Dendritic cells can convert vitamin A to retinoic acid. T and B cell activation in the presence of retinoic acid results in the up-regulation of gut-homing molecules and generation of IgA-secreting B cells (Mora, Iwata et al. 2008). Consequently, deficiency in vitamin A results in the impairment of mucosal responses (Mora, Iwata et al. 2008). Vitamin D has long been known to have a critical role in calcium and phosphorous homeostasis. In addition, antigen presenting cells convert vitamin D to 1,25(OH)2VD3, a physiologically active form of vitamin D that is highly concentrated in lymphoid tissues (Mora, Iwata et al. 2008) where it can modulate function of T and B cells which express vitamin D receptors. Vitamin D deficiency results in reduced differentiation, phagocytosis and oxidative burst, by monocytes as well as defective bactericidal activity by keratinocytes (Fabri, Stenger et al. 2011, Djukic, Onken et al. 2014).
