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*
Institute of Immunology and Allergology, Inselspital, University of Bern, Bern, Switzerland; and
Novartis Forschungsinstitut GmbH, Vienna, Austria
IgE Abs mediate allergic responses by binding to specific high
affinity receptors (Fc
RI) on mast cells and basophils. Therefore,
the IgE/Fc
RI interaction is a target for clinical intervention in
allergic disease. An anti-IgE mAb, termed BSW17, is
nonanaphylactogenic, although recognizing IgE bound to Fc
RI, and
interferes with binding of IgE to Fc
RI. Thus, BSW17 represents a
candidate Ab for treatment of IgE-mediated disorders. By panning BSW17
against random peptide libraries displayed on phages, we defined
mimotopes that mimic the conformational epitope recognized on human
IgE. Two types of mimotopes, one within the C
3 and one within the
C
4 domain, were identified, indicating that this mAb may recognize
either a large conformational epitope or eventually two distinct
epitopes on IgE. On the basis of alignments of the two mimotopes with
the human IgE sequence, we postulate that binding of BSW17 to the C
3
region predominantly blocks binding of IgE to Fc
RI, leading to
neutralization of IgE. Moreover, binding of BSW17 to the C
4 region
may explain how BSW17 recognizes Fc
RI-bound IgE, and binding to this
region may also interfere with degranulation of IgE sensitized cells
(basophils and mast cells). As a practical application of these
findings, mimotope peptides coupled to a carrier protein may be used
for the development of a peptide-based antiallergy vaccine by
induction of anti-IgE Abs similar to the current approach of using
humanized nonanaphylactogenic anti-IgE Abs as a passive
vaccine.
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