Glucocorticoids modulate the development of dendritic cells from blood precursors

Dendritic cells (DC) are professional antigen-presenting cells, capable of priming naive T cell responses. Glucocorticoids (GC) are frequently used in asthmatic patients. In this study we describe the effects of GC on the development and function of monocyte-derived DC (MoDC) in vitro and in vivo. Monocytes from healthy individuals were isolated and incubated with granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4 for 6 days, to induce maturation into MoDC. To study the role of GC on DC differentiation in vitro cells were incubated with dexamethasone at different stages of MoDC development. At day 6 cells were characterized phenotypically by flow cytometry and functionally in an allogeneic mixed leucocyte reaction. To study the effect of GC in vivo patients with mild/moderate atopic asthma were selected. In one group no GC were used, whereas the other group used inhalation GC. MoDC from these patients were generated as described above and tested functionally. Incubation of MoDC or its peripheral blood precursors with dexamethasone decreased the accessory potency dose-dependently. The functional differences could not be explained by the changes in the expression of MHC II and the costimulatory molecules CD40 and CD86. The relevance of this mechanism was confirmed for the in vivo situation as well. MoDC from patients using inhalation GC showed a decreased accessory potency. These data suggest a modulatory effect of GC therapy at the level of the peripheral blood monocyte. The results indicate that GC influence DC development and function in vitro as well as in vivo.