Pimecrolimus does not affect viability of dendritic cells, in contrast to corticosteroids

Abstract

Given the importance of dendritic cells (DC) for immune functions, we investigated the effect of pimecrolimus, a novel anti-inflammatory drug for the topical treatment of atopic dermatitis, on the integrity and survival of murine Langerhans’ cells (LC) and human DC, in comparison with corticosteroids (CS). BALB/c mice were treated twice on one day on both sides of the ears and on the tail with ethanolic solutions of the test compounds at their clinically used concentrations [1% hydrocortisone (HC), 0.05% clobetasol propionate (CL), 1% pimecrolimus], which effectively inhibit contact hypersensitivity responses in mice. Controls were treated with ethanol (vehicle) alone. After a period of 24–72 hours following the last application, we observed an up-regulation of Fas expression, induction of caspase-3 activity and fragmented DNA in most LC from mice treated with CS, as determined by flow cytometry of epidermal cell (EC) suspensions and TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling) staining of epidermal sheets. In contrast, no such changes were observed in LC of pimecrolimus- or vehicle-treated animals. We tested whether the topical application of CS blocks the secretion of soluble factors that are required for LC survival and maturation, and found that CS-EC supernatants, but not pimecrolimus-EC supernatants, contained significantly lower amounts of GM-CSF, TNF-a and IL-1a than EC supernatants from vehicle-treated mice. The addition of GM-CSF to EC suspensions prepared from CS-treated mice greatly improved LC viability. In conclusion, these data show that CS, but not pimecrolimus, induce apoptosis in LC, most likely occurring via both a direct and an indirect mechanism. These data are consistent with the results obtained in another study showing that CS, but not pimecrolimus, induced apoptosis in vitro during the GM-CSF/IL-4-mediated differentiation of human monocytes to dendritic cells, as determined by flow cytometric evaluation of caspase-3- and TUNEL-positive cells. This finding confirms that pimecrolimus has a more selective mode of action than CS, thus supporting a higher safety of topical pimecrolimus in the treatment of inflammatory skin diseases.