Vitamin A and D in allergy: from experimental animal models and cellular studies to human disease

INTRODUCTION: Vitamins A and D are able to modulate innate and adaptive immune responses and may therefore influence the development and the course of allergic diseases. MATERIALS AND METHODS: This article reviews the current evidence for the experimental effects of vitamins A and D in vivo in animal models and on immune cells in vitro, and discusses their translational implication. A systematic literature search over the last 10 years was performed using MEDLINE and PubMed databases. RESULTS: Deficiencies of vitamin A or vitamin D in mouse models of allergic asthma seem to exacerbate allergic symptoms along with enhanced lung inflammation and Th2 cytokine production. In contrast, supplementation regimes especially with vitamin D were able to attenuate symptoms in therapeutic mouse models. The active metabolites retinoic acid (RA) and 1,25-dihydroxyvitamin D3 (VD3) induced tolerogenic dendritic cells (DCs) and up-regulated T‑regulatory cells in the allergic sensitization phase, which likely contributes to tolerance induction. Additionally, RA and VD3 maintained the stability of eosinophils and mast cells in the effector phase, thereby reducing allergic mediator release. Thus, both active vitamin metabolites RA and VD3 are able to influence allergic immune responses at several immunological sites. CONCLUSION: Animal studies predict that vitamin A and D may also be attractive players in the control of allergy in humans. Whether these experimental observations can be translated to the human situation remains open, as results from clinical trials are controversial.