The influence of serum IgE levels of selected recipients, including patients with allergy, helminthiasis and tuberculosis, on the apparent P-K titre of a reaginic serum.

The P–K titre of a donor serum in different recipients was found to be inversely related to the serum IgE level of those recipients. The median serum IgE level of subjects who gave a negative P–K reaction with a 1:2 dilution of the donor serum was 3325 units/ml; patients who reacted positively to dilutions of 1:2, 1:8 and 1:32 of the test serum had median serum IgE levels of 1950, 410 and 155 units/ml respectively. Recipients included normal adults and selected patients with allergy, helminthiasis or tuberculosis. Most individuals with very high serum IgE levels had helminthiasis. All subjects gave normal reactions when skin-tested with histamine, codeine and anti-IgE antiserum. The inverse relationship between P–K reactivity and serum IgE level may be due to saturation of mast cell IgE-binding sites by endogenous serum IgE. Other possible mechanisms are discussed.