Modulation of IgE mediated reactions by FcgammaRII (HYP3P.406)

Abstract

Abstract Cross-linking two high affinity IgE Receptors (FcεRI) by incubation with an anti-IgE antibody binding to the receptor bound IgE’s leads to a dose dependent bell-shaped activation of basophils. Besides of the high affinity IgE receptor basophils also express two isotypes of the low affinity IgG Receptor CD32, the activatory CD32a and the inhibitory CD32b. Previous work has shown that cross-linking of FcεRI and the inhibitory CD32b decreases cell activation, hinting at the Fc part of IgG antibodies taking part in basophil modulation. To characterize the interaction between FcεRI and CD32 we used two anaphylactogenic monoclonal anti-IgE antibodies. First we produced F(ab’)2 fragments which showed an increased maximal activation of basophils compared to the full length antibodies. Blocking the binding of IgG-Fc to CD32 with an anti-CD32 molecule results as well in a higher activation, indicating an effect of IgG-Fc. Then we humanized Le27 to increase the affinity to CD32. Humanized Le27 activated basophils to the same extend as the original Le27. To investigate whether the cross-linking of FcεRI with CD32 solely has an effect on basophil activation we produced a monovalent Le27 that can cross-link FcεRI and CD32, but not two FcεRI’s. Surprisingly, this monovalent antibody did activate basophils in whole blood, but not isolated basophils. Experiments will be performed with the monovalent Le27 to investigate if it can inhibit allergen-induced basophil activation.