The role of interleukin-12 in the pathogenesis of psoriasis

Objectives: To verify the role of IL-12 in the pathogenesis of psoriasis and determine its relation to IFNγ. Design and methods: Skin biopsies from lesional and non-lesional skin of 30 patients and 10 healthy controls were obtained for quantitative PCR examination of IL-12 (P40) and IFNγ mRNA as well as in situ PCR of IL-12 (P40) and IFNγ mRNA. Results: IL-12 and IFNγ levels were higher in lesional skin than in non-lesional and control skin. A significant correlation between IL-12 and IFNγ was found. By in situ PCR hybridization, IL-12 expression was only found in the dermis, while IFNγ was invariably expressed in the dermis and/or epidermis. Conclusion: We suggest that IL-12 independently and through IFNγ induction may have a crucial role in the development of the active psoriatic lesion itself, where it is probably produced locally in the dermis as a step in the evolution of the psoriatic lesion.