Quantitative determination of total and specific human IgE with the use of monoclonal antibodies

We have used two monoclonal antibodies (BS17 and Le27) that recognize two different epitopes of the constant region of human IgE in order to determine the total and specific IgE contained in human serum. Both types of assay are based on classic PRIST and RAST procedures and involve one or two monoclonal antibodies labeled with 125I iodine. The performance of these two assays were compared systematically with those obtained with a commercially available polyclonal tracer. We first investigated the 125I-labeling conditions for monoclonal antibodies. In our hands the best results were obtained by use of a tracer of specific radioactivity close to 10 microCi/micrograms. We have been able to demonstrate that as a consequence of its limited affinity, the radioactive tracer is always incompletely bound to the solid-phase IgE. Nonetheless, the sensitivity of the assay is comparable to that obtained with the polyclonal antibody, since less than 0.5 IU/ml can be measured by the PRIST procedure. In contrast, the dilution curves obtained in the RAST with the monoclonal antibodies are very different from those observed with the polyclonal tracer. In fact, these curves are strictly parallel to the dilution curve and to the standard curve derived from the PRIST method, thus indicating that the monoclonal antibodies recognize all IgE equally well regardless of the way in which they are bound to the solid phase. On the basis of this observation, we propose a quantitative assay of specific IgE with the PRIST standard curve as reference. Our results demonstrate that this approach is indeed possible if high-capacity, solid-phase as well as long incubation times are used.