The Vitamin D3 Metabolite 1,25(OH)₂D₃ Binds to the Vitamin D $\gamma$

Multiple Choice

The vitamin D3 metabolite 1,25(OH) ₂D₃ binds to the vitamin D receptor (VDR) . This complex then functions as a transcriptional regulator. The activation of VDR following treatment of cells with 1,25(OH) ₂D₃ has been found to modulate the activity of antigen-presenting dendritic cells. In one study, dendritic cells were isolated from wild-type mice and activated in vitro by stimulation with LPS plus IFN- $\gamma$ in the presence or absence of 1,25(OH) ₂D₃ for 24 hours. These activated dendritic cells were then pulsed with a peptide from the chicken ovalbumin protein (OVA) that binds to MHC class II and is recognized by OT-II CD4 T cells. The peptide-pulsed dendritic cells and T cells were incubated together for 3 days, and then IL-2 levels in the supernatants were measured, as shown in Figure .
Based on these data, dendritic cells activated in the presence of 1,25(OH) ₂D₃ are likely to show:

A) Reduced MHC class II and reduced B7 expression compared to controls
B) Enhanced expression of IL-12 compared to controls
C) Reduced expression of IL-6 and TNF- $\alpha$ compared to controls
D) Increased expression of MHC class I and class II expression compared to controls
E) Reduced expression of proteins involved in antigen presentation compared to controls