ABSTRACT
BACKGROUND: Although vitamin D analogs have been used in the topical treatment of psoriasis, their mechanisms of action are not well understand. Calcitriol, the hormonally active vitamin D3 metabolite, has been demonstrated to exert immunomodulatory effects in the skin by down-regulating the expression of Toll-like receptors (TLRs) and proinflammatory cytokines. OBJECTIVE: We investigated the effects of calcitriol on the expression of TLR2, TLR4, antimicrobial peptide LL-37, and proinflammatory cytokines in cultured human keratinocytes. METHODS: The mRNA expression levels of TLR2, TLR4, tumor necrosis factor alpha (TNF-alpha), interleukin (IL)-1beta and LL-37 in cultured human keratinocytes were measured by real-time polymerase chain reaction (PCR) and reverse transcription (RT). Furthermore, we measured supernatant TNF-alpha levels by an enzyme-linked immunosorbent assay (ELISA) to confirm the effects of calcitriol on TLR2 and TLR4. RESULTS: As measured by RT-PCR and real-time PCR, calcitriol was found to suppress the lipopolysaccharide- and ultraviolet B radiation-mediated induction of expression of TLRs, LL-37 and proinflammatory cytokines such as TNF-alpha and IL-1beta in normal human keratinocytes. The supernatant TNF-alpha levels measured by ELISA were also suppressed after treatment with calcitriol. CONCLUSION: Calcitriol may down-regulate inflammatory stated over-expression of LL-37 and proinflammatory cytokines.