Keratinocyte differentiation program leading to an organized epidermis plays a key role in maintaining the first line of defense of the skin. Epidermal integrity is regulated by a tight communication between keratinocytes and leucocytes, particularly under cytokine control. Imbalance of the cytokine network leads to inflammatory diseases such as psoriasis. Our attempt to model skin inflammation showed that the combination of IL-17A, IL-22, IL-1α, OSM and TNFα (Mix M5) synergistically increases chemokine and antimicrobial-peptide expression, recapitulating some features of psoriasis. Other characteristics of psoriasis are acanthosis and down-regulation of keratinocyte differentiation markers. Our aim was to characterize the specific roles of these cytokines on keratinocyte differentiation, and to compare with psoriatic lesion features. All cytokines decrease keratinocyte differentiation markers, but IL-22 and OSM were the most powerful, and the M5 strongly synergized the effects. In addition, IL-22 and OSM induced epidermal hyperplasia in vitro and M5 induced epidermal thickening and decreased differentiation marker expression in a mouse model, as observed in human psoriatic skin lesions. This study highlights the precise role of cytokines in the skin inflammatory response. IL-22 and OSM more specifically drive epidermal hyperplasia and differentiation loss while IL-1α, IL-17A and TNFα were more involved in the activation of innate immunity.

Keywords: IL-1R r Imiquimod r MyD88 r NLRP3 inflammasome r Skin inflammation Additional supporting information may be found in the online version of this article at the publisher's web-site Correspondence: Dr. Franck Morel e-mail: f.morel@univ-poitiers.fr IntroductionPsoriasis is a chronic inflammatory skin disease estimated to affect 2-3% of the general population [1]. Clinical presentation is usually associated with red, scaly, and raised plaques. These are the C 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu 2848 Hanitriniaina Rabeony et al. Eur. J. Immunol. 2015. 45: 2847-2857 consequences of a marked thickening of the epidermis due to an increased proliferation of keratinocytes (acanthosis), a retention of nuclei in the stratum corneum (parakeratosis) caused by alterations of keratinocyte differentiation leading to reduced or loss of the granular layer, and the presence of inflammatory cell infiltrates in the epidermis and dermis [2]. The inflammatory infiltrate is composed mainly of dendritic cells, macrophages and T cells in the dermis and neutrophils, with some T cells in the epidermis [3]. The combination of this infiltration and acanthosis contributes to the overall thickness of lesions. Therefore, the pathogenesis of psoriasis clearly results from a cross-talk between immune cells, keratinocytes, endothelial cells, and fibroblasts, with the release of growth factors, chemokines, and cytokines required for the induction and the maintenance of this disease [3,4]. An important role of the IL-23/IL-17/IL-22 axis in the induction of psoriasis has become evident, in which IL-23 secreted by some DC is responsible for the production of the Th17-related proinflammatory cytokines . IL-1 family members also play an important role in the regulation of the immune response and dysregulation of their expressions leads to tissue destruction and severe pathological effects, including skin diseases such as psoriasis [5,6]. Clearly, IL-1 is considered as a key player in the initiation and the maintenance of psoriasis by inducing Th17-cell maturation and downstream cytokine production [7,8]. IL-1α and IL-1β, the original members of IL-1 family, recognize IL-1 receptor type 1 (IL-1R1) which leads to the recruitment of the adaptor molecule MyD88 (adaptor protein shared by IL-1R and TLR signaling) and activate transcription factors NF-κB and AP1, whereas the binding of IL-1 receptor antagonist (IL-1Ra) to IL-1R1 totally blocks the biological activity of both proinflammatory molecules 9]. The mature secreted form of IL-1β requires engagement of the protein complexes termed inflammasomes. NLRP3 inflammasome includes the adaptor protein ASC (apoptosis-associated Speck-like protein containing a Caspase recruitment domain) necessary for the activation of the cysteine protease caspase-1, responsible for cleaving pro-IL-1β to mature IL-1β, whereas IL-1α is already biologically active and its processing requires the protease calpain [5]. In vitro studies showed that IL-1α or IL-1β induces the production of CCL...

Measles is a highly contagious childhood disease associated with an immunological paradox: although a strong virus-specific immune response results in virus clearance and the establishment of a life-long immunity, measles infection is followed by an acute and profound immunosuppression leading to an increased susceptibility to secondary infections and high infant mortality. In certain cases, measles is followed by fatal neurological complications. To elucidate measles immunopathology, we have analyzed the immune response to measles virus in mice transgenic for the measles virus receptor, human CD150. These animals are highly susceptible to intranasal infection with wild-type measles strains. Similarly to what has been observed in children with measles, infection of suckling transgenic mice leads to a robust activation of both T and B lymphocytes, generation of virus-specific cytotoxic T cells and antibody responses. Interestingly, Foxp3+CD25+CD4+ regulatory T cells are highly enriched following infection, both in the periphery and in the brain, where the virus intensively replicates. Although specific anti-viral responses develop in spite of increased frequency of regulatory T cells, the capability of T lymphocytes to respond to virus-unrelated antigens was strongly suppressed. Infected adult CD150 transgenic mice crossed in an interferon receptor type I-deficient background develop generalized immunosuppression with an increased frequency of CD4+CD25+Foxp3+ T cells and strong reduction of the hypersensitivity response. These results show that measles virus affects regulatory T-cell homeostasis and suggest that an interplay between virus-specific effector responses and regulatory T cells plays an important role in measles immunopathogenesis. A better understanding of the balance between measles-induced effector and regulatory T cells, both in the periphery and in the brain, may be of critical importance in the design of novel approaches for the prevention and treatment of measles pathology.

Human herpesvirus 6 (HHV-6) is widely spread in the human population and has been associated with several neuroinflammatory diseases, including multiple sclerosis. To develop a small-animal model of HHV-6 infection, we analyzed the susceptibility of several lines of transgenic mice expressing human CD46, identified as a receptor for HHV-6. We showed that HHV-6A (GS) infection results in the expression of viral transcripts in primary brain glial cultures from CD46-expressing mice, while HHV-6B (Z29) infection was inefficient. HHV-6A DNA persisted for up to 9 months in the brain of CD46-expressing mice but not in the nontransgenic littermates, whereas HHV-6B DNA levels decreased rapidly after infection in all mice. Persistence in the brain was observed with infectious but not heat-inactivated HHV-6A. Immunohistological studies revealed the presence of infiltrating lymphocytes in periventricular areas of the brain of HHV-6A-infected mice. Furthermore, HHV-6A stimulated the production of a panel of proinflammatory chemokines in primary brain glial cultures, including CCL2, CCL5, and CXCL10, and induced the expression of CCL5 in the brains of HHV-6A-infected mice. HHV-6A-induced production of chemokines in the primary glial cultures was dependent on the stimulation of toll-like receptor 9 (TLR9). Finally, HHV-6A induced signaling through human TLR9 as well, extending observations from the murine model to human infection. Altogether, this study presents a first murine model for HHV-6A-induced brain infection and suggests a role for TLR9 in the HHV-6A-initiated production of proinflammatory chemokines in the brain, opening novel perspectives for the study of virus-associated neuropathology. IMPORTANCEHHV-6 infection has been related to neuroinflammatory diseases; however, the lack of a suitable small-animal infection model has considerably hampered further studies of HHV-6-induced neuropathogenesis. In this study, we have characterized a new model for HHV-6 infection in mice expressing the human CD46 protein. Infection of CD46 transgenic mice with HHV-6A resulted in long-term persistence of viral DNA in the brains of infected animals and was followed by lymphocyte infiltration and upregulation of the CCL5 chemokine in the absence of clinical signs of disease. The secretion of a panel of chemokines was increased after infection in primary murine brain glial cultures, and the HHV-6-induced chemokine expression was inhibited when TLR9 signaling was blocked. These results describe the first murine model for HHV-6A-induced brain infection and suggest the importance of the TLR9 pathway in HHV-6A-initiated neuroinflammation.

Oncostatin M (OSM) has been reported to be overexpressed in psoriasis skin lesions and to exert proinflammatory effects in vitro on human keratinocytes. Here, we report the proinflammatory role of OSM in vivo in a mouse model of skin inflammation induced by intradermal injection of murine OSM-encoding adenovirus (AdOSM) and compare with that induced by IL-6 injection. Here, we show that OSM potently regulates the expression of genes involved in skin inflammation and epidermal differentiation in murine primary keratinocytes. In vivo, intradermal injection of AdOSM in mouse ears provoked robust skin inflammation with epidermal thickening and keratinocyte proliferation, while minimal effect was observed after AdIL-6 injection. OSM overexpression in the skin increased the expression of the S100A8/9 antimicrobial peptides, CXCL3, CCL2, CCL5, CCL20, and Th1/Th2 cytokines, in correlation with neutrophil and macrophage infiltration. In contrast, OSM downregulated the expression of epidermal differentiation genes, such as cytokeratin-10 or filaggrin. Collectively, these results support the proinflammatory role of OSM when it is overexpressed in the skin. However, OSM expression was not required in the murine model of psoriasis induced by topical application of imiquimod, as demonstrated by the inflammatory phenotype of OSM-deficient mice or wild-type mice treated with anti-OSM antibodies.Keywords: Imiquimod · Keratinocyte · Oncostatin M · Psoriasis · Skin inflammation Additional supporting information may be found in the online version of this article at the publisher's web-site Correspondence: Dr. Jean-François Jégou e-mail: jean-francois.jegou@univ-poitiers.fr IntroductionPsoriasis is the most common inflammatory skin disease affecting 2-3% of the adult population, mainly in developed countries, Eur. J. Immunol. 2016Immunol. . 46: 1737Immunol. -1751 in which patients develop skin lesions characterized by erythematous and scaly plaques [1]. The histological features of psoriatic skins are a thickening of the epidermis resulting from an altered keratinocyte differentiation associated with a hyperplasia at the basement membrane, a hyperkeratosis and a parakeratosis (loss of the granular layer and abnormal presence of cell nuclei in the cornified layer) [1,2]. At the inflammatory site, these alterations of the epidermis are the consequence of a crosstalk between infiltrating immune cells and tissue resident cells (e.g. dermal fibroblasts, epidermal keratinocytes, and resident immune cells) through the release of numerous cytokines. In this complex network of interactions, keratinocytes are now considered to play a key role as bona fide innate immune cells, capable of secreting cytokines, chemokines, and antimicrobial peptides in response to various stimuli [3]. Psoriasis has been reported to be a Th1-and Th17-driven pathology [4]. The IL-23/IL-17 axis plays a crucial role in the pathogenesis of the disease, as demonstrated by the detection of IL-23 producing DCs and the expression of IL-17 and IL-22 by T cells and type 3...

Recent studies suggest that psoriasis may be more severe in patients with nonalcoholic fatty liver disease, particularly in those with the inflammatory stage of steatohepatitis [nonalcoholic steatohepatitis (NASH)]. Herein, we investigated the impact of diet-induced steatohepatitis on the severity of imiquimod-induced psoriasiform dermatitis. Mice fed with a high-fat diet developed steatohepatitis reminiscent of human NASH with ballooning hepatocytes and significant liver fibrosis. Mice with steatohepatitis also displayed moderate cutaneous inflammation characterized by erythema, dermal infiltrates of CD45(+) leukocytes, and a local production of IL-17A. Moreover, steatohepatitis was associated with an epidermal activation of caspase-1 and cutaneous overexpression of IL-1β. Imiquimod-induced psoriasiform dermatitis was exacerbated in mice with steatohepatitis as compared to animals fed with a standard diet. Scale formation and acanthosis were aggravated, in correlation with increased IL-17A and IL-22 expression in inflamed skins. Finally, intradermal injection of IL-17A in standard diet-fed mice recapitulated the cutaneous pathology of mice with steatohepatitis. The results show that high-fat diet-induced steatohepatitis aggravates the inflammation in psoriasiform dermatitis, via the cutaneous production of IL-17A. In agreement with clinical data, this description of a novel extrahepatic manifestation of NASH should sensitize dermatologists to the screening and the management of fatty liver in psoriatic patients.

BackgroundAcute-serum Amyloid A (A-SAA), one of the major acute-phase proteins, is mainly produced in the liver but extra-hepatic synthesis involving the skin has been reported. Its expression is regulated by the transcription factors NF-κB, C/EBPβ, STAT3 activated by proinflammatory cytokines.ObjectivesWe investigated A-SAA synthesis by resting and cytokine-activated Normal Human Epidermal Keratinocytes (NHEK), and their inflammatory response to A-SAA stimulation. A-SAA expression was also studied in mouse skin and liver in a model mimicking psoriasis and in the skin and sera of psoriatic and atopic dermatitis (AD) patients.MethodsNHEK were stimulated by A-SAA or the cytokines IL-1α, IL-17A, IL-22, OSM, TNF-α alone or in combination, previously reported to reproduce features of psoriasis. Murine skins were treated by imiquimod cream. Human skins and sera were obtained from patients with psoriasis and AD. A-SAA mRNA was quantified by RT qPCR. A-SAA proteins were dosed by ELISA or immunonephelemetry assay.ResultsIL-1α, TNF-α and mainly IL-17A induced A-SAA expression by NHEK. A-SAA induced its own production and the synthesis of hBD2 and CCL20, both ligands for CCR6, a chemokine receptor involved in the trafficking of Th17 lymphocytes. A-SAA expression was increased in skins and livers from imiquimod-treated mice and in patient skins with psoriasis, but not significantly in those with AD. Correlations between A-SAA and psoriasis severity and duration were observed.ConclusionKeratinocytes could contribute to psoriasis pathogenesis via A-SAA production, maintaining a cutaneous inflammatory environment, activating innate immunity and Th17 lymphocyte recruitment.

Wound healing is a complex physiological process that repairs a skin lesion and produces fibrous tissue. In some cases, this process can lead to hypertrophic scars (HS) or keloid scars (KS), for which the pathophysiology remains poorly understood. Previous studies have reported the presence of oncostatin M (OSM) during the wound healing process; however, the role of OSM in pathological scarring remains to be precisely elucidated. This study aims to analyse the presence and involvement of OSM in the pathological scarring process. It was conducted with 18 patients, including 9 patients with hypertrophic scarring and 9 patients with keloid scarring. Histological tissue analysis of HS and KS showed minor differences in the organization of the extracellular matrix, the inflammatory infiltrate and the keratinocyte phenotype. Transcriptomic analysis showed increased expression levels of fibronectin, collagen I, TGFβ1, β-defensin-2 and S100A7 in both pathological samples. OSM expression levels were greater in HS than in KS and control skin. In vitro, OSM inhibited TGFβ1-induced secretion of components of the extracellular matrix by normal and pathological fibroblasts. Overall, we suggest that OSM is involved in pathological wound healing processes by inhibiting the evolution of HS towards KS by controlling the fibrotic effect of TGFβ1.