A Monoclonal Antibody-Based Radioimmunoassay for the in vitro Production of IgE by Lymphocyte Cultures

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Abstract
Very sensitive radioimmunoassay systems have been described for the measurement of IgE produced in cultures of human peripheral blood mononuclear cells. However, differing results have been reported when cultures from non-atopic donors are stimulated with pokeweed mitogen, which may be due to cross-reactivity of anti-IgE antibodies with IgG. A monoclonal antibody specific for the Fc region of human IgE, and two polyclonal affinity-purified antibodies to IgE were tested for binding to 125I-labelled IgE myeloma proteins and polyclonal IgG in a sensitive double antibody precipitation assay. The monoclonal antibody and one of the polyclonal antibodies bound only IgE, whereas the other polyclonal antibody bound a significant proportion of labelled IgG. A solid phase radioimmunoassay was developed which combined the specificity of the monoclonal antibody with the sensitivity of the first polyclonal antibody as radioactive tracer. A second assay system was also tested using the cross-reacting antibody as tracer. Supernatants of pokeweed mitogen-stimulated peripheral blood mononuclear cell cultures from non-atopic donors were examined for IgE synthesis using both assays. The assay based on the monoclonal antibody did not detect IgE synthesis, whilst the second assay, based on the cross-reacting antibody indicated that spurious IgE had been produced in the same cultures. This study shows that protein-binding assays provide a simple means for checking the specificity of antibodies in solid phase radioimmunoassays, and confirms that pokeweed mitogen does not stimulate IgE production by cells from non-atopic donors when measured by a specific radioimmunoassay.