Autoimmune diseases develop when autoantigens activate previously quiescent self-reactive lymphocytes. Gene–gene interaction between certain HLA class I risk alleles and variants of the endoplasmic reticulum aminopeptidase ERAP1 controls the risk for common immune-mediated diseases, including psoriasis, ankylosing spondylitis, and Behçet disease. The functional mechanisms underlying this statistical association are unknown. In psoriasis, HLA-C*06:02 mediates an autoimmune response against melanocytes by autoantigen presentation. Using various genetically modified cell lines together with an autoreactive psoriatic TCR in a TCR activation assay, we demonstrate in this study that in psoriasis, ERAP1 generates the causative melanocyte autoantigen through trimming N-terminal elongated peptide precursors to the appropriate length for presentation by HLA-C*06:02. An ERAP1 risk haplotype for psoriasis produced the autoantigen much more efficiently and increased HLA-C expression and stimulation of the psoriatic TCR by melanocytes significantly more than a protective haplotype. Compared with the overall HLA class I molecules, cell surface expression of HLA-C decreased significantly more upon ERAP1 knockout. The combined upregulation of ERAP1 and HLA-C on melanocytes in psoriasis lesions emphasizes the pathogenic relevance of their interaction in patients. We conclude that in psoriasis pathogenesis, the increased generation of an ERAP1-dependent autoantigen by an ERAP1 risk haplotype enhances the likelihood that autoantigen presentation by HLA-C*06:02 will exceed the threshold for activation of potentially autoreactive T cells, thereby triggering CD8+ T cell–mediated autoimmune disease. These data identify ERAP1 function as a central checkpoint and promising therapeutic target in psoriasis and possibly other HLA class I–associated diseases with a similar genetic predisposition.

Three hundred and eight nanometer excimer light therapy has recently been reported to be effective against patchy alopecia areata (AA) in several clinical studies. However, these studies only included a few patients with severe forms of AA, and all of them exhibited poor outcomes. We further investigated the use of excimer light as a therapeutic option for cases of alopecia universalis (AU) that are resistant to other treatments. Eleven treatmentresistant AU patients were treated with a 308-nm excimer light at 2-week intervals for more than 16 sessions. Four patients achieved good responses and two patients exhibited poor responses. Three patients had Japanese skin type 1 and all of them achieved good responses. The radiation dose was increased until the patients exhibited marked erythema. The patients with Japanese skin type 3 who achieved good responses exhibited strong pigmentation at the irradiated sites. In conclusion, 308-nm excimer light therapy has significant effects on some AU patients who are resistant to other treatments and may be an alternative therapeutic option for AU. During the treatment of AU, high doses of radiation should be administrated until a strong inflammatory skin reaction is seen.

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Data availability statementThe data that support the findings of this study are available from the corresponding author upon reasonable request.A.A. and J.C.P. contributed equally and are joint last authors.

BackgroundSarcoidosis is a chronic and systemic inflammatory disease, in which patients present with noncaseating epithelioid granulomas. Cutaneous lesions of sarcoidosis develop in 9% to 35% of all sarcoidosis patients and comprise various clinical subtypes. It usually affects multiple organs and has a variable clinical course; this is called systemic sarcoidosis (SS). However, occasionally, it only affects the skin and is then called cutaneous sarcoidosis (CS). Recent observations suggest that serum levels of soluble CD163 correlate with immune cell activity in sarcoidosis patients; however, the contribution of M1 and M2 macrophages toward disease progression remains unclear.MethodsWe evaluated macrophage phenotypes histopathologically using skin biopsy samples obtained from patients with CS (n = 8) and SS (n = 31) and performed immunostaining with CD68, iNOS (M1 macrophages), PD‐L1, and CD163 (M2 macrophages).ResultsThe density of CD163‐positive cells in the SS group was significantly higher than that in the CS group. There was no significant correlation between the CD163 (+) cell density and serum angiotensin‐converting enzyme level, serum calcium, or tuberculin reaction.ConclusionsImmunostaining for CD163 may be a novel and useful marker to predict systemic involvement in patients with cutaneous lesions of epithelioid granulomas.