Objectives. Recent studies have shown the immunomodulatory effect of vitamin D₃ through down-regulation of Toll-like receptor (TLR) expression in human monocytes. To understand the implication of innate immunity with the role of vitamin D affecting TLR expression in Behçet's disease (BD), we focused on the association between the TLR expression and the serum vitamin D concentration in BD. Methods. The expression of TLR2, TLR4 and CD16 on monocytes was detected by flow cytometric analysis and RT-PCR. Serum 25-hydroxyvitamin D [25(OH)D] levels were measured in the patients with BD, psoriasis and healthy controls, and then the expression of TLRs was correlated with the value of serum 25(OH)D levels. To assess the influence of vitamin D₃ on expression and function of TLRs in vitro, human monocytes were treated with increasing concentrations of 1,25(OH)₂D₃. Results. We found that the monocytes of active BD patients showed higher expressions of TLR2 and TLR4 than those of controls, and serum 25(OH)D levels tended to be lower in active BD. Furthermore, 25(OH)D levels were inversely correlated with the expressions of TLR2, TLR4 and clinical indicators. In vitro analysis showed that vitamin D₃ was found to dose-dependently suppress the protein and mRNA expressions of TLR2 and TLR4. TNF-α synthesis was also decreased upon TLR ligand stimulation in vitamin D₃-treated monocytes. Conclusion. These results suggest that the inflammation triggered through TLR2 and TLR4 is important in the pathogenesis of BD. And it seems possible that vitamin D may be used as a therapeutic option by modulating TLR2 and TLR4 expression of monocytes in BD.

The prevalence of Behcet's disease is the highest in the East Asian and the Mediterranean countries. Behcet's disease is also distributed in the Asian countries, but the nationwide survey has not been performed in Korea yet. The Korean Study Group for Behcet's Disease, founded in 1999, conducted a multicenter, retrospective survey on epidemiologic and clinical features of the patients with Behcet's disease from 20 hospitals around the nation from 1997 to 1999. Of 3,497 patients, 1,527 were classified into complete or incomplete type of Behcet's disease according to the revised Shimizu's classification. The sex ratio was 1:1.75 with the female predominance. Geographical distribution showed the highest frequency in Seoul (38.5%). Clinically, 98.8% had oral ulcers, 83.2% had genital ulcers, 84.3% had skin lesions and 50.9% had ocular lesions. As for the minor clinical manifestations, articular symptoms were the most frequent. The pathergy test showed positive in 15.4% of patients and revealed a higher positive rate in males (20.2%) than in females (12.7%). In conclusion, we performed the first multicenter study on Behcet's disease in Korea and revealed the female predominance, higher frequency of ocular lesions, and lower positivity of pathergy test in the patients.