Figure 67. Overview of the pharmacological effects of 1,25(OH)₂D in the immune system. 1,25(OH)₂D inhibits the surface expression of MHC II-complexed antigen and of costimulatory molecules, as well as the production of the cytokine IL-12 in antgen presenting cells (such as dendritic cells), thereby shifting the polarization of T cells from an (auto-)aggressive effector (Te) toward a protective or regulatory (Tr) phenotype. 1,25(OH)₂D exerts its immunomodulatory effects also directly on the level of T cells. Together, these immunomodulatory effects of 1,25(OH)₂D onto players of the adaptive immune system can lead to the protection of target tissues in autoimmune diseases and transplantation. In the innate immune system on the other hand, 1,25(OH)₂D strengthens the antimicrobial function of monocytes and macrophages, for example through enhanced expression of the CAMP, eventually leading to better clearance of pathogenic microorganisms. Reproduced with permission from.¹⁵¹