Objective To evaluate the effect of calcipotriol on the proliferation of and cytokine secretion by melanocytes and perilesional CD8+ cytotoxic T lymphocytes (CTLs) from patients with vitiligo.Methods Melanocytes isolated from abdominal skin and CD8+ CTLs from perilesional skin of patients with vitiligo were subjected to successive culture in vitro.After several passages,the melanocytes and CD8+ CTLs were cultured alone or in combination with or without the presence of various concentrations of calcipotriol for 24 to 48 hours.MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfopheny)-2H-tetrazolium,inner salt) method was used to evaluate the proliferative activity of cells,enzyme-linked immunosorbent assay to determine the levels of interleukin (IL)-6,tumor necrosis factor (TNF)-α and interferon (IFN)-γ in the culture supematant of cells,flow cytometry to detect cell apoptosis.Some co-cultured melanocytes and CTLs were treated with calcipotriol of 10-8 mol/L and anti-IL-6 antibody of various concentrations (0,1,2,2.5,5,10 mg/L) for two days followed by enumeration of cells.The concentrations of 108 and 10-9 mol/L (calcipotriol) were chosen for relevant tests.Results There was a marked apoptosis in MCs after coculture with CD8+ CTLs.The 24-hour treatment with calcipotriol of 104 and 10-9 mol/L had no obvious effect on the proliferation of melanocytes cultured alone (both P ＞ 0.05),but accelerated the proliferation of melanocytes cocultured with CTLs (both P ＜0.05) as well as that of CD8+ CTLs cultured alone or in combination with melanocytes (all P ＜0.05).A statistical decrease was observed in IL-6,TNF-α and IFN-γlevels in the supernatant of cocultured melanocytes and CTLs compared with those in the supernatant of melanocytes and CTLs cultured alone,and calcipotriol of 10-9 mol/L intensified the decrease in supernatant IL-6 level (t =2.89,P ＜0.05),but no statistical changes were noted for the level of TNF-α or IFN-γin the supernatant of the coculture system after treatment with calcipotriol of 104 or 104 mol/L compared with that before treatment (both P ＞ 0.05).In the coculture system pretreated with calcipotriol of 10-8 mol/L,the number of CD8+ CTLs significantly decreased (t =3.15,P ＜0.05),whereas that of melanocytes significantly increased (t =3.53,P ＜0.05) after the treatment with anti-IL-6 antibody of 5 mg/L.Conclusions Perilesional CD8+ CTLs have a specific cytotoxic effect on melanocytes,and calcipotriol may inhibit the cytotoxic effect of CD8+ CTLs by suppressing the secretion of IL-6,which may partly explain the therapeutic mechanism of calcipotriol for vitiligo.