Introduction Dendritic cells (DC) can determine whether the mucosal immune system mounts an inflammatory or regulatory response to antigen and may contribute to the pathogenesis of Crohn’s disease. Vitamin D down-regulates DC inflammatory responses and could prove beneficial as a treatment adjunct in Crohn’s. This study assessed the effect of high dose parenteral vitamin D treatment on circulating DC phenotype and function in patients with active luminal Crohn’s receiving anti-TNFα therapy.

Methods Peripheral blood mononuclear cells were isolated from 13 patients with active luminal Crohn’s and suboptimal vitamin D levels prior to and 6 weeks after starting anti-TNFα (infliximab) therapy. Patients with low vitamin D (<50nmol/L) were also given a single high dose of parenteral vitamin D (300,000 international units 1,25(OH)₂ vitamin D3). Flow cytometry was used to identify total DC, (HLA-DR⁺ cells negative for markers of other cell lineages (CD3, CD14, CD16, CD19 & CD34)). DC were further subtyped as myeloid (mDC, CD11c⁺CD123⁻). Expression of phenotypic markers (including maturation and homing markers and pattern recognition receptors) and on-going DC cytokine production during 4 hours’ culture were assessed.

Results Production of TNFα by myeloid DC was significantly reduced (p = 0.016 Fig C) in those patients who received vitamin D alongside anti-TNFα therapy; without vitamin D treatment, TNFα production by myeloid DC did not decrease significantly after anti-TNFα therapy (p = 0.96 Fig B). There was a significant negative correlation between change in vitamin D level and change in TNFα production by myeloid DC (p = 0.025, correlation coefficient =0.68 Fig D). An increase of serum 25(OH)vitamin D greater than 20 nmol/m was associated with a decrease in myeloid DC TNFα production. Anti-TNFα therapy alone induced a significant upregulation of the skin homing marker cutaneous lymphocyte antigen (CLA) on myeloid DC (p = 0.0055), an effect which was not seen in patients receiving adjunctive vitamin D.

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Abstract PWE-023 Figure 1

A&B TNFα production by mDC before and after treatment with anti-TNFα therapy in: patients who did not (A) and patients who did (B) receive vitamin D. (C) Correlation of change in vitamin D level and decrease in TNFα production by mDC

Conclusion High doses of parenteral vitamin D in patients with Crohn’s promotes anti-TNFα down-regulation of circulating myeloid DC production of TNFα which may influence the subsequent interaction of DC and T cells. TNFα promotes a TH-1/ TH-17 response characteristic of Crohn’s inflammation; thus the ability of vitamin D to further block TNFα production may promote a more regulatory T cell response and improve outcomes when used as an adjunct to anti-TNFα therapy. The down-regulation of skin homing marker CLA by vitamin D may be clinically useful in those patients suffering cutaneous sequelae of anti-TNFα therapy.

Disclosure of Interest None Declared