Vitamin D3 has been shown in animal studies and in studies of human monocyte derived dendritic cells (MDDC) to influence function of myeloid dendritic cells (mDC). This study was undertaken to examine the effects of active vitamin D3 (1,25D) on synovial fluid (SF) mDC and MDDC. The study was in part designed to determine the authenticity of MDDC as a model for DC that differentiate naturally and accumulate within the inflammatory lesion.
SF was aspirated from knees with inflammatory effusions. PB samples were obtained contemporaneously. SFDC were separated by flow cytometry. Morphology was determined on cytosmears. Expression of accessory-molecules, cytokines, and prostaglandin-synthases (PGS) mRNA was quantified by RT-PCR. Analyses were undertaken on freshly prepared DC and after incubation with 1,25D and LPS, separately and in combination.
SF mDC displayed an immature phenotype comparable to iMDDC. SFDC but not MDDC expressed prostaglandin D-synthase (PGDS). PGDS was lost on incubation of SFDC but was induced by 1,25D in MDDC. Both SF mDC and iMDDC matured following LPS stimulation. LPS stimulation of SF mDC resulted in significantly higher expression IL23, IL1b and TNFa compared with MDDC. Combined stimulation of TLR-4 and 1,25D resulted in a marked enhancement of expression of PGES and IL6 in both SF mDC and MDDC.
The studies draw attention to the potentially complex effects of vitamin D on immune responses. The findings also highlight the need for studies that utilise DC isolated from inflammatory sites in order to complement studies of more conveniently obtained MDDC.