Assessment of the influence of irrelevant IgE on allergic sensitivity to two independent allergens

Serum samples from 31 patients sensitive to both ragweed and rye grass were quantitated for IgE specific for ragweed antigen E (AgE) and rye grass group I (rye I) antigens employing the previously described radioallergosorbent test (RAST) elution technique. IgE anti-AgE ranged from 0.4 to 320 ng/ml and comprised 0.4% to 14.2% of total serum IgE. The same sera contained IgE anti-rye I ranging from 7.9 to 1,168 ng/ml, comprising 1.6% to 29.6% of total serum IgE. A new theoretical parameter (RF), representing the percent of total IgE-Fc receptors of target cells occupied by allergen-specific IgE, was calculated for each IgE specificity by using the determinations of allergen-specific IgE antibody, total serum IgE, and assuming an equilibrium constant for binding of IgE molecules to basophils of 10⁹M^-1. This "% occupancy" parameter correlated with skin test titration, basophil cell sensitivity, and hay fever symptom scores as well as, but not better than, the absolute values of allergen-specific IgE. This finding suggests that in most atopic patients, the quantity of irrelevant IgE plays a relatively minor role in determining allergic sensitivity to a given allergen. The implications of this finding are discussed.