The role of vitamin D towards immune tolerance in white adipose tissue (WAT).

Vitamin D and its active form 1α,25(OH)2D3 has been recently indicated to have a fundamental role in immune regulation. An interplay between gut and white adipose tissue (WAT), mainly mediated by enterogastric hormones and adipokines, such as leptin, adiponectin and ghrelin, actively participate in the immune homeostasis and modulation both of the innate/acquired immune response and between T-cell effector/T-cell regulatory skewing. Particularly for leptin, this action promotes and enhances immune tolerance at the gut level and pro-inflammatory effect at WAT level, while calcitriol participates in promoting and increasing an M2 macrophage-like skewing, a T-reg activity at WAT level and a iNKT function at gut level. The role of active vitamin D3 therefore is fundamental in the immune homeostasis of the WAT immune microenvironment and to support the role of WAT as an endocrine, tolerogenic organ.