Figure 1.

Effect of vitamin A on the immune system: Vitamin A (Vit A; retinoic acid) is a fat-soluble vitamin. Passive diffusion is the main mechanism by which immune system cells acquire Vit A. Post entry, Vit A binds to its nuclear receptor, Retinoid X receptor (RXR), which modulates specific immune system cells subset. Vit A activates (upregulation of MHC-II, CD-80, CD86, IL-12) innate immune cells (macrophages and dendritic cells). In mucosal sites such as lungs and gut, treatment leads to an increase in mucin and secretory IgA antibody production. The activity of this vitamin is highly dose dependent, as low and high doses induce inflammatory and antiinflammatory responses respectively. Abbreviation: IL, interleukin.