PERIPHERAL-BLOOD DENDRITIC CELLS EXPRESS FC-EPSILON-RI AS A COMPLEX COMPOSED OF FC-EPSILON-RI-ALPHA-GAMMA-CHAIN AND FC-EPSILON-RI-GAMMA-CHAINS AND CAN USE THIS RECEPTOR FOR IGE-MEDIATED ALLERGEN PRESENTATION

Originally limited to basophils and mast cells, the spectrum of high a ffinity IgE receptor (Fc epsilon RI)-bearing cells has expanded recent ly to include Langerhans cells, dermal dendritic cells (DC), monocytes , and eosinophils. As a result of studies on the distribution, structu re, and function of Fc epsilon RI on APCs, we discovered a minor nonba sophil, nonmonocyte PBMC population that can bind IgE via Fc epsilon R I. This receptor occurs on the surface of these cells as a multimeric structure containing Fc epsilon RI alpha- and Fc epsilon RI gamma-chai ns but, unlike its counterpart on basophils, lacking Fc epsilon RI bet a. Further experiments revealed that these Fc epsilon RI alpha gamma-e xpressing cells closely resemble peripheral blood DC by immunophenotyp e (HLA-DR(high), HLA-DQ(high); CD4(+), CD11a(+), CD32(+), CD33(+), B7/ 2 (CD86)(+); CD11b(low), CD14(low), CD40(low), CD54(low), CD64(low)) a nd cell morphology. These features allowed us to isolate Fc epsilon RI -expressing DC from the peripheral blood and to investigate their immu nostimulatory properties. We found Fc epsilon RI-positive DC to be eff icient stimulators of both primary (allogeneic MLR) and Fc epsilon RI/ IgE-dependent, secondary T cell responses at low cell numbers. Thus, F c epsilon RI-expressing DC may not only amplify established type I all ergic immune reactions but, unlike Fc epsilon RI-positive semiprofessi onal APCs, may be able to prime naive T cells to common and/or cryptic epitopes of IgE-reactive Ags.