IL-1 Family Antagonists in Mouse and Human Skin Inflammation.

Interleukin (IL)-1 family cytokines initiate inflammatory responses, and shape innate and adaptive immunity. They play important roles in host defense, but excessive immune activation can also lead to the development of chronic inflammatory diseases. Dysregulated IL-1 family signaling is observed in a variety of skin disorders. In particular, IL-1 family cytokines have been linked to the pathogenesis of psoriasis and atopic dermatitis. The biological activity of pro-inflammatory IL-1 family agonists is controlled by the natural receptor antagonists IL-1Ra and IL-36Ra, as well as by the regulatory cytokines IL-37 and IL-38. These four anti-inflammatory IL-1 family members are constitutively and highly expressed at steady state in the epidermis, where keratinocytes are a major producing cell type. In this review, we provide an overview of the current knowledge concerning their regulatory roles in skin biology and inflammation and their therapeutic potential in human inflammatory skin diseases. We further highlight some common misunderstandings and less well-known observations, which persist in the field despite recent extensive interest for these cytokines.

Broadly reactive human CD4+ T cells against Enterobacteriaceae are found in the naïve repertoire and are clonally expanded in the memory repertoire.

Enterobacteriaceae are a large family of Gram-negative bacteria that includes both commensals and opportunistic pathogens. The latter can cause severe nosocomial infections, with outbreaks of multi-antibiotics resistant strains, thus being a major public health threat. In this study, we report that Enterobacteriaceae-reactive memory Th cells were highly enriched in a CCR6+ CXCR3+ Th1*/17 cell subset and produced IFN-γ, IL-17A, and IL-22. This T cell subset was severely reduced in septic patients with K. pneumoniae bloodstream infection who also selectively lacked circulating K. pneumonie-reactive T cells. By combining heterologous antigenic stimulation, single cell cloning and TCR Vß sequencing, we demonstrate that a large fraction of memory Th cell clones was broadly cross-reactive to several Enterobacteriaceae species. These cross-reactive Th cell clones were expanded in vivo and a large fraction of them recognized the conserved outer membrane protein A antigen. Interestingly, Enterobacteriaceae broadly cross-reactive T cells were also prominent among in vitro primed naïve T cells. Collectively, these data point to the existence of immunodominant T cell epitopes shared among different Enterobacteriaceae species and targeted by cross-reactive T cells that are readily found in the pre-immune repertoire and are clonally expanded in the memory repertoire.

IL-36 signaling in keratinocytes controls early IL-23 production in psoriasis-like dermatitis.

IL-36R signaling plays an important role in the pathogenesis of psoriasis. We ought to assess the specific function of IL-36R in keratinocytes for the pathology of Aldara-induced psoriasis-like dermatitis. Il36r ΔK mice presenting deletion of IL-36R in keratinocytes were similarly resistant to Aldara-induced ear inflammation as Il36r -/- mice, but acanthosis was only prevented in Il36r -/- mice. FACS analysis revealed that IL-36R signaling in keratinocytes is mandatory for early neutrophil infiltration in Aldara-treated ears. RNASeq and qRT-PCR experiments demonstrated the crucial role of IL-36R signaling in keratinocytes for induction of IL-23, IL-17, and IL-22 at early time points. Taken together, our results demonstrate that IL-36R signaling in keratinocytes plays a major role in the induction of Aldara-induced psoriasis-like dermatitis by triggering early production of IL-23/IL-17/IL-22 cytokines and neutrophil infiltration.

Intracellular IL-1 Receptor Antagonist Isoform 1 Released from Keratinocytes upon Cell Death Acts as an Inhibitor for the Alarmin IL-1α.

The inflammatory effects of IL-1α/ß are controlled by IL-1R antagonist (IL-1Ra). One IL-1Ra isoform is secreted, whereas three other isoforms (intracellular IL-1Ra [icIL-1Ra] 1, 2, and 3) are supposed to remain intracellular because of the absence of a signal peptide. In contrast to the well-characterized function of the secreted isoform, the biological role of the intracellular isoforms remains largely unclear. icIL-1Ra1 represents the major isoform in keratinocytes. We created icIL-1Ra1-/- mice and investigated the role of icIL-1Ra1 in Aldara (5% imiquimod)-induced psoriasis-like skin inflammation. Naive icIL-1Ra1-/- mice bred habitually and exhibited a normal phenotype. icIL-1Ra1 deficiency aggravated Aldara-induced skin inflammation, as demonstrated by increased ear thickness and increased mRNA levels of key proinflammatory cytokines. No intracellular effect of icIL-1Ra1 could be detected in isolated keratinocytes using RNA-sequencing analysis; however, Aldara treatment led to caspase 1/11-, caspase 8-, and RIPK3-independent keratinocyte cell death accompanied by the release of both icIL-1Ra1 and IL-1α. Furthermore, blocking IL-1α attenuated the clinical severity of Aldara-induced ear thickening in icIL-1Ra1-/- mice. Our data suggest that upon keratinocyte damage icIL-1Ra1 acts extracellularly as an antagonist of the alarmin IL-1α to immediately counteract its inflammatory effects.

Combination of IL-2, rapamycin, DNA methyltransferase and histone deacetylase inhibitors for the expansion of human regulatory T cells.

FOXP3+ regulatory T cell (Treg) based cellular therapies represent promising therapeutic options in autoimmunity, allergy, transplantation and prevention of Graft Versus Host (GVH) Disease. Among human FOXP3-expressing CD4+T cells, only the CD45RA+ naïve Treg (nTreg) subset is suitable for in vitro expansion. However, FoxP3 expression decays in cells using currently described culture protocols. Rapamycin alone was not able to prevent FOXP3 loss in nTregs cells, as only a half of them maintained FOXP3 expression after 14 days of culture. In contrast we report a novel combined drug regimen that can drastically stabilize FOXP3 expression in cultured Tregs. IL-2, rapamycin, histone deacetylase and DNA methyltransferase inhibitors act in synergy to allow expansion of human regulatory T cells with sustained high expression of FOXP3 and CD15s with potent suppressive capacities in vitro and control of murine xeno-GVH reactions. Of note, an additional subsequent infusion of expanded nTreg cells did not improve survival of mice. Combination of IL-2, rapamycin, histone deacetylase and DNA methyltransferase inhibitors is optimal for the expansion in vitro of pure effective nTreg maintaining high levels of FOXP3 for therapeutic purposes.

Inhibition of the JAK/STAT Signaling Pathway in Regulatory T Cells Reveals a Very Dynamic Regulation of Foxp3 Expression.

The IL-2/JAK3/STAT-5 signaling pathway is involved on the initiation and maintenance of the transcription factor Foxp3 in regulatory T cells (Treg) and has been associated with demethylation of the intronic Conserved Non Coding Sequence-2 (CNS2). However, the role of the JAK/STAT pathway in controlling Foxp3 in the short term has been poorly investigated. Using two different JAK/STAT pharmacological inhibitors, we observed a detectable loss of Foxp3 after 10 min. of treatment that affected 70% of the cells after one hour. Using cycloheximide, a general inhibitor of mRNA translation, we determined that Foxp3, but not CD25, has a high turnover in IL-2 stimulated Treg. This reduction was correlated with a rapid reduction of Foxp3 mRNA. This loss of Foxp3 was associated with a loss in STAT-5 binding to the CNS2, which however remains demethylated. Consequently, Foxp3 expression returns to normal level upon restoration of basal JAK/STAT signaling in vivo. Reduced expression of several genes defining Treg identity was also observed upon treatment. Thus, our results demonstrate that Foxp3 has a rapid turn over in Treg partly controlled at the transcriptional level by the JAK/STAT pathway.

Role of cytokines in thymus- versus peripherally derived-regulatory T cell differentiation and function.

CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) are essential players in the control of immune responses. Recently, accordingly to their origin, two main subsets of Tregs have been described: thymus-derived Tregs (tTregs) and peripherally derived Tregs (pTregs). Numerous signaling pathways including the IL-2/STAT5 or the TGF-ß/Smad3 pathways play a crucial role in segregating the two lineages. Here, we review some of the information existing on the distinct requirements of IL-2, TGF-ß, and TNF-α three major cytokines involved in tTreg and pTreg generation, homeostasis and function. Today it is clear that signaling via the IL-2Rß chain (CD122) common to IL-2 and IL-15 is required for proper differentiation of tTregs and for tTreg and pTreg survival in the periphery. This notion has led to the development of promising therapeutic strategies based on low-dose IL-2 administration to boost the patients' own Treg compartment and dampen autoimmunity and inflammation. Also, solid evidence points to TGF-ß as the master regulator of pTreg differentiation and homeostasis. However, therapeutic administration of TGF-ß is difficult to implement due to toxicity and safety issues. Knowledge on the role of TNF-α on the biology of Tregs is fragmentary and inconsistent between mice and humans. Moreover, emerging results from the clinical use of TNF-α inhibitors indicate that part of their anti-inflammatory effect may be dependent on their action on Tregs. Given the profusion of clinical trials testing cytokine administration or blocking to modulate inflammatory diseases, a better knowledge of the effects of cytokines on tTregs and pTregs biology is necessary to improve the efficiency of these immunotherapies.

Intrathymic injection of lentiviral vector curtails the immune response in the periphery of normal mice.

BACKGROUND: Gene transfer in the thymus, based on HIV-derived lentiviral vectors, is a promising avenue for modulation of T cell selection and autoimmunity. However, the impact of intrathymic (IT) injections on an antigen-specific immune response elicited in the periphery of normal mice has not been investigated yet. METHODS: Highly concentrated stocks of lentiviral vectors expressing the soluble form of hemaglutinin of the influenza virus (LvHA) were injected in the thymus of normal BALB/c mice. The CD4 and CD8-mediated immune responses to HA after peripheral immunization were measured by various parameters. RESULTS: We first show that a lentiviral vector expressing the luciferase was detected for at least 2 months after IT-injections. We then show that the LvHA vector could elicit a functional CD4- and CD8-T cell-mediated immune responses in the peripheral lymphoid organs of BALB/c mice. IT-injection of the LvHA vector significantly curbed this response: lower numbers of transferred HA-specific CD4(+) T cells were found in LvHA-injected compared to control animals. Furthermore, lower frequencies of HA-specific CD8(+) T cells, interferon γ-producing cells and cytotoxic cells were detected from 3 weeks to 3 months in LvHA-injected mice compared to controls. However, these reduced CD8-mediated responses were not increased after depletion of CD25(+) cells in vitro or in vivo. CONCLUSIONS: The results obtained in the present study show that injection of the LvHA lentiviral vector significantly curtailed the immune response to the same antigen in the periphery. Increased selection of HA-specific regulatory T cells and negative selection of HA-specific CD8(+) T cell precursors may explain the results. Our work establish the feasibility of IT-injections of lentiviral vectors to manipulate T cell tolerance in the thymus of normal mice, for basic and pre-clinical research.

Continuous activation of the CD122/STAT-5 signaling pathway during selection of antigen-specific regulatory T cells in the murine thymus.

Signaling events affecting thymic selection of un-manipulated polyclonal natural CD25(+)foxp3(+) regulatory T cells (nTreg) have not been established ex vivo. Here, we report a higher frequency of phosphorylated STAT-5 (pSTAT-5) in nTreg cells in the adult murine thymus and to a lesser extent in the periphery, compared to other CD4(+)CD8(-) subsets. In the neonatal thymus, the numbers of pSTAT-5(+) cells in CD25(+)foxp3(-) and nTreg cells increased in parallel, suggesting that pSTAT-5(+)CD25(+)foxp3(-) cells might represent the precursors of foxp3(+) regulatory T cells. This "specific" pSTAT-5 expression detected in nTreg cells ex vivo was likely due to a very recent signal given by IL-2/IL-15 cytokines in vivo since (i) it disappeared rapidly if cells were left unstimulated in vitro and (ii) was also observed if total thymocytes were stimulated in vitro with saturating amounts of IL-2 and/or IL-15 but not IL-7. Interestingly, STAT-5 activation upon IL-2 stimulation correlated better with foxp3 and CD122 than with CD25 expression. Finally, we show that expression of an endogenous superantigen strongly affected the early Treg cell repertoire but not the proportion of pSTAT-5(+) cells within this repertoire. Our results reveal that continuous activation of the CD122/STAT-5 signaling pathway characterize regulatory lineage differentiation in the murine thymus.

Pathogenic T cells have a paradoxical protective effect in murine autoimmune diabetes by boosting Tregs.

CD4+CD25+Foxp3+ Tregs play a major role in prevention of autoimmune diseases. The suppressive effect of Tregs on effector T cells (Teffs), the cells that can mediate autoimmunity, has been extensively studied. However, the in vivo impact of Teff activation on Tregs during autoimmunity has not been explored. In this study, we have shown that CD4+ Teff activation strongly boosts the expansion and suppressive activity of Tregs. This helper function of CD4+ T cells, which we believe to be novel, was observed in the pancreas and draining lymph nodes in mouse recipients of islet-specific Teffs and Tregs. Its physiological impact was assessed in autoimmune diabetes. When islet-specific Teffs were transferred alone, they induced diabetes. Paradoxically, when the same Teffs were cotransferred with islet-specific Tregs, they induced disease protection by boosting Treg expansion and suppressive function. RNA microarray analyses suggested that TNF family members were involved in the Teff-mediated Treg boost. In vivo experiments showed that this Treg boost was partially dependent on TNF but not on IL-2. This feedback regulatory loop between Teffs and Tregs may be critical to preventing or limiting the development of autoimmune diseases.