Background: The aim of this study was to better define how glucocorticoids influence primary human T cell responses. Dendritic cells (DC*) are the most effective antigen presenting cells able to activate naive T cells. Previous studies have shown that dexamethasone impaired the function of murine DC. Here, we analyzed how methylprednisolone (MP) might affect the function and maturation of human DC.
Methods: Human DC were generated from peripheral blood mononuclear cells cultured in granulocyte macrophage-colony stimulating factor and interleukin (IL)4. DC maturation was induced either by lipopolysaccharide (LPS) or by fibroblast transfected with the CD40-ligand gene (3T6-CD40L). DC phenotype was characterized by flow cytometric analysis, their cytokine production by ELISA. The ability of DC to activate naive T cells was evaluated in mixed leukocyte reactivity.
Results: Although MP did not affect viability of DC, it enhanced their antigen uptake and down-regulated their basal expression of CD86. The expression of CD80 and CD54 by DC was slightly decreased and HLA-DR expression was not modified. MP prevented LPS-induced DC maturation as assessed by the inhibition of CD86, CD80 and CD54 up-regulation, CD83 induction and production of TNF-alpha, IL-6, and IL-12. In contrast, when DC were stimulated by 3T6-CD40L, MP prevented only the synthesis of IL-12. Moreover, MP-treated DC were deficient in their ability to elicit proliferative responses of CD4+CD45RA+ allogeneic T cells as well as their synthesis of interferon (IFN)-gamma, IL-5, and IL-13. CONCLUSION. Glucocorticoids exert potent suppressive effects on human DC and thereby inhibit the induction of primary T cell responses.