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Hidradenitis suppurativa (HS) (also designated acne inversa) is a chronic inflammatory disease characterized by painful purulent skin lesions and progressive destruction of skin architecture. Despite the high burden for the patients, pathogenetic pathways underlying HS alterations remain obscure. When we examined the HS cytokine pattern, IL-1β turned out to be a highly prominent cytokine, overexpressed even compared with psoriatic lesions. Analyses of IL-1β-induced transcriptome in various cell types showed overlapping profiles, with upregulations of molecules causing immune cell infiltration and extracellular matrix degradation, and of specific cytokines including IL-6, IL-32, and IL-36. Matching cellular IL-1 receptor levels, dermal fibroblasts showed both the strongest and broadest IL-1β response, which was not clearly shared or strengthened by other cytokines. The IL-1β signature was specifically present in HS lesions and could be reversed by application of IL-1 receptor antagonist. Search for blood parameters associated with IL-1β pathway activity in HS identified serum amyloid A, which was synergistically induced by IL-1β and IL-6 in hepatocytes. Consequently, strongly elevated blood serum amyloid A levels in HS correlated positively with the extent of inflammatory skin alterations. In summary, the IL-1β pathway represents a pathogenetic cascade, whose activity may be therapeutically targeted and monitored by blood SAA levels., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

Psoriasis is a common chronic inflammatory disease with characteristic skin alterations and functions as a model of immune-mediated disorders. Cytokines have a key role in psoriasis pathogenesis. Here, we demonstrated that out of 30 individually quantified cytokines, IL-19 showed the strongest differential expression between psoriatic lesions and healthy skin. Cutaneous IL-19 overproduction was reflected by elevated IL-19 blood levels that correlated with psoriasis severity. Accordingly, anti-psoriatic therapies substantially reduced both cutaneous and systemic IL-19 levels. IL-19 production was induced in keratinocytes by IL-17A and was further amplified by tumor necrosis factor-α and IL-22. Among skin cells, keratinocytes were found to be important targets of IL-19. IL-19 alone, however, regulated only a few keratinocyte functions. While increasing the production of S100A7/8/9 and, to a moderate extent, also IL-1β, IL-20, chemokine C-X-C motif ligand 8, and matrix metalloproteinase 1, IL-19 had no clear influence on the differentiation, proliferation, or migration of these cells. Importantly, IL-19 amplified many IL-17A effects on keratinocytes, including the induction of β-defensins, IL-19, IL-23p19, and T helper type 17-cell- and neutrophil-attracting chemokines. In summary, IL-19 as a component of the IL-23/IL-17 axis strengthens the IL-17A action and might be a biomarker for the activity of this axis in chronic inflammatory disorders.

Ultraviolet irradiation represents a well-established treatment modality for inflammatory skin diseases. The aim of this study was to investigate the mechanisms of ultraviolet B radiation-induced keratinocyte insensitivity towards interferon-gamma. Flow cytometric analyses indicated that ultraviolet B radiation temporarily inhibits the interferon-gamma-induced activation of primary keratinocyte and HaCaT cells as measured by reduced intercellular adhesion molecule-1 (CD54) and HLA-DR upregulation. Western blot experiments have suggested that this is mediated by the ultraviolet B radiation-induced inhibition of signal transduction and transcription factor-1 phosphorylation. Neither interleukin-10 neutralization nor interleukin-10 addition had any effect on the ultraviolet B radiation-induced inhibition of interferon-gamma induced intercellular adhesion molecule-1 expression. Furthermore, the supernatant from ultraviolet B-irradiated cells failed to inhibit the interferon-gamma-induced CD54 and HLA-DR upregulation in nonradiated HaCaT cells. Moreover, irradiated cells from whom the supernatant was withdrawn 4 h after irradiation still showed a diminished interferon-gamma-induced response after 24 h. Thus, not soluble but intracellular factors might be involved in the ultraviolet B radiation-induced inhibition of interferon-gamma-induced keratinocyte activation. Therefore, we analyzed the expression of members of suppressors of cytokine-signaling (SOCS) molecules using real-time polymerase chain reaction. We found a fast and strong upregulation of SOCS1 and SOCS3 but not of SOCS2 after ultraviolet B radiation. Similarly, ultraviolet B radiation induced the expression of these particular SOCS molecules in lesional psoriatic skin. As SOCS molecules are known inhibitors of signal transduction and transcription factor phosphorylation, which is essential for interferon-gamma-induced intercellular adhesion molecule-1 and HLA-DR upregulation, this may explain the interferon-gamma unresponsiveness after ultraviolet B radiation.