It is now well recognized that IgE plays a key role in the sequence of cellular events leading to an allergic reaction such as occurs in allergic rhinitis and asthma. Various strategies have been attempted to interfere with the IgE-dependent activation of mast cells and basophils, including trying to find antagonists to block the interaction between IgE and its high affinity receptor FceRI. However, the affinity of IgE for FceRI is extremely high, of the order of 10 10 –10 12 /mol/l. For any drug to compete with IgE it would have to interact with FceRI with comparable affinity: it is not surprising that this has been difficult to achieve and no such drugs have yet been described. An alternative approach would be to decrease the level of IgE available to interact with FceRI. This rationale is supported by evidence that serum levels of IgE have been reported to correlate with the severity of allergic symptoms, including in allergic asthma. At the cellular level, the amount of IgE bound to FceRI on human basophils correlates closely with serum levels of IgE. However, cell sensitivity to receptor cross-linking is influenced also by intracellular pathways such that in vitro the extent of mediator release appears to be independent of the number of IgE molecules per basophil. Also, cross-linking of only a small number of IgE receptors (relative to the total available) is sufficient to stimulate secretion.
