Most of the immunosuppressive effects of interleukin-10 (IL-10) are related to functional inhibition of antigen-presenting cells (APC). Herein, we investigate the influence of recombinant (r)IL-10 on human dendritic cells (DC) purified from peripheral blood of healthy volunteers. First, we found that rIL-10 inhibited in a dose-dependent manner the proliferative responses as well as the production of IL-2 and interferon-gamma (IFN-gamma) in mixed lymphocyte reaction (MLR) between purified T cells and DC. This rIL-10 effect could be attributed to a direct effect on DC, as DC preincubated with rIL-10 were found to be deficient in the induction of alloreactive T cells even when anti-IL-10 neutralizing mAb was added at the time of MLR. Flow cytometric analysis indicated that rIL-10 did not modify the expression of ICAM-1 (CD54) and B7-1 (CD80), but decreased HLA-DR and B7-2 (CD86) expression at the DC surface. We conclude that the inhibitory effect of rIL-10 on primary alloreactive T cell responses involves down-regulation of class II MHC and B7-2 expression at the DC surface.

We evaluated the effects of interleukin (IL)-10 on the differentiation of dendritic cells (DC) obtained by culturing plastic-adherent peripheral blood mononuclear cells for 7 days in presence of granulocyte/macrophage-colony-stimulating factor (GM-CSF) + IL-4. The addition of IL-10 at the initiation of culture resulted in the generation of macrophage-like cells with expressing high levels of CD14 and decreased levels of CD1a and CD1c. Furthermore, cells generated in presence of IL-10 secreted lower levels of IL-12, but higher levels of IL-8 compared with DC generated in absence of IL-10, both spontaneously and after CD40 engagement. Finally, cells generated in presence of IL-10 were less efficient than DC in stimulating the production of IL-2, interferon-gamma, and IL-4 by allogeneic T cells. We conclude that IL-10 prevents the generation of DC induced by GM-CSF + IL-4 and favors the development of macrophages with a lower T cell stimulatory potential, but secreting higher levels of IL-8 than DC.

We evaluated the effects of interleukin (IL)-10 on the maturation of human dendritic cells (DC) induced either by lipopolysaccharide (LPS) or CD40 engagement. For this purpose, DC generated by culturing plastic-adherent peripheral blood mononuclear cells for 7 days with granulocyte/macrophage-colony-stimulating factor and IL-4 were incubated for 3 days with either LPS (10 ng/ml) or 3T6 fibroblasts transfected with the gene encoding CD40 ligand, in absence or presence of IL-10. First we found that the membrane expression of CD83, a marker of mature DC, was inhibited by IL-10 when induced by LPS but not by CD40 engagement. Likewise, IL-10 inhibited LPS-induced but not CD40-dependent CD86 (B7.2) up-regulation on DC. Furthermore, IL-10 inhibited the production of IL-8 and tumor necrosis factor-alpha by DC when activated by LPS but not by CD40. In contrast, IL-10 inhibited IL-12 production in both activation systems. We conclude that IL-10 differentially influences LPS-dependent and CD40-dependent pathways of DC maturation.