Endocrine Abstracts

In recent years, great attention has been given to the pleiotropic effect of vitamin D, a vitamin well known from its role in bone and calcium homeostasis. Also in the immune system, modulating effects by vitamin D have been described. Receptors for vitamin D are present in cells throughout the immune system and a central role for the antigen presenting dendritic cell and the macrophage in the effect of vitamin D in the immune system is described. The latter cells not only carry receptors, but also contain the machinery to produce themselves the activated form of vitamin D, 1,25-dihydroxyvitamin D3. These data suggest a physiological role for vitamin D as an immune modulator. Epidemiology confirms this possible role, indicating correlations between vitamin D deficiency and adverse immune outcomes (more infections, more autoimmune diseases). Animal models confirm this detrimental effect of vitamin D deficiency on immune function and even point towards the possibility of exploiting these effects of vitamin D in a pharmacological way, using analogues of vitamin D as immune modulators or treating immune cells ex vivo. Clinical intervention studies using vitamin D or its activated form, 1,25-dihydroxyvitamin D3, have yielded confusing results. The place for vitamin D in a healthy immune system and in disease will be discussed.