PPARγ regulates multiple aspects of skin physiology, including sebocyte differentiation, keratinocyte proliferation, epithelial stem cell survival, adipocyte biology, and inflammatory skin responses. However, the effects of its global deletion, namely of nonredundant key functions of PPARγ signaling in mammalian skin, are yet unknown because of embryonic lethality. Here, we describe the skin and hair phenotype of a whole-body PPARγ-null mouse (Pparg), obtained by preserving PPARγ expression in the placenta. Pparg mice exhibited total lipoatrophy and complete absence of sebaceous glands. Right after birth, hair follicle (HF) morphogenesis was transiently delayed, along with reduced expression of HF differentiation markers and of transcriptional regulators necessary for HF development. Later, adult Pparg mice developed scarring alopecia and severe perifollicular inflammation. Skin analyses in other models of lipodystrophy, AZIP and Adipoq-CrePparg mice, coupled with skin graft experiments, showed that the early defects observed in hair morphogenesis were caused by the absence of adipose tissue. In contrast, the late alteration of HF cycle and appearance of inflammation were observed only in Pparg mice and likely were due to the lack sebaceous glands. Our findings underscore the increasing appreciation for the importance of adipose tissue-mediated signals in HF development and function.

T cells are key players in autoimmune diseases by supporting the production of autoantibodies. However, their contribution to the effector phase of antibody-mediated autoimmune dermatoses, i.e., tissue injury and inflammation of the skin, has not been investigated. In this paper, we demonstrate that T cells amplify the development of autoantibody-induced tissue injury in a prototypical, organspecific autoimmune disease, namely epidermolysis bullosa acquisita ( T cells are essential regulators of host defense and exhibit direct cytotoxic as well as regulatory properties. The presence or absence of pro-inflammatory compared with regulatory T cell subsets affects the development and outcome of inflammatory reactions. Misbalance of T cell populations leads to autoimmune disorders, including systemic lupus erythematosus (SLE), different autoimmune bullous dermatoses (AIBDs) and rheumatoid arthritis (RA) [1][2][3] . In these diseases, the contribution of T cells to antibody production and maintenance of the autoimmune response has clearly been demonstrated 4,5 . In recent decades, the understanding of autoantibody-induced tissue injury has greatly improved. However, the role of T cells during the effector phase of autoimmune skin blistering diseases, i.e., tissue injury and inflammation in the targeted organs, is not completely understood. In this study, we investigated the role of T cells during this phase, using a mouse model of epidermolysis bullosa acquisita (EBA), a prototypical organ-specific autoimmune disease 6,7 . EBA is caused by autoantibodies directed against type VII collagen (COL7), an integral component of anchoring fibrils 8 . Animal models, employing antibody transfer into mice 9,10 , have added to a greater understanding of the mechanisms leading to blistering in EBA 9,11,12 . Based on the current understanding of EBA pathogenesis, the effector phase of EBA is predominantly driven by neutrophils -their depletion leading to a complete absence of experimental EBA 13. With regard to T cell involvement during this phase, in vivo and in vitro data have been contradictory. In vivo data indicated a T cell-independent process: Transfer of total IgG isolated from rabbits that had been immunized with COL7 into T cell-deficient mice induced subepidermal blistering 9 . However, in that study, no wild-type control for evaluation of the extent of blistering was included. In other

Background and Purpose: Pemphigus is caused by autoantibodies against desmoglein (Dsg) 1, Dsg3, and/or non-Dsg antigens. Pemphigus vulgaris (PV) is the most common manifestation of pemphigus, with painful erosions on mucous membranes. In most cases, blistering also occurs on the skin, leading to areas of extensive denudation. Despite improvements in pemphigus treatment, time to achieve remission is long, severe adverse events are frequent and 20% of patients do not respond adequately. Current clinical developments focus exclusively on modulating B cell function or autoantibody half-life. However, topical modulation of PV autoantibody-induced blistering is an attractive target because it could promptly relieve symptoms. Experimental Approach: To address this issue, we performed an unbiased screening in a complex biological system using 141 low MW inhibitors from a chemical library. Specifically, we evaluated PV IgG-induced Dsg3 internalization in HaCaT keratinocytes. Validation of the 20 identified compounds was performed using keratinocyte fragmentation assays, as well as a human skin organ culture (HSOC) model. key Results: Overall, this approach led to the identification of four molecules involved in PV IgG-induced skin pathology: MEK1, TrkA, PI3Kα, and VEGFR2. Conclusion and Implications: This unbiased screening revealed novel mechanisms by which PV autoantibodies induce blistering in keratinocytes and identified new treatment targets for this severe and potentially life-threatening skin disease.

(227 words)Epidermolysis bullosa acquisita (EBA) is a difficult-to-treat subepidermal autoimmune blistering skin disease (AIBD) with circulating and tissue-bound anti-type VII collagen

The full human skin organ culture (HSOC) model is a standardized test system for evaluating pharmacological substances on human skin in vitro. The acantholysis associated with pemphigus vulgaris (PV), a severe and potentially life‐threatening autoimmune skin blistering disease, can be induced in HSOC by injecting a bi‐specific anti‐desmoglein (dsg) 1 and 3 single‐chain antibody variable fragment (scFv). Compared to cell culture experiments (e.g., induction of dsg3‐internalization or keratinocyte dissociation using HaCaT cells or normal human epidermal keratinocytes) the HSOC model is more sophisticated and physiologically relevant. In this model, all three layers of the human skin are present, all cells are sustained in their physiological niche and orientation, and the cell‐cell‐contacts remain intact. Here we describe a protocol for HSOC, an ex vivo model of human skin, that has proved to be well‐established and informative in our laboratory. © 2019 by John Wiley & Sons, Inc.

Background While clustering of bullous pemphigoid (BP) with neuropsychiatric diseases is well‐established, the clinical and immunological profile of BP patients with this comorbidity remains to be decisively determined. Objectives To evaluate the burden of neurological and psychiatric comorbidities among patients with BP and to elucidate the clinical, immunological and immunopathological features of patients with BP and comorbid neuropsychiatric conditions. Methods We performed a retrospective study encompassing patients diagnosed with BP throughout the years 2009–2020 in a specialized tertiary referral centre. Multivariate logistic regression model was used to identify predictors of neuropsychiatric conditions among patients with BP. Results The study included 273 patients with BP, of whom 123 (45.1%) presented with comorbid neuropsychiatric disease. Compared to the remaining patients with BP (n = 150), those with pre‐existing neuropsychiatric diseases demonstrated older mean [standard deviation (SD)] age [81.7 (9.1) vs. 76.9 (10.1); P < 0.001], female preponderance (65.0% vs. 49.3%; P = 0.009), higher seropositivity rate of anti‐BP230 (67.7% vs. 36.5%; P = 0.006) and higher levels of anti‐BP180 NC16A IgG [651.3 (1279.6) vs. 370.4 (818.6) U/mL; P = 0.039]. In multivariate analysis, anti‐BP230 seropositivity was independently associated with coexistence of BP with neuropsychiatric conditions [adjusted odds ratio (OR), 3.43; 95% CI, 1.24–9.52; P = 0.018]. In a sensitivity analysis confined to patients with neurological diseases (n = 103), older age [82.1 (8.4) vs. 77.2 (10.3); P < 0.001] and increased anti‐BP230 seropositivity (68.0% vs. 39.7%; P = 0.018) were identified. Conclusions The coexistence of BP with neuropsychiatric diseases is independently associated with the generation of anti‐BP230 antibodies.

COVID-19 infection caused by the newly discovered coronavirus severe acute respiratory distress syndrome virus-19 (SARS-CoV-2) has become a pandemic issue across the globe. There are currently many investigations taking place to look for specific, safe and potent anti-viral agents. Upon transmission and entry into the human body, SARS-CoV-2 triggers multiple immune players to be involved in the fight against the viral infection. Amongst these immune cells are NK cells that possess robust antiviral activity, and which do not require prior sensitization. However, NK cell count and activity were found to be impaired in COVID-19 patients and hence, could become a potential therapeutic target for COVID-19. Several drugs, including glatiramer acetate (GA), vitamin D 3 , dimethyl fumarate (DMF), monomethyl fumarate (MMF), natalizumab, ocrelizumab, and IFN-β, among others have been previously described to increase the biological activities of NK cells especially their cytolytic potential as reported by upregulation of CD107a, and the release of perforin and granzymes. In this review, we propose that such drugs could potentially restore NK cell activity allowing individuals to be more protective against COVID-19 infection and its complications.

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