The Epidermal Vitamin D System and Innate Immunity: Some More Light Shed on This Unique Photoendocrine System?

The document from 2008 discusses the role of the epidermal vitamin D system in innate immunity and its potential implications for skin health and disease. It highlights that the skin, particularly epidermal keratinocytes, can synthesize vitamin D3 and convert it into its active form, calcitriol, which affects keratinocyte proliferation, differentiation, and cytokine production. The paper also notes that vitamin D is involved in the skin's response to UVB radiation, potentially contributing to the therapeutic effects of phototherapy in conditions like psoriasis and lupus vulgaris. Furthermore, the document discusses the link between vitamin D and innate immunity, particularly through the induction of antimicrobial peptides like cathelicidin, which is a vitamin D target gene. This connection is suggested to have implications for susceptibility to infections like tuberculosis and the seasonal nature of viral infections. The paper also explores the role of vitamin D in wound healing and the regulation of cathelicidin expression in various skin conditions, including psoriasis and atopic dermatitis. It concludes that more research is needed to fully understand the physiological significance of cutaneous vitamin D synthesis and its impact on innate immunity and skin health.