LIGHT, a novel ligand for lymphotoxin beta receptor and TR2/HVEM induces apoptosis and suppresses in vivo tumor formation via gene transfer

Targeting lymphotoxin beta receptor with tumor-specific T lymphocytes for tumor regression

PURPOSE

One of the impediments of immunotherapy against cancer is the suppression of tumor-specific CTLs in the tumor microenvironment, partly due to the selective inhibition of the perforin pathway and the emergence of Fas-resistant tumors. Therefore, we sought to identify perforin- and Fas-independent cytotoxic pathways and explored the potential of targeting LTbetaR with tumor-specific CTLs to induce tumor rejection in vivo.

EXPERIMENTAL DESIGN

Fas-resistant tumors were examined for their susceptibility to perforin-deficient (pfp) CTLs via CTL adoptive transfer in mouse models of experimental lung metastasis. The specificity of LTbetaR, a cell surface death receptor, in causing tumor rejection by CTLs was analyzed by LTbetaR-specific neutralizing monoclonal antibody in vitro. The specificity and efficacy of LTbetaR in the suppression of established tumors was further investigated by silencing LTbetaR in tumor cells in vivo.

RESULTS

pfp CTLs exhibited significant cytotoxicity against Fas-resistant tumors in vivo. The perforin- and Fas-independent cytotoxicity was directly mediated, at least in part, by the adoptively transferred CTLs. It was observed that LTbetaR was expressed on the tumor cell surface, and LTalpha, LTbeta, and LIGHT, all of which are ligands for LTbetaR, were either constitutively expressed or activated in the tumor-specific CTLs and primary CD8(+) T cells. Blocking LTbetaR with LTbetaR-specific neutralizing monoclonal antibody decreased CTL cytotoxicity in vitro. Silencing LTbetaR using LTbetaR-specific short hairpin RNA reduced the ability of pfp CTLs to induce tumor rejection in vivo.

CONCLUSION

LTbetaR directly mediates CTL-directed tumor rejection in vivo. Targeting LTbetaR with tumor-specific CTLs is a potential therapeutic approach.

A New Class of Reverse Signaling Costimulators Belongs to the TNF Family

Recent evidence shows that many molecules of the TNF family serve as counter-receptors, inducing costimulation through reverse signals in addition to delivering signals through their respective TNF receptors. In this review, we will discuss this new class of costimulators with a focus on the mechanism of costimulation transduced by reverse signaling through Fas ligand.

LIGHT--a new member of the TNF superfamily in the plasma, dialysate and urine of uremic patients; the impact of residual diuresis and presence of viral hepatitis

OBJECTIVES

LIGHT is a cytokine involved in atherosclerosis and cardiovascular disease in general population.

DESIGN AND METHODS

We determined the levels of LIGHT in the plasma, dialysate and urine of uremic patients undergoing hemodialysis (HD) and healthy controls.

RESULTS

There were no significant differences in the pre and post-HD plasma levels of LIGHT between HD patients with residual diuresis (HD-RD) and HD anuric group (HD-A) compared to controls. HD-RD patients had the lower LIGHT values in dialysate compared to HD-A patients (p<0.001), and higher urinary LIGHT excretion compared to controls (p<0.05). Moreover, the presence of RD and chronic viral hepatitis were independent factors influencing the levels of this cytokine in dialysate.

CONCLUSIONS

The plasma levels of LIGHT seem to be similar in HD patients and healthy subjects and were not affected by gender, age, the mean period of HD history, disease etiology, type of medication and type of using dialysis membrane.

Targeting the primary tumor to generate CTL for the effective eradication of spontaneous metastases

Metastatic disease is the major cause of morbidity and mortality in cancer. Although surgery, chemotherapy, or radiation can often control primary tumor growth, successful eradication of disseminated metastases remains rare. We have now tested whether direct targeting tumor tissues to generate antitumor immune response before surgical excision produces sufficient CTL against micrometastases. One unsolved problem is whether such response allows coming CTL to be educated and then exit the tumor site. Another unsolved problem is whether these CTL can then patrol and effectively eliminate spontaneously metastasized tumor cells in the periphery. In this study, we have shown that adenovirus-expressing TNFSF14 [LIGHT (name derived from homologous to lymphotoxins, shows inducible expression, and competes with herpes simplex virus glycoprotein D for herpes virus entry mediator, a receptor expressed by T lymphocytes); Ad-LIGHT] inoculated directly into primary 4T1 tumor, a highly aggressive, spontaneously metastasizing mammary carcinoma, followed by surgical removal of the primary tumor can eradicate established and disseminated metastatic tumor cells in the peripheral tissues. Furthermore, we clearly show with a fibrosarcoma model Ag104L(d) that local treatment can generate plenty of tumor-specific CTL that exit the primary tumor and infiltrate distal tumors to completely eradicate distal tumors. Therefore, targeting the primary tumor with Ad-LIGHT before surgical excision is a new strategy to elicit better immune response for the eradication of spontaneous metastases.

LIGHT, a member of the TNF superfamily, activates Stat3 mediated by NIK pathway

Stat3, a member of the signal transducers and activators of transcription (STAT) family, is a key signal transduction protein activated by numerous cytokines, growth factors, and oncoproteins that controls cell proliferation, differentiation, development, survival, and inflammation. Constitutive activation of Stat3 has been found frequently in a wide variety of human tumors and induces cellular transformation and tumor formation. In this study, we demonstrated that LIGHT, a member of tumor necrosis factor superfamily, activates Stat3 in cancer cells. LIGHT induces dose-dependent activation of Stat3 by phosphorylation at both the tyrosine 705 and serine 727 residues. The activation of Stat3 by LIGHT appears to be mediated by NIK phosphorylation. Expression of a kinase-inactive NIK mutant abolished LIGHT induced Stat3 activation. Overexpression of an active NIK induces Stat3 activation by phosphorylation at the both tyrosine 705 and serine 727 residues. Activation of Stat3 by NIK requires NIK kinase activity as showed by kinase assays. In addition, LIGHT increases the expression of Stat3 target genes including cyclin D1, survivin, and Bcl-xL, and stimulates human LNCaP prostate cancer cell growth in vitro which can be blocked by expression of a dominant-negative Stat3 mutant. Taken together, these results indicate that in addition to activating NF-kappaB/p52, LIGHT also activates Stat3. Activation of Stat3 together with activating non-canonical NF-kappaB/p52 signaling by LIGHT may maximize its effects on cellular proliferation, survival, and inflammation.

LIGHT up-regulated on B lymphocytes and monocytes in rheumatoid arthritis mediates cellular adhesion and metalloproteinase production by synoviocytes

OBJECTIVE

To study the expression of LIGHT (tumor necrosis factor superfamily 14) and herpesvirus entry mediator (HVEM; tumor necrosis factor receptor superfamily 14) in rheumatoid arthritis (RA) and to determine the regulatory role of LIGHT on the effector functions of fibroblast-like synoviocytes (FLS).

METHODS

The expression of LIGHT and HVEM was assessed by immunohistochemical staining of synovial tissue and by flow cytometric analysis of mononuclear cells. The presence of HVEM and lymphotoxin beta receptor was measured by reverse transcriptase-polymerase chain reaction and by flow cytometry. The regulation of effector molecules, including matrix metalloproteinases (MMPs) and adhesion molecules, was evaluated. The adhesiveness of FLS was determined by adhesion assay.

RESULTS

HVEM was detected in most cell types within rheumatoid synovial tissue, while only a few cells were positive for LIGHT. In RA patients, LIGHT expression was significantly up-regulated only in CD20+ B cells and monocytes, whereas the mean fluorescence intensity of HVEM was down-regulated in mononuclear cells. The stimulation of FLS with LIGHT resulted in the production of MMPs and the expression of adhesion molecules, which were efficiently inhibited by dexamethasone. LIGHT-mediated up-regulation of MMPs and intercellular adhesion molecule 1 was blocked by inhibitors of NF-kappaB and JNK, whereas up-regulation of vascular cell adhesion molecule 1 was blocked by inhibitors of phosphatidylinositol 3-kinase, as well as NF-kappaB.

CONCLUSION

These data suggest that binding of LIGHT with its receptors may play a role in the progression of inflammation within rheumatoid synovium, especially by mediating the interactions between infiltrating inflammatory cells and stromal cells. These findings thus emphasize the relevance of LIGHT as a potential therapeutic target in RA.

Tumor-specific T cells signal tumor destruction via the lymphotoxin beta receptor

Background

Previously, we reported that adoptively transferred perforin k/o (PKO), and IFN-γ k/o (GKO), or perforin/IFN-γ double k/o (PKO/GKO) effector T cells mediated regression of B16BL6-D5 (D5) pulmonary metastases and showed that TNF receptor signaling played a critical role in mediating tumor regression. In this report we investigated the role of lymphotoxin-α (LT-α) as a potential effector molecules of tumor-specific effector T cells.

Methods

Effector T cells were generated from tumor vaccine-draining lymph node (TVDLN) of wt, GKO, LT-α deficient (LKO), or PKO/GKO mice and tested for their ability to mediate regression of D5 pulmonary metastases in the presence or absence of LT-βR-Fc fusion protein or anti-IFN-γ antibody. Chemokine production by D5 tumor cells was determined by ELISA, RT-PCR and Chemotaxis assays.

Results

Stimulated effector T cells from wt, GKO, or PKO/GKO mice expressed ligands for LT-β receptor (LT-βR). D5 tumor cells were found to constitutively express the LT-βR. Administration of LT-βR-Fc fusion protein completely abrogated the therapeutic efficacy of GKO or PKO/GKO but not wt effector T cells (p < 0.05). Consistent with this observation, therapeutic efficacy of effector T cells deficient in LT-α, was greatly reduced when IFN-γ production was neutralized. While recombinant LT-α1β2 did not induce apoptosis of D5 tumor cells in vitro, it induced secretion of chemokines by D5 that promoted migration of macrophages.

Conclusion

The contribution of LT-α expression by effector T cells to anti-tumor activity in vivo was not discernable when wt effector T cells were studied. However, the contribution of LT-β R signaling was identified for GKO or PKO/GKO effector T cells. Since LT-α does not directly induce killing of D5 tumor cells in vitro, but does stimulate D5 tumor cells to secrete chemokines, these data suggest a model where LT-α expression by tumor-specific effector T cells interacts via cross-linking of the LT-βR on tumor cells to induce secretion of chemokines that are chemotactic for macrophages. While the contribution of macrophages to tumor elimination in our system requires additional study, this model provides a possible explanation for the infiltration of inate effector cells that is seen coincident with tumor regression.

Signaling pathways of LIGHT induced macrophage migration and vascular smooth muscle cell proliferation

The biological actions of LIGHT, a member of the tumor necrosis factor superfamily, are mediated by the interaction with lymphotoxin-beta receptor (LTbetaR) and/or herpes virus entry mediator (HVEM). Previous study demonstrated high-level expressions of LIGHT and HVEM receptors in atherosclerotic plaques. To investigate the role of LIGHT in the functioning of macrophages and vascular smooth muscle cells (VSMC) in relation to atherogenesis, we determined the effects of LIGHT on macrophage migration and VSMC proliferation. We found LIGHT through HVEM activation can induce both events. LIGHT-induced macrophage migration was associated with activation of signaling kinases, including MAPKs, PI3K/Akt, NF-kappaB, Src members, and FAK. Proliferation of VSMC was also shown relating to the activation of MAPKs, PI3K/Akt, and NF-kappaB, which consequently led to alter the expression of cell cycle regulatory molecules. Down-regulation of p21, p27, and p53, and inversely up-regulation of cyclin D and RB hyper-phosphorylation were demonstrated. In conclusion, LIGHT acts as a novel mediator for macrophage migration and VSMC proliferation, suggesting its involvement in the atherogenesis.

B and T lymphocyte attenuator regulates CD8+ T cell-intrinsic homeostasis and memory cell generation

B and T lymphocyte attenuator (BTLA) is a negative regulator of T cell activation, but its function in vivo is not well characterized. Here we show that mice deficient in full-length BTLA or its ligand, herpesvirus entry mediator, had increased number of memory CD8(+) T cells. The memory CD8(+) T cell phenotype resulted from a T cell-intrinsic perturbation of the CD8(+) T cell pool. Naive BTLA-deficient CD8(+) T cells were more efficient than wild-type cells at generating memory in a competitive antigen-specific system. This effect was independent of the initial expansion of the responding antigen-specific T cell population. In addition, BTLA negatively regulated antigen-independent homeostatic expansion of CD4(+) and CD8(+) T cells. These results emphasize two central functions of BTLA in limiting T cell activity in vivo.

Herpes virus entry mediator synergizes with Toll-like receptor mediated neutrophil inflammatory responses

In microbial infections polymorphnuclear neutrophils (PMN) constitute a major part of the innate host defence, based upon their ability to rapidly accumulate in inflamed tissues and clear the site of infection from microbial pathogens by their potent effector mechanisms. The recently described transmembrane receptor herpes virus entry mediator (HVEM) is a member of the tumour necrosis factor receptor super family and is expressed on many haematopoietic cells, including T cells, B cells, natural killer cells, monocytes and PMN. Interaction of HVEM with the natural ligand LIGHT on T cells has a costimulatory effect, and increases the bactericidal activity of PMN. To further characterize the function of HVEM on PMN, we evaluated the effect of receptor ligation on human PMN effector functions using an agonistic monoclonal antibody. Here we demonstrate that activation of HVEM causes activation of neutrophil effector functions, including respiratory burst, degranulation and release of interleukin-8 in synergy with ligands for Toll-like receptors or GM-CSF. In addition, stimulation via HVEM enhanced neutrophil phagocytic activity of complement opsonized, but not of non-opsonized, particles. In conclusion, these results indicate a new, as yet unknown, participation of HVEM in the innate immune response and points to a new link between innate and adaptive immunity.

Induction of potent anti-tumor immunity by direct injection of Ad-LIGHT at the site of tumor inoculation

BACKGROUND

The aim of this study was to observe the therapeutic effects of adenovirus-mediated LIGHT gene transfer in murine B16 melanoma in vivo.

METHODS

C57BL/6 mice were inoculated subcutaneously with B16 cells to establish the murine melanoma model. The tumor-bearing mice were injected at the site of tumor inoculation with recombinant adenoviral vectors expressing the murine LIGHT gene. The tumor growth and survival period of tumor-bearing mice were observed. The splenic NK and CTL activity were measured in vitro by lactate dehydrogenase (LDH) release assay. The amounts of cytokines were determined with ELISA kits.

RESULTS

The LIGHT gene could be efficiently transduced into tumor tissue after injection of Ad-LIGHT. Treatment with Ad-LIGHT significantly inhibited the tumor growth and prolonged the survival period of the tumor-bearing mice. The splenic NK and CTL activity of the mice was also enhanced after LIGHT gene transfer. The production of IL-2 and IFN-gamma from lymphocytes derived from mice treated with Ad-LIGHT was increased significantly compared with control groups.

DISCUSSION

Our results indicate that local expression of the LIGHT gene can induce potent anti-tumor immunity and may be a promising treatment strategy for melanoma.

Lymphtoxin beta receptor-Ig protects from T-cell-mediated liver injury in mice through blocking LIGHT/HVEM signaling

LIGHT is a member of the TNF superfamily, which is transiently expressed on the surface of activated T lymphocytes and immature dendritic cells. Its known receptors are herpesvirus entry mediator (HVEM) prominently in T lymphocytes, and lymphtoxin beta receptor (LTbetaR) in stromal cells or nonlymphoid hematopoietic cells. Previous studies have shown that overexpression of LIGHT on T cells could lead to autoimmune reaction including lymphocytes activation, inflammation, and tissue destruction. To address the role of LIGHT/HVEM signaling in autoimmune hepatitis, an experimental colitis model induced by intravenous administration of concanavalin A (ConA) was given a soluble LTbetaR-Ig fusion protein as a competitive inhibitor of LIGHT/HVEM pathway. Marked elevation of LIGHT expression was detected in isolate intrahepatic leukocytes (IHLs) of the experimental animal. Treatment with LTbetaR-Ig significantly attenuated the progression and histological manifestations of the hepatic inflammation and reduced the production of inflammatory cytokines including TNF-alpha, IFN-gamma. Moreover, LTbetaR-Ig treatment significantly down-regulated LIGHT expression, leading to reduced lymphocytes (particularly CD4+ T cells), infiltrating into the hepatic inflammation and inhibited NF-kappaB activation and expression. We postulated that blockade of LIGHT/HVEM signaling by LTbetaR-Ig may ameliorate hepatitis by down-regulating LIGHT expression, and therefore we envision that LTbetaR-Ig would prove to a promising strategy for the clinical treatment of human autoimmune hepatitis.

Balancing co-stimulation and inhibition with BTLA and HVEM

The interaction between B- and T-lymphocyte attenuator (BTLA), an inhibitory receptor whose extracellular domain belongs to the immunoglobulin superfamily, and herpesvirus-entry mediator (HVEM), a co-stimulatory tumour-necrosis factor receptor, is unique in that it is the only receptor-ligand interaction that directly bridges these two families of receptors. This interaction has raised many questions about how receptors from two different families could interact and what downstream signalling events might occur as a result of receptor ligation. As we discuss, recent studies show that engagement of HVEM with its endogenous ligand (LIGHT) from the tumour-necrosis factor family induces a powerful immune response, whereas HVEM interactions with BTLA negatively regulate T-cell responses.

RP101 improves the efficacy of chemotherapy in pancreas carcinoma cell lines and pancreatic cancer patients

RP101 [(E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU)], which supports apoptosis and prevents the acquisition of chemoresistance, was tested in cultured human pancreatic tumor cells. RP101 downregulated uridine phosphorylase, a marker of poor prognosis, and APEX1, which is involved in DNA repair, and repressed Stat3 and its target vascular endothelial growth factor. Furthermore, RP101 activated antitumor immunity as demonstrated by enhanced cytolytic activity of NK-92 natural killer cells. This was concomitant with an enhanced expression of lymphotoxins alpha and beta, natural killer cell transcript 4, tumor necrosis factor LIGHT/TNFSF-14, and intercellular adhesion molecule-1 in pancreas carcinoma cells. These results encouraged us to investigate the effect of RP101 in pancreas cancer patients. Here, we present data from two RP101 combination therapy schemes. In a first pilot study, 13 patients in stage III and VI of the disease were treated with gemcitabine +cisplatin+RP101. RP101 co-treatment enhanced remissions, survival and time to progression. Seventy-seven percent of the patients lived or have lived longer than 1 year, and 23% have lived more than 2 years. Median survival was 447 days, time to progression 280 days and the response rate 33%. A second study with 21 patients in similar stages of disease, treated with RP101+gemcitabine alone, confirmed the results of the pilot study. Eighty-three percent of the presently evaluable patients live or lived 0.5 years or longer and 33% 1 year or longer. Considering both studies, the tumor control was 94%. The data indicate that acquisition of chemoresistance was prevented and the antitumor efficacy of standard chemotherapy was improved. To our knowledge, RP101 co-treatment is more efficient than any other regimen published.

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.

LIGHT (TNFSF14), a novel mediator of bone resorption, is elevated in rheumatoid arthritis

OBJECTIVE

Human osteoclast formation from mononuclear phagocyte precursors involves interactions between tumor necrosis factor (TNF) ligand superfamily members and their receptors. LIGHT is a transmembrane protein expressed and shed from the surface of activated T cells. Since activated T cells have been implicated in osteoclastogenesis in rheumatoid arthritis (RA), this study sought to determine whether LIGHT can regulate RANKL/cytokine-induced osteoclast formation, to identify the mechanism by which LIGHT influences osteoclastogenesis, and to investigate the presence of LIGHT in the serum of RA patients.

METHODS

The effect of LIGHT on human and murine osteoclast formation was assessed in the presence and absence of neutralizing reagents to known osteoclastogenic factors. Serum levels of LIGHT in RA patients were measured by enzyme-linked immunosorbent assay.

RESULTS

In the presence and absence of RANKL, LIGHT induced osteoclast formation from both human peripheral blood mononuclear cells and murine macrophage precursors, in a dose-dependent manner, whereas no inhibition was observed by adding osteoprotegerin, RANK:Fc, TNFalpha, or interleukin-8 or by blocking the LIGHT receptors herpesvirus entry mediator or lymphotoxin beta receptor. However, formation of osteoclasts was significantly decreased by the soluble decoy receptor for LIGHT, DcR3, and by blocking antibodies to the p75 component of the TNF receptor. A significant increase in LIGHT levels in the serum of RA patients compared with normal controls was also noted.

CONCLUSION

Our results indicate that LIGHT promotes RANKL-mediated osteoclastogenesis and that it can induce osteoclast formation by a mechanism independent of RANKL. The increased concentration of LIGHT in patients with RA raises the possibility that LIGHT may play a role in immunopathogenic conditions that are associated with localized or systemic bone loss.

T Cell Costimulation in the Development of Cardiac Allograft Vasculopathy

Cardiac allograft vasculopathy (CAV) is a form of coronary arterial stenosis and a leading cause of death in patients who survive beyond the first year after heart transplantation. Histopathologically, this lesion is concentric diffuse intimal hyperplasia of the arterial wall that is accompanied by extensive infiltration of inflammatory cells, including T cells. Many studies have explored the potential risk factors related to this arterial lesion and its pathogenesis. Continuous minor endothelial cell damage evokes inflammatory processes including T cell activation. Costimulatory molecules play crucial roles in this T cell activation. Many costimulatory pathways have been described, and some are involved in the pathogenesis of CAV, atherogenesis, and subsequent plaque formation. In this review, we summarize the present knowledge of the role of these pathways in CAV development and the possibility of manipulating these pathways as a means to treat heart allograft vascular disease and atherosclerosis.

Expression and function of the B and T lymphocyte attenuator (BTLA/CD272) on human T cells

Co-signal receptors provide crucial activating or attenuating signals for T cells. The B and T lymphocyte attenuator (BTLA/CD272) is a third member of co-inhibitory receptors, which belongs to the CD28 immunoglobulin-superfamily. Using monoclonal antibodies (mAbs) against human BTLA, we show that BTLA is constitutively expressed on most CD4+ and CD8+ T cells and its expression progressively decreases upon T cell activation. Polarized Th1 and Th2 cells contained both BTLA-positive and BTLA-negative populations, but the extended culture diminished BTLA expression. Cross-linking BTLA with an agonistic mAb inhibited T cell proliferation and the production of the cytokines IFN-gamma and IL-10 in response to anti-CD3 stimulation. BTLA-mediated inhibition of T cell activation occurred during both primary CD4+ T cell responses and secondary CD4+ and CD8+ T cell responses, suggesting that BTLA ligation sends a constitutive "off" signal to T cells and thus might play an important role in the maintenance of T cell tolerance.

Essential role of TNF family molecule LIGHT as a cytokine in the pathogenesis of hepatitis

LIGHT is an important costimulatory molecule for T cell immunity. Recent studies have further implicated its role in innate immunity and inflammatory diseases, but its cellular and molecular mechanisms remain elusive. We report here that LIGHT is upregulated and functions as a proinflammatory cytokine in 2 independent experimental hepatitis models, induced by concanavalin A and Listeria monocytogenes. Molecular mutagenesis studies suggest that soluble LIGHT protein produced by cleavage from the cell membrane plays an important role in this effect through the interaction with the lymphotoxin-beta receptor (LTbetaR) but not herpes virus entry mediator. NK1.1+ T cells contribute to the production, but not the cleavage or effector functions, of soluble LIGHT. Importantly, treatment with a mAb that specifically interferes with the LIGHT-LTbetaR interaction protects mice from lethal hepatitis. Our studies thus identify a what we believe to be a novel function of soluble LIGHT in vivo and offer a potential target for therapeutic interventions in hepatic inflammatory diseases.

LIGHT is dispensable for CD4+ and CD8+ T cell and antibody responses to influenza A virus in mice

The tumor necrosis factor family ligands, LIGHT (lymphotoxin like, exhibits inducible expression and competes with HSV glycoprotein D for HVEM, a receptor expressed by T lymphocytes), 4-1BBL and CD70, are found in the same gene cluster on mouse chromosome 17. Although the roles of 4-1BB-4-1BBL and CD27-CD70 interactions in anti-viral T cell responses have been well established, the role of LIGHT in T cell activation/expansion in vivo is less clear. Under conditions that were previously employed to demonstrate a role for 4-1BBL in CD8+ T cell memory, wild-type and LIGHT-/- mice were infected with influenza A virus and primary and memory/recall responses were measured at various time points thereafter. Neither primary expansion nor memory/recall CD8+ T cell responses were affected by the absence of LIGHT, as measured up to 2 months post-infection. CD4+ T cell responses were also unaffected by LIGHT deficiency. Furthermore, we found that LIGHT played no role in the induction of influenza-specific IgG1 and IgG2a serum antibodies. Taken together, these data suggest that LIGHT is dispensable for the acquired immune response to influenza virus in mice with no effect on the induction, maintenance or reactivation of CD8+ T cell memory.

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.

Tumor-infiltrating T lymphocytes: friends or foes?

The prognostic significance of tumor-infiltrating lymphocytes (TILs) has been a longstanding topic of debate. In cases where TILs have improved patient outcome, T lymphocytes are recognized as the main effectors of antitumor immune responses. However, recent studies have revealed that a subset of CD4(+) T cells, referred to as CD4(+)CD25(+) regulatory T cells (Treg), may accumulate in the tumor environment and suppress tumor-specific T-cell responses, thereby hindering tumor rejection. Hence, predicting tumor behavior on the basis of an indiscriminate evaluation of tumor-infiltrating T cells may result in inconsistent prognostic accuracy. The presence of infiltrating CD4(+)CD25(+) Treg may be detrimental to the host defense against the tumor, while the presence of effector T lymphocytes, including CD8(+) T cells and non-regulatory CD4(+) helper T cells may be beneficial. Enhanced recruitment of antitumor effector T lymphocytes to tumor tissue in addition to inhibition of local Treg, may therefore be an ideal target for improving cancer immunotherapy. This article reviews the antitumor functions of T-lymphocytes, with special attention given to CD4(+) regulatory T-cells within the tumor environment.

The role of stroma in immune recognition and destruction of well-established solid tumors

Well-established solid tumors (at least 14 days old and >1cm in average diameter) are extremely difficult to eradicate immunologically in mice. Most cancer patients that seek medical attention bear primary or metastatic tumors that have grown for longer and that are larger than the tumors we call established. Therefore, focusing research on the problems of rejecting well-established mouse tumors might help in the development of novel concepts and protocols for destroying tumors in patients. A particular problem with established cancers is that even when treatments induce temporary regression, cancer often recurs. Recent studies suggest that manipulation of the stromal microenvironment of these tumors can induce immune recognition and regression. Furthermore, targeting cancer cells as well as tumor stroma for immune destruction might be needed to prevent recurrence.

LIGHT regulates CD86 expression on dendritic cells through NF-kappaB, but not JNK/AP-1 signal transduction pathway

The members of the tumor necrosis factor (TNF) family play pivotal roles in the regulation of the immune system. LIGHT is a type II transmembrane protein belonging to the TNF family that was originally identified as a weak inducer of apoptosis. This cytokine has been extensively studied for its role in T cell regulation. Recently, we identified its role in inducing maturation of dendritic cells, such as LIGHT upregulated CD86 expression on dendritic cells in our previous report. However, the signal transduction pathway on this regulation remains unknown. In this study, we found that LIGHT activated NF-kappaB, p44/42 MAPK, but not JNK. LIGHT upregulates CD86 expression on DCs through activation of NF-kappaB, but not p44/42 signal pathway, because inhibition of NF-kappaB activity by its inhibitor could blunt the effect of LIGHT in up-regulation of CD86 expression, but neither inhibitor of p44/42 MAPK nor JNK inhibitor has this effect. Thus we demonstrate that LIGHT regulates CD86 expression through NF-kappaB signal transduction pathway but neither p44/42 MAPK nor JNK/AP-1 signaling pathway. We conclude that NF-kappaB signal plays a key role in LIGHT-mediated upregulation of CD86 expression.

BTLA and HVEM Cross Talk Regulates Inhibition and Costimulation

Recently a new inhibitory immunoglobulin domain-containing lymphocyte receptor was identified on the basis of its T helper 1 (T(H)1)-selective expression in murine T cell lines, which was named B and T lymphocyte attenuator (BTLA). Several groups have confirmed the initial characterization of BTLA as an inhibitory receptor, which was initially inferred from the mild increases in several parameters of BTLA-deficient mice. The initial expectation that BTLA would interact with a B7 family ligand, such as the B7x protein, was surprisingly overturned with the functional cloning of the actual BTLA ligand as herpesvirus entry mediator (HVEM). This was unexpected largely due to the fact that this interaction represents the convergence of two very different, although each quite extensive, families of receptors and ligands. The interaction of BTLA, which belongs to the CD28 family of the immunoglobulin superfamily, and HVEM, a costimulatory tumor-necrosis factor (TNF) receptor (TNFR), is quite unique in that it is the only receptor-ligand interaction that directly bridges these two families of receptors. This interaction has raised many questions about how receptors from two different families could interact and which are the signaling events downstream of receptor ligation. As we discuss here and recently demonstrated, HVEM interaction with BTLA serves to negatively regulate T cell responses, in contrast to the strong activation observed when HVEM engages its endogenous ligand from the TNF family. Finally, as studies of BTLA are just now beginning to extend beyond the initial characterizations, it is becoming clear that there are many complex issues remaining to be resolved, particularly potential polymorphisms that may engender disease susceptibility in the human.

Attenuation of Th1 response in decoy receptor 3 transgenic mice

The soluble decoy receptor 3 (DcR3) is a member of the TNFR superfamily. Because DcR3 is up-regulated in tumor tissues and is detectable in the sera of cancer patients, it is regarded as an immunosuppressor to down-regulate immune responses. To understand the function of DcR3 in vivo, we generated transgenic mice overexpressing DcR3 systemically. In comparison with HNT-TCR (HNT) transgenic mice, up-regulation of IL-4 and IL-10 and down-regulation of IFN-gamma, IL-12, and TNF-alpha were observed in the influenza hemagglutinin(126-138) peptide-stimulated splenocytes of HNT-DcR3 double-transgenic mice. When infected with Listeria monocytogenes, DcR3 transgenic mice show attenuated expression of IFN-gamma as well as increased susceptibility to infection. The Th2 cell-biased phenotype in DcR3 transgenic mice is attributed to decreased IL-2 secretion by T cells, resulting in the suppression of IL-2 dependent CD4(+) T cell proliferation. This suggests that DcR3 might help tumor growth by attenuating the Th1 response and suppressing cell-mediated immunity.

Preparation and characterization of a monoclonal antibody against the protein LIGHT

LIGHT (which is homologous to lymphotoxins, shows inducible expression, and competes with HSV glycoprotein D for HVEM, a receptor expressed by T lymphocytes [Genome Database designation, TNFSF14]), a newly identified member of the TNF superfamily, is up-regulated upon activation of T-cells. LIGHT plays an important role in the T-cell-mediated tumor and graft-versus-host disease via LIGHT/HVEM/LT beta R signaling. To prepare specific monoclonal antibody (MAb) against murine LIGHT, a fragment containing the extracellular domain of LIGHT was inserted into prokaryotic expression vector pET-32a(+). The his-tagged fusion protein was expressed in BL21(DE3) in the form of inclusion bodies. The fusion protein was purified and refolded on-column using immobilized mental affinity chromatography. Rat MAb against murine LIGHT was obtained with hybridoma technique and specific ELISA screening. Western blotting and flow cytometry assays showed that MAb 4C11 had specific binding ability with LIGHT protein in eukaryotic cells. Lymphocyte proliferation assays indicated that this MAb could co-stimulate the proliferation of T-cells. Thus, this MAb may be the basis for detection of LIGHT protein in tissue or cell and be beneficial for the study of LIGHT/HVEM/LT beta R pathway.

LIGHT enhances the bactericidal activity of human monocytes and neutrophils via HVEM

Human monocytes and neutrophils play major roles in clearing bacteria from human blood and tissues. We found that the herpes virus entry mediator (HVEM) was highly expressed in monocytes and neutrophils, and its interaction with "homologous to lymphotoxins, shows inducible expression, and competes with herpes simplex virus glycoprotein D for HVEM/tumor necrosis factor (TNF)-related 2" (LIGHT) enhanced bactericidal activity against Listeria monocytogenes and Staphylococcus aureus. The LIGHT-HVEM interaction increased levels of phagocytosis, interleukin (IL)-8, TNF-alpha, nitric oxide (NO), and reactive oxygen species (ROS) in monocytes and neutrophils. Anti-HVEM monoclonal antibody was able to block LIGHT-induced bactericidal activity, cytokine production (IL-8 and TNF-alpha), and ROS generation. Moreover, inhibition of ROS and NO production blocked LIGHT-induced bactericidal activity. Our results indicate that the LIGHT/HVEM interaction in monocytes and neutrophils contributes to antibacterial activity.

Proinflammatory effects of LIGHT through HVEM and LTbetaR interactions in cultured human umbilical vein endothelial cells

Members of the tumor necrosis factor (TNF) receptor (TNFR) superfamily are known to be potent mediators of immune responses. LIGHT is a member of the TNF superfamily, and its receptors have been identified as lymphotoxin beta receptor (LTbetaR), herpes virus entry mediator (HVEM), and decoy receptor 3 (DcR3). LIGHT can induce either cell death and/or NF-kappaB activation via its interaction with LTbetaR and/or HVEM. In this study, we investigated the effects of LIGHT in human umbilical vein endothelial cells (HUVECs). We demonstrated that both LTbetaR and HVEM, but not DcR3, are present in HUVECs, and LIGHT can induce the secretion of chemokines (IL-8 and GRO-alpha), cell surface expression of adhesion molecules (ICAM-1 and VCAM-1), PGI2 release, and COX-2 expression. However, the LIGHT mutein, LIGHT-R228E, which has been shown to exhibit binding specificity to LTbetaR, could not induce the secretion of GRO-alpha, PGI2, or the expression of COX-2. These results indicate that both LTbetaR and HVEM can discriminatively mediate the expression of different genes in HUVECs, and suggest that LIGHT is a proinflammatory cytokine.

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.

TNF/TNFR family members in costimulation of T cell responses

Several members of the tumor necrosis factor receptor (TNFR) family function after initial T cell activation to sustain T cell responses. This review focuses on CD27, 4-1BB (CD137), OX40 (CD134), HVEM, CD30, and GITR, all of which can have costimulatory effects on T cells. The effects of these costimulatory TNFR family members can often be functionally, temporally, or spatially segregated from those of CD28 and from each other. The sequential and transient regulation of T cell activation/survival signals by different costimulators may function to allow longevity of the response while maintaining tight control of T cell survival. Depending on the disease condition, stimulation via costimulatory TNF family members can exacerbate or ameliorate disease. Despite these complexities, stimulation or blockade of TNFR family costimulators shows promise for several therapeutic applications, including cancer, infectious disease, transplantation, and autoimmunity.

Constitutive expression and costimulatory function of LIGHT/TNFSF14 on human melanoma cells and melanoma-derived microvesicles

Neoplastic cells are thought to have defective expression of costimulatory molecules. However, in this study, we show that human melanoma cells express LIGHT/TNFSF14, a ligand of herpesvirus entry mediator on T cells and of lymphotoxin beta receptor on stromal cells. In vitro, melanoma cells stained for LIGHT in the intracellular compartment, with weak or negative cell surface expression. However, LIGHT was expressed on tumor-derived microvesicles released from melanoma cells. In vivo, LIGHT was found in metastatic lesions, and the extent of lymphotoxin beta receptor expression on the stromal cells was significantly associated with a "brisk" T-cell infiltrate in the neoplastic tissue. In the lesions with a brisk T-cell infiltrate, stromal cells surrounding the tumor also stained for the T-cell attractant chemokine CCL21. The intratumoral T lymphocytes frequently expressed herpesvirus entry mediator and were characterized by a differentiated phenotype. Coculture of lymphocytes with LIGHT(+) melanoma-derived microvesicles or even with LIGHT(+) melanoma cells in the presence of interleukin-2 costimulated LIGHT-dependent CD3(+)CD8(+) T-cell proliferation. However, lymphocyte coculture with LIGHT(+) microvesicles in the presence of interleukin-2 was also associated with an apoptotic response as documented by increased binding of Annexin V by CD3(+)CD8(+) T cells. These data suggest that LIGHT constitutively expressed in human melanoma cells and microvesicles may contribute to regulate T-cell responses to tumor cells.

Tumor vaccine based on cell surface expression of DcR3/TR6

DcR3/TR6, a secreted protein belonging to the TNF receptor superfamily, interacts with lymphotoxin-like, exhibits inducible expression, and competes with herpes simplex virus glycoprotein D for herpes virus entrance mediator (LIGHT), Fas ligand (FasL), and TL1A, all members of the TNF superfamily. Solid-phase TR6 can trigger reverse signaling of LIGHT and FasL expressed on T cells, and lead to T cell costimulation. In this study, we engineered tumor cells to express cell surface TR6 and used these cells as a tumor vaccine. We demonstrated that mastocytoma P815 cells expressing surface TR6 (TR6-P815) effectively augmented the T cells response in vitro and ex vivo in terms of proliferation, as well as IL-2 and IFN-gamma secretion. TR6-P815 cells had reduced tumorigenicity compared with parental P815 cells. When inactivated TR6-P815 cells were employed as a vaccine, they protected the mice from challenge with live parental P815 cells, and eliminated established P815 tumors. The cell surface TR6-based tumor vaccine was also effective against low antigenicity tumors, such as B16 melanoma; co-administration of bacillus Calmette-Guérin further enhanced the vaccine's efficacy. Thus, cell surface TR6 expression is a useful addition to our tumor vaccine arsenal.

The role of herpesvirus entry mediator as a negative regulator of T cell-mediated responses

Herpesvirus entry mediator (HVEM), a TNF receptor superfamily member, has been previously described as a T cell costimulatory receptor. Surprisingly, HVEM-/- T cells showed enhanced responses to in vitro concanavalin A (ConA) stimulation when compared with WT T cells. Consistent with these findings, HVEM-/- mice exhibited increased morbidity and mortality as compared with WT mice in a model of ConA-mediated T cell-dependent autoimmune hepatitis. HVEM-/- mice produced higher levels of multiple cytokines, which were dependent on the presence of CD4+ T cells. Furthermore, HVEM-/- mice were more susceptible to MOG peptide-induced experimental autoimmune encephalopathy, and they showed increased T cell proliferation and cytokine production in response to antigen-specific challenge. Taken together, our data revealed an unexpected regulatory role of HVEM in T cell-mediated immune responses and autoimmune diseases.

The role of herpesvirus entry mediator as a negative regulator of T cell-mediated responses

Herpesvirus entry mediator (HVEM), a TNF receptor superfamily member, has been previously described as a T cell costimulatory receptor. Surprisingly, HVEM-/- T cells showed enhanced responses to in vitro concanavalin A (ConA) stimulation when compared with WT T cells. Consistent with these findings, HVEM-/- mice exhibited increased morbidity and mortality as compared with WT mice in a model of ConA-mediated T cell-dependent autoimmune hepatitis. HVEM-/- mice produced higher levels of multiple cytokines, which were dependent on the presence of CD4+ T cells. Furthermore, HVEM-/- mice were more susceptible to MOG peptide-induced experimental autoimmune encephalopathy, and they showed increased T cell proliferation and cytokine production in response to antigen-specific challenge. Taken together, our data revealed an unexpected regulatory role of HVEM in T cell-mediated immune responses and autoimmune diseases.

The intriguing biology of the tumour necrosis factor/tumour necrosis factor receptor superfamily: players, rules and the games

The members of the tumour necrosis factor (TNF)/tumour necrosis factor receptor (TNFR) superfamily are critically involved in the maintenance of homeostasis of the immune system. The biological functions of this system encompass beneficial and protective effects in inflammation and host defence as well as a crucial role in organogenesis. At the same time, members of this superfamily are responsible for host damaging effects in sepsis, cachexia, and autoimmune diseases. This review summarizes recent progress in the immunobiology of the TNF/TNFR superfamily focusing on results obtained from animal studies using gene targeted mice. The different modes of signalling pathways affecting cell proliferation, survival, differentiation, apoptosis, and immune organ development as well as host defence are reviewed. Molecular and cellular mechanisms that demonstrate a therapeutic potential by targeting individual receptors or ligands for the treatment of chronic inflammatory or autoimmune diseases are discussed.

TRAF2 plays a key, nonredundant role in LIGHT-lymphotoxin beta receptor signaling

LIGHT is a member of the tumor necrosis factor (TNF) superfamily, and its function is mediated by at least two receptors, including lymphotoxin beta receptor (LTbetaR) and herpes simplex virus entry mediator. However, the molecular mechanism of LIGHT signaling mediated by LTbetaR has not been clearly defined. In this report, we demonstrate that TRAF2 is critical for LIGHT- and LTbetaR-mediated activation of both the transcription factor NF-kappaB and the mitogen-activated protein kinase JNK. In HeLa cells, LIGHT induces NF-kappaB and JNK activation, which can be blocked by the dominant negative mutant of TRAF2. In these cells, LIGHT causes the recruitment of TRAF2, TRAF3, and IkappaB kinase into the LTbetaR complex. Importantly, while both NF-kappaB and JNK are activated by LIGHT in wild-type mouse embryonic fibroblasts, no activation of either of these two pathways is observed in TRAF2 null fibroblasts. However, LIGHT-induced NF-kappaB and JNK activation can be restored by ectopic expression of TRAF2 in TRAF2-/- cells. Interestingly, in contrast to TNF signaling, the activation of both NF-kappaB and JNK by LIGHT was normal in RIP-/- and TRAF5-/- cells. Taken together, our data demonstrate that TRAF2, an important effector molecule of TNF signaling, plays a critical, nonredundant role in LIGHT-LTbetaR signaling.

Lymphotoxin and LIGHT signaling pathways and target genes

Lymphotoxins (LT alpha and LT beta), LIGHT [homologous to LT, inducible expression, competes with herpes simplex virus (HSV) glycoprotein D for HSV entry mediator (HVEM), a receptor expressed on T lymphocytes], tumor necrosis factor (TNF), and their specific receptors LT beta R, HVEM, and TNF receptor 1 (TNFR1) and TNFR2, form the immediate family of the larger TNF superfamily. These cytokines establish a critical communication system required for the development of secondary lymphoid tissues; however, knowledge of the target genes activated by these signaling pathways is limited. Target genes regulated by the LT alpha beta-LT beta R pathway include the tissue-organizing chemokines, CXCL13, CCL19, and CCL21, which establish cytokine circuits that regulate LT expression on lymphocytes, leading to organized lymphoid tissue. Infectious disease models have revealed that LT alpha beta pathways are also important for innate and adaptive immune responses involved in host defense. Here, regulation of interferon-beta by LT beta R and TNFR signaling may play a crucial role in certain viral infections. Regulation of autoimmune regulator in the thymus via LT beta R implicates LT/LIGHT involvement in central tolerance. Dysregulated expression of LIGHT overrides peripheral tolerance leading to T-cell-driven autoimmune disease. Blockade of TNF/LT/LIGHT pathways as an intervention in controlling autoimmune diseases is attractive, but such therapy may have risks. Thus, identifying and understanding the target genes may offer an opportunity to fine-tune inhibitory interventions.

Interdependency of beta-adrenergic receptors and CFTR in regulation of alveolar active Na+ transport

Beta-adrenergic receptors (betaAR) regulate active Na+ transport in the alveolar epithelium and accelerate clearance of excess airspace fluid. Accumulating data indicates that the cystic fibrosis transmembrane conductance regulator (CFTR) is important for upregulation of the active ion transport that is needed to maintain alveolar fluid homeostasis during pulmonary edema. We hypothesized that betaAR regulation of alveolar active transport may be mediated via a CFTR dependent pathway. To test this hypothesis we used a recombinant adenovirus that expresses a human CFTR cDNA (adCFTR) to increase CFTR function in the alveolar epithelium of normal rats and mice. Alveolar fluid clearance (AFC), an index of alveolar active Na+ transport, was 92% greater in CFTR overexpressing lungs than controls. Addition of the Cl- channel blockers NPPB, glibenclamide, or bumetanide and experiments using Cl- free alveolar instillate solutions indicate that the accelerated AFC in this model is due to increased Cl- channel function. Conversely, CFTR overexpression in mice with no beta1- or beta2-adrenergic receptors had no effect on AFC. Overexpression of a human beta2AR in the alveolar epithelium significantly increased AFC in normal mice but had no effect in mice with a non-functional human CFTR gene (Deltaphi508 mutation). These studies indicate that upregulation of alveolar CFTR function speeds clearance of excess fluid from the airspace and that CFTRs effect on active Na+ transport requires the betaAR. These studies reveal a previously undetected interdependency between CFTR and betaAR that is essential for upregulation of active Na+ transport and fluid clearance in the alveolus.

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.

Tumor necrosis factor-related apoptosis-inducing ligand and CD56 expression in patients with type 1 diabetes mellitus

OBJECTIVES

Our previous report showed that beta-cell antigen-specific CD56+ T-cells and cytokine TRAIL mediate destruction of human pancreatic [beta] cells in vitro. To determine whether CD56 and TRAIL are present during islet cell destruction at the onset of clinical symptoms of type 1 diabetes mellitus (T1D), we studied cell marker and cytokine expression in the pancreatic islets of 2 children who died at presentation of acute-onset T1D and in T-cell lines derived from a group of children with new-onset T1D.

METHODS

TRAIL, CD56, and other T-cell markers and cytokine expression were studied using immunohistochemistry on pancreatic sections from 2 children with acute-onset T1D. TRAIL and CD56 expression was analyzed by flow cytometry in the antigen-activated T-cell lines derived from 29 children with new-onset T1D.

RESULTS

TRAIL+, CD56+, CD45RO+, and CD3+ cells were present in the islets of acute-onset T1D patients, while none were present in the normal islets. T-cell lines from new-onset T1D expressed TRAIL and CD56 in response to stimulation with beta-cell antigens GAD, IA-2 and insulin beta chain.

CONCLUSION

The presence of TRAIL and CD56 markers is part of the T-cell response repertoire in beta-cell destruction.

Testosterone responsiveness of spleen and liver in female lymphotoxin β receptor-deficient mice resistant to blood-stage malaria

Disrupted signaling through lymphotoxin beta receptor (LTbetaR) results in severe defects of the spleen and even loss of all other secondary lymphoid tissues, making mice susceptible to diverse infectious agents. Surprisingly, however, we find that female LTbetaR-deficient mice are even more resistant to blood stages of Plasmodium chabaudi malaria than wild-type C57BL/6 mice. Higher resistance of LTbetaR-deficient mice correlates with an earlier onset of reticulocytosis, and the period of anemia is shorter. After surviving fulminant parasitemias of about 35%, mice develop long-lasting protective immunity against homologous rechallenge, with both spleen and liver acting as anti-malaria effectors. Testosterone suppresses resistance, i.e. all mice succumb to infections during or shortly after peak parasitemia. At peak parasitemia, testosterone does not essentially affect cellularity and apoptosis in the spleen, but aggravates liver pathology in terms of increased cell swelling, numbers of apoptotic and binucleated cells and reduced serum alkaline phosphatase levels, and conversely, reduces inflammatory lymphocytic infiltrates in the liver. In the spleen, hybridization of cDNA arrays identified only a few testosterone-induced changes in gene expression, in particular upregulation of INFgamma and IFN-regulated genes. By contrast, a much larger number of testosterone-affectable genes was observed in the liver, including genes involved in regulation of the extracellular matrix, in chemokine and cytokine signaling, and in cell cycle control. Collectively, our data suggest that testosterone dysregulates the inflammatory response in spleen and liver during their differentiation to anti-malaria effectors in malaria-resistant female LTbetaR-deficient mice, thus contributing to the testosterone-induced lethal outcome of malaria.

High expression of bfl-1 contributes to the apoptosis resistant phenotype in B-cell chronic lymphocytic leukemia

In order to identify regulatory genes involved in the development of an apoptosis-resistant phenotype in patients with chemotherapy refractory B-cell chronic lymphocytic leukemia (B-CLL) expression of apoptosis-regulating genes in B-CLL cells was quantified using cDNA arrays and RT-PCR. Data were obtained from and compared between 2 groups of B-CLL patients with either nonprogressive, indolent, previously untreated disease and with leukemic cells sensitive to in vitro fludarabine-induced apoptosis, referred to as sensitive B-CLL (sB-CLL) or with progressive, chemotherapy refractory disease and with leukemic cells resistant to in vitro fludarabine-induced apoptosis, referred to as resistant B-CLL (rB-CLL). By performing a supervised clustering of genes that most strongly discriminated between rB-CLL vs. sB-CLL a small group of genes was identified, where bfl-1 was the strongest discriminating gene (p < 0.05), with higher expression in rB-CLL. A group of apoptosis-regulating genes were modulated during induction of apoptosis by serum deprivation in vitro in a similar manner in all cases studied. However, bfl-1 was preferentially downregulated in sB-CLL as compared to rB-CLL (p < 0.05). We conclude that bfl-1 may be an important regulator of B-CLL apoptosis, which could contribute to disease progression and resistance to chemotherapy, and as such represent a future potential therapeutic target.

Differential lymphotoxin-beta and interferon gamma signaling during mouse liver regeneration induced by chronic and acute injury

The liver regenerates after acute injury via hepatocyte cell division; during chronic injury, when hepatocyte replication is impaired or blocked, liver progenitor oval cells mediate liver regeneration. If both regeneration options are blocked in animal models, then liver failure and death ensues. The mechanisms underlying oval cell induction, proliferation, and subsequent liver regeneration remain poorly characterized. In particular, cell-signaling pathways that distinguish the alternative pathways are unknown. This study shows that in a mouse model, hepatic expression of lymphotoxin-beta (LTbeta) and interferon gamma (IFNgamma) transcripts is increased in response to the choline-deficient, ethionine-supplemented (CDE) diet, which induces oval cell-mediated liver regeneration. Oval cells express LTbeta and IFNgamma transcripts, contributing to the increased expression in the liver of mice fed the CDE diet. An attenuated oval cell response to such a diet was observed in LTbeta receptor-, LTbeta-, and IFNgamma-gene targeted mice. Loss of LTbeta and LTbeta receptor signaling reduced the number of oval cells expressing A6 and muscle pyruvate kinase. The lack of IFNgamma signaling reduced muscle pyruvate kinase(+), but not A6(+), oval cells. In contrast, partial hepatectomy suppressed LTbeta and IFNgamma transcripts. We also show that IFNgamma induces STAT-3 phosphorylation in an oval cell line. In conclusion, LTbeta, LTbeta receptor, and IFNgamma are involved in oval cell-mediated, but not hepatocyte-mediated, liver regeneration, and the absence of these pathways impairs the oval cell-dependent regenerative response.

Role of T cell costimulation in anti-viral immunity

Members of both the CD28 and TNFR families can have costimulatory roles in T cell activation. Gene targeted mice as well as in vivo blocking experiments have established distinct roles for CD28/B7; ICOS/ICOSL; CD27/CD70; 4-1BB/4-1BBL and OX40/OX40L during viral infection. Many issues remain to be addressed, including the timing and location of the interactions, the possibility of partial redundancy between related family members and the molecular basis for the specific phenotypes observed in the different gene targeted mice.

Soluble receptor (DcR3) and cellular inhibitor of apoptosis-2 (cIAP-2) protect human cytotrophoblast cells against LIGHT-mediated apoptosis

LIGHT (tumor necrosis factor superfamily 14) is among the powerful apoptosis-inducing cytokines synthesized in human placentas. Here, we investigated mechanisms protecting cytotrophoblast (CTB) cells from LIGHT-mediated apoptosis. Viability assays and caspase-3 immunoblots using recombinant LIGHT were done to establish that CTB cells purified from term placentas resist LIGHT-induced apoptosis. Although the cells were also resistant to killing by another placental cytokine, interferon-gamma (IFN-gamma), a combination of the two induced apoptosis. Killing was prevented by DcR3-Fc fragment but not control human-Fc fragment, showing that apoptosis occurs via the LIGHT pathway and that soluble receptors provide protection. Next, two cellular inhibitors of apoptosis expressed in CTB cells, cellular inhibitor of apoptosis (cIAP)-1 and cIAP-2, were investigated for protection. Cellular IAP-1 was unchanged after stimulation with LIGHT whereas cIAP-2 mRNA and protein were elevated. The increase was abrogated by treating CTB cells with LIGHT + IFN-gamma, implying a central role for cIAP-2 in preventing LIGHT-mediated apoptosis and an ability of IFN-gamma to overcome cIAP-2 protection. Definitive evidence was provided in experiments that showed that cIAP-2 anti-sense morpholinos permit LIGHT to induce apoptosis in HT-29 cells. In summary, the data are consistent with the postulate that placental CTB cells are protected from LIGHT-mediated apoptosis by both soluble receptor, DcR3, and cIAP-2.

Mutations in herpes simplex virus glycoprotein D that prevent cell entry via nectins and alter cell tropism

Glycoprotein D (gD) determines which cells can be infected by herpes simplex virus (HSV) by binding to one of the several cell surface receptors that can mediate HSV entry or cell fusion. These receptors include the herpesvirus entry mediator (HVEM), nectin-1, nectin-2, and sites in heparan sulfate generated by specific 3-O-sulfotransferases. The objective of the present study was to identify residues in gD that are critical for physical and functional interactions with nectin-1 and nectin-2. We found that double or triple amino acid substitutions at positions 215, 222, and 223 in gD caused marked reduction in gD binding to nectin-1 and a corresponding inability to function in cell fusion or entry of HSV via nectin-1 or nectin-2. These substitutions either enhanced or did not significantly inhibit functional interactions with HVEM and modified heparan sulfate. These and other results demonstrate that different domains of gD, with some overlap, are critical for functional interactions with each class of entry receptor. Viral entry assays, using gD mutants described here and previously, revealed that nectins are the principal entry receptors for selected human cell lines of neuronal and epithelial origin, whereas HVEM or nectins could be used to mediate entry into a T lymphocyte line. Because T cells and fibroblasts can be infected via HVEM, HSV strains carrying gD mutations that prevent entry via nectins may establish transient infections in humans, but perhaps not latent infections of neurons, and are therefore candidates for development of safe live virus vaccines and vaccine vectors.

Attenuation of graft arterial disease by manipulation of the LIGHT pathway

OBJECTIVE

The tumor necrosis factor (TNF) superfamily member LIGHT, which binds herpes virus entry mediator (HVEM) and lymphotoxin beta receptor (LTbetaR), plays important roles in regulating the immune response. To clarify the mechanism underlying graft arterial disease (GAD), we investigated the role of the LIGHT pathway in the progression of GAD.

METHODS AND RESULTS

Hearts from Bm12 mice were transplanted into C57BL/6 (B/6) mice (class II mismatch). Recipients were injected intraperitoneally with HVEMIg (100 microg per treatment) every 7 days for 8 weeks. Treatment with HVEMIg significantly attenuated GAD (luminal occlusion=16.5+/-7.7% versus control allograft=62.6+/-12.1%, P<0.05), and significantly decreased intragraft IL-4, IL-6, and interferon-gamma (IFN-gamma) mRNA expression compared with controls. LTbetaR was expressed in smooth muscle cells (SMCs) with or without cytokine stimulation, whereas HVEM was detected in SMCs stimulated by IFN-gamma. Coculture of SMCs with T cells after transplantation induced SMC proliferation, and addition of HVEMIg resulted in inhibition of SMC proliferation.

CONCLUSIONS

These results indicate that the LIGHT pathway plays important roles in the regulation not only of T-cell activation but also of SMC proliferation. Blockade of the LIGHT pathway is a promising avenue for the prevention of GAD.

Soluble decoy receptor 3 induces angiogenesis by neutralization of TL1A, a cytokine belonging to tumor necrosis factor superfamily and exhibiting angiostatic action

TL1A is a member of the tumor necrosis factor superfamily and plays an important role in regulating endothelial cell apoptosis. A previous study shows TL1A is able to interact with death receptor 3 and decoy receptor 3 (DcR3). Here, we demonstrate that DcR3 is able to induce angiogenesis in human umbilical vein endothelial cells (HUVECs). DcR3 promotes HUVEC proliferation and migration and up-regulates matrix metalloproteinase-2 mRNA expression and enzyme activity. Furthermore, DcR3 enhances EC differentiation into cord vascular-like structures in vitro, as well as neovascularization in vivo. The effects of DcR3 on HUVECs are also mimicked by anti-TL1A and antideath receptor 3 antibodies. In contrast, human aortic endothelial cells, which do not express TL1A, are not responsive to DcR3 treatment, including cell proliferation, migration, and angiogenic differentiation. These data demonstrate DcR3 might not only help tumor cells to escape immune surveillance but also induce angiogenesis by blocking TL1A action in endothelial cells. The pathological role of DcR3 in promoting cancer progress raises the possibility to target DcR3 for antiangiogenic therapy in the future.

LIGHT sensitizes IFNγ–mediated apoptosis of HT-29 human carcinoma cells through both death receptor and mitochondria pathways

LIGHT [homologous to lymphotoxins, shows inducible expression, and competes with herpes simplex virus glycoprotein D for herpes virus entry mediator (HVEM/TR2)] is a new member of TNF superfamily. The HT-29 colon cancer cell line is the most sensitive to LIGHT-induced, IFNg-mediated apoptosis among the cell lines we have examined so far. Besides downregulation of Bcl-XL, upregulation of Bak, and activation of both PARP [poly (ADP-ribose) polymerase] and DFF45 (DNA fragmentation factor), LIGHT-induced, IFNg-mediated apoptosis of HT-29 cells involves extensive caspase activation. Caspase-8 and caspase-9 activation, as shown by their cleavages appeared as early as 24 h after treatment, whereas caspase-3 and caspase-7 activation, as shown by their cleavages occurred after 72 h of LIGHT treatment. Caspase-3 inhibitor Z-DEVD-FMK (benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethylketone) and a broad range caspase inhibitor Z-VAD-FMK (benzyloxycarbonyl-Val-Ala-Asp fluoromethylketone) were able to block LIGHT-induced, IFNg-mediated apoptosis of HT-29 cells. The activity of caspase-3, which is one of the major executioner caspases, was found to be inhibited by both Z-DEVD-MFK and Z-VAD-FMK. These results suggest that LIGHT-induced, IFNg-mediated apoptosis of HT-29 cells is caspase-dependent, and LIGHT signaling is mediated through both death receptor and mitochondria pathways.