Allergen-specific IgE levels and the ability of IgE-allergen complexes to cross-link determine the extent of CD23-mediated T-cell activation.

Abstract

CD23 mediates IgE-facilitated allergen presentation and subsequent allergen-specific T-cell activation in allergic patients. We sought to investigate key factors regulating IgE-facilitated allergen presentation through CD23 and subsequent T-cell activation. To study T-cell activation by free allergens and different types of IgE-Bet v 1 complexes, we used a molecular model based on monoclonal human Bet v 1-specific IgE, monomeric and oligomeric Bet v 1 allergen, an MHC-matched CD23-expressing B-cell line, and a T-cell line expressing a human Bet v 1-specific T-cell receptor. The ability to cross-link Fcε receptors of complexes consisting of either IgE and monomeric Bet v 1 or IgE and oligomeric Bet v 1 was studied in human FcεRI-expressing basophils. T-cell proliferation by monomeric or oligomeric Bet v 1, which cross-links Fcε receptors to a different extent, was studied in allergic patients' PBMCs with and without CD23-expressing B cells. In our model non-cross-linking IgE-Bet v 1 monomer complexes, as well as cross-linking IgE-Bet v 1 oligomer complexes, induced T-cell activation, which was dependent on the concentration of specific IgE. However, T-cell activation by cross-linking IgE-Bet v 1 oligomer complexes was approximately 125-fold more efficient. Relevant T-cell proliferation occurred in allergic patients' PBMCs only in the presence of B cells, and its magnitude depended on the ability of IgE-Bet v 1 complexes to cross-link CD23. The extent of CD23-mediated T-cell activation depends on the concentration of allergen-specific IgE and the cross-linking ability of IgE-allergen complexes.