Abstract: The regulatory effects of 1,25-dihydroxyvitamin D₃ and its analogue MC903 (calcipotriol) on the secretion of interleukin-1α and IL-8 by human keratinocytes were studied. Cultured human keratinocytes spontaneously secreted low level-of IL-1α and IL-8. 1,25-dihydroxyvitamin D₃ and MC903 showed no effect on IL-1α secretion while slightly enhanced IL-8 secretion on non-stimulated keratinocytes. Stimulation with tumor necrosis factor-α(TNFα)caused marked increase in IL-8 and slight increase in IL-1α secretion. 1,25-dihydroxyvitamin D₃ and MC903 significantly inhibited IL-1α and IL-8 secretion induced by TNFα. Stimulation with phorbol 12-myristate 13-acetate(PMA) and lipopolysaccharide(LPS) induced a significant increase in IL-8 level and decrease in IL-1α, a pattern similar to those seen in psoriatic lesions. 1,25-dihydroxyvitamin D₃ and MC903 inhibited the increase of IL-8 and the decrease of IL-1α. These results suggest that the regulatory effects of 1,25-dihydroxyvitamin D₃ and MC903 on IL-1α and IL-8 secretion by keratinocytes may contribute to their efficacy in the treatment of psoriasis.

Key words: Hydroxycholecalciferols, Keratinocyte, Interleukin 1, Interleukin 8