An 131I-labelled IgE myeloma, standardized against the WHO reference serum for IgE was bound in varying concentrations to discs bearing anti-human light chain. These were used to construct a calibration curve for the subsequent binding of 125I-labelled anti-IgE, thus relating 125I counts to WHO IgE units. The calibrated anti-IgE could then be used to measure the actual amount of specific IgE bound to an allergen disc in the radioallergosorbent test. Using this standardized system, soluble allergen extracts could then be assayed by their ability to inhibit the binding of a defined amount of specific IgE, thereby enabling their activity to be expressed in WHO IgE units.
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