Two faces of IgE-mediated allergic reactions.

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We tested the possibility that IgE crosslinking stimulation may act on FcεRI-bearing cells via paradoxical effects : namely activation versus inhibition of activation. Using human basophils, we found that IgE-mediated weak stimulation consistently induces profound inhibition of basophil releasability against subsequent, IgE-mediated strong stimulation. Intracellular amount of tyrosine kinases, Lyn, Syk, and Btk were semiquantified using intracellular FACS analysis ; however, the amount of these kinases, as shown by their fluorescence intensity, did not change in the treated cells, compared to untreated cells. Interestingly, the delicate balance of IgE and anti-IgE was important in regulating the fate of cellular releasability ; when anti-IgE antibody is too excess, the basophils are immediately activated, but when IgE and anti-IgE antibody are balanced, the cells lose their releasability without releasing their granule contents (demonstrating desensitization).These results imply that IgE-mediated effects on FcεRI-bearing cells are not just cellular stimulation ; IgE can mediate complicated effects on the following IgE-mediated cellular response. The balance between IgE and antigen may be critical in regulating the extent of cellular activation. These results may be important in understanding the pathogenesis of complicated alteration of allergic inflammation under local, continuous antigen exposure.