However, autoimmune diseases, which are characterized by a loss of self-antigen tolerance (29) and increased auto-antibodies and/or auto-reactive lymphocytes (30), depend not only on the gut microbiota diversity and function but also on other factors such as vitamin D deficiency (5, 31) and VDR functions to regulate immune responses [Figure 1; (32, 33)]. Here, VDR is linked to vitamin D deficiency.