Polystyrene microtubes, coated with extracts of either Dermatophagoides pteronyssinus (DPT) or grass pollens, were used as the solid-phase in a radioimmunoassay for the measurement of specific IgG antibodies to the corresponding allergen. Radiolabelled protein A from Staphylococcus aureus (SpA) was used to determine the IgG antibodies attached to the tubes. The binding of IgG from either normal or allergic sera to DPT-coated tubes was antigen specific and mediated by the Fab fragment of the immunoglobulin. IgG antibodies purified by affinity chromatography from non-allergic serum competed with IgE antibodies to DPT.
IgE antibodies do not significantly interfere with the assay. Indeed, heating a reaginic serum resulted in a striking reduction of the (125I) anti-IgE binding to allergen-coated tubes without modifying the (125I)-SpA binding. Furthermore, filtration of a reaginic serum through Sephacryl S-200 separated a peak of IgE antibodies, characterized by a high binding of labelled a-IgE and a low binding of (125I)-SpA from the peak of IgG antibodies defined by low a-IgE and high SpA binding.
The solid phase method is more sensitive than a double-antibody technique employing the same DPT extract as labelled antigen. Non-allergic subjects had less IgG antibodies to DPT or grass pollens than allergic patients.
In untreated patients, there was a good correlation between levels of IgG and IgE antibodies to grass pollens but not to DPT. Patients hyposensitized to house dust mite had on the average three times more specific IgG antibodies than untreated cases.