Clusterin Neutralizes the Inflammatory and Cytotoxic Properties of Extracellular Histones in Sepsis.

Rationale: Extracellular histones, released into the surrounding environment during extensive cell death, promote inflammation and cell death, and these deleterious roles have been well documented in sepsis. Clusterin (CLU) is a ubiquitous extracellular protein that chaperones misfolded proteins and promotes their removal. Objectives: We investigated whether CLU could protect against the deleterious properties of histones. Methods: We assessed CLU and histone expression in patients with sepsis and evaluated the protective role of CLU against histones in in vitro assays and in vivo models of experimental sepsis. Measurements and Main Results: We show that CLU binds to circulating histones and reduces their inflammatory, thrombotic, and cytotoxic properties. We observed that plasma CLU levels decreased in patients with sepsis and that the decrease was greater and more durable in nonsurvivors than in survivors. Accordingly, CLU deficiency was associated with increased mortality in mouse models of sepsis and endotoxemia. Finally, CLU supplementation improved mouse survival in a sepsis model. Conclusions: This study identifies CLU as a central endogenous histone-neutralizing molecule and suggests that, in pathologies with extensive cell death, CLU supplementation may improve disease tolerance and host survival.

IL-26 inhibits hepatitis C virus replication in hepatocytes.

BACKGROUND & AIMS: Interleukin-26 (IL-26) is a proinflammatory cytokine that has properties atypical for a cytokine, such as direct antibacterial activity and DNA-binding capacity. We previously observed an accumulation of IL-26 in fibrotic and inflammatory lesions in the livers of patients with chronic HCV infection and showed that infiltrating CD3+ lymphocytes were the principal source of IL-26. Surprisingly, IL-26 was also detected in the cytoplasm of hepatocytes from HCV-infected patients, even though these cells do not produce IL-26, even when infected with HCV. Based on this observation and possible interactions between IL-26 and nucleic acids, we investigated the possibility that IL-26 controlled HCV infection independently of the immune system. METHODS: We evaluated the ability of IL-26 to interfere with HCV replication in hepatocytes and investigated the mechanisms by which IL-26 exerts its antiviral activity. RESULTS: We showed that IL-26 penetrated HCV-infected hepatocytes, where it interacted directly with HCV double-stranded RNA replication intermediates, thereby inhibiting viral replication. IL-26 interfered with viral RNA-dependent RNA polymerase activity, preventing the de novo synthesis of viral genomic single-stranded RNA. CONCLUSIONS: These findings reveal a new role for IL-26 in direct protection against HCV infection, independently of the immune system, and increase our understanding of the antiviral defense mechanisms controlling HCV infection. Future studies should evaluate the possible use of IL-26 for treating other chronic disorders caused by RNA viruses, for which few treatments are currently available, or emerging RNA viruses. LAY SUMMARY: This study sheds new light on the body's arsenal for controlling hepatitis C virus (HCV) infection and identifies interleukin-26 (IL-26) as an antiviral molecule capable of blocking HCV replication. IL-26, which has unique biochemical and structural characteristics, penetrates infected hepatocytes and interacts directly with viral RNA, thereby blocking viral replication. IL-26 is, therefore, a new player in antiviral defenses, operating independently of the immune system. It is of considerable potential interest for treating HCV infection and other chronic disorders caused by RNA viruses for which few treatments are currently available, and for combating emerging RNA viruses.

Acetoacetate protects macrophages from lactic acidosis-induced mitochondrial dysfunction by metabolic reprograming.

Lactic acidosis, the extracellular accumulation of lactate and protons, is a consequence of increased glycolysis triggered by insufficient oxygen supply to tissues. Macrophages are able to differentiate from monocytes under such acidotic conditions, and remain active in order to resolve the underlying injury. Here we show that, in lactic acidosis, human monocytes differentiating into macrophages are characterized by depolarized mitochondria, transient reduction of mitochondrial mass due to mitophagy, and a significant decrease in nutrient absorption. These metabolic changes, resembling pseudostarvation, result from the low extracellular pH rather than from the lactosis component, and render these cells dependent on autophagy for survival. Meanwhile, acetoacetate, a natural metabolite produced by the liver, is utilized by monocytes/macrophages as an alternative fuel to mitigate lactic acidosis-induced pseudostarvation, as evidenced by retained mitochondrial integrity and function, retained nutrient uptake, and survival without the need of autophagy. Our results thus show that acetoacetate may increase tissue tolerance to sustained lactic acidosis.

Age-Related Expression of IFN-λ1 Versus IFN-I and Beta-Defensins in the Nasopharynx of SARS-CoV-2-Infected Individuals.

SARS-CoV-2 coronavirus infection induces heterogeneous symptoms, ranging from asymptomatic to lethal forms. Severe forms usually occur in the elderly and/or individuals with comorbidities. Children generally remain asymptomatic to primary infection, suggesting that they may have an effective local innate immune response. IFN-I and -III have non-redundant protective roles against SARS-CoV-2, although sometimes damaging the host. The expression and role of anti-viral peptides during SARS-CoV-2 infection have thus far been little studied. We aimed to identify the innate immune molecules present at the SARS-CoV-2 entry point. We analyzed the mRNA levels of type I (IFN-α and -ß) and type III (IFN-λ1-3) interferons and selected antiviral peptides (i.e., ß-defensins 1-3, α-defensins [HNP1-3, HD5] pentraxin-3, surfactant protein D, the cathelicidin LL-37 and interleukin-26) in nasopharyngeal swabs from 226 individuals of various ages, either infected with SARS-CoV-2 (symptomatic or asymptomatic) or negative for the virus. We observed that infection induced selective upregulation of IFN-λ1 expression in pediatric subjects (≤15 years), whereas IFN-α, IFN-ß, IFN-λ2/λ3, and ß-defensin 1-3 expression was unaffected. Conversely, infection triggered upregulation of IFN-α, IFN-ß, IFN-λ2/λ3, and ß-defensin 1-3 mRNA expression in adults (15-65 years) and the elderly (≥ 65 years), but without modulation of IFN-λ1. The expression of these innate molecules was not associated with gender or symptoms. Expression of the interferon-stimulated genes IFITM1 and IFITM3 was upregulated in SARS-CoV-2-positive subjects and reached similar levels in the three age groups. Finally, age-related differences in nasopharyngeal innate immunity were also observed in SARS-CoV-2-negative subjects. This study shows that the expression patterns of IFN-I/-III and certain anti-viral molecules in the nasopharyngeal mucosa of SARS-CoV-2-infected subjects differ with age and suggests that susceptibility to SARS-CoV-2 may be related to intrinsic differences in the nature of mucosal anti-viral innate immunity.

Insights into the ligand binding specificity of SREC-II (scavenger receptor expressed by endothelial cells).

SREC-II (scavenger receptor expressed by endothelial cells II) is a membrane protein encoded by the SCARF2 gene, with high homology to class F scavenger receptor SR-F1, but no known scavenging function. We produced the extracellular domain of SREC-II in a recombinant form and investigated its capacity to interact with common scavenger receptor ligands, including acetylated low-density lipoprotein (AcLDL) and maleylated or acetylated BSA (MalBSA or AcBSA). Whereas no binding was observed for AcLDL, SREC-II ectodomain interacted strongly with MalBSA and bound with high affinity to AcBSA, a property shared with the SR-F1 ectodomain. SREC-II ectodomain also interacted with two SR-F1-specific ligands, complement C1q and calreticulin, with affinities in the 100 nm range. We proceeded to generate a stable CHO cell line overexpressing full-length SREC-II; binding of MalBSA to these cells was significantly increased compared with nontransfected CHO cells. In contrast, no increase in binding could be detected for C1q and calreticulin. We show for the first time that SREC-II has the capacity to interact with the common scavenger receptor ligand MalBSA. In addition, our data highlight similarities and differences in the ligand binding properties of SREC-II in soluble form and at the cell surface, and show that endogenous protein ligands of the ectodomain of SREC-II, such as C1q and calreticulin, are shared with the corresponding domain of SR-F1.

Murlentamab, a Low Fucosylated Anti-Müllerian Hormone Type II Receptor (AMHRII) Antibody, Exhibits Anti-Tumor Activity through Tumor-Associated Macrophage Reprogrammation and T Cell Activation.

AMHRII, the anti-Müllerian hormone receptor, is selectively expressed in normal sexual organs but is also re-expressed in gynecologic cancers. Hence, we developed murlentamab, a humanized glyco-engineered anti-AMHRII monoclonal antibody currently in clinical trial. Low-fucosylated antibodies are known to increase the antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) potency of effector cells, but some preliminary results suggest a more global murlentamab-dependent activation of the immune system. In this context, we demonstrate here that the murlentamab opsonization of AMHRII-expressing ovarian tumor cells, in the presence of unstimulated- or tumor-associated macrophage (TAM)-like macrophages, significantly promotes macrophage-mediated ADCC and shifts the whole microenvironment towards a pro-inflammatory and anti-tumoral status, thus triggering anti-tumor activity. We also report that murlentamab orients both unstimulated- and TAM-like macrophages to an M1-like phenotype characterized by a strong expression of co-stimulation markers, pro-inflammatory cytokines and chemokines, favoring T cell recruitment and activation. Moreover, we show that murlentamab treatment shifts CD4+ Th1/Th2 balance towards a Th1 response and activates CD8+ T cells. Altogether, these results suggest that murlentamab, through naïve macrophage orientation and TAM reprogrammation, stimulates the anti-tumor adaptive immune response. Those mechanisms might contribute to the sustained clinical benefit observed in advanced cancer patients treated with murlentamab. Finally, the enhanced murlentamab activity in combination with pembrolizumab opens new therapeutic perspectives.

Transcriptomic features of tumour-infiltrating CD4lowCD8high double positive αß T cells in melanoma.

Peripheral CD4+CD8+ double positive (DP) T cells are a phenotypically and functionally heterogeneous population depending on their origin and pathologic context. We previously identified among tumour infiltrating lymphocytes in melanoma, a tumour-reactive MHC class-I restricted CD4lowCD8high DP αß T-cell subpopulation with CD4-like function. In this study, we used an in-depth comparative transriptomic analysis of intra-melanoma DP T cells and CD4 and CD8 single positive (SP) T cells, to better comprehend the origin of this DP phenotype, and define the transcriptomic signature of activated DP T cells. We observed that intra-melanoma DP T cells were transcriptome-wise closer to their CD8 SP T-cell counterparts in terms of number of genes differentially expressed (97 in common with CD8 SP T cells and 15 with CD4 SP T cells) but presented hallmarks of a transition to a CD4-like functional profile (CD40LG) with a decreased cytotoxic signature (KLRC1) in favour of an increased cytokine-receptor interaction signature (IL4, IL24, IL17A…). This unleashed CD4-like program could be the results of the observed unbalanced expression of the THPOK/Runx3 transcription factors in DP T cells. Overall, this study allow us to speculate that intra-melanoma DP T cells arise from CD8 SP T cells being reprogrammed to a helper function.

Lactic Acidosis Together with GM-CSF and M-CSF Induces Human Macrophages toward an Inflammatory Protumor Phenotype.

In established tumors, tumor-associated macrophages (TAM) orchestrate nonresolving cancer-related inflammation and produce mediators favoring tumor growth, metastasis, and angiogenesis. However, the factors conferring inflammatory and protumor properties on human macrophages remain largely unknown. Most solid tumors have high lactate content. We therefore analyzed the impact of lactate on human monocyte differentiation. We report that prolonged lactic acidosis induces the differentiation of monocytes into macrophages with a phenotype including protumor and inflammatory characteristics. These cells produce tumor growth factors, inflammatory cytokines, and chemokines as well as low amounts of IL10. These effects of lactate require its metabolism and are associated with hypoxia-inducible factor-1α stabilization. The expression of some lactate-induced genes is dependent on autocrine M-CSF consumption. Finally, TAMs with protumor and inflammatory characteristics (VEGFhigh CXCL8+ IL1ß+) are found in solid ovarian tumors. These results show that tumor-derived lactate links the protumor features of TAMs with their inflammatory properties. Treatments that reduce tumor glycolysis or tumor-associated acidosis may help combat cancer.

IL-26 Confers Proinflammatory Properties to Extracellular DNA.

In physiological conditions, self-DNA released by dying cells is not detected by intracellular DNA sensors. In chronic inflammatory disorders, unabated inflammation has been associated with a break in innate immune tolerance to self-DNA. However, extracellular DNA has to complex with DNA-binding molecules to gain access to intracellular DNA sensors. IL-26 is a member of the IL-10 cytokine family, overexpressed in numerous chronic inflammatory diseases, in which biological activity remains unclear. We demonstrate in this study that IL-26 binds to genomic DNA, mitochondrial DNA, and neutrophil extracellular traps, and shuttles them in the cytosol of human myeloid cells. As a consequence, IL-26 allows extracellular DNA to trigger proinflammatory cytokine secretion by monocytes, in a STING- and inflammasome-dependent manner. Supporting these biological properties, IL-10-based modeling predicts two DNA-binding domains, two amphipathic helices, and an in-plane membrane anchor in IL-26, which are structural features of cationic amphipathic cell-penetrating peptides. In line with these properties, patients with active autoantibody-associated vasculitis, a chronic relapsing autoimmune inflammatory disease associated with extensive cell death, exhibit high levels of both circulating IL-26 and IL-26-DNA complexes. Moreover, in patients with crescentic glomerulonephritis, IL-26 is expressed by renal arterial smooth muscle cells and deposits in necrotizing lesions. Accordingly, human primary smooth cells secrete IL-26 in response to proinflammatory cytokines. In conclusion, IL-26 is a unique cationic protein more similar to a soluble pattern recognition receptor than to conventional cytokines. IL-26 expressed in inflammatory lesions confers proinflammatory properties to DNA released by dying cells, setting up a positive amplification loop between extensive cell death and unabated inflammation.

IL-9 promotes the survival and function of human melanoma-infiltrating CD4(+) CD8(+) double-positive T cells.

We previously demonstrated an accumulation of tumor-reactive CD4(+) CD8(+) double positive (DP) T cells within melanoma-infiltrating lymphocytes, supporting their role in the regulation of anti-tumor immune responses. Similarly to their CD8(+) counterparts, intra-tumor DP T cells are MHC class-I restricted but differed by a limited lytic activity against autologous melanoma cells. Based on these observations and to further characterize DP T cells, both populations were compared at the transcriptional level. Our results revealed the overexpression of the IL-9 receptor (IL-9R) by DP T cells and prompted us to investigate the impact of IL-9 on their biology. We show that IL-9 favors DP T-cell survival by protecting them from apoptosis and by promoting their proliferation. In addition, IL-9 enhances their ability to produce cytokines and increased their levels of granzyme B/perforin as well as degranulation capacity, leading to a strengthened cytotoxic activity against melanoma cells. Taken together, the IL-9R(high) DP T-cell population could be a new preferential target for IL-9, which could take part in their retention within the melanoma infiltrate while also favoring their anti-tumor activity. More generally, our results extend the pleiotropic effects of IL-9 to IL-9R-expressing intra-tumor T cells, which could further potentiate anti-tumor immune responses.

FVB/N Mice Spontaneously Heal Ulcerative Lesions Induced by Mycobacterium ulcerans and Switch M. ulcerans into a Low Mycolactone Producer.

Buruli ulcer, a debilitating disease, is caused by Mycobacterium ulcerans. The incidence of this neglected tropical disease is steadily increasing. As a rule, without treatment, skin ulcers occur and a lengthy healing process may be observed associated with severe functional disabilities. Mouse models are already available to study establishment of lesions or evaluation of therapy but a lack of a suitable animal model, mimicking all clinical stages, in particular the healing process, remains an obstacle to understand the pathophysiology of M. ulcerans infection. M. ulcerans was s.c. inoculated in three consanguine mouse strains, that is, BALB/c and C57BL/6, classically used to study mycobacterial infection, and FVB/N. Strikingly, FVB/N mice, although as sensitive as all other mouse strains with respect to M. ulcerans infection, presented a spontaneous healing after the ulcerative phase despite stable bacterial load, and mycolactone toxin was not detected in the healed tissues. The spontaneous healing process was accompanied by an activation of the innate immune system. The adaptive response initiated by FVB/N mice was not involved in the healing process and did not confer protection against M. ulcerans. Our work highlights the importance of innate immune responses to control M. ulcerans infection. This in vivo model of M. ulcerans infection now paves the way for new avenues of research toward the elucidation of critical stages of this disease, such as the characterization of the regulation of mycolactone production, a better understanding of the pathophysiology of M. ulcerans infection, and the development of new therapeutic strategies.

CD40L confers helper functions to human intra-melanoma class-I-restricted CD4+CD8+ double positive T cells.

Although CD4+CD8+ double positive (DP) T cells represent a small fraction of peripheral T lymphocytes in healthy human donors, their frequency is often increased under pathological conditions (in blood and targeted tissues). In solid cancers such as melanoma, we previously demonstrated an enrichment of tumor reactive CD4lowCD8highαß DP T cells among tumor-infiltrating lymphocytes of unknown function. Similarly to their single positive (SP) CD8+ counterparts, intra-melanoma DP T cells recognized melanoma cell lines in an HLA-class-I restricted context. However, they presented a poor cytotoxic activity but a strong production of diverse Th1 and Th2 cytokines. The aim of this study was to clearly define the role of intra-melanoma CD4lowCD8highαß DP T cells in the antitumor immune response. Based on a comparative transcriptome analysis between intra-melanoma SP CD4+, SP CD8+ and DP autologous melanoma-infiltrating T-cell compartments, we evidenced an overexpression of the CD40L co-stimulatory molecule on activated DP T cells. We showed that, like SP CD4+ T cells, and through CD40L involvement, DP T cells are able to induce both proliferation and differentiation of B lymphocytes and maturation of functional DCs able to efficiently prime cytotoxic melanoma-specific CD8 T-cell responses. Taken together, these results highlight the helper potential of atypical DP T cells and their role in potentiating antitumor response.

IL-26 is overexpressed in chronically HCV-infected patients and enhances TRAIL-mediated cytotoxicity and interferon production by human NK cells.

OBJECTIVE: Interleukin-26 (IL-26) is a member of the IL-10 cytokine family, first discovered based on its peculiar expression by virus-transformed T cells. IL-26 is overexpressed in chronic inflammation (rheumatoid arthritis and Crohn's disease) and induces proinflammatory cytokines by myeloid cells and some epithelial cells. We thus investigated the expression and potential role of IL-26 in chronic HCV infection, a pathology associated with chronic inflammation. DESIGN: IL-26 was quantified in a cohort of chronically HCV-infected patients, naive of treatment and its expression in the liver biopsies investigated by immunohistochemistry. We also analysed the ability of IL-26 to modulate the activity of natural killer (NK) cells, which control HCV infection. RESULTS: The serum levels of IL-26 are enhanced in chronically HCV-infected patients, mainly in those with severe liver inflammation. Immunohistochemistry reveals an intense IL-26 staining in liver lesions, mainly in infiltrating CD3+ cells. We also show that NK cells from healthy subjects and from HCV-infected patients are sensitive to IL-26. IL-26 upregulates membrane tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) expression on CD16- CD56(bright) NK cells, enabling them to kill HCV-infected hepatoma cells, with the same efficacy as interferon (IFN)-α-treated NK cells. IL-26 also induces the expression of the antiviral cytokines IFN-ß and IFN-γ, and of the proinflammatory cytokines IL-1ß and TNF-α by NK cells. CONCLUSIONS: This study highlights IL-26 as a new player in the inflammatory and antiviral immune responses associated with chronic HCV infection.

IL-34- and M-CSF-induced macrophages switch memory T cells into Th17 cells via membrane IL-1α.

Macrophages orchestrate the immune response via the polarization of CD4(+) T helper (Th) cells. Different subsets of macrophages with distinct phenotypes, and sometimes opposite functions, have been described. M-CSF and IL-34 induce the differentiation of monocytes into IL-10(high) IL-12(low) immunoregulatory macrophages, which are similar to tumor-associated macrophages (TAMs) in ovarian cancer. In this study, we evaluated the capacity of human macrophages induced in the presence of M-CSF (M-CSF macrophages) or IL-34 (IL-34 macrophages) and ovarian cancer TAMs to modulate the phenotype of human CD4(+) T cells. Taken together, our results show that M-CSF-, IL-34 macrophages, and TAMs switch non-Th17 committed memory CD4(+) T cells into conventional CCR4(+) CCR6(+) CD161(+) Th17 cells, expressing or not IFN-gamma. Contrary, the pro-inflammatory GM-CSF macrophages promote Th1 cells. The polarization of memory T cells into Th17 cells is mediated via membrane IL-1α (mIL-1α), which is constitutively expressed by M-CSF-, IL-34 macrophages, and TAMs. This study elucidates a new mechanism that allows macrophages to maintain locally restrained and smoldering inflammation, which is required in angiogenesis and metastasis.

IL-34 and macrophage colony-stimulating factor are overexpressed in hepatitis C virus fibrosis and induce profibrotic macrophages that promote collagen synthesis by hepatic stellate cells.

UNLABELLED: Chronic hepatitis C virus (HCV) infection is characterized by progressive hepatic fibrosis, a process dependent on monocyte recruitment and accumulation into the liver. The mediators expressed in chronically injured liver that control the differentiation of human monocytes into profibrotic macrophages (Mφ) remain poorly defined. We report that chronically HCV-infected patients with high fibrosis stages have higher serum levels of macrophage colony-stimulating factor (M-CSF) and interleukin (IL)-34 than HCV-infected patients with lower fibrosis stages and healthy subjects. Immunohistochemistry reveals an intense expression of IL-34 and M-CSF by hepatocytes around liver lesions. In addition, HCV infection and inflammatory cytokines enhance the in vitro production of IL-34 and M-CSF by hepatocytes. We next analyzed the acquisition of profibrotic properties by Mφ generated with M-CSF (M-CSF-Mφ) or IL-34 (IL-34-Mφ). M-CSF and IL-34 up-regulate the expression, by differentiating monocytes, of chemokine (C-C motif) ligand (CCL)2, CCL4, C-C chemokine receptor (CCR)1, and CCR5, which are involved in monocyte recruitment/Mφ accumulation in liver lesions. M-CSF-Mφ and IL-34-Mφ also express the hepatic stellate cell (HSC) activators, platelet-derived growth factor, transforming growth factor beta, and galectin-3. IL-34-Mφ and M-CSF-Mφ induce type I collagen synthesis by HSCs, the main collagen-producing cells in liver fibrosis. IL-13, whose expression correlates with the fibrosis stage in HCV-infected patients, decreases the expression of the collagenase, matrix metalloproteinase 1, by IL-34-Mφ and M-CSF-Mφ, thereby enhancing collagen synthesis. By inhibiting the production of interferon-gamma (IFN-γ) by activated natural killer cells, IL-34-Mφ and M-CSF-Mφ prevent the IFN-γ-induced killing of HSCs. CONCLUSION: These results identify M-CSF and IL-34 as potent profibrotic factors in HCV liver fibrosis.

Mycobacterial toxin induces analgesia in buruli ulcer by targeting the angiotensin pathways.

Mycobacterium ulcerans, the etiological agent of Buruli ulcer, causes extensive skin lesions, which despite their severity are not accompanied by pain. It was previously thought that this remarkable analgesia is ensured by direct nerve cell destruction. We demonstrate here that M. ulcerans-induced hypoesthesia is instead achieved through a specific neurological pathway triggered by the secreted mycobacterial polyketide mycolactone. We decipher this pathway at the molecular level, showing that mycolactone elicits signaling through type 2 angiotensin II receptors (AT2Rs), leading to potassium-dependent hyperpolarization of neurons. We further validate the physiological relevance of this mechanism with in vivo studies of pain sensitivity in mice infected with M. ulcerans, following the disruption of the identified pathway. Our findings shed new light on molecular mechanisms evolved by natural systems for the induction of very effective analgesia, opening up the prospect of new families of analgesics derived from such systems.

CD4CD8αα lymphocytes, a novel human regulatory T cell subset induced by colonic bacteria and deficient in patients with inflammatory bowel disease.

How the microbiota affects health and disease is a crucial question. In mice, gut Clostridium bacteria are potent inducers of colonic interleukin (IL)-10-producing Foxp3 regulatory T cells (Treg), which play key roles in the prevention of colitis and in systemic immunity. In humans, although gut microbiota dysbiosis is associated with immune disorders, the underlying mechanism remains unknown. In contrast with mice, the contribution of Foxp3 Treg in colitis prevention has been questioned, suggesting that other compensatory regulatory cells or mechanisms may exist. Here we addressed the regulatory role of the CD4CD8 T cells whose presence had been reported in the intestinal mucosa and blood. Using colonic lamina propria lymphocytes (LPL) and peripheral blood lymphocytes (PBL) from healthy individuals, and those with colon cancer and irritable bowel disease (IBD), we demonstrated that CD4CD8αα (DP8α) T lymphocytes expressed most of the regulatory markers and functions of Foxp3 Treg and secreted IL-10. Strikingly, DP8α LPL and PBL exhibited a highly skewed repertoire toward the recognition of Faecalibacterium prausnitzii, a major Clostridium species of the human gut microbiota, which is decreased in patients with IBD. Furthermore, the frequencies of DP8α PBL and colonic LPL were lower in patients with IBD than in healthy donors and in the healthy mucosa of patients with colon cancer, respectively. Moreover, PBL and LPL from most patients with active IBD failed to respond to F. prausnitzii in contrast to PBL and LPL from patients in remission and/or healthy donors. These data (i) uncover a Clostridium-specific IL-10-secreting Treg subset present in the human colonic LP and blood, (ii) identify F. prausnitzii as a major inducer of these Treg, (iii) argue that these cells contribute to the control or prevention of colitis, opening new diagnostic and therapeutic strategies for IBD, and (iv) provide new tools to address the systemic impact of both these Treg and the intestinal microbiota on the human immune homeostasis.

IL-34 induces the differentiation of human monocytes into immunosuppressive macrophages. antagonistic effects of GM-CSF and IFNγ.

IL-34 is a recently identified cytokine that signals via the M-CSF receptor and promotes monocyte survival. Depending on the environment, monocytes can differentiate into macrophages (Mφ) or dendritic cells (DC). A wide spectrum of Mφ and DC subsets, with distinct phenotypes and functions, has been described. To date, the phenotype of monocytes exposed to IL-34 remains unexplored. We report here that IL-34 induces the differentiation of monocytes into CD14(high) CD163(high) CD1a(-) Mφ (IL-34-Mφ). Upon LPS stimulation, IL-34-Mφ exhibit an IL-10(high) IL-12(low) M2 profile and express low levels of the costimulatory molecules CD80 and CD86. IL-34-Mφ exhibit poor T cell costimulatory properties, and have potent immunosuppressive properties (decrease of TCR-stimulated T cell proliferation). For all the parameters analyzed, IL-34-Mφ are phenotypically and functionally similar to M-CSF-Mφ. IL-34 appears as efficient as M-CSF in inducing the generation of immunosuppressive Mφ. Moreover, the generation of IL-34-Mφ is mediated through the M-CSF receptor, is independent of endogenous M-CSF consumption and is potentiated by IL-6. In an attempt to identify strategies to prevent a deleterious M2 cell accumulation in some pathological situations, we observed that IFNγ and GM-CSF prevent the generation of immunosuppressive Mφ induced by IL-34. IFNγ also switches established IL-34-Mφ into immunostimulatory Mφ. In conclusion, we demonstrate that IL-34 drives the differentiation of monocytes into immunosuppressive M2, in a manner similar to M-CSF, and that IFNγ and GM-CSF prevent this effect.

IL-26 is overexpressed in rheumatoid arthritis and induces proinflammatory cytokine production and Th17 cell generation.

Interleukin-26 (IL-26), a member of the IL-10 cytokine family, induces the production of proinflammatory cytokines by epithelial cells. IL-26 has been also reported overexpressed in Crohn's disease, suggesting that it may be involved in the physiopathology of chronic inflammatory disorders. Here, we have analyzed the expression and role of IL-26 in rheumatoid arthritis (RA), a chronic inflammatory disorder characterized by joint synovial inflammation. We report that the concentrations of IL-26 are higher in the serums of RA patients than of healthy subjects and dramatically elevated in RA synovial fluids compared to RA serums. Immunohistochemistry reveals that synoviolin(+) fibroblast-like synoviocytes and CD68(+) macrophage-like synoviocytes are the main IL-26-producing cells in RA joints. Fibroblast-like synoviocytes from RA patients constitutively produce IL-26 and this production is upregulated by IL-1-beta and IL-17A. We have therefore investigated the role of IL-26 in the inflammatory process. Results show that IL-26 induces the production of the proinflammatory cytokines IL-1-beta, IL-6, and tumor necrosis factor (TNF)-alpha by human monocytes and also upregulates the expression of numerous chemokines (mainly CCL20). Interestingly, IL-26-stimulated monocytes selectively promote the generation of RORgamma t(+) Th17 cells, through IL-1-beta secretion by monocytes. More precisely, IL-26-stimulated monocytes switch non-Th17 committed (IL-23R(-) or CCR6(-) CD161(-)) CD4(+) memory T cells into Th17 cells. Finally, synovial fluids from RA patients also induce Th17 cell generation and this effect is reduced after IL-26 depletion. These findings show that IL-26 is constitutively produced by RA synoviocytes, induces proinflammatory cytokine secretion by myeloid cells, and favors Th17 cell generation. IL-26 thereby appears as a novel proinflammatory cytokine, located upstream of the proinflammatory cascade, that may constitute a promising target to treat RA and chronic inflammatory disorders.

Irinotecan induces steroid and xenobiotic receptor (SXR) signaling to detoxification pathway in colon cancer cells.

BACKGROUND: Resistance to chemotherapy remains one of the principle obstacles to the treatment of colon cancer. In order to identify the molecular mechanism of this resistance, we investigated the role of the steroid and xenobiotic receptor (SXR) in the induction of drug resistance. Indeed, this nuclear receptor plays an important role in response to xenobiotics through the upregulation of detoxification genes. Following drug treatments, SXR is activated and interacts with the retinoid X receptor (RXR) to induce expression of some genes involved in drug metabolism such as phase I enzyme (like CYP), phase II enzymes (like UGT) and transporters (e.g. MDR1). RESULTS: In this study, we have shown that endogenous SXR is activated in response to SN-38, the active metabolite of the anticancer drug irinotecan, in human colon cancer cell lines. We have found that endogenous SXR translocates into the nucleus and associates with RXR upon SN-38 treatment. Using ChIP, we have demonstrated that endogenous SXR, following its activation, binds to the native promoter of the CYP3A4 gene to induce its expression. RNA interference experiments confirmed SXR involvement in CYP3A4 overexpression and permitted us to identify CYP3A5 and MRP2 transporter as SXR target genes. As a consequence, cells overexpressing SXR were found to be less sensitive to irinotecan treatment. CONCLUSIONS: Altogether, these results suggest that the SXR pathway is involved in colon cancer irinotecan resistance in colon cancer cell line via the upregulation of select detoxification genes.