RELATIONSHIP BETWEEN FACILITATED ALLERGEN PRESENTATION AND THE PRESENCE OF ALLERGEN-SPECIFIC IGE IN SERUM OF ATOPIC PATIENTS

Allergen presentation to allergen-specific T cells can be facilitated when IgE-allergen complexes are endocytosed by antigen-presenting cell s (APC) after binding to the low-affinity Fc epsilon R type II (CD23). Here we present a study on the relative capabilities of sera of atopi c patients to mediate facilitated antigen presentation (FAP). To this aim FAP was studied in an in vitro model in which CD23-expressing Epst ein-Barr virus (EBV)-B cells act as APC to T lymphocyte clones (TLC) t hat are specific for Der p 2, a major allergen of housedust mite Derma tophagoides pteronyssinus (Dp). Der p 2 is immune-complexed by preincu bation in sera from atopic patients, containing allergen-specific IgE. If EBV-B cells are preincubated with these complexes before using the cells as APC, the allergen-specific TLC proliferate at 100-1000-fold lower allergen concentration than required for T cell activation after presentation of uncomplexed allergen. The relative capability of vari ous sera to mediate FAP was correlated with total serum IgE, and espec ially with Der p 2-specific serum IgE. In the model used, a high FAP c apacity could be demonstrated only in sera with a total serum IgE conc entration above approximately 2 mu g/ml or with Der p 2-specific IgE a bove approximately 100 ng/ml. Maximal FAP, i.e, the ability to induce maximal proliferation of the TLC, was obtained in the presence of more than +/- 600 ng Der p 2-specific IgE/ml. At 100-600 ng/ml Der p 2-spe cific IgE the level of FAP was correlated with the concentration of al lergen-specific IgE, whereas at lower concentrations FAP was low or ab sent. All tested sera from eczema patients, all having serum anti-Der p 2-IgE concentrations > 600 ng/ml, showed a high FAP capacity, wherea s all tested sera from atopic patients without eczema, which had serum anti-Der p 2-IgE levels < 600 ng/ml, showed no or a low FAP capacity. The association of high FAP capacity with eczema may reflect a functi onal role of FAP in the pathogenesis of atopic dermatitis.