During diet-induced dysbiosis the gut vascular barrier is disrupted. Gut vascular barrier disruption is responsible for the translocation of bacteria or bacterial products systemically. Inhibiting gut vascular barrier disruption prevents the development of non-alcoholic steatohepatitis. Obeticholic acid can control gut vascular barrier disruption both in a preventive and therapeutic way.

Cross-presentation is a crucial mechanism in tumoral and microbial immunity because it allows internalized cell associated or exogenous antigens (Ags) to be delivered into the major histocompatibility complex I pathway. This pathway is important for the development of CD8 ؉ T-cell responses and for the induction of tolerance. In mice, cross-presentation is considered to be a unique property of CD8␣ ؉ conventional dendritic cells (DCs). Here we show that splenic plasmacytoid IntroductionCross-presentation is a mechanism that involves the uptake and processing of exogenous antigens (Ags) within the major histocompatibility complex (MHC) class I pathway. 1 This process differs from the classical MHC class I processing pathway in which MHC class I molecules present Ags that are synthesized within the cells. Cross-presentation occurs subsequent to transport of Ag from the endosome to cytosol and digestion by the proteasome and may concern different forms of exogenous Ags, such as soluble, 2 particulate, 3 or cell-associated Ags. 4 However, alternative mechanisms have been described, and the cellular and molecular pathways that lead to the presentation of endocytosed proteins on MHC class I molecules are not yet fully defined. 5 Cross-presentation is a crucial mechanism allowing induction of naive CD8 ϩ T-cell responses against exogenous Ag and has been implicated in the elicitation of protective cytotoxic T lymphocyte (CTL) responses against tumors as well as in the generation of immune responses against clinically relevant pathogens that do not infect tissues of hemopoietic origin. 6,7 In addition to cross-priming of naive CD8 ϩ T cells, cross-presentation appears to be central to the maintenance of peripheral tolerance to self-Ag, called "cross-tolerance." 8,9 With very few exceptions, 10,11 cross-presentation is restricted to dendritic cells (DCs) 2,12 and macrophages 13,14 but is not normally seen in other nucleated cells. DCs are considered the only Ag-presenting cell (APC) able to prime naive T cells and are thus involved in the induction of both adaptive immunity and tolerance. The outcome of T-cell responses depends on DC maturation state, as immature or semimature DCs have been described to induce tolerance. 15 Immature DCs are present in the periphery where they sample Ags. They are characterized by high expression of receptors involved in endocytosis and phagocytosis. 16 Maturation of DCs can be induced by pathogens or by inflammatory signals. Pathogens are recognized through pathogen-associated molecular patterns, which interact with pattern recognition receptors, including Toll-like receptors (TLRs), constitutively expressed by DCs. 17,18 Maturation involves the migration of DCs to lymphoid organs, the activation of proteolytic activity for Ag processing, and the up-regulation of MHC and costimulatory molecules. After maturation, DCs prime naive T cells, leading to their differentiation into effector T cells. 19 Several populations of DCs have been described, and it is unclear whether all these DC types...

Cross-presentation allows exogenous antigen presentation in association with major histocompatibility complex class I molecules, a process crucial for the priming of CD8+ T-cell responses against viruses and tumors. By contrast to conventional dendritic cells (cDC), which cross-present antigens in the steady state, plasmacytoid dendritic cells (pDC) acquire this ability only after stimulation by Toll-like receptor (TLR) ligands. The intracellular pathways accounting for this functional difference are still unknown. Here we show that the induction of cross-presentation by pDCs is regulated by mitochondria through a reactive oxygen species (ROS)-dependent mechanism, involving pH alkalization and antigen protection. The reduction of mitochondrial ROS production dramatically decreases the cross-presentation capacity of pDCs, leading to a strong reduction of their capacity to trigger CD8+ T-cell responses. Our results demonstrate the importance of mitochondrial metabolism in pDC biology, particularly for the induction of adaptive immune responses.

West Nile virus (WNV) is an emerging neurotropic flavivirus. We investigated the dynamics of immune cell recruitment in peripheral tissues and in the CNS during WNV encephalitis in an immunocompetent mouse model. In the periphery, immune cell expansion can successfully limit viremia and lymphoid tissue infection. However, viral clearance in the periphery is too late to prevent viral invasion of the CNS. In the CNS, innate immune cells, including microglia/macrophages, NK cells, and plasmacytoid dendritic cells, greatly expand as the virus invades the brain, whereas B and T cells are recruited after viral invasion, and fail to control the spread of the virus. Thus, the onset of WNV encephalitis was correlated both with CNS viral infection and with a large local increase of innate immune cells. Interestingly, we identify a new immune cell type: CD19+B220− BST-2+, which we name G8-ICs. These cells appear during peripheral infection and enter the CNS. G8-ICs express high levels of MHC class II, stain for viral Ag, and are localized in the paracortical zone of lymph nodes, strongly suggesting they are previously unidentified APCs that appear in response to viral infection.

b ␤2 (CD18) integrins with ␣-chains CD11a, -b, -c, and -d are important adhesion molecules necessary for leukocyte migration and cellular interactions. CD18 deficiency leads to recurrent bacterial infections and poor wound healing due to reduced migration of leukocytes to inflammatory sites. CD8 T cells also upregulate CD11a, CD11b, and CD11c upon activation. However, the role these molecules play for CD8 T cells in vivo is not known. To determine the function of individual ␤2 integrins, we examined CD8 T cell responses to Listeria monocytogenes infection in CD11a-, CD11b-, and CD11c-deficient mice. The absence of CD11b or CD11c had no effect on the generation of antigen-specific CD8 T cells. In contrast, the magnitude of the primary CD8 T cell response in CD11a-deficient mice was significantly reduced. Moreover, the response in CD11a ؊/؊ mice exhibited reduced differentiation of short-lived effector cells (KLRG1 hi CD127 lo ), although cytokine and granzyme B production levels were unaffected. Notably, CD11a deficiency resulted in greatly enhanced generation of CD62L؉ central memory cells. Surprisingly, CD8 T cells lacking CD11a mounted a robust secondary response to infection. Taken together, these findings demonstrated that CD11a expression contributes to expansion and differentiation of primary CD8 T cells but may be dispensable for secondary responses to infection.

The physiologic role played by plasmacytoid dendritic cells (pDCs) in the induction of innate responses and inflammation in response to pathogen signaling is not well understood. Here, we describe a new mouse model lacking pDCs and establish that pDCs are essential for the in vivo induction of NK-cell activity in response to Toll-like receptor 9 (TLR9) triggering. Furthermore, we provide the first evidence that pDCs are critical for the systemic production of a wide variety of chemokines in response to TLR9 activation. Consequently, we observed a profound alteration in monocyte, macrophage, neutrophil, and NK-cell recruitment at the site of inflammation in the absence of pDCs in response to CpG-Dotap and stimulation by microbial pathogens, such as Leishmania major, Escherichia coli, and Mycobacterium bovis. This study, which is based on the development of a constitutively pDC-deficient mouse model, highlights the pivotal role played by pDCs in the induction of innate immune responses and inflammation after TLR9 triggering. (Blood. 2012;120(1): 90-99) IntroductionPlasmacytoid DCs (pDCs) are characterized by their ability to contribute to antiviral innate immunity by producing type I IFNs on stimulation. 1 These cells display a CD11c low B220 ϩ Ly6C ϩ CD45RA ϩ phenotype and also express markers, such as CD317 (BST-2) 2 and SiglecH. 3 Their Toll-like receptor (TLR) expression pattern is limited to TLR7 and TLR9, which recognize viral single-stranded RNA and unmethylated DNA, respectively. The constitutive expression of IFN regulatory factor 7 enables pDCs to rapidly produce high levels of type I IFNs after TLR stimulation. After activation via TLR7 or TLR9 signaling, pDCs produce cytokines, such as IL-12, IL-6, and TNF-␣, and chemokines, including CCL3, CCL4, CCL5, CXCL9, and CXCL10, in addition to type I IFNs. 4 NK cells exhibit potent cytotoxic activity against infected or tumor cells and are efficient producers of several cytokines and chemokines. 5 NK-cell activation is controlled by the recognition of ligands expressed on the surface of target cells. However, NK cells require additional signals for activation, including type I IFNs and IL-12. 6 Because of their ability to produce these cytokines, pDCs may play an important role in stimulating and inducing NK-cell responses. Indeed, pDCs can promote murine cytomegalovirus clearance by NK cells through TLR9 interaction. 7 Furthermore, NK cells express the chemokine receptors CCR5 and CXCR3, which interact with the chemokines produced by activated pDCs, 8 suggesting that pDCs may also influence their recruitment. In addition to NK cells, immature conventional DCs (cDCs), monocytes, macrophages, polymorphonuclear basophiles (PMBs) and eosinophils (PMEs) also respond to type I IFNs 9 and to CCL3, CCL4, and CCL5, 8 suggesting that pDCs participate in the activation and recruitment of inflammatory cells.To directly assess the physiologic role of pDCs in innate immunity, it is crucial to analyze these responses in vivo in the absence of pDCs. pDCs could be immunodeple...

BackgroundNatural killer (NK) cells require a functional lytic granule machinery to mediate effective antitumor responses. Evading the lytic cargo deployed at the immune synapse (IS) could be a critical step for cancer progression through yet unidentified mechanisms.MethodsNK cell antibody-dependent cellular cytotoxicity (ADCC) is a major determinant of the clinical efficacy of some therapeutic antibodies including the anti-HER2 Trastuzumab. Thus, we screened sera of Trastuzumab-resistant HER2 +patients with breast cancer for molecules that could inhibit NK cell ADCC. We validated our findings in vitro using cytotoxicity assays and confocal imaging of the lytic granule machinery and in vivo using syngeneic and xenograft murine models.ResultsWe found that sera from Trastuzumab-refractory patients could inhibit healthy NK cell ADCC in vitro. These sera contained high levels of the inflammatory protein chitinase 3-like 1 (CHI3L1) compared with sera from responders and healthy controls. We demonstrate that recombinant CHI3L1 inhibits both ADCC and innate NK cell cytotoxicity. Mechanistically, CHI3L1 prevents the correct polarization of the microtubule-organizing center along with the lytic granules to the IS by hindering the receptor of advanced glycation end-products and its downstream JNK signaling. In vivo, CHI3L1 administration drastically impairs the control of NK cell-sensitive tumors, while CHI3L1 blockade synergizes with ADCC to cure mice with HER2 +xenografts.ConclusionOur work highlights a new paradigm of tumor immune escape mediated by CHI3L1 which acts on the cytotoxic machinery and prevents granule polarization. Targeting CHI3L1 could mitigate immune escape and potentiate antibody and cell-based immunotherapies.

Dendritic cell (DC) maturation state is a key parameter for the issue of DC-T cell cognate interaction, which determines the outcome of T cell activation. Indeed, immature DCs induce tolerance while fully mature DCs generate immunity. Here we show that, in the absence of any deliberate activation signal, DCs freshly isolated from mouse spleen spontaneously produce IL-12 and tumor necrosis factor-alpha and up-regulate co-stimulation molecules, even when directly re-injected into their natural environment. Furthermore, after their isolation, these cells acquire the capacity to induce specific T(h)1 responses in vivo. These results demonstrate that the sole isolation of spleen DCs leads to the full maturation of these cells, which therefore cannot be considered as immature DCs. Moreover, we also show that the kinetics of DC activation do not influence the polarization of T(h) response in vivo challenging the idea that exhausted DCs induce preferentially T(h)2 response. Altogether, these observations should be taken into account in all experiments based on the transfer of ex vivo purified DCs.