SUMMARYClinically, corticosteroids (CS) are among the first line drugs in the therapy of autoimmune and allergic diseases and potently inhibit the activation of immune cells. However, due to their pleiotropic mode of action, the prolonged use of CS is generally associated with a range of undesirable side-effects. In this study, we compared the activity of pimecrolimus, a novel immunomodulatory drug for the treatment of inflammatory skin disorders, and the CS dexamethasone (Dex) and beta-methasone-valerate ( b -MSV) in different in vitro assays addressing the cytokine-induced differentiation and maturation of monocytederived dendritic cells (M-DC), the susceptibility of M-DC to drug-induced apoptosis and the potency of differentiated M-DC to induce primary T cell activation. In contrast to pimecrolimus, Dex and b -MSV strongly induced apoptosis of M-DC precursors if added at the start of the DC differentiation culture. Flow cytometric analysis of surviving cells on day 6 of culture showed that the expression of several DC-specific antigens such as CD1a, CD40 and CD80 was inhibited by 50% to 80% at concentrations between 1 n M and 10 n M of either Dex or b -MSV. Furthermore, the presence of CS during the final maturation of M-DC inhibited the synthesis of IL-12p70, the expression of critical DC costimulatory molecules, such as CD83 and CD86 and impaired their ability to activate primary CD4 + T cell proliferation. In contrast, pimecrolimus did not inhibit the LPS-induced secretion of IL-12, surface expression of costimulatory molecules or the maturation of M-DC into potent stimulators of T cells. Taken together, these data indicate that pimecrolimus does not interfere with the differentiation and viability of dendritic cells and their precursors or with the function of mature M-DC to prime naïve T lymphocytes, and thus may have a lower potential than CS to interfere with DC-mediated immunosurveillance.