rabbit anti-mouse IgG. Monoclonal anti-IgG1. anti-IgC3 and anti-IgG4 reacted only with their complementary IgG subclass, whereas the anti-lgG2 showed slight cross-reactivity to immunoglobins of other subclasses and classes and to light chain proteins. The observed cross-reactivity was found to be without importance, when the TIRA was applied to measurement of IgG subclass antibodies. Equipotency was established by use of appropriate dilutions of the monoclonal antibodies, and the assay was calibrated by use of human reference serum. The TIRA therefore permits reliable inter-individual and intra-individual comparisons of the IgG antibody response in all four subclasses. Von-sped fie binding obtained with pooled normal human serum was below 0.33'#. Inter-assay coefficient of variation was between 18 and 27%, The TIRA was applied to measurement of IgG subclass antibodies to timothy grass pollen in sera from grass pollen allergies undergoing immunotherapy.