Epithelial HVEM maintains intraepithelial T cell survival and contributes to host protection

Intraepithelial T cells (IETs) are in close contact with intestinal epithelial cells and the underlying basement membrane, and they detect invasive pathogens. How intestinal epithelial cells and basement membrane influence IET survival and function, at steady state or after infection, is unclear. The herpes virus entry mediator (HVEM), a member of the TNF receptor superfamily, is constitutively expressed by intestinal epithelial cells and is important for protection from pathogenic bacteria. Here, we showed that at steady-state LIGHT, an HVEM ligand, binding to epithelial HVEM promoted the survival of small intestine IETs. RNA-seq and addition of HVEM ligands to epithelial organoids indicated that HVEM increased epithelial synthesis of basement membrane proteins, including collagen IV, which bound to β₁ integrins expressed by IETs. Therefore, we proposed that IET survival depended on β₁ integrin binding to collagen IV and showed that β₁ integrin-collagen IV interactions supported IET survival in vitro. Moreover, the absence of β₁ integrin expression by T lymphocytes decreased TCR αβ⁺ IETs in vivo. Intravital microscopy showed that the patrolling movement of IETs was reduced without epithelial HVEM. As likely consequences of decreased number and movement, protective responses to Salmonella enterica were reduced in mice lacking either epithelial HVEM, HVEM ligands, or β₁ integrins. Therefore, IETs, at steady state and after infection, depended on HVEM expressed by epithelial cells for the synthesis of collagen IV by epithelial cells. Collagen IV engaged β₁ integrins on IETs that were important for their maintenance and for their protective function in mucosal immunity.

Patient-Derived Organoid Serves as a Platform for Personalized Chemotherapy in Advanced Colorectal Cancer Patients

Background

Addition of oxaliplatin to adjuvant 5-FU has significantly improved the disease-free survival and served as the first line adjuvant chemotherapy in advanced colorectal cancer (CRC) patients. However, a fraction of patients remains refractory to oxaliplatin-based treatment. It is urgent to establish a preclinical platform to predict the responsiveness toward oxaliplatin in CRC patients as well as to improve the efficacy in the resistant patients.

Methods

A living biobank of organoid lines were established from advanced CRC patients. Oxaliplatin sensitivity was assessed in patient-derived tumor organoids (PDOs) in vitro and in PDO-xenografted tumors in mice. Based on in vitro oxaliplatin IC₅₀ values, PDOs were classified into either oxaliplatin-resistant (OR) or oxaliplatin-sensitive (OS) PDOs. The outcomes of patients undergone oxaliplatin-based treatment was followed. RNA-sequencing and bioinformatics tools were performed for molecular profiling of OR and OS PDOs. Oxaliplatin response signatures were submitted to Connectivity Map algorithm to identify perturbagens that may antagonize oxaliplatin resistance.

Results

Oxaliplatin sensitivity in PDOs was shown to correlate to oxaliplatin-mediated inhibition on PDO xenograft tumors in mice, and parallelled clinical outcomes of CRC patients who received FOLFOX treatment. Molecular profiling of transcriptomes revealed oxaliplatin-resistant and -sensitive PDOs as two separate entities, each being characterized with distinct hallmarks and gene sets. Using Leave-One-Out Cross Validation algorithm and Logistic Regression model, 18 gene signatures were identified as predictive biomarkers for oxaliplatin response. Candidate drugs identified by oxaliplatin response signature-based strategies, including inhibitors targeting c-ABL and Notch pathway, DNA/RNA synthesis inhibitors, and HDAC inhibitors, were demonstrated to potently and effectively increase oxaliplatin sensitivity in the resistant PDOs.

Conclusions

PDOs are useful in informing decision-making on oxaliplatin-based chemotherapy and in designing personalized chemotherapy in CRC patients.

Btla signaling in conventional and regulatory lymphocytes coordinately tempers humoral immunity in the intestinal mucosa

The Btla inhibitory receptor limits innate and adaptive immune responses, both preventing the development of autoimmune disease and restraining anti-viral and anti-tumor responses. It remains unclear how the functions of Btla in diverse lymphocytes contribute to immunoregulation. Here, we show that Btla inhibits activation of genes regulating metabolism and cytokine signaling, including Il6 and Hif1a, indicating a regulatory role in humoral immunity. Within mucosal Peyer's patches, we find T-cell-expressed Btla-regulated Tfh cells, while Btla in T or B cells regulates GC B cell numbers. Treg-expressed Btla is required for cell-intrinsic Treg homeostasis that subsequently controls GC B cells. Loss of Btla in lymphocytes results in increased IgA bound to intestinal bacteria, correlating with altered microbial homeostasis and elevations in commensal and pathogenic bacteria. Together our studies provide important insights into how Btla functions as a checkpoint in diverse conventional and regulatory lymphocyte subsets to influence systemic immune responses.

IL-22 initiates an IL-18-dependent epithelial response circuit to enforce intestinal host defence

IL-18 is emerging as an IL-22-induced and epithelium-derived cytokine which contributes to host defence against intestinal infection and inflammation. In contrast to its known role in Goblet cells, regulation of barrier function at the molecular level by IL-18 is much less explored. Here we show that IL-18 is a bona fide IL-22-regulated gate keeper for intestinal epithelial barrier. IL-22 promotes crypt immunity both via induction of phospho-Stat3 binding to the Il-18 gene promoter and via Il-18 independent mechanisms. In organoid culture, while IL-22 primarily increases organoid size and inhibits expression of stem cell genes, IL-18 preferentially promotes organoid budding and induces signature genes of Lgr5+ stem cells via Akt-Tcf4 signalling. During adherent-invasive E. coli (AIEC) infection, systemic administration of IL-18 corrects compromised T-cell IFNγ production and restores Lysozyme+ Paneth cells in Il-22-/- mice, but IL-22 administration fails to restore these parameters in Il-18-/- mice, thereby placing IL-22-Stat3 signalling upstream of the IL-18-mediated barrier defence function. IL-18 in return regulates Stat3-mediated anti-microbial response in Paneth cells, Akt-Tcf4-triggered expansion of Lgr5+ stem cells to facilitate tissue repair, and AIEC clearance by promoting IFNγ+ T cells.

Lumenal Galectin-9-Lamp2 interaction regulates lysosome and autophagy to prevent pathogenesis in the intestine and pancreas

Intracellular galectins are carbohydrate-binding proteins capable of sensing and repairing damaged lysosomes. As in the physiological conditions glycosylated moieties are mostly in the lysosomal lumen but not cytosol, it is unclear whether galectins reside in lysosomes, bind to glycosylated proteins, and regulate lysosome functions. Here, we show in gut epithelial cells, galectin-9 is enriched in lysosomes and predominantly binds to lysosome-associated membrane protein 2 (Lamp2) in a Asn(N)-glycan dependent manner. At the steady state, galectin-9 binding to glycosylated Asn175 of Lamp2 is essential for functionality of lysosomes and autophagy. Loss of N-glycan-binding capability of galectin-9 causes its complete depletion from lysosomes and defective autophagy, leading to increased endoplasmic reticulum (ER) stress preferentially in autophagy-active Paneth cells and acinar cells. Unresolved ER stress consequently causes cell degeneration or apoptosis that associates with colitis and pancreatic disorders in mice. Therefore, lysosomal galectins maintain homeostatic function of lysosomes to prevent organ pathogenesis.

The HVEM-BTLA Axis Restrains T Cell Help to Germinal Center B Cells and Functions as a Cell-Extrinsic Suppressor in Lymphomagenesis

The tumor necrosis factor receptor superfamily member HVEM is one of the most frequently mutated surface proteins in germinal center (GC)-derived B cell lymphomas. We found that HVEM deficiency increased B cell competitiveness during pre-GC and GC responses. The immunoglobulin (Ig) superfamily protein BTLA regulated HVEM-expressing B cell responses independently of B-cell-intrinsic signaling via HVEM or BTLA. BTLA signaling into T cells through the phosphatase SHP1 reduced T cell receptor (TCR) signaling and preformed CD40 ligand mobilization to the immunological synapse, thus diminishing the help delivered to B cells. Moreover, T cell deficiency in BTLA cooperated with B cell Bcl-2 overexpression, leading to GC B cell outgrowth. These results establish that HVEM restrains the T helper signals delivered to B cells to influence GC selection outcomes, and they suggest that BTLA functions as a cell-extrinsic suppressor of GC B cell lymphomagenesis.

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HVEM deficiency increases B cell competitiveness in response to T cell help

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Preformed CD40L upregulation is tuned to TCR signal strength

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HVEM engagement of Tfh BTLA signals via SHP1 to restrain CD40L and B cell proliferation

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T cell BTLA is an extrinsic repressor of Bcl-2-overexpressing GC B cell accumulation

CD160-HVEM signaling in intestinal epithelial cells modulates gut microbial homeostasis

Intestinal epithelial cells (IEC) are a first barrier that segregates host and commensal bacteria to maintain intestinal homeostasis. Intestinal intraepithelial lymphocytes (IEL) are located beneath or between adjacent IEC and directly contact IEC. The herpes virus entry mediator (HVEM), a member of the tumor necrosis factor receptor superfamily (TNFRSF), is highly expressed by IEC. Epithelial HVEM expression was previously reported as a regulator of innate immune defense during acute infections in the intestine (Shui et al., Nature, 2012). Here, we identify that HVEM signaling in IEC is important for the regulation of the gut microbiota at steady state. Mice with an epithelial-specific deletion of the gene encoding HVEM (HvemΔIEC) had significantly increased segmented filamentous bacteria (SFB) which caused an increase in Th17 cells in the ileum. Treatment with the antibiotic vancomycin eliminated SFB and decreased Th17 cells in HvemΔIEC mice. Additionally, mice with a deletion of the gene encoding CD160, which is a ligand for HVEM and is highly expressed by IEL, including intraepithelial innate lymphoid cells (ILC) and intraepithelial T cells, had increased SFB in the ileum. Our findings suggest that the interaction of CD160 expressed by IEL with HVEM expressed by IEC is important at steady state for shaping the microbiota in the intestine.

HVEM signaling in pulmonary epithelial cells is required for protection against Streptococcus pneumoniae

The most common cause of community-acquired pneumonia in the world is Streptococcus pneumoniae (S. pneumoniae). It is a serious and urgent issue to develop new therapies including non-antibiotic treatments for this pathogen. The herpes virus entry mediator (HVEM), a member of the tumor necrosis receptor super family 14 (TNFRSF14), has been reported to provide host innate immune defense in intestinal mucosal barriers against Citrobacter rodentium infection. Here we show using C10-Cre transgenic mice crossed to mice with a floxed Hvemallele that mice with pulmonary bronchiolar non-ciliated Clara cell-specific deletion of HVEM (HvemdelCC10) display higher bacterial burden and increased mortality after S. pneumoniae infection. Injection of an HVEM neutralizing antibody had a similar effect. This indicates that epithelial HVEM is also critical for pulmonary mucosal protection during the infection. In response to S. pneumonia, HVEM-deficiency led to reduced CXCL1 secretion, accompanied by impaired neutrophil recruitment to the lung. Likewise, deletion of part of the cytoplasmic tail of HVEM (HvemdelCT), causing loss of the ability of HVEM to signal, showed a similar susceptibility to S. pneumonia, indicating the importance of the intracellular signaling of HVEM in epithelial cells for the bacterial clearance. Taken together, these results reveal the protective role of HVEM in epithelial cells against S. pneumonia infection and suggest that activated HVEM signaling in epithelial cells could be used for the treatment of S. pneumoniae infection.

ATF3 Sustains IL-22-Induced STAT3 Phosphorylation to Maintain Mucosal Immunity Through Inhibiting Phosphatases

In gut epithelium, IL-22 transmits signals through STAT3 phosphorylation (pSTAT3) which provides intestinal immunity. Many components in the IL-22-pSTAT3 pathway have been identified as risk factors for inflammatory bowel disease (IBD) and some of them are considered as promising therapeutic targets. However, new perspectives are still needed to understand IL-22-pSTAT3 signaling for effective clinical interventions in IBD patients. Here, we revealed activating transcription factor 3 (ATF3), recently identified to be upregulated in patients with active IBD, as a crucial player in the epithelial IL-22-pSTAT3 signaling cascade. We found ATF3 is central to intestinal homeostasis and provides protection during colitis. Loss of ATF3 led to decreased crypt numbers, more shortened colon length, impaired ileal fucosylation at the steady state, and lethal disease activity during DSS-induced colitis which can be effectively ameliorated by rectal transplantation of wild-type colonic organoids. Epithelial stem cells and Paneth cells form a niche to orchestrate epithelial regeneration and host-microbe interactions, and IL-22-pSTAT3 signaling is a key guardian for this niche. We found ATF3 is critical for niche maintenance as ATF3 deficiency caused compromised stem cell growth and regeneration, as well as Paneth cell degeneration and loss of anti-microbial peptide (AMP)-producing granules, indicative of malfunction of Paneth/stem cell network. Mechanistically, we found IL-22 upregulates ATF3, which is required to relay IL-22 signaling leading to STAT3 phosphorylation and subsequent AMP induction. Intriguingly, ATF3 itself does not act on STAT3 directly, instead ATF3 regulates pSTAT3 by negatively targeting protein tyrosine phosphatases (PTPs) including SHP2 and PTP-Meg2. Furthermore, we identified ATF3 is also involved in IL-6-mediated STAT3 activation in T cells and loss of ATF3 leads to reduced capacity of Th17 cells to produce their signature cytokine IL-22 and IL-17A. Collectively, our results suggest that via IL-22-pSTAT3 signaling in the epithelium and IL-6-pSTAT3 signaling in Th17 cells, ATF3 mediates a cross-regulation in the barrier to maintain mucosal homeostasis and immunity.

LIGHT-HVEM Signaling in Innate Lymphoid Cell Subsets Protects Against Enteric Bacterial Infection

Innate lymphoid cells (ILCs) are important regulators of early infection at mucosal barriers. ILCs are divided into three groups based on expression profiles, and are activated by cytokines and neuropeptides. Yet, it remains unknown if ILCs integrate other signals in providing protection. We show that signaling through herpes virus entry mediator (HVEM), a member of the tumor necrosis factor (TNF) receptor superfamily, in ILC3 is important for host defense against oral infection with the bacterial pathogen Yersinia enterocolitica. HVEM stimulates protective interferon-γ (IFN-γ) secretion from ILCs, and mice with HVEM-deficient ILC3 exhibit reduced IFN-γ production, higher bacterial burdens and increased mortality. In addition, IFN-γ production is critical as adoptive transfer of wild-type but not IFN-γ-deficient ILC3 can restore protection to mice lacking ILCs. We identify the TNF superfamily member, LIGHT, as the ligand inducing HVEM signals in ILCs. Thus HVEM signaling mediated by LIGHT plays a critical role in regulating ILC3-derived IFN-γ production for protection following infection. VIDEO ABSTRACT.

LIGHT-HVEM Signaling in Group3 Innate Lymphoid Cells Protects Against Enteric Bacterial Infection

Innate lymphoid cells (ILC) are important regulators of early infection at mucosal barriers. They are known to be activated by cytokines and neuropeptides, but it remains to be determined if they integrate other signals in providing protection. The herpes virus entry mediator (HVEM), a member of the TNF receptor superfamily, is expressed by all intestinal ILC subsets. Here, we show that HVEM signaling of ILC3 is important for host defense against oral infection with the enteric bacterial pathogen Yersinia enterocolitica (Y. enterocolitica). Surprisingly, IFNγ production by CCR6 negative ILC3 was strongly implicated in protection, likely because these cells were more numerous than other innate lymphocytes that produced IFNγ early after infection. We identified the TNF superfamily member LIGHT, as the ligand inducing HVEM signals in ILC. Therefore, our results demonstrate a novel role for LIGHT-HVEM signaling in regulating ILC3 IFNγ production and protection following infection.

LIGHT-HVEM signaling in keratinocytes controls development of dermatitis

Factors that control skin inflammation are still being defined. Herro et al. demonstrate that the tumor necrosis factor superfamily protein LIGHT acts on keratinocytes via its receptor HVEM to promote characteristic features of atopic dermatitis, including epidermal hyperplasia and production of periostin.

Dermatitis is often associated with an allergic reaction characterized by excessive type 2 responses leading to epidermal acanthosis, hyperkeratosis, and dermal inflammation. Although factors like IL-4, IL-13, and thymic stromal lymphopoietin (TSLP) are thought to be instrumental for the development of this type of skin disorder, other cytokines may be critical. Here, we show that the tumor necrosis factor (TNF) superfamily protein LIGHT (homologous to lymphotoxin, exhibits inducible expression, and competes with HSV glycoprotein D for binding to HVEM, a receptor expressed on T lymphocytes) is required for experimental atopic dermatitis, and LIGHT directly controls keratinocyte hyperplasia, and production of periostin, a matricellular protein that contributes to the clinical features of atopic dermatitis as well as other skin diseases such as scleroderma. Mice with a conditional deletion of the LIGHT receptor HVEM (herpesvirus entry mediator) in keratinocytes phenocopied LIGHT-deficient mice in exhibiting reduced epidermal thickening and dermal collagen deposition in a model of atopic dermatitis driven by house dust mite allergen. LIGHT signaling through HVEM in human epidermal keratinocytes directly induced proliferation and periostin expression, and both keratinocyte-specific deletion of HVEM or antibody blocking of LIGHT–HVEM interactions after disease onset prevented expression of periostin and limited atopic dermatitis symptoms. Developing reagents that neutralize LIGHT–HVEM signaling might be useful for therapeutic intervention in skin diseases where periostin is a central feature.

Murine Corneal Inflammation and Nerve Damage After Infection With HSV-1 Are Promoted by HVEM and Ameliorated by Immune-Modifying Nanoparticle Therapy

Purpose

To determine cellular and temporal expression patterns of herpes virus entry mediator (HVEM, Tnfrsf14) in the murine cornea during the course of herpes simplex virus 1 (HSV-1) infection, the impact of this expression on pathogenesis, and whether alterations in HVEM or downstream HVEM-mediated effects ameliorate corneal disease.

Methods

Corneal HVEM levels were assessed in C57BL/6 mice after infection with HSV-1(17). Leukocytic infiltrates and corneal sensitivity loss were measured in the presence, global absence (HVEM knockout [KO] mice; Tnfrsf14-/-), or partial absence of HVEM (HVEM conditional KO). Effects of immune-modifying nanoparticles (IMPs) on viral replication, corneal sensitivity, and corneal infiltrates were measured.

Results

Corneal HVEM+ populations, particularly monocytes/macrophages during acute infection (3 days post infection [dpi]) and polymorphonuclear neutrophils (PMN) during the chronic inflammatory phase (14 dpi), increased after HSV-1 infection. Herpes virus entry mediator increased leukocytes in the cornea and corneal sensitivity loss. Ablation of HVEM from CD45+ cells, or intravenous IMP therapy, reduced infiltrates in the chronic phase and maintained corneal sensitivity.

Conclusions

Herpes virus entry mediator was expressed on two key populations: corneal monocytes/macrophages and PMNs. Herpes virus entry mediator promoted the recruitment of myeloid cells to the cornea in the chronic phase. Herpes virus entry mediator-associated corneal sensitivity loss preceded leukocytic infiltration, suggesting it may play an active role in recruitment. We propose that HVEM on resident corneal macrophages increases nerve damage and immune cell invasion, and we showed that prevention of late-phase infiltration of PMN and CD4+ T cells by IMP therapy improved clinical symptoms and mortality and reduced corneal sensitivity loss caused by HSV-1.

HVEM-BTLA interactions stimulate lung innate immunity following S. pneumoniae infection

Streptococcus pneumoniae (S. pneumoniae) is the leading cause of bacterial pneumonia in children and the elderly and it kills close to half a million children under 5 years old worldwide every year. Recent reports indicate that epithelial cells act not only as a physical barrier to pathogen invasion, but also as an extension of the immune system to prevent infection or eliminate pathogen. The herpes virus entry mediator (HVEM) is a member of the tumor necrosis factor (TNF) receptor super family. HVEM polymorphisms are a risk factor for several inflammatory and infectious diseases. Although lymphocytes and myeloid cells express HVEM, our previous data suggested that HVEM expression by epithelial cells was critical for innate immunity in the lung. However, the mechanism of HVEM-mediated host defense against S. pneumoniae is still unknown. To address the issue, we have analyzed mice with a lung epithelial cell-specific deletion of HVEM (Cc10-cre x Hvemfl/fl). We found that Cc10-cre x Hvemfl/fl mice were highly susceptible to S. pneumoniae, with an increased bacterial load by 24h and reduced survival. Mice treated with an antibody that blocks HVEM had a similar outcome, confirming that HVEM expression is required during the infection. HVEM has three ligands: the TNF super family member LIGHT and the Ig super family members BTLA and CD160. We determined that BTLA-deficient mice showed increased bacterial load in the lung and reduced survival, similar to HVEM deficiency. Moreover, CD11c-cre x BTLA fl/fl mice were highly susceptible to S. pneumoniae. Our data show that interaction between BTLA expressed by a CD11c positive myeloid cell type and HVEM expressed by lung epithelial cells leads to a protective innate response in the lung after infection.

HVEM expression by intestinal epithelial cells modulates the microbiome and epithelial immunity

The herpes virus entry mediator (HVEM), a member of the tumor necrosis factor receptor superfamily (TNFRSF), is highly expressed by intestinal epithelial cells (IEC). Previously, we reported that HVEM expression by epithelial cells was required for innate immune defense from acute infections in the lung and the intestine (Nature 488:222,2012). Here, we demonstrate a novel, constitutive role of HVEM expression by IEC in microbial homeostasis and epithelial immunity. Mice with an epithelial-specific deletion of the gene encoding HVEM (HvemΔIEC) had significantly increased segmented filamentous bacteria (SFB). This caused an increase in Th17 cells and IL-22+ILC3s in the intestine lamina propria. HvemΔIEC mice also exhibited increased goblet cell hypertrophy and hyperplasia, crypt hyperplasia, villous atrophy as they aged, and they showed a severe defect in fucosylation of cell surface proteins, even at younger ages. Treatment with the antibiotic vancomycin eliminated SFB and decreased Th17 cells and ILC3, but did not reverse the defect in fucosylation. Our findings suggest that epithelial cell expression of HVEM is important at steady state both for shaping the intestinal microbiota and for the homeostasis of IEC in the intestine.

HVEM expression by innate lymphoid cells protects against enteric bacterial infection

Yersinia enterocolitica causes food-borne disease and targets the small intestine, in which ILC3 are the predominant ILC subset. Here we show that ILC3 are required for protection of mice from oral Y. enterocolitica, as mice lacking ILC3 were more susceptible and transfer of ILC to recipients was protective. IFNγ is a cytokine required for host defense from this pathogen, and while ILC in the small intestine did not increase in number they greatly increased IFNγ production after infection. The herpes virus entry mediator (HVEM), a member of the TNF receptor superfamily (TNFRSF), is expressed by all intestinal ILC subsets. Mice with a deficiency of HVEM expression in RORγt+ ILC had a reduced steady-state IL-22 production, and in vitro HVEM could signal to ILC3 to stimulate IL-22 secretion. Moreover, following oral infection with Y. enterocolitica, mice with HVEM deficiency mediated by Rorc-cre showed reduced survival and increased bacterial translocation early after infection. Cytokines are known to induce ILC activation, but our results demonstrate a novel role for the cell surface receptor HVEM in regulating ILC3 cytokine production, both at steady state, and as a critical survival factor during acute infection.

Hvem expression in innate lymphoid cells mediates host defense against intestinal infection

The herpes virus entry mediator (HVEM), a member of the tumor necrosis factor receptor super family (TNFRSF14), has diverse functions in augmenting or inhibiting the immune response. We previously reported that epithelial HVEM signaling at mucosal barriers provides host defense against pathogenic bacteria, but the role of HVEM expression in innate lymphoid cells (ILC) in the mucosal immune system was unknown. To address this issue, we exposed RORgt-Cre × Hvemfl/fl mice with Yersinia enterocolitica (Y. enterocolitica), a small intestine infection model. We found increased bacterial translocation and decreased survival at an early time point. In these mice, Hvem is deleted in NK cells, ILC3 and in all T lymphocytes. Ifng−/− mice also showed reduced survival and increased bacterial translocation early after infection with Y. enterocolitica, demonstrating the importance of this cytokine for host defense. Interestingly, ILC from infected RORgt-Cre × Hvemfl/fl mice produced less IFNg after infection, but IFNg production by CD4+ T cells was not affected. Furthermore, in CD4-Cre × Hvemfl/fl mice, which deleted HVEM only in CD4+ T cells but not in ILCs, were not more susceptible to Y. enterocolitica. Additionally, we found that depletion of ILC from Rag1-deficient mice resulted in increased bacterial translocation and decreased body weight at an early time point. Taken together, our data indicate first, that IFNg production by ILCs, such as NK cells and ILC3, is important for host defense during Y. enterocolitica infection. Second, although the activation of ILCs is regulated by cytokines, our data show that HVEM, a member of the TNF super family, also is required for their ability to respond by producing IFNg early after infection.

IL-10-producing intestinal macrophages prevent excessive antibacterial innate immunity by limiting IL-23 synthesis

Innate immune responses are regulated in the intestine to prevent excessive inflammation. Here we show that a subset of mouse colonic macrophages constitutively produce the anti-inflammatory cytokine IL-10. In mice infected with Citrobacter rodentium, a model for enteropathogenic Escherichia coli infection in humans, these macrophages are required to prevent intestinal pathology. IL-23 is significantly increased in infected mice with a myeloid cell-specific deletion of IL-10, and the addition of IL-10 reduces IL-23 production by intestinal macrophages. Furthermore, blockade of IL-23 leads to reduced mortality in the context of macrophage IL-10 deficiency. Transcriptome and other analyses indicate that IL-10-expressing macrophages receive an autocrine IL-10 signal. Interestingly, only transfer of the IL-10 positive macrophages could rescue IL-10 deficient infected mice. Therefore, these data indicate a pivotal role for intestinal macrophages that constitutively produce IL-10, in controlling excessive innate immune activation and preventing tissue damage after an acute bacterial infection.

Protein phosphatase 4 is an essential positive regulator for Treg development, function, and protective gut immunity

BACKGROUND

Protein phosphates 4 (PP4), encoded by the ppp4c gene, is a ubiquitously expressed phosphatase that has been implicated in the regulation of cytokine signaling and lymphocyte survival; recent reports suggest that PP4 may be involved in pre-TCR signaling and B cell development. However, whether PP4 also modulates the functions of peripheral T cells has not been investigated due to the lack of a suitable in vivo model. Treg cells are a specialized subset of CD4 helper T cells that can suppress the proliferation of activated effector T cells. In the absence of this negative regulation, autoimmune syndromes and inflammatory diseases, such as human Crohn's disease, will arise.

RESULTS

In this report, we generated mice with T cell-specific ablation of the ppp4c gene (CD4cre:PP4(f/f)) and a Foxp3-GFP reporter gene to examine the roles of PP4 in Treg development and function. Characterizations of the CD4cre:PP4(f/f) mice showed that PP4 deficiency induced partial αβ T lymphopenia and T cell hypo-proliferation. Further analyses revealed significant reductions in the numbers of thymic and peripheral Treg cells, as well as in the efficiency of in vitro Treg polarization. In addition, PP4-deficient Treg cells exhibited reduced suppressor functions that were associated with decreased IL-10, CTLA4, GITR and CD103 expression. More interestingly, the CD4cre:PP4(f/f) mice developed spontaneous rectal prolapse and colitis with symptoms similar to human Crohn's disease. The pathogenesis of colitis required the presence of commensal bacteria, and was correlated with reduced Treg cells in the gut. Nevertheless, PP4-deficient Treg cells were still capable of suppressing experimental colitis, suggesting that multiple factors contributed to the onset of the spontaneous colitis.

CONCLUSIONS

While the molecular mechanisms remain to be investigated, our results clearly show that PP4 plays a non-redundant role for the differentiation, suppressor activity and gut homeostasis of Treg cells. The onset of spontaneous colitis in the CD4cre:PP4(f/f) mice further suggests that PP4 is essential for the maintenance of protective gut immunity. The CD4cre:PP4(f/f) mice thus may serve as a good model for studying the interactions between Treg cells and gut commensal bacteria for the regulation of mucosal immunity.

HVEM is a TNF Receptor with Multiple Regulatory Roles in the Mucosal Immune System

The herpes virus entry mediator (HVEM) is a member of the tumor necrosis factor receptor superfamily (TNFRSF), and therefore it is also known as TNFRSF14 or CD270 (1,2). In recent years, we have focused on understanding HVEM function in the mucosa of the intestine, particularly on the role of HVEM in colitis pathogenesis, host defense and regulation of the microbiota (2,3,4). HVEM is an unusual TNF receptor because of its high expression levels in the gut epithelium, its capacity to bind ligands that are not members of the TNF super family, including immunoglobulin (Ig) superfamily members BTLA and CD160, and its bi-directional functionality, acting as a signaling receptor or as a ligand for the receptor BTLA. Clinically, Hvem recently was reported as an inflammatory bowel disease (IBD) risk gene as a result of genome wide association studies (5,6). This suggests HVEM could have a regulatory role influencing the regulation of epithelial barrier, host defense and the microbiota. Consistent with this, using mouse models, we have revealed how HVEM is involved in colitis pathogenesis, mucosal host defense and epithelial immunity (3,7). Although further studies are needed, our results provide the fundamental basis for understanding why Hvem is an IBD risk gene, and they confirm that HVEM is a mucosal gatekeeper with multiple regulatory functions in the mucosa.

HVEM is a TNF family receptor that is a crucial regulator of epithelial and lymphocyte responses in the mucosal immune system (P3192)

HVEM is a TNF super family receptor, and previously we showed that epithelial HVEM is required for innate immune responses to pathogenic bacteria in the intestine and lung, and that it acts by enhancing epithelial Stat3 activation (Nature 488:222, 2012). Now, we show that HVEM is also an important regulator of lymphoid cells in the mucosal immune response. IL-17 and IL-22 are protective cytokines after oral infection with Citrobacter rodentium. Mice deficient for HVEM have a reduced IL-22 response by innate lymphoid cells (ILC) in the colon lamina propria at early times after infection. The adaptive immune response is also affected, with reductions in IL-17 and IL-22 by colonic lamina propria CD4+ T cells at days 9-21 after infection. The role of HVEM in mucosal lymphoid cells is more important for controlling bacterial burden and pathology at later times after infection, with the HVEM-dependent epithelial response acting earlier. Also striking, however, is the strong decrease in all intestinal epithelial lymphocyte populations (IEL) in mice deficient for HVEM, at steady state, even in the absence of infection. This reflects a decreased proliferative potential of IEL when HVEM is not expressed. Collectively, our findings establish HVEM as a crucial regulator of the mucosal immunity, affecting IEL homeostasis, innate epithelial responses and innate and adaptive responses by lamina propria lymphocytes.

Immune regulation by CD11b+ myeloid cells in the intestine (P3195)

We found that a subset of CD11b+ myeloid cells in the intestinal lamina propria constitutively produce IL-10 mRNA, and adoptive transfer of these IL-10 producing cells to recipients helped to maintain Foxp3 expression and the function of Treg. Although much emphasis has been placed on the regulatory role of T cell derived IL-10, our data show that IL-10 synthesis by intestinal myeloid cells has a nonredundant and dramatic effect on maintaining Treg function and preventing T cell-mediated colitis in mice. Here, we further investigate the role of intestinal myeloid cell derived IL-10 in the regulation of gut inflammation. IL-10 producing intestinal myeloid cells expressed higher CD11b, CD11c, F4/80, Gr-1 and CX3CR1 messenger RNA and protein, compared to their non-IL-10 producing intestinal myeloid counterparts. Myeloid cell specific (LysM-Cre driven) IL-10 deficient mice had a similar Treg population in the large intestine compared to controls. C. rodentium infection caused a decrease in the number of Treg in the large intestine, but not in the spleen, and moreover, this defect was more pronounced in mice with a myeloid cell specific IL-10 deficiency. Inflammation in colitis models or following acute infections leads to decreased intestinal Treg. IL-10 producing myeloid cells has a role in maintaining the Treg population in the intestine under inflammatory conditions, as exemplified by C. rodentium infection.

HVEM: An unusual TNF receptor family member important for mucosal innate immune responses to microbes

The herpes virus entry mediator (HVEM or CD270) is a member of the tumor necrosis factor receptor superfamily (TNFRSF), and therefore it is also known as TNFRSF14. We have recently provided evidence showing a novel signaling pathway downstream of HVEM leading to signal transducer and activator of transcription 3 (STAT3) activation in epithelial cells. As STAT3 regulates the expression of genes important for host defense in epithelial cells, as well as the differentiation of retinoid-related orphan receptor (ROR)γt+ Th17 and innate lymphoid cells (ILC), our finding that HVEM activates STAT3 has revealed fresh insights into the potential regulatory function of HVEM in different cellular contexts. Therefore, although further investigations will be required, HVEM is emerging as a major player in mucosal host defense, capable of regulating several cellular responses.

Transcriptional reprogramming of mature CD4⁺ helper T cells generates distinct MHC class II-restricted cytotoxic T lymphocytes

TCRαβ thymocytes differentiate to either CD8αβ cytotoxic T lymphocytes or CD4⁺ T helper cells. This functional dichotomy is controlled by key transcription factors, including the T helper master regulator, ThPOK, which suppresses the cytolytic program in MHC class II-restricted CD4⁺ thymocytes. ThPOK continues to repress CD8-lineage genes in mature CD4⁺ T cells, even as they differentiate to T helper effector subsets. Here we show that the T helper-fate was not fixed and that mature antigen-stimulated CD4⁺ T cells could terminate Thpok expression and reactivate CD8-lineage genes. This unexpected plasticity resulted in the post-thymic termination of the T helper-program and the functional differentiation of distinct MHC class II-restricted CD4⁺ cytotoxic T lymphocytes.

HVEM signalling at mucosal barriers provides host defence against pathogenic bacteria

The herpes virus entry mediator (HVEM), a member of the tumour-necrosis factor receptor family, has diverse functions, augmenting or inhibiting the immune response. HVEM was recently reported as a colitis risk locus in patients, and in a mouse model of colitis we demonstrated an anti-inflammatory role for HVEM, but its mechanism of action in the mucosal immune system was unknown. Here we report an important role for epithelial HVEM in innate mucosal defence against pathogenic bacteria. HVEM enhances immune responses by NF-κB-inducing kinase-dependent Stat3 activation, which promotes the epithelial expression of genes important for immunity. During intestinal Citrobacter rodentium infection, a mouse model for enteropathogenic Escherichia coli infection, Hvem−/− mice showed decreased Stat3 activation, impaired responses in the colon, higher bacterial burdens and increased mortality. We identified the immunoglobulin superfamily molecule CD160 (refs 7 and 8), expressed predominantly by innate-like intraepithelial lymphocytes, as the ligand engaging epithelial HVEM for host protection. Likewise, in pulmonary Streptococcus pneumoniae infection, HVEM is also required for host defence. Our results pinpoint HVEM as an important orchestrator of mucosal immunity, integrating signals from innate lymphocytes to induce optimal epithelial Stat3 activation, which indicates that targeting HVEM with agonists could improve host defence.

A TNF family receptor regulates epithelial innate responses and host defense against pathogenic bacterial infections of the mucosa (49.1)

Previously, in a mouse colitis model, we demonstrated an anti-inflammatory role for the herpes virus entry mediator (HVEM), a TNF superfamily receptor, when expressed by a radiation resistant cell population (J. Exp. Med. 205: 1463, 2008). However, the molecular mechanism for HVEM function remained to be determined. We therefore explored the role of HVEM in colonic epithelial cells, a radiation resistant cell type critical for preventing colitis and enhancing host defense. During Citrobacter rodentium infection, Hvem-/- mice had impaired colonic epithelial responses, resulting in higher bacterial burdens, inflammation and increased mortality. HVEM stimulation induced epithelial responses by NIK-dependent Stat3 activation, resulting in the expression of genes important for mucosal immunity. HVEM signaling also induced IL-22R1 expression, which boosted IL-22 signaling, leading to enhanced Stat3 activation in the epithelium. While HVEM or IL-22R signaling alone induced Stat3 activation in epithelial cells in vitro, during infection in vivo, both Stat3-activating pathways were required. Likewise, in Streptococcus pneumoniae infection, HVEM was required not only for survival and bacterial clearance, but also for Stat3 activation and induction of innate responses in the lung. Collectively, our findings establish HVEM as a crucial regulator of innate defense at mucosal surfaces via directly enhancing epithelial Stat3 activation and by inducing epithelial IL-22R1 expression.

Regulation of inflammation, autoimmunity, and infection immunity by HVEM-BTLA signaling

The HVEM, or TNFRSF14, is a membrane-bound receptor known to activate the NF-κB pathway, leading to the induction of proinflammatory and cell survival-promoting genes. HVEM binds several ligands that are capable of mediating costimulatory pathways, predominantly through its interaction with LIGHT (TNFSF14). However, it can also mediate coinhibitory effects, predominantly by interacting with IGSF members, BTLA or CD160. Therefore, it can function like a "molecular switch" for various activating or inhibitory functions. Furthermore, recent studies suggest the existence of bidirectional signaling with HVEM acting as a ligand for signaling through BTLA, which may act as a ligand in other contexts. Bidirectional signaling, together with new information indicating signaling in cis by cells that coexpress HVEM and its ligands, makes signaling within a HVEM-mediated network complicated, although potentially rich in biology. Accumulating in vivo evidence has shown that HVEM-mediated, coinhibitory signaling may be dominant over HVEM-mediated costimulatory signaling. In several disease models the absence of HVEM-BTLA signaling predominantly resulted in severe mucosal inflammation in the gut and lung, autoimmune-like disease, and impaired immunity during bacterial infection. Here, we will summarize the current view about how HVEM-BTLA signaling is involved in the regulation of mucosal inflammation, autoimmunity, and infection immunity.

Regulating the mucosal immune system: the contrasting roles of LIGHT, HVEM, and their various partners

LIGHT and herpes virus entry mediator (HVEM) comprise a ligand-receptor pair in the tumor necrosis factor superfamily. These molecules play an important role in regulating immunity, particularly in the intestinal mucosa. LIGHT also binds the lymphotoxin beta receptor, and HVEM can act as a ligand for immunoglobulin family molecules, including B- and T-lymphocyte attenuator, which suppresses immune responses. Complexity in this pivotal system arises from several factors, including the non-monogamous pairing of ligands and receptors, and reverse signaling or the ability of some ligands to serve as receptors. As a result, recognition events in this fascinating network of interacting molecules can have pro- or anti-inflammatory consequences. Despite complexity, experiments we and others are carrying out are establishing rules for understanding when and in what cell types these molecules contribute to intestinal inflammation.

Hematopoietic progenitor kinase 1 negatively regulates T cell receptor signaling and T cell-mediated immune responses

HPK1 is a Ste20-related serine-threonine kinase that inducibly associates with the adaptors SLP-76 and Gads after T cell receptor (TCR) signaling. Here, HPK1 deficiency resulted in enhanced TCR-induced phosphorylation of SLP-76, phospholipase C-gamma1 and the kinase Erk, more-persistent calcium flux, and increased production of cytokines and antigen-specific antibodies. Furthermore, HPK1-deficient mice were more susceptible to experimental autoimmune encephalomyelitis. Although the interaction between SLP-76 and Gads was unaffected, the inducible association of SLP-76 with 14-3-3tau (a phosphorylated serine-binding protein and negative regulator of TCR signaling) was reduced in HPK1-deficient T cells after TCR stimulation. HPK1 phosphorylated SLP-76 and induced the interaction of SLP-76 with 14-3-3tau. Our results indicate that HPK1 negatively regulates TCR signaling and T cell-mediated immune responses.

Conditional knockout mice reveal an essential role of protein phosphatase 4 in thymocyte development and pre-T-cell receptor signaling

Okadaic acid-sensitive serine/threonine phosphatases have been shown to regulate interleukin-2 transcription and T-cell activation. Okadaic acid inhibits protein phosphatase 4 (PP4), a novel PP2A-related serine/threonine phosphatase, at a 50% inhibitory concentration (IC(50)) comparable to that for PP2A. This raises the possibility that some cellular functions of PP2A, determined in T cells by using okadaic acid, may in fact be those of PP4. To investigate the in vivo roles of PP4 in T cells, we generated conventional and T-cell-specific PP4 conditional knockout mice. We found that the ablation of PP4 led to the embryonic lethality of mice. PP4 gene deletion in the T-cell lineage resulted in aberrant thymocyte development, including T-cell arrest at the double-negative 3 stage (CD4(-) CD8(-) CD25(+) CD44(-)), abnormal thymocyte maturation, and lower efficacy of positive selection. PP4-deficient thymocytes showed decreased proliferation and enhanced apoptosis in vivo. Analysis of pre-T-cell receptor (pre-TCR) signaling further revealed impaired calcium flux and phospholipase C-gamma1-extracellular signal-regulated kinase activation in the absence of PP4. Anti-CD3 injection in PP4-deficient mice led to enhanced thymocyte apoptosis, accompanied by increased proapoptotic Bim but decreased antiapoptotic Bcl-xL protein levels. In the periphery, antigen-specific T-cell proliferation and T-cell-mediated immune responses in PP4-deficient mice were dramatically compromised. Thus, our results indicate that PP4 is essential for thymocyte development and pre-TCR signaling.

HIP-55 is important for T-cell proliferation, cytokine production, and immune responses

Engagement of the T-cell receptor (TCR) triggers a series of signaling events that lead to the activation of T cells. HIP-55 (SH3P7 or mAbp1), an actin-binding adaptor protein, interacts with and is tyrosine phosphorylated by ZAP-70, which is a crucial proximal protein tyrosine kinase for TCR signaling. HIP-55 is important for JNK and HPK1 activation induced by TCR signaling. In this study, we report the generation and characterization of HIP-55 knockout mice. We found that HIP-55 knockout mice were viable and fertile but showed decreased body weight and increased occurrence of death within the first 4 weeks after birth. The lymphoid organs in HIP-55 knockout mice showed cellularity and T-cell development comparable to that of the wild-type mice. HIP-55 knockout T cells displayed defective T-cell proliferation, decreased cytokine production, and decreased up-regulation of the activation markers induced by TCR stimulation. TCR internalization was slightly increased in HIP-55 knockout T cells. These phenotypes were accompanied by reduced immune responses, including antigen-specific antibody production and T-cell proliferation in HIP-55 knockout mice. The TCR-induced signaling events, including LAT/phospholipase Cgamma1 phosphorylation and HPK1/JNK activation, were partially defective in HIP-55 knockout T cells. These results demonstrate the importance of HIP-55 as an adaptor protein in the TCR signaling and immune system.

Germline transmission and efficient DNA recombination in mouse embryonic stem cells mediated by adenoviral-Cre transduction

Following gene targeting, a loxP-neo-loxP cassette was introduced into ES cells. The presence of a selectable marker such as neo in the targeted allele may result in gene interference in flox mice or unexpected phenotypes due to genetic ambiguity in direct knockout mice. Typically, the neo cassette is selectively removed by transient expression of the Cre recombinase in targeted ES cell. However, this method involves a tedious process of selecting, expanding, and screening ES cell clones which may compromise germline competency. Here, we describe a novel method of combining adenovirus-Cre mediated gene recombination with ES gene targeting to facilitate efficient loxP-neo-loxP removal in ES cells. We demonstrate that adenovirus-Cre infected ES cells can retain their germline competency. The procedures described here facilitate a rapid genetic manipulation of ES cells to obtain neo-free knockout animals, multiple gene targeting, homozygous mutant ES cells ideal for in vitro characterization, or Rag-deficient blastocyst complementation.

The SH3 Domain-containing Adaptor HIP-55 Mediates c-Jun N-terminal Kinase Activation in T Cell Receptor Signaling

HIP-55 (hematopoietic progenitor kinase 1 (HPK1)-interacting protein of 55 kDa, also called SH3P7 and mAbp1) is a novel SH3 domain-containing protein. HIP-55 binds to actin filaments both in vitro and in vivo. HIP-55 activates HPK1 and c-Jun N-terminal kinase (JNK), which are two important lymphocyte signaling molecules. Until now, the regulation and function of HIP-55 in T cell receptor (TCR) signaling were unknown. We found that HIP-55 was recruited to glycolipid-enriched microdomains upon TCR stimulation, which indicates that HIP-55 is regulated by TCR signaling. HIP-55 interacted with ZAP-70, a critical protein-tyrosine kinase in TCR signaling, and this interaction was induced by TCR signaling. ZAP-70 phosphorylated HIP-55 at Tyr-334 and Tyr-344 in vitro and in vivo, and the HIP-55 mutant (Y334F/Y344F) was not tyrosine-phosphorylated in stimulated T cells. To study its function in T cell activation, HIP-55-deficient Jurkat T cells were established using the RNA interference approach. In the HIP-55-deficient cells, TCR (but not UV)-stimulated JNK activation was decreased. Furthermore, the activation of HPK1, a known JNK upstream activator and HIP-55-interacting protein, was also decreased in the HIP-55-deficient cells. Our data reveal the regulation of HIP-55 during TCR signaling, and using a genetic approach, we demonstrate for the first time that HIP-55 plays a functional role in TCR signaling.

Genomic structure of the mouse PP4 gene: a developmentally regulated protein phosphatase

Protein phosphatases play important roles in the control of various cellular processes. Here, we report the cloning and characterization of the murine cDNA and genomic DNA encoding the serine/threonine protein phosphatase 4 (PP4), also called PPX. While the nucleotide sequences of murine and human PP4 are distinct, their amino acid sequences are identical. We have analyzed the protein, cDNA and genomic PP4 sequences to provide insight into the structure, function and potential regulation of PP4. Genomic Southern blots demonstrated the conservation of PP4 across species. Using Northern blotting and in situ hybridization, we have examined the expression of PP4 in murine embryos and adult tissues. In adult tissues, PP4 was expressed at high levels in the testis, kidney, liver, and lung, and at lower levels in virtually all tissues. PP4 was differentially expressed in murine embryos at different developmental stages, suggesting that PP4 is a developmentally regulated protein phosphatase.

Involvement of hematopoietic progenitor kinase 1 in T cell receptor signaling

Hematopoietic progenitor kinase 1 (HPK1), a mammalian Ste20-related serine/threonine protein kinase, is a hematopoietic-specific upstream activator of the c-Jun N-terminal kinase. Here, we provide evidence to demonstrate the involvement of HPK1 in T cell receptor (TCR) signaling. HPK1 was activated and tyrosine-phosphorylated with similar kinetics following TCR/CD3 or pervanadate stimulation. Co-expression of protein-tyrosine kinases, Lck and Zap70, with HPK1 led to HPK1 activation and tyrosine phosphorylation in transfected mammalian cells. Upon TCR/CD3 stimulation, HPK1 formed inducible complexes with the adapters Nck and Crk with different kinetics, whereas it constitutively interacted with the adapters Grb2 and CrkL in Jurkat T cells. Interestingly, HPK1 also inducibly associated with linker for activation of T cells (LAT) through its proline-rich motif and translocated into glycolipid-enriched microdomains (also called lipid rafts) following TCR/CD3 stimulation, suggesting a critical role for LAT in the regulation of HPK1. Together, these results identify HPK1 as a new component of TCR signaling. T cell-specific signaling molecules Lck, Zap70, and LAT play roles in the regulation of HPK1 during TCR signaling. Differential complex formation between HPK1 and adapters highlights the possible involvement of HPK1 in multiple signaling pathways in T cells.