Peripheral blood regulatory T cell measurements correlate with serum vitamin D level in patients with psoriasis

Vitamin D is the precursor of a hormone (1,25-dihydroxyvitamin D3), which has many biological effects in the skin. The immune modulator properties of vitamin D are mediated in part through effects on regulatory T cells (T-reg). Currently, in psoriasis, the relationship between vitamin D and T-reg has not well elucidated. We assess whether vitamin D status is correlated with circulating T-reg in patients affected by psoriasis and if there is a correlation with the severity of the disease evaluated with Psoriasis Area Severity Index (PASI) score.

For each patient we have analyzed, PASI-score, serum levels vitamin D and regulatory T cell percentages. Spearmen's coefficient was used between serum vitamin D levels and the predictors. Subsequently, the independent predictive factors were assessed by Multiple Regression.

A total of 26 patients were included in our analysis. Using no parametric Spearman's Coefficient test between serum levels of vitamin D and the single variables, we found an association with T-reg population (p < 0.001) and with PASI-score (p = 0.04).

While vitamin D treatment induces a cytokine profile known to favor the differentiation of T cells with suppressive activity, at the same time, several studies showed how vitamin D can prime for tolerogenic dendritic cells able to favor the differentiation of Treg from T naïve cells. Low levels of vitamin-D may decrease the number of circulatory T-reg, disrupting the immunological homeostasis in psoriatic patients and encouraging the inflammatory activity.