Abstract
Vitamin A, a generic designation for an array of organic molecules that includes retinal, retinol and retinoic acid, is an essential nutrient needed in a wide array of aspects including the proper functioning of the visual system, maintenance of cell function and differentiation, epithelial surface integrity, erythrocyte production, reproduction, and normal immune function. Vitamin A deficiency is one of the most common micronutrient deficiencies worldwide and is associated with defects in adaptive immunity. Reports from epidemiological studies, clinical trials and experimental studies have clearly demonstrated that vitamin A plays a central role in immunity and that its deficiency is the cause of broad immune alterations including decreased humoral and cellular responses, inadequate immune regulation, weak response to vaccines and poor lymphoid organ development. In this review, we will examine the role of vitamin A in immunity and focus on several aspects of T cell biology such as T helper cell differentiation, function and homing, as well as lymphoid organ development. Further, we will provide an overview of the effects of vitamin A deficiency in the adaptive immune responses and how retinoic acid, through its effect on T cells can fine-tune the balance between tolerance and immunity.
Highlights
In the early 20th century, several researchers performed studies on laboratory animals to identify essential dietary components
dendritic cells (DCs) obtained from spleen express only marginal levels isolated from Peyer’s patches and mesenteric lymph nodes, but not those isolated from spleen of produce retinoic acid (RA) from retinol when co‐cultured with T cells and their specific antigen [27]
Activation upon T cell receptor stimulation [67]. These results strongly argue in favor of RA as an essential metabolite in the development of an appropriate immune response
Summary
In the early 20th century, several researchers performed studies on laboratory animals to identify essential dietary components. Several studies have reported that vitamin A increases antibody production which has led to the supplementation of vaccines with vitamin A, results from human immunization programs have not shown a significant effect on vaccine efficacy upon vitamin A supplementation [4]. Despite all these efforts, today vitamin A deficiency (VAD) is still one of the most common micronutrient deficiencies, affecting approximately one-third of the world’s preschool-age population [5] and remains the primary. With the development of better models and experimental techniques, it has become clear that vitamin A, through its metabolite retinoic acid (RA), has a broad impact on diverse aspects of the immune response, including mucosal immunity, tolerance, leukocyte trafficking and lymph node organogenesis
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