The Role of Ultraviolet B Light Induced Vitamin D in Gastrointestinal Pathology

A low vitamin D status is linked to a high incidence rate and a worse outcome of both Ulcerative colitis (UC) and Crohn’s disease (CD) - the most common forms of inflammatory bowel disease (IBD). Since the gastrointestinal pathology due to IBD, the major source of vitamin D for patients is generated in the skin after ultraviolet B (UVB) exposure. We would like to characterize the impact of UVB-light induced vitamin D on the development of colitis, as well as its impact on host responses to gut bacteria (both pathogens and commensals). For this study, we use UVB emitting lamps (emission peak at 311 nm) to increase blood circulating vitamin D precursor, 25(OH)₂D₃, in C57BL/6 mice and vitamin D receptor (VDR) knockout mice. Preliminary results implicate that UVB radiation protects against bacterial burdens, epithelial barrier disruption and increases expression of anti-inflammatory cytokines in both cecum and colon after oral infection with Salmonella Typhimurium. Furthermore, UVB light induced vitamin D showed similar protective effect against DSS colitis in C57BL/6 mice. Ongoing studies focus on the induction of immunosuppressive of T regulatory cells after vitamin D and gut-homing 103⁺ dendritic cell signaling in both colitis models. We are the first group to report the interplay between topical UVB light, vitamin D and colitis in mice. These results show that UVB phototherapy is a promising non-invasive application for IBD patients for future therapy.