The effects of topical treatment with steroids or dithranol on epidermal T lymphocytes and dendritic cells in psoriasis.

We describe the effects of treatment with topical steroids or dithranol on T and dendritic cells in the skin of patients with chronic plaque psoriasis. Resolution of lesions by both types of topical treatments was accompanied by a marked decrease in epidermal T cells. In steroid treated lesions there was also a reduction in DR+ dendritic cells to normal numbers during treatment and the rate of disappearance of both cell types correlated with the rate of resolution. However, a significant reduction of dendritic cells was not usually observed until after the T cells had almost disappeared from the epidermis and substantial healing of lesions had taken place. Dendritic cells in steroid-treated uninvolved skin had decreased to a lower level than in normal skin. In contrast, dithranol did not affect dendritic cells, either in lesional or in unaffected psoriatic epidermis. The decrease in dermal T cells observed with both treatments was more marked in steroid-treated lesions and correlated with resolution. However, blood T cells were unaffected by both treatments. The findings provide further support for the role of T cells in the pathogenesis of psoriasis.