The effect of IFN-gamma on healthy and psoriatic keratinocytes in a skin equivalent model is influenced by the source of the keratinocytes and by their interactions with fibroblasts.

We investigated the effect of interferon-gamma (IFN-gamma) on skin equivalents. Keratinocytes from involved and uninvolved skin from psoriatic subjects and from healthy subjects were grown on preproduced dermal equivalents (DE) containing fibroblasts from healthy skin or psoriatic lesions. Healthy keratinocytes were added when the dermal equivalents were either 22 days (DE(22)) or 37 days old (DE(37)) and psoriatic keratinocytes when the dermal equivalents were 28-52 days old (DE(28-52)). The skin equivalents were cultured for 11 days in a serum-free medium, and then with or without 500 U/ml IFN-gamma for 6 days. The expression of markers associated with differentiation and proliferation were investigated by immunohistochemistry. Differentiation was assessed by computed scores for the expression of cytokeratin 16, involucrin, filaggrin and the receptor for epidermal growth factor. The differentiating effect of IFN-gamma on healthy keratinocytes grown on DE(37) was significantly stronger than on psoriatic keratinocytes grown on DE(28-52). In healthy keratinocytes, the differentiating effect of IFN-gamma was significantly stronger in skin equivalents containing DE(37) than in those containing DE(22). The proliferation rate, i.e. the percentage of Ki-67+ keratinocytes in the basal layer, was studied in healthy keratinocytes grown on DE(22). In these cultures IFN-gamma increased the proliferation rate in the presence of psoriatic fibroblasts but not in the presence of healthy fibroblasts. HLA-DR expression was induced only in healthy keratinocytes grown on DE(22). We conclude that the influence of IFN-gamma epidermal differentiation and proliferation is influenced by the origins of both the keratinocytes and the fibroblasts. These findings suggest that interactions between keratinocytes and fibroblasts might be involved in the pathogenesis of psoriasis.