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...

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.