Abstract: Objective To elucidate the therapeutic mechanism of 1,25-dihydroxyvitamin D₃ and its analogues in psoriasis. Methods The modulating role of calcitriol, calcipotriol and tacalcitol on the expression and secretion of IL-10 in monocyte-derived dendritic cells (MDDCs) was investigated. Human monocytes were differentiated into MDDCs in vitro in the presence of GM-CSF and IL-4. Semi-quantitative RT-PCR and ELISA were used to analyze the mRNA expression and protein production of IL-10 in MDDCs. In each experiment, 24,25-dihydroxyvitamin D₃ (a vitamin D₃ metabolite with a low affinity to the vitamin D receptor) was used as a control. Results The mRNA expression and protein secretion of IL-10 in MDDCs was up-regulated by calcitriol, calcipotriol or tacalcitol with a similar potency, but not by 24,25-dihydroxyvitamin D₃. The up-regulatory role of calcitriol on IL-10 protein secretion was dose dependent. Conclusion The therapeutic effect of calcitriol and its analogues in the treatment of psoriasis may be related to the induction of IL-10 production.

Key words: 1, 25-Dihydroxyvitamin D₃, Dendritic cells, Interleukin-10