EFFECT OF CALCITRIOL ON GROWTH, DIFFERENTIATION, CHEMOKINE MESSENGER-RNA EXPRESSION OF CULTURED KERATINOCYTES AND ON KERATINOCYTE-T CELL-BINDING

Calcitriol has recently been shown to be effective against psoriasis. However, its mode of action is not exactly known. The present study fo cused on the influence of calcitriol on growth, differentiation, chemo kine mRNA and ICAM-1 mRNA expression of keratinocytes (KC) and on the binding of T-cells to keratinocytes. In vitro studies showed that calc itriol has a strong anti-proliferative effect and induces terminal dif ferentiation. gamma-IP-10 and ICAM-1 mRNA were induced by gamma-IFN, a n induction not influenced by calcitriol. Moreover, the functional exp ression of ICAM-1 on the KC cell surface as measured by a cell adhesio n assay, was not influenced either. IL-8 and huGRO mRNAs were constitu tively produced in KC, as was demonstrated after incubation with cyclo heximide. Up-regulation of both IL-8 and huGRO mRNA by IL-1 alpha was also not affected by calcitriol. It is concluded that calcitriol has a strong antiproliferative activity and does not interfere with KC resp onsiveness to gamma-IFN and IL-alpha induced chemokine expression or w ith the adhesion of T-cells to keratinocytes.