Summary Background Psoriasis vulgaris is an inflammatory skin disease mediated by Th1 and Th17 cytokines, yet the relative contribution of interferon (IFN)-γ, interleukin (IL)-17 and IL-22 on disease pathogenesis is still unknown. Objectives In this study, we sought to identify the cytokines produced by skin-resident T cells in normal skin, localize the receptors for these cytokines, and examine how these cytokines alter gene expression profiles of the cells bearing cognate receptors. Methods We used intracellular cytokine staining and flow cytometry to evaluate T cell cytokine production, and immunohistochemistry and double-label immunofluorescence to localize cytokine receptors in skin. Gene array analysis of cytokine-treated keratinocytes was performed using moderated paired t-test controlling for false discovery rate using the Benjamini–Hochberg procedure. Results We demonstrate that T-helper cells producing IL-17, IL-22 and/or IFN-γ, as well as the cells bearing cognate cytokine receptors, are present in normal human skin. Keratinocytes stimulated with IL-17 expressed chemokines that were different from those induced by IFN-γ, probably contributing to the influx of neutrophils, dendritic cells and memory T cells into the psoriatic lesion. In contrast, IL-22 downregulated genes associated with keratinocyte differentiation and caused epidermal alterations in an organotypic skin model. Conclusions Our results suggest that the Th17 cytokines IL-17 and IL-22 mediate distinct downstream pathways that contribute to the psoriatic phenotype: IL-17 is more proinflammatory, while IL-22 retards keratinocyte differentiation.

Biological agents have dramatically improved treatment options for patients with severe psoriasis. Etanercept (tumor necrosis factor [TNF] receptor–immunoglobulin fusion protein) is an effective treatment for many psoriasis patients, and blockade of TNF is considered to be its primary action. However, in this clinical trial, we show that etanercept has early inhibitory effects on a newly appreciated type of T cells: T helper type 17 (Th17) cells. Etanercept reduced the inflammatory dendritic cell products that drive Th17 cell proliferation (interleukin [IL] 23), as well as Th17 cell products and downstream effector molecules (IL-17, IL-22, CC chemokine ligand 20, and β-defensin 4). In contrast, Th1 cellular products and effector molecules (interferon γ, lymphotoxin α, and myxovirus resistance 1) were reduced late in disease resolution. This study suggests a role for Th17 in addition to Th1 cells in the pathogenesis of psoriasis. Th17 cells may be particularly important in driving epidermal activation in psoriatic plaques, whereas Th1 cells must also be eliminated for final disease resolution.

The classical Th1/Th2 paradigm previously defining atopic dermatitis (AD) and psoriasis has recently been challenged with the discovery of Th17 T cells that synthesize IL-17 and IL-22. Although it is becoming evident that many Th1 diseases including psoriasis have a strong IL-17 signal, the importance of Th17 T cells in AD is still unclear. We examined and compared skin biopsies from AD and psoriasis patients by gene microarray, RT-PCR, immunohistochemistry, and immunofluorescence. We found a reduced genomic expression of IL-23, IL-17, and IFN-γ in AD compared with psoriasis. To define the effects of IL-17 and IL-22 on keratinocytes, we performed gene array studies with cytokine-treated keratinocytes. We found lipocalin 2 and numerous other innate defense genes to be selectively induced in keratinocytes by IL-17. IFN-γ had no effect on antimicrobial gene-expression in keratinocytes. In AD skin lesions, protein and mRNA expression of lipocalin 2 and other innate defense genes (hBD2, elafin, LL37) were reduced compared with psoriasis. Although AD has been framed by the Th1/Th2 paradigm as a Th2 polar disease, we present evidence that the IL-23/Th17 axis is largely absent, perhaps accounting for recurrent skin infections in this disease.

No abstract

Psoriasis vulgaris, a skin disease that is considered to be the result of a type 1 autoimmune response, provides an opportunity for studying the changes that occur in a target-diseased tissue during innovative immunotherapies. To gain a more comprehensive picture of the response to an approved biological therapy, we studied alfacept, which is a CD2 binding fusion protein. amevive ͉ autoimmune disease ͉ CD2