High-Dose Vitamin D3 Treatment Decreases CD103+ Intestinal Dendritic Cells in Healthy Subjects

Background: Vitamin D has been shown to modulate intestinal dendritic cells (DCs) and induce regulatory T cells (Treg) in vitro and in animals. However, it is still unclear whether vitamin D treatment affects human intestinal DCs in vivo.

Methods: 10 healthy subjects consumed a total of 12 mg vitamin D₃ over 15 days and underwent endoscopy with colonic biopsies before and after the intervention. Mononuclear cells were isolated from the biopsies and stained with the DC surface markers HLA-DR, CD11c and CD103 and analysed with flow cytometry. Snap-frozen biopsies were analysed with q-PCR for DC and Treg related genes.

Results: Vitamin D₃ treatment significantly decreased the total number of CD103+ DCs (p = 0.01) as well as the fraction of CD103+ DCs (p = 0.002) of all DCs and of all live cells (p = 0.006). The transcription of DC and Treg related genes did not change significantly.

Conclusion: Oral high-dose vitamin D₃ treatment significantly decreases the number of CD103+ DCs in the colonic mucosa of healthy subjects without changing the transcription of DC-related genes. Thus, further studies are needed to clarify the underlying mechanisms of the observed changes.