LIGHT Expression by Mucosal T Cells May Regulate IFN-γ Expression in the Intestine

Realigning the LIGHT signaling network to control dysregulated inflammation

Advances in understanding the physiologic functions of the tumor necrosis factor superfamily (TNFSF) of ligands, receptors, and signaling networks are providing deeper insight into pathogenesis of infectious and autoimmune diseases and cancer. LIGHT (TNFSF14) has emerged as an important modulator of critical innate and adaptive immune responses. LIGHT and its signaling receptors, herpesvirus entry mediator (TNFRSF14), and lymphotoxin β receptor, form an immune regulatory network with two co-receptors of herpesvirus entry mediator, checkpoint inhibitor B and T lymphocyte attenuator, and CD160. Deciphering the fundamental features of this network reveals new understanding to guide therapeutic development. Accumulating evidence from infectious diseases points to the dysregulation of the LIGHT network as a disease-driving mechanism in autoimmune and inflammatory reactions in barrier organs, including coronavirus disease 2019 pneumonia and inflammatory bowel diseases. Recent clinical results warrant further investigation of the LIGHT regulatory network and application of target-modifying therapeutics for disease intervention.

Circulating LIGHT (TNFSF14) and Interleukin-18 Levels in Sepsis-Induced Multi-Organ Injuries

The novel therapeutic target cytokine LIGHT (TNFSF14) was recently shown to play a major role in COVID-19-induced acute respiratory distress syndrome (ARDS). This study aims to investigate the associations of plasma LIGHT and another potentially targetable cytokine, interleukin-18 (IL-18), with ARDS, acute hypoxic respiratory failure (AHRF), or acute kidney injury (AKI), caused by non-COVID-19 viral or bacterial sepsis. A total of 280 subjects diagnosed with sepsis, including 91 cases with sepsis triggered by viral infections, were investigated in this cohort study. Day 0 plasma LIGHT and IL-18, as well as 59 other biomarkers (cytokines, chemokines, and acute-phase reactants) were measured by sensitive bead immunoassay and associated with symptom severity. We observed significantly increased LIGHT level in both bacterial sepsis patients (p = 1.80 × 10⁻⁵) and patients with sepsis from viral infections (p = 1.78 × 10⁻³). In bacterial sepsis, increased LIGHT level was associated with ARDS, AKI, and higher Apache III scores, findings also supported by correlations of LIGHT with other biomarkers of organ failure. IL-18 levels were highly variable across individuals and consistently correlated with Apache III scores, mortality, and AKI in both bacterial and viral sepsis. There was no correlation between LIGHT and IL-18. For the first time, we demonstrate independent effects of LIGHT and IL-18 in septic organ failure. The association of plasma LIGHT with AHRF suggests that targeting the pathway warrants exploration, and ongoing trials may soon elucidate whether this is beneficial. Given the large variance of plasma IL-18 among septic subjects, targeting this pathway requires precise application.

Elevation of Circulating LIGHT (TNFSF14) and Interleukin-18 Levels in Sepsis-Induced Multi-Organ Injuries

Objective

The cytokines, LIGHT (TNFSF14) and Interleukin-18 (IL-18), are two important therapeutic targets due to their central roles in the function of activated T cells and inflammatory injury. LIGHT was recently shown to play a major role in COVID19 induced acute respiratory distress syndrome (ARDS), reducing mortality and hospital stay. This study aims to investigate the associations of LIGHT and IL-18 with non-COVID19 related ARDS, acute hypoxic respiratory failure (AHRF) or acute kidney injury (AKI), secondary to viral or bacterial sepsis.

Research Design and Methods

A cohort of 280 subjects diagnosed with sepsis, including 91 cases with sepsis triggered by viral infections, were investigated in this study and compared to healthy controls. Serum LIGHT, IL-18, and 59 other biomarkers (cytokines, chemokines and acute-phase reactants) were measured and associated with symptom severity.

Results

ARDS was observed in 36% of the patients, with 29% of the total patient cohort developing multi-organ failure (failure of two or more organs). We observed significantly increased LIGHT level (>2SD above mean of healthy subjects) in both bacterial sepsis patients (P=1.80E-05) and patients with sepsis from viral infections (P=1.78E-03). In bacterial sepsis, increased LIGHT level associated with ARDS, AKI and higher Apache III scores, findings also supported by correlations of LIGHT with other biomarkers of organ failures, suggesting LIGHT may be an inflammatory driver. IL-18 levels were highly variable across individuals, and consistently correlated with Apache III scores, mortality, and AKI, in both bacterial and viral sepsis.

Conclusions

For the first time, we demonstrate independent effects of LIGHT and IL-18 in septic organ failures. LIGHT levels are significantly elevated in non-COVID19 sepsis patients with ARDS and/or multi-organ failures suggesting that anti-LIGHT therapy may be effective therapy in a subset of patients with sepsis. Given the large variance of plasma IL-18 among septic subjects, targeting this pathway raises opportunities that require a precision application.

Increased Production of LIGHT by T Cells in Eosinophilic Esophagitis Promotes Differentiation of Esophageal Fibroblasts Toward an Inflammatory Phenotype

BACKGROUND & AIMS

Eosinophilic esophagitis (EoE) is an antigen-mediated eosinophilic disease of the esophagus that involves fibroblast activation and progression to fibrostenosis. Cytokines produced by T-helper type 2 cells and transforming growth factor beta 1 (TGFβ1) contribute to the development of EoE, but other cytokines involved in pathogenesis are unknown. We investigate the effects of tumor necrosis factor superfamily member 14 (TNFSF14, also called LIGHT) on fibroblasts in EoE.

METHODS

We analyzed publicly available esophageal CD3+ T-cell single-cell sequencing data for expression of LIGHT. Esophageal tissues were obtained from pediatric patients with EoE or control individuals and analyzed by immunostaining. Human primary esophageal fibroblasts were isolated from esophageal biopsy samples of healthy donors or patients with active EoE. Fibroblasts were cultured; incubated with TGFβ1 and/or LIGHT; and analyzed by RNA sequencing, flow cytometry, immunoblots, immunofluorescence, or reverse transcription polymerase chain reaction. Eosinophils were purified from peripheral blood of healthy donors, incubated with interleukin 5, cocultured with fibroblasts, and analyzed by immunohistochemistry.

RESULTS

LIGHT was up-regulated in the esophageal tissues from patients with EoE, compared with control individuals, and expressed by several T-cell populations, including T-helper type 2 cells. TNF receptor superfamily member 14 (TNFRSF14, also called HVEM) and lymphotoxin beta receptor are receptors for LIGHT that were expressed by fibroblasts from healthy donors or patients with active EoE. Stimulation of esophageal fibroblasts with LIGHT induced inflammatory gene transcription, whereas stimulation with TGFβ1 induced transcription of genes associated with a myofibroblast phenotype. Stimulation of fibroblasts with TGFβ1 increased expression of HVEM; subsequent stimulation with LIGHT resulted in their differentiation into cells that express markers of myofibroblasts and inflammatory chemokines and cytokines. Eosinophils tethered to esophageal fibroblasts after LIGHT stimulation via intercellular adhesion molecule-1.

CONCLUSIONS

T cells in esophageal tissues from patients with EoE express increased levels of LIGHT compared with control individuals, which induces differentiation of fibroblasts into cells with inflammatory characteristics. TGFβ1 increases fibroblast expression of HVEM, a receptor for LIGHT. LIGHT mediates interactions between esophageal fibroblasts and eosinophils via ICAM1. This pathway might be targeted for the treatment of EoE.

Restoring Herpesvirus Entry Mediator (HVEM) Immune Function in HVEM-/- Mice Rescues Herpes Simplex Virus 1 Latency and Reactivation Independently of Binding to Glycoprotein D

The immune modulatory protein herpes virus entry mediator (HVEM) is one of several cellular receptors used by herpes simplex virus 1 (HSV-1) for cell entry. HVEM binds to HSV-1 glycoprotein D (gD) but is not necessary for HSV-1 replication in vitro or in vivo Previously, we showed that although HSV-1 replication was similar in wild-type (WT) control and HVEM-/- mice, HSV-1 does not establish latency or reactivate effectively in mice lacking HVEM, suggesting that HVEM is important for these functions. It is not known whether HVEM immunomodulatory functions contribute to latency and reactivation or whether its binding to gD is necessary. We used HVEM-/- mice to establish three transgenic mouse lines that express either human WT HVEM or human or mouse HVEM with a point mutation that ablates its ability to bind to gD. Here, we show that HVEM immune function, not its ability to bind gD, is required for WT levels of latency and reactivation. We further show that HVEM binding to gD does not affect expression of the HVEM ligands BTLA, CD160, or LIGHT. Interestingly, our results suggest that binding of HVEM to gD may contribute to efficient upregulation of CD8α but not PD1, TIM-3, CTLA4, or interleukin 2 (IL-2). Together, our results establish that HVEM immune function, not binding to gD, mediates establishment of latency and reactivation.IMPORTANCE HSV-1 is a common cause of ocular infections worldwide and a significant cause of preventable blindness. Corneal scarring and blindness are consequences of the immune response induced by repeated reactivation events. Therefore, HSV-1 therapeutic approaches should focus on preventing latency and reactivation. Our data suggest that the immune function of HVEM plays an important role in the HSV-1 latency and reactivation cycle that is independent of HVEM binding to gD.

Role of TGFβ3-Smads-Sp1 axis in DcR3-mediated immune escape of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a leading cause of tumour-associated mortality worldwide, but no significant improvement in treating HCC has been reported with currently available systemic therapies. Immunotherapy represents a new frontier in tumour therapy. Therefore, the immunobiology of hepatocarcinoma has been under intensive investigation. Decoy receptor 3 (DcR3), a member of the tumour necrosis factor receptor (TNFR) superfamily, is an immune suppressor associated with tumourigenesis and cancer metastasis. However, little is known about the role of DcR3 in the immunobiology of hepatocarcinoma. In this study, we found that overexpression of DcR3 in HCC is mediated by the TGFβ3-Smad-Sp1 signalling pathway, which directly targets DcR3 promoter regions. Moreover, overexpression of DcR3 in HCC tissues is associated with tumour invasion and metastasis and significantly promotes the differentiation and secretion of Th2 and Treg cells while inhibiting the differentiation and secretion of Th1 cells. Conversely, knockdown of DcR3 expression in HCC significantly restored the immunity of CD4⁺ T cells. Inhibition of DcR3 expression may provide a novel immunotherapeutic approach to restoring immunity in HCC patients.

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.

A Randomized Phase 1 Study to Assess the Safety and Pharmacokinetics of the Subcutaneously Injected Anti-LIGHT Antibody, SAR252067

LIGHT, a member of the tumor necrosis factor superfamily, is potentially involved in mucosal inflammation associated with inflammatory bowel disease. The safety and pharmacokinetics of the fully human monoclonal anti-LIGHT antibody, SAR252067, was evaluated in healthy volunteers in a phase 1 study as a potential treatment for diseases related to LIGHT-mediated mucosal inflammation. This double-blind, randomized, placebo-controlled, sequential ascending single-dose, single-center, 16-week study randomized 48 subjects to a single subcutaneous dose of SAR252067 (40, 120, 300, 600, 900, or 1200 mg) or placebo. Safety assessments included adverse events (AEs), injection-site reactions, and antidrug antibody (ADA) titer. Pharmacokinetic end points were serum parameters of SAR252067 (C_max , AUC_0-∞ , t_max , t_1/2z ). Serum-soluble LIGHT concentrations were also determined. Safety analyses included all 48 participants; pharmacokinetic analyses included 36 subjects who received SAR252067. No serious AEs were reported, and no dose-effect relationship was apparent. Injection-site reactions were minimal. ADAs were not clinically relevant. SAR252067 exposure increased in a near-dose-proportional manner, median t_max ranged from 5.0 to 8.5 days, and t_1/2z ranged from 18.0 to 27.0 days. Serum-soluble LIGHT significantly increased after SAR252067 administration with the 40-mg dose only. SAR252067 had a good safety profile, was well tolerated in healthy humans, and displayed a predictable pharmacokinetic profile.

Increased Serum LIGHT Levels Correlate with Disease Progression and Severity of Interstitial Pneumonia in Patients with Dermatomyositis: A Case Control Study

BACKGROUND

Activated CD8+ T cells play an important role in the pathogenesis of dermatomyositis (DM) with interstitial pneumonia (IP). Serum CD8+ T-cell activator, LIGHT, and Th1/Th2/Th17 cytokines were measured in DM-IP patients and compared with clinical parameters to investigate their usefulness.

METHODS

The correlations between the clinical findings and serum LIGHT and Th1/Th2/Th17 cytokine levels were investigated in 21 patients with DM-IP (14 with rapidly progressive IP [RPIP] and 7 with chronic IP [CIP], including 4 fatal cases of IP).

RESULTS

The median serum LIGHT level was 119 (16-335.4) pg/ml, which was higher than that in healthy control subjects and DM patients without IP. The median serum IL-6 level was 14.7 (2.4-154.5) pg/ml (n = 13). The other cytokines were detected in only a few patients. The median serum LIGHT level in DM-RPIP patients (156 [49.6-335.4] pg/ml) was significantly higher than that in DM-CIP patients (94.3 [16-164.2] pg/ml) (P = 0.02). The serum IL-6 level did not correlate with either progression or outcome of DM-IP. ROC curve analysis determined a serum LIGHT level of ≥120 pg/ml to be the cut-off value for the rapid progression of DM-IP. Serum LIGHT levels correlated significantly with %DLco (R = 0.55, P = 0.04) and total ground-glass opacity scores (R = 0.72, P = 0.0002). The serum LIGHT level significantly decreased to 100.5 (12.4-259.3) pg/ml 4 weeks after treatment initiation (P = 0.04).

CONCLUSIONS

The serum LIGHT level may be a promising marker of disease progression and severity in patients with DM-IP.

Role of the tumor necrosis factor family member LIGHT in the pathogenesis of atopic dermatitis

BACKGROUND

LIGHT (the name of which is derived from "homologous to lymphotoxins, exhibits inducible expression, competes with herpes simplex virus glycoprotein D for herpes simplex virus entry mediator, and expressed by T lymphocytes"), is a member of the tumor necrosis factor superfamily that is involved in various inflammatory diseases.

OBJECTIVES

To assess serum LIGHT levels in patients with atopic dermatitis (AD) before and after treatment and compare it with controls. To correlate serum LIGHT with the severity scoring of AD (SCORAD) index. Another objective is to compare LIGHT levels between lesional skin in patients with AD and controls.

METHODS

Twenty patients with AD and 20 healthy controls were enrolled in the study. Serum LIGHT levels were examined using an enzyme immunoassay technique. Serum total IgE levels, absolute eosinophil count, and eosinophil percentage were also done for both patients and controls. The SCORAD index was done for every patient before and after treatment. Skin LIGHT levels were analyzed using enzyme-linked immunosorbent assay kit and compared with control skin.

RESULTS

Serum LIGHT levels in patients with AD were significantly higher than that of healthy controls and correlated positively with SCORAD index. LIGHT concentrations decreased as the symptoms were improved by treatment. A significant correlation was found on comparing the LIGHT serum levels and other established markers of disease severity. LIGHT levels in lesional skin in these patients were markedly higher than LIGHT levels in normal skin.

CONCLUSION

LIGHT may play an important role in the pathogenesis of AD. This may presumably have possible future implications on the treatment of this chronic disease.

Therapeutic blockade of LIGHT interaction with herpesvirus entry mediator and lymphotoxin β receptor attenuates in vivo cytotoxic allogeneic responses

BACKGROUND

Tumor necrosis factor/tumor necrosis factor receptor superfamily members conform a group of molecular interaction pathways of essential relevance during the process of T-cell activation and differentiation toward effector cells and particularly for the maintenance phase of the immune response. Specific blockade of these interacting pathways, such as CD40-CD40L, contributes to modulate the deleterious outcome of allogeneic immune responses. We postulated that antagonizing the interaction of LIGHT expression on activated T cells with its receptors, herpesvirus entry mediator and lymphotoxin β receptor, may decrease T cell-mediated allogeneic responses.

METHODS

A flow cytometry competition assay was designed to identify anti-LIGHT monoclonal antibodies capable to prevent the interaction of mouse LIGHT with its receptors expressed on transfected cells. An antibody with the desired specificity was evaluated in a short-term in vivo allogeneic cytotoxic assay and tested for its ability to detect endogenous mouse LIGHT.

RESULTS

We provide evidence for the first time that in mice, as previously described in humans, LIGHT protein is rapidly and transiently expressed after T-cell activation, and this expression was stronger on CD8 T cells than on CD4 T cells. Two anti-LIGHT antibodies prevented interactions of mouse LIGHT with its two known receptors, herpesvirus entry mediator and lymphotoxin β receptor. In vivo administration of anti-LIGHT antibody (clone 10F12) ameliorated host antidonor short-term cytotoxic response in wild type B6 mice, although to a lesser extent than that observed in LIGHT-deficient mice.

CONCLUSION

The therapeutic targeting of LIGHT may contribute to achieve a better control of cytotoxic responses refractory to current immunosuppressive drugs in transplantation.

The tumor necrosis factor family member TNFSF14 (LIGHT) is required for resolution of intestinal inflammation in mice

BACKGROUND & AIMS

The pathogenesis of inflammatory bowel disease (IBD) is associated with a dysregulated mucosal immune response. Expression of the tumor necrosis factor (TNF) superfamily member 14 (TNFSF14, also known as LIGHT [homologous to lymphotoxins, exhibits inducible expression, and competes with HSV glycoprotein D for HVEM, a receptor expressed by T lymphocytes]) on T cells is involved in their activation; transgenic expression of LIGHT on T cells in mice promotes inflammation in multiple organs, including intestine. We investigated the roles for LIGHT in recovery from intestinal inflammation in mice.

METHODS

We studied the role of LIGHT in intestinal inflammation using Tnfsf14(-/-) and wild-type mice. Colitis was induced by transfer of CD4(+)CD45RB(high) T cells into Rag1(-/-) or Tnfsf14(-/-)Rag1(-/-) mice, or by administration of dextran sulfate sodium to Tnfsf14(-/-) or wild-type C57BL/6J mice. Mice were weighed, colon tissues were collected and measured, and histology analyses were performed. We measured infiltrating cell populations and expression of cytokines, chemokines, and LIGHT.

RESULTS

After administration of dextran sulfate sodium, Tnfsf14(-/-) mice developed more severe colitis than controls, based on their reduced survival, accelerated loss of body weight, and histologic scores. LIGHT protected mice from colitis via the lymphotoxin β receptor and was expressed mainly by myeloid cells in the colon. Colons of Tnfsf14(-/-) mice also had increased accumulation of innate immune cells and higher levels of cytokines than colons from control mice. LIGHT, therefore, appears to regulate inflammation in the colon.

CONCLUSIONS

Tnfsf14(-/-) mice develop more severe colitis than control mice. LIGHT signals through the lymphotoxin β receptor in the colon to regulate the innate immune response and mediate recovery from intestinal inflammation.

HVEM gene polymorphisms are associated with sporadic breast cancer in Chinese women

As a costimulatory molecule, Herpesvirus entry mediator (HVEM) can bind with several costimulatory members, thus HVEM plays different roles in T cell immunity. HVEM and its ligands have been involved in the pathogenesis of various autoimmune, inflammatory diseases and tumors. In the current study, we conducted a case-control study comparing polymorphisms of HVEM and breast cancer. Subjects included 575 females with breast cancer and 604 age-matched healthy controls. Six HVEM SNPs (rs2281852, rs1886730, rs2234163, rs11573979, rs2234165, and rs2234167) were genotyped by PCR-RFLP. The results showed significant differences in genotypes and alleles between rs1886730 and rs2234167 (P<0.05). One haplotype (CTGCGG) that was associated with breast cancer was found via haplotype analysis. Our research also indicated an association between polymorphisms of HVEM and clinicopathologic features, including lymph node metastasis, estrogen receptor, progesterone receptor and P53. Our results primarily indicate that polymorphisms of the HVEM gene were associated with the risk of sporadic breast cancer in northeast Chinese females.

Changes of the cytokine profile in inflammatory bowel diseases

Cytokines are indispensable signals of the mucosa-associated immune system for maintaining normal gut homeostasis. An imbalance of their profile in favour of inflammation initiation may lead to disease states, such as that is observed in inflammatory bowel diseases (IBD). Although Crohn's disease (CD) is often described as a prototype of T-helper 1-type diseases, and ulcerative colitis (UC) is traditionally viewed as a T-helper 2-mediated condition, the classic paradigm, which categorises cytokines into pro- and anti-inflammatory groups, has recently been changed. The inflammation regulatory pathways may not be mutually exclusive as individual cytokines can have diverse and even opposing functions in various clinical and immunological settings. None the less there are many common immunological responses in IBD that are mediated by cytokines. Although they regulate and influence the development, course and recurrence of the inflammatory process, the concrete pathogenic role of these small signaling molecules is sometimes not unambiguous in the subtypes of the disease. Our aim is to review the current information about pro- and anti-inflammatory effects of traditionally studied and recently discovered cytokines in the pathogenesis of UC and CD. The better understanding of their production and functional activity may lead to the development of new therapeutic modalities.

A decoy receptor 3 analogue reduces localised defects in phagocyte function in pneumococcal pneumonia

Background

Therapeutic strategies to modulate the host response to bacterial pneumonia are needed to improve outcomes during community-acquired pneumonia. This study used mice with impaired Fas signalling to examine susceptibility to pneumococcal pneumonia and decoy receptor 3 analogue (DcR3-a) to correct factors associated with increased susceptibility.

Methods

Wild-type mice and those with varying degrees of impairment of Fas (lpr) or Fas ligand signalling (gld) were challenged with Streptococcus pneumoniae and microbiological and immunological outcomes measured in the presence or absence of DcR3-a.

Results

During established pneumonia, neutrophils became the predominant cell in the airway and gld mice were less able to clear bacteria from the lungs, demonstrating localised impairment of pulmonary neutrophil function in comparison to lpr or wild-type mice. T-cells from gld mice had enhanced activation and reduced apoptosis in comparison to wild-type and lpr mice during established pneumonia. Treatment with DcR3-a reduced T-cell activation and corrected the defect in pulmonary bacterial clearance in gld mice.

Conclusions

The results suggest that imbalance in tumour necrosis factor superfamily signalling and excessive T-cell activation can impair bacterial clearance in the lung but that DcR3-a treatment can reduce T-cell activation, restore optimal pulmonary neutrophil function and enhance bacterial clearance during S pneumoniae infection.

The signaling networks of the herpesvirus entry mediator (TNFRSF14) in immune regulation

The tumor necrosis factor (TNF) receptor superfamily member herpesvirus entry mediator (HVEM) (TNFRSF14) regulates T-cell immune responses by activating both inflammatory and inhibitory signaling pathways. HVEM acts as both a receptor for the canonical TNF-related ligands, LIGHT [lymphotoxin-like, exhibits inducible expression, and competes with herpes simplex virus glycoprotein D for HVEM, a receptor expressed on T lymphocytes] and lymphotoxin-α, and as a ligand for the immunoglobulin superfamily proteins BTLA (B and T lymphocyte attenuator) and CD160, a feature distinguishing HVEM from other immune regulatory molecules. The ability of HVEM to interact with multiple ligands in distinct configurations creates a functionally diverse set of intrinsic and bidirectional signaling pathways that control both inflammatory and inhibitory responses. The HVEM system is integrated into the larger LTβR and TNFR network through extensive shared ligand and receptor usage. Experimental mouse models and human diseases indicate that dysregulation of HVEM network may contribute to autoimmune pathogenesis, making it an attractive target for drug intervention.

HVEM signalling promotes colitis

BACKGROUND

Tumor necrosis factor super family (TNFSF) members regulate important processes involved in cell proliferation, survival and differentiation and are therefore crucial for the balance between homeostasis and inflammatory responses. Several members of the TNFSF are closely associated with inflammatory bowel disease (IBD). Thus, they represent interesting new targets for therapeutic treatment of IBD.

METHODOLOGY/PRINCIPAL FINDINGS

We have used mice deficient in TNFSF member HVEM in experimental models of IBD to investigate its role in the disease process. Two models of IBD were employed: i) chemical-induced colitis primarily mediated by innate immune cells; and ii) colitis initiated by CD4(+)CD45RB(high) T cells following their transfer into immuno-deficient RAG1(-/-) hosts. In both models of disease the absence of HVEM resulted in a significant reduction in colitis and inflammatory cytokine production.

CONCLUSIONS

These data show that HVEM stimulatory signals promote experimental colitis driven by innate or adaptive immune cells.

CD161 DEFINES EFFECTOR T CELLS THAT EXPRESS LIGHT AND RESPOND TO TL1A-DR3 SIGNALING

Expression of NK cell markers identifies pro-inflammatory T cell subsets in the liver and intestinal immune compartments. Specifically, CD161 is expressed on Th17 cells which play an important role in the regulation of mucosal inflammation. In this study, we characterized human peripheral blood CD161+ T cells as an effector population partially resembling a gut T cell phenotype. CD161+ CD4+ T cells express the gut-associated TNF family member, LIGHT, and respond to crosslinking of DR3, a receptor to another gut-associated cytokine, TL1A. Robust IFN-γ production in response to DR3 signaling correlated with enhanced expression of surface DR3 on CD161+ T cells and co-stimulation with IL12 and IL18. CD161+ T cell effector function was directly demonstrated by activation of responder monocytes in co-culture leading to CD40 upregulation and CD14 downregulation. CD161+ T cells reciprocally responded to activated monocytes, inducing expression of activation marker, CD69, and production of IL2 and IFN-γ, further demonstrating effective CD161+ T cell cross-talk with monocytes. Finally, CD161 defined a subset of T cells that co-express CD56, a second NK marker. Our findings implicate human CD161+ T cells in gut-associated signaling mechanisms, and suggest a monocyte mediated effector function in mucosal inflammation.

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.

Neutralization of LIGHT ameliorates acute dextran sodium sulphate-induced intestinal inflammation

Emerging data indicate that alterations in the expression of tumour necrosis factor (TNF) superfamily members play a crucial role in the pathogenesis of intestinal inflammation. Recent results demonstrated that sustained transgenic expression of lymphotoxin-like inducible protein that competes with glycoprotein D for binding herpesvirus entry mediator on T cells (LIGHT; TNFSF14) induced severe intestinal inflammation, suggesting a specific role of LIGHT-mediated signalling to the intestinal compartment. In order to dissect the role of LIGHT in intestinal inflammation, we used LIGHT-deficient mice in the mouse model of acute dextran sodium sulphate-induced colitis. Interestingly, LIGHT-deficient mice were characterized by strongly reduced signs of intestinal inflammation compared with wild-type mice in this experimental model. Determination of mouse LIGHT mRNA expression in colon tissues of wild-type mice revealed a strong induction of mouse LIGHT mRNA expression during acute DSS-induced colitis. We therefore generated anti-mouse LIGHT monoclonal antibodies in LIGHT-deficient mice which bind specifically to LIGHT and are capable of neutralizing the activity of LIGHT in vitro and in vivo. With these antibodies, we demonstrated that neutralization of LIGHT during acute DSS-induced colitis resulted in reduced signs of intestinal inflammation. These data suggest that LIGHT is an important mediator in intestinal inflammation and may serve as a new target for therapeutic intervention.

TNFSF14 coordinately enhances CXCL10 and CXCL11 productions from IFN-gamma-stimulated human gingival fibroblasts

TNFSF14 is involved in the pathogenesis of some inflammatory diseases such as arthritis. CXCL10 and CXCL11 recruit Th1 cells, and the productions of these chemokines are related to the exacerbation of some inflammatory diseases including arthritis and periodontal disease. We examined in vitro effects of TNFSF14 on IFN-gamma-induced CXCL10 and CXCL11 production in human gingival fibroblasts (HGFs). HGFs constitutively expressed TNFSF14 receptors, LTbetaR and HVEM. TNFSF14 enhanced IFN-gamma-induced secretion of CXCL10 and CXCL11 from HGFs. IFN-gamma treatment increased HVEM expression on HGFs. TNFSF14 in combination with IFN-gamma resulted in increased activation of p38 MAPK, ERK and IkappaB-alpha compared with TNFSF14 or IFN-gamma alone. Moreover, inhibitors of p38 MAPK, ERK and NF-kappaB abolished the CXCL10 and CXCL11 productions from TNFSF14 with IFN-gamma-stimulated HGFs. These effects of TNFSF14 may promote the infiltration of Th1 cells into lesions with inflammatory diseases. TNFSF14 might act as a proinflammatory cytokine in some inflammatory diseases thus is a candidate therapeutic target.

Depot-specific differences in inflammatory mediators and a role for NK cells and IFN-gamma in inflammation in human adipose tissue

BACKGROUND

Adipose tissue is a primary in vivo site of inflammation in obesity. Excess visceral adipose tissue (VAT), when compared to subcutaneous adipose tissue (SAT), imparts an increased risk of obesity-related comorbidities and mortality, and exhibits differences in inflammation. Defining depot-specific differences in inflammatory function may reveal underlying mechanisms of adipose-tissue-based inflammation.

METHODS

Stromovascular cell fractions (SVFs) from VAT and SAT from obese humans undergoing bariatric surgery were studied in an in vitro culture system with transcriptional profiling, flow cytometric phenotyping, enzyme-linked immunosorbent assay and intracellular cytokine staining.

RESULTS

Transcriptional profiling of SVF revealed differences in inflammatory transcript levels in VAT relative to SAT, including elevated interferon-gamma (IFN-gamma) transcript levels. VAT demonstrated a broad leukocytosis relative to SAT that included macrophages, T cells and natural killer (NK) cells. IFN-gamma induced a proinflammatory cytokine expression pattern in SVF and adipose tissue macrophages (ATM). NK cells, which constitutively expressed IFN-gamma, were present at higher frequency in VAT relative to SAT. Both T and NK cells from SVF expressed IFN-gamma on activation, which was associated with tumor necrosis factor-alpha expression in macrophages.

CONCLUSION

These data suggest involvement of NK cells and IFN-gamma in regulating ATM phenotype and function in human obesity and a potential mechanism for the adverse physiologic effects of VAT.

Targeting lymphocyte activation through the lymphotoxin and LIGHT pathways

SUMMARY

Cytokines mediate key communication pathways essential for regulation of immune responses. Full activation of antigen-responding lymphocytes requires cooperating signals from the tumor necrosis factor (TNF)-related cytokines and their specific receptors. LIGHT, a lymphotoxin-beta (LTbeta)-related TNF family member, modulates T-cell activation through two receptors, the herpesvirus entry mediator (HVEM) and indirectly through the LT-beta receptor. An unexpected finding revealed a non-canonical binding site on HVEM for the immunoglobulin superfamily member, B and T lymphocyte attenuator (BTLA), and an inhibitory signaling protein suppressing T-cell activation. Thus, HVEM can act as a molecular switch between proinflammatory and inhibitory signaling. The non-canonical HVEM-BTLA pathway also acts to counter LTbetaR signaling that promotes the proliferation of antigen-presenting dendritic cells (DCs) within lymphoid tissue microenvironments. These results indicate LTbeta receptor and HVEM-BTLA pathways form an integrated signaling circuit. Targeting these cytokine pathways with specific antagonists (antibody or decoy receptor) can alter lymphocyte differentiation and activation. Alternately, agonists directed at their cell surface receptors can restore homeostasis and potentially reset immune and inflammatory processes, which may be useful in treating autoimmune and infectious diseases and cancer.

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.

A crucial role for HVEM and BTLA in preventing intestinal inflammation

The interaction between the tumor necrosis factor (TNF) family member LIGHT and the TNF family receptor herpes virus entry mediator (HVEM) co-stimulates T cells and promotes inflammation. However, HVEM also triggers inhibitory signals by acting as a ligand that binds to B and T lymphocyte attenuator (BTLA), an immunoglobulin super family member. The contribution of HVEM interacting with these two binding partners in inflammatory processes remains unknown. In this study, we investigated the role of HVEM in the development of colitis induced by the transfer of CD4(+)CD45RB(high) T cells into recombination activating gene (Rag)(-/-) mice. Although the absence of HVEM on the donor T cells led to a slight decrease in pathogenesis, surprisingly, the absence of HVEM in the Rag(-/-) recipients led to the opposite effect, a dramatic acceleration of intestinal inflammation. Furthermore, the critical role of HVEM in preventing colitis acceleration mainly involved HVEM expression by radioresistant cells in the Rag(-/-) recipients interacting with BTLA. Our experiments emphasize the antiinflammatory role of HVEM and the importance of HVEM expression by innate immune cells in preventing runaway inflammation in the intestine.

Immunopathogenesis of inflammatory bowel disease

Crohn’s disease and ulcerative colitis are chronic relapsing immune mediated disorders that results from an aberrant response to gut luminal antigen in genetically susceptible host. The adaptive immune response that is then triggered was widely considered to be a T-helper-1 mediated condition in Crohn’s disease and T-helper-2 mediated condition in ulcerative colitis. Recent studies in animal models, genome wide association, and basic science has provided important insights in in the immunopathogenesis of inflammatory bowel disease, one of which was the characterization of the interleukin-23/Th-17 axis.

CD56 marks an effector T cell subset in the human intestine

T cells are key mediators of intestinal immunity, and specific T cell subsets can have differing immunoregulatory roles in animal models of mucosal inflammation. In this study, we describe human CD56+ T cells as a morphologically distinct population expressing a mature, nonproliferative phenotype that is frequent in the gut. Enhanced potential for IFN-gamma and TNF synthesis suggested a proinflammatory function, and we directly demonstrate effector function mediated by direct T-T interaction with responder cells in vitro. CD56+ T cells from peripheral blood responded to the gut-related CD2 signal, and were necessary for effective CD2-mediated proliferation of peripheral blood CD56- T cells. Our findings associate CD56+ T cells with the intestinal immune compartment and suggest a putative effector function in human mucosal immunity.

LIGHT signals directly to intestinal epithelia to cause barrier dysfunction via cytoskeletal and endocytic mechanisms

BACKGROUND & AIMS

LIGHT (lymphotoxin-like inducible protein that competes with glycoprotein D for herpes virus entry on T cells) is a tumor necrosis factor core family member that regulates T-cell activation and causes experimental inflammatory bowel disease. Additional data suggest that LIGHT may be involved in the pathogenesis of human inflammatory bowel disease. The aim of this study was to determine if LIGHT is capable of signaling directly to intestinal epithelia and to define the mechanisms and consequences of such signaling.

METHODS

The effects of LIGHT and interferon-gamma on barrier function, cytoskeletal regulation, and tight junction structure were assessed in mice and intestinal epithelial monolayers.

RESULTS

LIGHT induced barrier loss in cultured epithelia via myosin II regulatory light chain (MLC) phosphorylation; both barrier loss and MLC phosphorylation were reversed by MLC kinase (MLCK) inhibition. Pretreatment with interferon-gamma, which induced lymphotoxin beta receptor (LT beta R) expression, was required for these effects, and neither barrier dysfunction nor intestinal epithelial MLC phosphorylation occurred in LT beta R knockout mice. In cultured monolayers, endocytosis of the tight junction protein occludin correlated with barrier loss. Internalized occludin colocalized with caveolin-1. LIGHT-induced occludin endocytosis and barrier loss were both prevented by inhibition of caveolar endocytosis.

CONCLUSIONS

T cell-derived LIGHT activates intestinal epithelial LT beta R to disrupt barrier function. This requires MLCK activation and caveolar endocytosis. These data suggest a novel role for LIGHT in disease pathogenesis and suggest that inhibition of MLCK-dependent caveolar endocytosis may represent an approach to restoring barrier function in inflammatory bowel disease.

BAFF induces a hyper-IgA syndrome in the intestinal lamina propria concomitant with IgA deposition in the kidney independent of LIGHT

BAFF is a peripheral B cell survival factor and can mediate antibody (Ab) class switching. Over-expression of BAFF in mice results in B cell hyperplasia, elevated serum immunoglobulin (Ig), spontaneous germinal centre (GC) reactions and mild glomerulonephritis (GN). Here we show that, in addition to driving excessive levels of serum IgA, BAFF over-expression results in increased IgA levels within the intestinal lamina propria (LP) and deposition of IgA immune complexes in the renal glomerular mesangium. LIGHT has been previously shown to mediate a similar phenotype via signaling through the lymphotoxin-beta receptor (LTbetaR). We evaluated if LIGHT and BAFF cooperate in the etiology of a hyper-IgA syndrome in BAFF-overexpressing transgenic (BAFF-Tg) mice. We find that LIGHT-deficient BAFF-Tg mice exhibit similar levels of IgA in the serum, gut and kidney and develop nephritis to the same degree as LIGHT-sufficient BAFF-Tg mice. Therefore, in the context of BAFF over-expression, LIGHT is dispensable for the generation of a hyper-IgA syndrome accompanied by nephritis.

Restoring immune defenses via lymphotoxin signaling: lessons from cytomegalovirus

Although primary infection with human cytomegalovirus (HCMV), a beta-herpesvirus, is widespread and acquired early in life, it rarely causes disease in immune-competent individuals. However, in immune-compromised patients HCMV infection or reactivation invariably leads to serious disease, the effective treatment of which remains a difficult clinical problem. Current antiviral therapy is limited not only by toxicity but also by the continual emergence of drugresistant viruses. The limitations of these current therapeutics provides a strong impetus to develop novel approaches that will enhance the host's immune responsiveness while at the same time effectively controlling virus replication. Type I interferon (IFN) plays a critical role in initiating innate antiviral defenses and promoting adaptive responses and lymphotoxin (LT)-alphabeta has recently been identified as an essential effector cytokine regulating the induction of type I IFN during CMV infection. In particular, CMV infection of immune-compromised mice has revealed the immunotherapeutic potential of the lymphotoxin-beta receptor (LTbetaR) signaling pathway to restore immune function and provide protection from CMV mortality. In this review, we discuss the potential benefits and risks associated with LTbetaR-directed immunotherapy for CMV disease and other persistent viral infections.

Distinctive pattern of cytokine production and adhesion molecule expression in peripheral blood memory CD4+ T cells from patients with active Crohn's disease

An expansion of both circulating and intestinal lamina propria CD4+ CD45RO+ T cells has been described in patients with Crohn's disease. We studied both the cytokine profile and the expression of adhesion molecules on this T-cell subset. Peripheral blood CD4+ CD45RO+ T cells from patients with Crohn's disease (n=45) were assessed by flow cytometry and RT-PCR methods. The cytokine profile was also measured in intestinal lamina propria from seven patients. They were classified according to the CDAI and the results were compared with those of patients with ulcerative colitis (n=21) and noninflammatory intestinal conditions (n=15), and healthy controls (n=39). The mean percentage of circulating CD4+ CD45RO+ T cells producing intracellular TNF was higher in active than in inactive Crohn's disease patients (p < 0.001), active (p = 0.49) and inactive ulcerative colitis (p = 0.019), and healthy controls (p =0. 017). TNF expression correlated with CDAI (p < 0.001). An increased expression of intracellular IL-2, IL-6, and IL-10 in active Crohn's disease patients was also found. CD62L was downregulated in active Crohn's disease patients while no differences were observed in CD49d and CD11a expression. Lamina propria CD4+ CD45RO+ T cells from active Crohn's disease lesions showed an increased intracellular staining of TNF, IFN-gamma, and IL-10. Both peripheral and intestinal mucosa CD4+ CD45RO+ T cells from active Crohn's disease patients show an increased production of TNF. In addition, the circulating CD4+ CD45RO+ T-cell subset expresses a pattern of adhesion molecules that promotes homing to extranodal lymphoid tissues. This T-cell subset may play a relevant role in the immunopathogenesis of Crohn's disease.

Inhibition of Lymphotoxin-β Receptor–Mediated Cell Death by Survivin-ΔEx3

TNFSF14/LIGHT is a member of the tumor necrosis factor superfamily that binds to lymphotoxin-beta receptor (LTbetaR) to induce cell death via caspase-dependent and caspase-independent pathways. It has been shown that cellular inhibitor of apoptosis protein-1 inhibits cell death by binding to LTbetaR-TRAF2/TRAF3 complexes and caspases. In this study, we found that both Kaposi's sarcoma-associated herpesvirus K7 (KSHV-K7), a viral inhibitor of apoptosis protein, and the structurally related protein survivin-DeltaEx3 could inhibit LTbetaR-mediated caspase-3 activation. However, only survivin-DeltaEx3 could protect cells from LTbetaR-mediated cell death. The differential protective effects of survivin-DeltaEx3 and KSHV-K7 can be attributed to the fact that survivin-DeltaEx3, but not KSHV-K7, is able to maintain mitochondrial membrane potential and inhibit second mitochondria-derived activator of caspase/DIABLO release. Moreover, survivin-DeltaEx3 is able to inhibit production of reactive oxygen species and can translocate from nucleus to cytosol to associate with apoptosis signal-regulating kinase 1 after activation of LTbetaR. Furthermore, survivin-DeltaEx3 protects LTbetaR-mediated cell death in caspase-3-deficient MCF-7 cells. Thus, survivin-DeltaEx3 is able to regulate both caspase-dependent and caspase-independent pathways, whereas inhibition of caspase-independent pathway is both sufficient and necessary for its protective effect on LTbetaR-mediated cell death.

Defects in mucosal immunity leading to Crohn's disease

Crohn's disease (CD) is characterized by patchy transmural inflammation involving any part of the intestinal tract. Animal models have provided a great deal of insight into the pathogenesis of CD, but no animal model has recapitulated the full spectrum of manifestations witnessed in human disease. The defects in mucosal immunity in CD can be divided into those that involve the epithelial barrier, those that involve the innate immune response, and finally, defects in the adaptive immune response. Defects in the epithelial barrier in CD include an increase in intestinal permeability, increased adherence of bacteria, and decreased expression of defensins. Murine and human studies have demonstrated an increased expression of T-helper 1 (Th1) cytokines by lamina propria lymphocytes. This increased Th1 cytokine expression is driven by interleukin-12 (IL-12)/IL-23 and tumor necrosis factor-like 1A (TL1A) production by antigen-presenting cells, resulting in Tbet expression by CD4+ T cells. Another dimension of the inappropriate immune response in CD is T-cell and B-cell reactivity to luminal microbes. With the identification of the nucleotide-binding oligomerization domain 2 (NOD2) gene as a susceptibility gene, defects in the innate immune response are beginning to be explored. One may consider a model in which defective innate immune clearance of pathogens or commensal bacteria in CD leads to an inappropriate adaptive immune response to the commensal flora.

Network communications: lymphotoxins, LIGHT, and TNF

Lymphotoxins (LT) provide essential communication links between lymphocytes and the surrounding stromal and parenchymal cells and together with the two related cytokines, tumor necrosis factor (TNF) and LIGHT (LT-related inducible ligand that competes for glycoprotein D binding to herpesvirus entry mediator on T cells), form an integrated signaling network necessary for efficient innate and adaptive immune responses. Recent studies have identified signaling pathways that regulate several genes, including chemokines and interferons, which participate in the development and function of microenvironments in lymphoid tissue and host defense. Disruption of the LT/TNF/LIGHT network alleviates inflammation in certain autoimmune disease models, but decreases resistance to selected pathogens. Pharmacological disruption of this network in human autoimmune diseases such as rheumatoid arthritis alleviates inflammation in a significant number of patients, but not in other diseases, a finding that challenges our molecular paradigms of autoimmunity and perhaps will reveal novel roles for this network in pathogenesis.

LIGHT is involved in the pathogenesis of rheumatoid arthritis by inducing the expression of pro-inflammatory cytokines and MMP-9 in macrophages

Macrophages play a crucial role in the perpetuation of inflammation and irreversible cartilage damage during the development of rheumatoid arthritis (RA). LIGHT (TNFSF14) and its receptor TR2 (TNFRSF14) are known to have pro-inflammatory activities in foam cells of atherosclerotic plaques. We tested a hypothesis that LIGHT and TR2 are involved in activation of monocyte/macrophages in RA synovium. Immunohistochemical analysis of RA synovial tissue samples revealed that both LIGHT and TR2 are expressed in CD68 positive macrophages. In contrast, synovial tissue samples from osteoarthritis (OA) patients failed to reveal the expression of LIGHT. Expression of TR2 in RA synovial macrophages was also detected using flow cytometry analysis. To identify the role of LIGHT in the functioning of macrophages in RA, we isolated macrophage enriched cells from RA synovial fluid and stimulated them with LIGHT. LIGHT induced expression of matrix metalloproteinase-9 and pro-inflammatory cytokines such as tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and IL-8. These data indicate that LIGHT and TR2 expressed in macrophages are involved in the pathogenesis of RA by inducing the expression pro-inflammatory cytokines and matrix degrading enzymes.

LIGHT Is Constitutively Expressed on T and NK Cells in the Human Gut and Can Be Induced by CD2-Mediated Signaling

The TNF superfamily cytokine, lymphotoxin-like inducible protein that competes with glycoprotein D for binding herpesvirus entry mediator on T cells (LIGHT; TNFSF14), can augment T cell responses inducing IFN-gamma production and can drive pathological gut inflammation when expressed as a transgene in mouse T cells. LIGHT expression by human intestinal T cells suggests the possibility that LIGHT may play a key role in regulation of the mucosal immune system. A nonenzymatic method was developed for the isolation of T cells from the human lamina propria, permitting analysis of native cell surface protein expression. Cell surface LIGHT was constitutively expressed on mucosal T and NK cells and a subpopulation of gut-homing CD4(+) T cells in the periphery. In addition, CD2-mediated stimulation induced efficient LIGHT expression on intestinal CD4(+) T cells, but not on peripheral blood T cells, suggesting a gut-specific, Ag-independent mechanism for LIGHT induction. By contrast, herpesvirus entry mediator expression on gut T cells was unperturbed, implicating the transcriptional regulation of LIGHT as a mechanism modulating signaling activity in the gut. Quantitative analysis of LIGHT mRNA in a cohort of inflammatory bowel disease patients indicated elevated expression in biopsies from small bowel and from inflamed sites, implicating LIGHT as a mediator of mucosal inflammation.