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.

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.

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.

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.

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.

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.