University of California, Los Angeles, David Geffen School of Medicine, Department of Orthopedic Surgery, 615 Charles E Young Drive South, Los Angeles, CA 90095, USA. mhewison@mednet.ucla.edu
It is becoming increasingly clear that vitamin D can exert effects on human physiology beyond its long-standing association with skeletal homeostasis. In particular, the ability of active 1,25-dihydroxyvitamin D (1,25(OH)2D) to function as a potent modulator of human immune responses has attracted much attention. Over the last ten years, most studies on the relationship between vitamin D and immunity have focused on the effects of 1,25(OH)2D on lymphocytes and adaptive immunity; however, studies have shown that local macrophage synthesis of 1,25(OH)2D in response to TLR signaling is also a key feature of innate immunity. This new facet of 'non-classical' roles of vitamin D action is discussed in this review.