In situ expression of interleukin-6 in psoriatic epidermis during treatment.

Interleukin-6 (IL-6) is a multipotential cytokine which may act as a growth factor for keratinocytes. The epidermal hyperplasia of psoriasis may be explained in part by an overproduction of this cytokine. We have previously shown by in situ hybridization that IL-6 mRNA is most strongly expressed in the peripheral lesion of an advancing psoriatic plaque. In the present study, we investigated whether there were differences between the expression of IL-6 in untreated psoriatic epidermis and the lesion during the course of clinical improvement. In the untreated psoriatic lesion, the weak expression of IL-6 mRNA was localized in the lower epidermis. However, IL-6 mRNA was not detected in the clearly improved lesion. In the improving lesion, with clinically less scaling, less induration, and histologically thinner epidermis, IL-6 mRNA-expressing keratinocytes were detectable in a greater proportion of the total epidermal components than in the untreated, fully developed lesion. These results showed that IL-6 mRNA was strongly expressed in lesions with moderate epidermal hyperproliferation, indicating that this cytokine may play a role in the transitional phase during the course of improvement as well as in the lesion's formation.