The vitamin D receptor is expressed on immune cells such as B cells, T cells, and antigen presenting cells, which are all capable of synthesizing the active vitamin D metabolite. Vitamin D binds to intracellular receptors that lead to the activation of cell signaling cascades or gene transcription events which can modulate immune cell function. It can also have a controlling influence on the natural and adaptive immune response of these cells. Deficiency in vitamin D may influence immune function.