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 ceils 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.