["Low serum vitamin D levels may provoke or aggravate Crohn's disease (CrD). Vitamin D3 is a well-known immune modulator that affects immune functions in vitro and may prevent CrD flares. Dendritic cells (DC) are key mediators of vitamin D3 effects. In this study, we describe changes in monocyte-derived DC (mo-DC) maturation marker expression and cytokine production following 26 weeks of oral vitamin D3 supplementation in CrD patients.", 'Ten CrD patients who had increased serum 25-hydroxy vitamin D levels after oral vitamin D3 and calcium treatment and ten seasonally matched placebo-treated patients were selected for this study. Mo-DC were generated before and after the 26 weeks and induced to mature upon lipopolysaccharide (LPS) stimulation. Maturation marker expression and cytokine production were analysed. Mo-DC function was analysed in a mixed leucocyte reaction (MLR).', 'Compared with baseline values, LPS-matured mo-DC exhibited reduced expression of CD80 and reduced production of the cytokines IL-10, IL-1β, and IL-6 following 26 weeks of oral vitamin D3 supplementation. Mo-DC performance in an allogeneic MLR was unchanged after vitamin D3 supplementation. Treatment with the placebo did not affect maturation markers, cytokine production, or the MLR.'] Does oral vitamin D3 supplementation reduce monocyte-derived dendritic cell maturation and cytokine production in Crohn 's disease patients?