T lymphocytes derived from skin lesions of patients with psoriasis vulgaris express a novel cytokine pattern that is distinct from that of T helper type 1 and T helper type 2 cells

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Abstract
In various immunological disorders the pathomechanisms of tissue damage are causally associated with specific patterns of locally produced cytokines. To study the molecular and cellular mechanisms involved in the manifestation of psoriasis vulgaris we have assessed the cytokine mRNA profile expressed in lesional psoriatic skin and in T cell clones (TCC) that were established from skin lesions of patients with psoriasis. As demonstrated by use of the polymerase chain reaction (PCR), psoriasis lesions consistently exhibit transcription of a complex pattern of cytokines. It includes mediators selectively produced by T lymphocytes [interferon (IFN)-γ, tumor necrosis factor (TNF)-β, interleukin (IL)-2, IL-3 and IL-5] as well as cytokines secreted by various cell types [transforming growth factor (TGF)-α/-β, TNF-α, IL-6/-8 and granulocyte-macrophage-colony stimulating factor], while IL-4 is missing. With the exception of TGF-α, this cytokine profile was also observed in lesional psoriatic T cell clones yielding supernatants mitogenic for keratinocytes in vitro (MTCC), but not in T cell clones yielding supernatants that inhibited keratinocyte proliferation (STCC). The congruent cytokine expression of psoriatic skin lesions and MTCC emphasizes that inflammation in psoriasis is driven by a sofar unrecognized regulatory T cell subset that may serve to control epidermal regeneration and convey immunosurveillance over epithelial surfaces. It is characterized by the combined expression of IFN-γ, TGF-β, IL-2 and IL-5 in the absence of IL-4 and by its selective capacity to enhance keratinocyte proliferation. This newly defined combination of regulatory properties of a distinct T cell population cannot be reconciled with an immune response of the T helper cells (TH)0, TH1 or TH2 type.