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      Melanocyte antigen triggers autoimmunity in human psoriasis

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          Abstract

          Arakawa et al. discovered that the autoimmune response in psoriasis is directed against melanocytes. They show that the main psoriasis risk allele HLA-C*06:02 mediates melanocyte-specific autoimmunity and identify ADAMTSL5 as a melanocyte autoantigen, which stimulates IL-17 and IFN-γ production in CD8 + T cells.

          Abstract

          Psoriasis vulgaris is a common T cell–mediated inflammatory skin disease with a suspected autoimmune pathogenesis. The human leukocyte antigen (HLA) class I allele, HLA-C*06:02, is the main psoriasis risk gene. Epidermal CD8 + T cells are essential for psoriasis development. Functional implications of HLA-C*06:02 and mechanisms of lesional T cell activation in psoriasis, however, remained elusive. Here we identify melanocytes as skin-specific target cells of an HLA-C*06:02–restricted psoriatic T cell response. We found that a Vα3S1/Vβ13S1 T cell receptor (TCR), which we had reconstituted from an epidermal CD8 + T cell clone of an HLA-C*06:02–positive psoriasis patient specifically recognizes HLA-C*06:02–positive melanocytes. Through peptide library screening, we identified ADAMTS-like protein 5 (ADAMTSL5) as an HLA-C*06:02–presented melanocytic autoantigen of the Vα3S1/Vβ13S1 TCR. Consistent with the Vα3S1/Vβ13S1-TCR reactivity, we observed numerous CD8 + T cells in psoriasis lesions attacking melanocytes, the only epidermal cells expressing ADAMTSL5. Furthermore, ADAMTSL5 stimulation induced the psoriasis signature cytokine, IL-17A, in CD8 + T cells from psoriasis patients only, supporting a role as psoriatic autoantigen. This unbiased analysis of a TCR obtained directly from tissue-infiltrating CD8 + T cells reveals that in psoriasis HLA-C*06:02 directs an autoimmune response against melanocytes through autoantigen presentation. We propose that HLA-C*06:02 may predispose to psoriasis via this newly identified autoimmune pathway.

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          Most cited references28

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          Pathogenesis and clinical features of psoriasis.

          Psoriasis, a papulosquamous skin disease, was originally thought of as a disorder primarily of epidermal keratinocytes, but is now recognised as one of the commonest immune-mediated disorders. Tumour necrosis factor alpha, dendritic cells, and T-cells all contribute substantially to its pathogenesis. In early-onset psoriasis (beginning before age 40 years), carriage of HLA-Cw6 and environmental triggers, such as beta-haemolytic streptococcal infections, are major determinants of disease expression. Moreover, at least nine chromosomal psoriasis susceptibility loci have been identified. Several clinical phenotypes of psoriasis are recognised, with chronic plaque (psoriasis vulgaris) accounting for 90% of cases. Comorbidities of psoriasis are attracting interest, and include impairment of quality of life and associated depressive illness, cardiovascular disease, and a seronegative arthritis known as psoriatic arthritis. A more complete understanding of underlying pathomechanisms is leading to new treatments, which will be discussed in the second part of this Series.
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            Pathogenesis and therapy of psoriasis.

            Psoriasis is one of the most common human skin diseases and is considered to have key genetic underpinnings. It is characterized by excessive growth and aberrant differentiation of keratinocytes, but is fully reversible with appropriate therapy. The trigger of the keratinocyte response is thought to be activation of the cellular immune system, with T cells, dendritic cells and various immune-related cytokines and chemokines implicated in pathogenesis. The newest therapies for psoriasis target its immune components and may predict potential treatments for other inflammatory human diseases.
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              Deconstructing the peptide-MHC specificity of T cell recognition.

              In order to survey a universe of major histocompatibility complex (MHC)-presented peptide antigens whose numbers greatly exceed the diversity of the T cell repertoire, T cell receptors (TCRs) are thought to be cross-reactive. However, the nature and extent of TCR cross-reactivity has not been conclusively measured experimentally. We developed a system to identify MHC-presented peptide ligands by combining TCR selection of highly diverse yeast-displayed peptide-MHC libraries with deep sequencing. Although we identified hundreds of peptides reactive with each of five different mouse and human TCRs, the selected peptides possessed TCR recognition motifs that bore a close resemblance to their known antigens. This structural conservation of the TCR interaction surface allowed us to exploit deep-sequencing information to computationally identify activating microbial and self-ligands for human autoimmune TCRs. The mechanistic basis of TCR cross-reactivity described here enables effective surveillance of diverse self and foreign antigens without necessitating degenerate recognition of nonhomologous peptides. Copyright © 2014 Elsevier Inc. All rights reserved.
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                Author and article information

                Journal
                J Exp Med
                J. Exp. Med
                jem
                jem
                The Journal of Experimental Medicine
                The Rockefeller University Press
                0022-1007
                1540-9538
                14 December 2015
                : 212
                : 13
                : 2203-2212
                Affiliations
                [1 ]Department of Dermatology, Ludwig-Maximilian-University, D-80337 Munich, Germany
                [2 ]Institute of Clinical Neuroimmunology, Ludwig-Maximilian-University, D-82152 Planegg-Martinsried, Germany
                [3 ]Gene Center Munich, Ludwig-Maximilian-University, D-81377 Munich, Germany
                [4 ]Laboratory of Immunogenetics and Molecular Diagnostics, Ludwig-Maximilian-University, D-81377 Munich, Germany
                [5 ]German Cancer Research Center, D-69120 Heidelberg, Germany
                Author notes
                Correspondence to Jörg C. Prinz: joerg.prinz@ 123456med.uni-muenchen.de
                [*]

                A. Arakawa, K. Siewert, and J. Stöhr contributed equally to this paper and are listed in alphabetic order.

                Article
                20151093
                10.1084/jem.20151093
                4689169
                26621454
                cb751e61-2f75-437d-8d50-2e05bf5b7adf
                © 2015 Arakawa et al.

                This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

                History
                : 02 July 2015
                : 04 November 2015
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