A rapid screening assay for detection of IgE-binding factors in humans

During the last few years studies in rats and mice have demonstrated IgE-binding factors, some of which have IgE-selective regulatory activities. This prompted us to develop a rapid, sensitive screening assay for measuring IgE-binding factors in humans. The principle of the assay is to measure the degree of inhibition of binding between anti-human IgE antibodies and human IgE. Thus, 200 pg IgE plus testing samples were added to each well precoated with anti-human IgE antiserum. After an overnight incubation, the wells were washed and radiolabeled anti-IgE antibodies were added to the wells. Under the optimum conditions, the assay can detect 10(-11)M anti-human IgE antibodies. With this assay, we have been able to detect IgE-binding factors in the supernatants of 2 human B cell lines which bear Fc receptors for IgE (FcR epsilon) on their surface membranes (e.g., WIL-2 and RPMI 8866), but not in the supernatants of DAUDI cells (a human cell line without FcR epsilon). Furthermore, the IgE-binding factors of WIL-2 cells were specifically adsorbed to, and eluted from, IgE-coupled Sepharose, but not BSA-Sepharose. These findings prove that the inhibition factors are indeed human IgE-binding factors, and that the assay described herein is a specific and sensitive screening assay for detecting human IgE-binding factors.