Measurement of the potency of allergy extracts by their inhibitory capacities in the radioallergosorbent test

The potencies of 11 commercial extracts of short ragweed pollen were analyzed by skin test end point titration and compared to potency as measured in vitro: (1) by the radioallergosorbent test (RAST), (2) by AgE concentrations, and (3) by protein nitrogen determinations (PNU). RAST potency was determined by the capacity of the extract to inhibit the binding of IgE antibody to solid-phase allergen in the first step of the RAST, and it was expressed as the quantity of extract needed for 50 per cent inhibition of binding. Potencies determined by skin testing in 7 patients were strongly related among the various patients in spite of a 1,000-fold difference in the patients' sensitivity to the extracts. Similarly, potency as measured by RAST inhibition showed about a 1,000-fold difference among the extracts, and the RAST potencies were strongly related to potency as measured by skin testing. Purified antigens derived from short ragweed inhibited binding of IgE antibodies, but the slopes of the inhibition curves were significantly less than those produced by crude or partially purified short ragweed. AgE concentration and PNU concentrations also were correlated with skin test potency, but the range of potencies was less than that found by RAST inhibition. Measurement of the potency of extracts by RAST inhibition should prove useful as a general procedure for the standardization of allergy extracts.