Potential role of IL-10-treated dendritic cells in the control of the immune response to allergens

Several lines of evidence indicate that a defect in immunoregulatory mechanisms is involved in the pathogenesis of allergic asthma. The aim of this study is to determine whether IL-10-treated dendritic cells (DC) are able to modulate allergen-specific T cell responses in children affected by allergic asthma. 41 children (4-14 years) allergic to House Dust Mite (HDM), and 10 healthy age-matched children were recruited. DC were differentiated from peripheral blood CD14+ precursors and cultured with GM-CSF and IL-4 for 5 days. Der p2 (a major HDM allergen) was added alone or in combination with IL-10 for 48 hours to obtain Dp2-DC and IL10 Dp2-DC, respectively. Alternatively, DC were differentiated in the presence of IL-10 and pulsed with Der p2 during the 2 last days of culture (Dp2-DC10). The ability of the resulting DC to stimulate allergen-specific autologous T cells and to promote allergen-specific T cell anergy was analyzed. Dp2-DC induced allergen-specific T cell proliferation in 32 out of 41 patients but not in healthy controls. In 25 out of 26 allergic patients IL10 Dp2-DC and Dp2 DC10 induced a significantly lower allergen-specific T cell proliferation. The analysis of DC phenotype showed that IL-10 treatment significantly downregulated CD86 expression on Dp2-DC. However, no correlation between the reduction of CD86 expression and of T cell proliferation was observed. Dp2-DC stimulation induced a Th2 cytokine profile characterized by an increase of IL-5, IL-13 and IL-4 production and IL-5/IFN-gamma ratio. In the same patients, the co-culture with both IL-10 Dp2-DC and Dp2-DC10 caused a marked reduction of IL-5 production and of IL-13, with a parallel decrease of IL-5/IFN-gamma ratio. Moreover, in 8 children we observed an increase in IL-10 production. T cell lines generated with Dp2-DC10, compared to those generate with Dp2-DC, were hyporesponsive to reactivation with Der p2 in 4 out of 5 patients tested, both in terms of proliferation and cytokine production: IL-5, IL-13, and IL-5/IFN-gamma ratio. Our data show that IL-10 reduced the stimulatory capacity of DC through a mechanism independent from the downregulation of costimulatory signals. IL-10 treatment of DC promoted a suppression of allergen-specific Th2 cell responses. Moreover, Dp2-DC10 are able to promote T cell anergy associated with a reduction in the Th2 cytokine production. These results represent an important step forward to the prospective clinical application of Dp2-DC10 to modulate allergen-specific T cells responses in vivo.