Vitamin D status influences transcriptional levels of RANKL and inflammatory biomarkers which are associated with activation of PBMC.

Vitamin D status is involved in the risk of many chronic diseases including cancer, inflammatory and autoimmune disease. The RANK/RANKL/OPG system is also implicated in the orchestration of immune functions. We aimed to investigate the expression of RANKL, OPG and markers of inflammation and immune activation in peripheral blood mononuclear cells (PBMC) from healthy subjects with different 25(OH)D3 plasma levels. The 25(OH)D3 plasma concentrations were assessed by HPLC. The gene expression was evaluated by qRT-PCR. The expression of CYP27B1 was lower in subjects with 25(OH)D3 levels below 50 nmol/L (deficiency) than subjects with both insufficient and sufficient levels of 25(OH)D3. In subjects with deficiency, we observed the up-regulation of RANKL, TNF-α, IFN-γ, ICAM and LFA-1, and a reduction of the anti-inflammatory cytokines IL-13 and IL-4 in comparison to other subjects. Finally, we found a negative correlation between RANKL mRNA levels and 25(OH)D3 and between 25(OH)D3 and ICAM mRNA levels. A positive correlation between ICAM and RANKL was observed. Our results give evidence of the modulatory effects of circulating 25(OH)D3 levels on gene expression of biomarkers of immune activation in PBMC, suggesting the possible use of PBMC as ex-vivo model to characterize molecular mechanisms of immune/inflammatory response in hypovitaminosis conditions.