Th17 cells undergo Fas-mediated activation-induced cell death independent of IFN-gamma

Dose-dependent effects of human umbilical cord-derived mesenchymal stem cell treatment in hyperoxia-induced lung injury of neonatal rats

Background

Mesenchymal stem cells (MSCs) are multipotent stromal cells that have been reported to possess great potential for the treatment of bronchopulmonary dysplasia (BPD).

Objective

Our study aims to assess the effects of three different doses of intraperitoneal administration of human umbilical cord-derived MSCs (hUC-MSCs) on a hyperoxia-induced BPD model of newborn rat.

Methods

Neonatal Sprague Dawley (SD) rats were reared in either hyperoxia (75% O2) or room air (RA) from postnatal days (PN) 1-14. At PN5, hUC-MSCs (1 × 106, 5× 106,or 1× 107 cells per pup) were given intraperitoneally to newborn rats exposed to 75% O2 from birth; the controls received an equal volume of normal saline (NS). At PN14, the lung tissues, serum, and bronchoalveolar fluid (BALF) were collected for histologic examination, wet/dry (W/D) weight ratio analysis, engraftment, myeoloperoxidase (MPO) activity analysis, cytokine analysis, and western blot analysis of protein expression.

Results

Compared to rat pups reared in RA, rat pups reared in hyperoxia had a significant lower survival rate (53.3%) (P < 0.01). Hyperoxia-exposed rats exhibited pulmonary inflammation accompanied by alveolar-capillary leakage, neutrophile infiltration, augmented myeloperoxidase (MPO) activity, prominent alveolar simplification, and increased mean linear intercept (MLI), which was ameliorated by hUC-MSCs treatment. Increased oxidative stress and inflammatory cytokine production were also reduced. Importantly, the expression of Fas, an apoptosis-associated protein that was increasingly expressed in hyperoxia-exposed rats (P < 0.05), was downregulated after administration of hUC-MSCs (P < 0.05).

Conclusions

Our results suggest that intraperitoneal administration of high number hUC-MSCs (1 × 107 cells) may represent an effective modality for the treatment of hyperoxia-induced BPD in neonatal rats.

Persistent, Asymptomatic Colonization with Candida is Associated with Elevated Frequencies of Highly Activated Cervical Th17-Like Cells and Related Cytokines in the Reproductive Tract of South African Adolescents

Cervicovaginal inflammation, nonoptimal microbiota, T-cell activation, and hormonal contraceptives may increase HIV risk, yet associations between these factors and subclinical Candida colonization or hyphae are unknown. We collected cervicovaginal samples from 94 South African adolescents, aged 15 to 19 years, who were randomized to injectable norethisterone enanthate (Net-En), an etonorgesterol/ethinyl estradiol vaginal ring (NuvaRing), or oral contraceptives in the UChoose trial (NCT02404038) at baseline and 16 weeks post-randomization. We assessed cervicovaginal samples for subclinical Candida colonization (by quantitative PCR [qPCR]), hyphae (by Gram stain), microbiota composition (by 16S rRNA gene sequencing), cytokine concentrations (by Luminex), and cervical T-cell phenotypes and activation (by multiparameter flow cytometry). While hormonal contraceptive type did not influence incidence of Candida colonization or hyphae, hyphae presence was associated with significantly elevated concentrations of IL-22, IL-17A and IL-17F, all produced by Th17 cells, but not of other cytokines, such as IL-1β or IL-6, after adjustment for confounders. Subclinical Candida colonization was associated with reduced frequencies of Th17-like cells and elevated frequencies of CCR6-CCR10 T cells. Women with Candida hyphae were less likely to have bacterial vaginosis (BV). Persistent, subclinical colonization with Candida over 16 weeks was associated with significant increases in Th17-related cytokine concentrations and highly activated Th17-like and CCR6-CCR10 T-cell frequencies. These data suggest that vaginal Candida colonization and hyphae increase Th17-related cytokines, but not overall female genital tract inflammation in Sub-Saharan African adolescents. Persistent Candida colonization, even when asymptomatic, may increase Th17 cell frequencies and related cytokines and thereby could subsequently increase HIV risk, although the causal relationship requires confirmation. IMPORTANCE Sub-Saharan African female adolescents are globally at the highest risk of HIV acquisition, and genital inflammation, microbial dysbiosis, and cervical HIV target cell activation are thought to contribute to this risk. Previously, the relationship between these mucosal factors and subclinical vaginal Candida colonization or hyphae has not been described, and the role of HIV-susceptible Th17 cells in mediating anti-Candida immunity in the human female genital tract has not been clearly established. We show that presence of yeast hyphae was associated with increases in Th17 cell-related cytokines and the absence of microbial dysbiosis, and that persistent Candida colonization resulted in significant increases in Th17-related cytokines and highly activated Th17-like cell frequencies. Our results suggest that Th17 cells are important for anti-Candida immunity in the human female genital tract and that prolonged vaginal Candida colonization may contribute to increased HIV risk in Sub-Saharan African adolescents by increasing HIV target cell frequencies and activation.

Presence of Natural Killer B Cells in Simian Immunodeficiency Virus-Infected Colon That Have Properties and Functions Similar to Those of Natural Killer Cells and B Cells but Are a Distinct Cell Population

There is low-level but significant mucosal inflammation in the gastrointestinal tract secondary to human immunodeficiency virus (HIV) infection that has long-term consequences for the infected host. This inflammation most likely originates from the immune response that appears as a consequence of HIV. Here, we show in an animal model of HIV that the chronically SIV-infected gut contains cytotoxic natural killer B cells that produce inflammatory cytokines and proliferate during infection.

Activation of Functional Somatic Stem Cells Promotes Endogenous Tissue Regeneration

Periodontal ligament derived stem cells (PDLSCs) are capable of differentiating into multiple cell types and inducing a promising immunomodulation for tissue regeneration and disease treatment. However, it is still challenging to develop a practical approach to activate endogenous stem cells for tissue self-healing and regeneration. In this study, transcriptome analysis reveals that resveratrol promotes PDLSC stemness through activation of stem cell, osteoprogenitor, and chondroprogenitor markers. Self-renewal and multipotent differentiation abilities are also improved in resveratrol-treated PDLSCs. In addition, immunomodulation of PDLSCs is dramatically increased after resveratrol treatment. Mechanistically, we show that resveratrol activates ERK/WNT crosstalk through elevation of olfactory and growth factor signaling pathways to upregulate the expression levels of RUNX2 and FASL for osteogenesis and immunomodulation, respectively. By using a periodontitis animal model, administration of resveratrol partially rescues bone loss through activation of endogenous somatic stem cells and inhibition of inflammatory T-cell infiltration. Taken together, our findings identify a novel pharmacological approach to achieve autotherapies for endogenous tissue regeneration.

Enhanced Suppression of Immune Cells In Vitro by MSC Overexpressing FasL

Mesenchymal stromal cells (MSC) display several mechanisms of action that may be harnessed for therapeutic purposes. One of their most attractive features is their immunomodulatory activity that has been extensively characterized both in vitro and in vivo. While this activity has proven to be very efficient, it is transient. We aimed to enhance it by transforming MSC to overexpress a first apoptosis signal (Fas) ligand (FasL). In this study, our goal was to induce FasL overexpression through adenoviral transduction in MSC to improve their immunomodulatory activity. We characterized the impact of FasL overexpression on the morphology, proliferation, viability, phenotype, multilineage differentiation potential and immunomodulation of MSC. Moreover, we determined their suppressive properties in mixed reactions with A20 cells, as well as with stimulated splenocytes. Our findings demonstrate that FasL-overexpressing MSC exhibit improved immunosuppressive properties, while maintaining their MSC-characteristic features. In conclusion, we establish, in a proof-of-concept set-up, that FasL-overexpressing MSC represent good candidates for therapeutic intervention targeted at autoimmune disorders.

Aging-Affected MSC Functions and Severity of Periodontal Tissue Destruction in a Ligature-Induced Mouse Periodontitis Model

Mesenchymal stem cells (MSCs) are known to play important roles in the repair of lost or damaged tissues and immunotolerance. On the other hand, aging is known to impair MSC function. However, little is currently known about how aged MSCs affect the host response to the local inflammatory condition and tissue deterioration in periodontitis, which is a progressive destructive disease of the periodontal tissue potentially leading to multiple tooth loss. In this study, we examined the relationship between aging-induced impairment of MSC function and the severity of periodontal tissue destruction associated with the decrease in host immunomodulatory response using a ligature-induced periodontitis model in young and aged mice. The results of micro computerized tomography (micro-CT) and histological analysis revealed a more severe bone loss associated with increased osteoclast activity in aged (50-week-old) mice compared to young (5-week-old) mice. Immunostaining analysis revealed that, in aged mice, the accumulation of inflammatory T and B cells was higher, whereas the percentage of platelet-derived growth factor receptor α (PDGFRα)⁺ MSCs, which are known to modulate the apoptosis of T cells, was significantly lower than in young mice. In vitro analysis of MSC function showed that the expression of surface antigen markers for MSCs (Sca-1, CD90, CD146), colony formation, migration, and osteogenic differentiation of aged MSCs were significantly declined compared to those of young MSCs. Moreover, a significantly higher proportion of aged MSCs were positive for the senescence-associated β galactosidase activity. Importantly, aged MSCs presented a decreased expression of FAS-L, which was associated with a lower immunomodulatory property of aged MSCs to induce T cell apoptosis in co-cultures compared with young MSCs. In summary, this is the first study showing that aging-induced impairment of MSC function, including immunomodulatory response, is potentially correlated with progressive periodontal tissue deterioration.

Acetylsalicylic acid rescues the immunomodulation of inflamed gingiva-derived mesenchymal stem cells via upregulating FasL in mice

Background

Gingiva-derived mesenchymal stem cells (GMSCs) obtained multipotent differentiation and immunomodulatory properties. However, collecting healthy gingival tissues may be challenging in the clinical situation. Thus, in our present study, we aim to evaluate whether the immunomodulatory capacity of gingiva-derived mesenchymal stem cells from inflamed gingival tissues (iGMSCs) is impaired and find a way to rescue their deficient properties.

Methods

We compared the immunomodulation capacity of GMSCs and iGMSCs using an in vitro co-culture system and a mouse colitis model. T cell apoptosis, T helper 17 (Th17), and regulatory T (Treg) cell differentiation were detected by flow cytometry analysis.

Results

We demonstrated that iGMSCs obtained a decreased immunomodulatory capacity compared with GMSCs. Acetylsalicylic acid (ASA) pretreatment was able to rescue iGMSCs’ impaired immunomodulatory properties. Mechanistically, ASA was capable of upregulating the expression of Fas ligand (FasL) in iGMSCs, leading to an improvement in iGMSC-mediated T cell apoptosis and therapeutic efficacy in the treatment in colitis mice.

Conclusions

This study indicates that the deficient immunomodulatory function of iGMSCs could be rescued by ASA pretreatment via upregulating of FasL in mice. This strategy might serve as a practical approach to rescue deficient MSC function for further therapeutic application.

Effect of Chronic Oxidative Stress on Neuroinflammatory Response Mediated by CD4+T Cells in Neurodegenerative Diseases

In a state of oxidative stress, there is an increase of reactive species, which induce an altered intracellular signaling, leading to dysregulation of the inflammatory response. The inability of the antioxidant defense systems to modulate the proinflammatory response is key to the onset and progression of neurodegenerative diseases. The aim of this work is to review the effect of the state of oxidative stress on the loss of regulation of the inflammatory response on the microglia and astrocytes, the induction of different CD4⁺T cell populations in neuroinflammation, as well as its role in some neurodegenerative diseases. For this purpose, an intentional search of original articles, short communications, and reviews, was carried out in the following databases: PubMed, Scopus, and Google Scholar. The articles reviewed included the period from 1997 to 2017. With the evidence obtained, we conclude that the loss of redox balance induces alterations in the differentiation and number of CD4⁺T cell subpopulations, leading to an increase in Th1 and Th17 response. This contributes to the development of neuroinflammation as well as loss of the regulation of the inflammatory response in neurodegenerative diseases such as Alzheimer's (AD), Parkinson's (PD), and Multiple Sclerosis (MS). In contrast, regulatory T cells (Tregs) and Th2 modulate the inflammatory response of effect of T cells, microglia, and astrocytes. In this respect, it has been found that the mobilization of T cells with anti-inflammatory characteristics toward damaged regions of the CNS can provide neuroprotection and become a therapeutic strategy to control inflammatory processes in neurodegeneration.

Ibrutinib treatment improves T cell number and function in CLL patients

BACKGROUND

Ibrutinib has been shown to have immunomodulatory effects by inhibiting Bruton's tyrosine kinase (BTK) and IL-2-inducible T cell kinase (ITK). The relative importance of inhibiting these 2 kinases has not been examined despite its relevance to immune-based therapies.

METHODS

Peripheral blood mononuclear cells from chronic lymphocytic leukemia (CLL) patients on clinical trials of ibrutinib (BTK/ITK inhibitor; n = 19) or acalabrutinib (selective BTK inhibitor; n = 13) were collected serially. T cell phenotype, immune function, and CLL cell immunosuppressive capacity were evaluated.

RESULTS

Ibrutinib markedly increased CD4+ and CD8+ T cell numbers in CLL patients. This effect was more prominent in effector/effector memory subsets and was not observed with acalabrutinib. Ex vivo studies demonstrated that this may be due to diminished activation-induced cell death through ITK inhibition. PD-1 and CTLA-4 expression was significantly markedly reduced in T cells by both agents. While the number of Treg cells remained unchanged, the ratio of these to conventional CD4+ T cells was reduced with ibrutinib, but not acalabrutinib. Both agents reduced expression of the immunosuppressive molecules CD200 and BTLA as well as IL-10 production by CLL cells.

CONCLUSIONS

Ibrutinib treatment increased the in vivo persistence of activated T cells, decreased the Treg/CD4+ T cell ratio, and diminished the immune-suppressive properties of CLL cells through BTK-dependent and -independent mechanisms. These features provide a strong rationale for combination immunotherapy approaches with ibrutinib in CLL and other cancers.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01589302 and NCT02029443. Samples described here were collected per OSU-0025.

FUNDING

The National Cancer Institute.

Transplantation of gingiva-derived mesenchymal stem cells ameliorates collagen-induced arthritis

Background

Rheumatoid arthritis (RA) is a chronic, progressive, and inflammatory autoimmune disease which primarily affects the small arthrodial joints. The aim of this study was to test whether transplantation of mesenchymal stem cells derived from gingival tissue (GMSCs) could ameliorate collagen-induced arthritis (CIA), and to explore the role of the FasL/Fas pathway in the underlying mechanism.

Methods

DBA/1 mice with collagen II-induced arthritis were treated with GMSCs from the C57BL/6 J mouse, the B6Smn.C3-FasL^gld/J mouse (FasL^–/– GMSCs), and FasL overexpressed FasL^–/– GMSCs (FasL TF GMSCs). Inflammation was evaluated by measuring clinical score, tumor necrosis factor (TNF)-α and anti-collagen II antibody levels, and histological analyses. The levels of CD4⁺ Th cell subsets in spleens and draining lymph nodes were assessed by flow cytometric analysis.

Results

Systemic infusion of GMSCs can significantly reduce the severity of experimental arthritis, and resume the balance of Th cell subsets. FasL^–/– GMSCs failed to induce apoptosis of activated T cells in vitro and in vivo, and therefore show no therapeutic effects, whereas FasL TF GMSCs can rescue the immunosuppressant effects in the treatment of CIA.

Conclusions

GMSC-based therapy induces T-cell apoptosis via the FasL/Fas pathway and results in immune tolerance and amelioration of the CIA inflammation.

Inherent low Erk and p38 activity reduce Fas Ligand expression and degranulation in T helper 17 cells leading to activation induced cell death resistance

Activation Induced Cell Death of T helper cells is central to maintaining immune homeostasis and a perturbation often manifests in aberrant T helper cells that is associated with immunopathologies. Significant presence of T cells positive for IL-17A (Th17) and dual positive for IFN-γ/IL-17A (Th1/Th17) in both effector (CD45RA+RO+) and memory (CD45RA-RO+) compartments with differential FasL protein in RA peripheral blood suggested their differential TCR AICD sensitivity. Lowered active caspase-3 in Th17 and Th1/Th17 over Th1 cells confirmed their capability to resist AICD and pointed to early upstream events. Differential MAPK activities, FasL protein and downstream caspase-3 activities in murine Th1 and Th17 cells established distinct TCR mediated signaling pathways and suggested low Erk and p38 activity as pivotal for AICD sensitivity. We extrapolated our mouse and human data and report that Fas-FasL is the preferred death pathway for both Th1 and Th17 and that inherently low Erk2 activity protected Th17 cells from TCR AICD. The presence of significantly higher numbers of aberrant T helper cells in RA also suggest an inflammatory cytokine milieu and AICD insensitive T cell link to sustained inflammation. Re sensitization to apoptosis by targeting MAPK activity especially Erk2 in RA might be of therapeutic value.

Osteoblast-induced osteoclast apoptosis by fas ligand/FAS pathway is required for maintenance of bone mass

The interplay between osteoblasts and osteoclasts has a crucial role in maintaining bone homeostasis. In this study, we reveal that osteoblasts are capable of inducing osteoclast apoptosis by FAS ligand (FASL)/FAS signaling. Conditional knockout of FASL in osteoblasts results in elevated osteoclast numbers and activity, along with reduced bone mass, suggesting that osteoblast-produced FASL is required to maintain physiological bone mass. More interestingly, we show that osteoblasts from ovariectomized (OVX) osteoporotic mice exhibit decreased FASL expression that results from the IFN-γ- and TNF-α-activated NF-κB pathway, leading to reduced osteoclast apoptosis and increased bone resorption. Systemic administration of either IFN-γ or TNF-α ameliorates the osteoporotic phenotype in OVX mice and rescues FASL expression in osteoblasts. In addition, ovariectomy induces more significant bone loss in FASL conditional knockout mice than in control group with increased osteoclast activity in which the levels of RANKL and OPG remain unchanged. Taken together, this study suggests that osteoblast-induced osteoclast apoptosis via FASL/FAS signaling is a previously unrecognized mechanism that has an important role in the maintenance of bone mass in both physiological conditions and OVX osteoporosis.

Licochalcone A up-regulates of FasL in mesenchymal stem cells to strengthen bone formation and increase bone mass

The role of bone marrow-derived mesenchymal stem cells(BMSCs)in the pathogenesis and therapy of osteoporosis has drawn increasing attention in recent years. In the development of osteoporosis, it has been demonstrated that many changes occurred in the behavior of BMSCs. For example, the biological system of FasL pathways mediated differentiation of ERK and GSK-3β-catenin pathway was damaged. Here we found that 0.35 mg/L Licochalcone A (L-A) had a strong effect in increasing the osteogenic differentiation and mineralization of BMSCs both in vivo and in vitro by up-regulating FasL and further playing a role in regulating the ERK and GSK-3β-catenin systems. It has also demonstrated that the administration of L-A could restore the biological function of the damaged BMSCs differentiation by recovering or protecting bone mass in a disease state through activating the endosteal bone formation and partially inhibiting bone resorption in acute estrogen deficiency model. Results of our study suggested that careful titration of MSC was response to L-A and up-regulated FasL pathways mediating differentiation of ERK and GSK-3β-catenin biological systems under disease state in vivo, restore the impaired function, is one of the ways of L-A relieve or treatment osteoporosis.

Acetylsalicylic acid treatment improves differentiation and immunomodulation of SHED

Stem cells from exfoliated deciduous teeth (SHED) possess multipotent differentiation and immunomodulatory properties. They have been used for orofacial bone regeneration and autoimmune disease treatment. In this study, we show that acetylsalicylic acid (ASA) treatment is able to significantly improve SHED-mediated osteogenic differentiation and immunomodulation. Mechanistically, ASA treatment upregulates the telomerase reverse transcriptase (TERT)/Wnt/β-catenin cascade, leading to improvement of SHED-mediated bone regeneration, and also upregulates TERT/FASL signaling, leading to improvement of SHED-mediated T-cell apoptosis and ameliorating disease phenotypes in dextran sodium sulfate-induced colitis mice. These data indicate that ASA treatment is a practical approach to improving SHED-based cell therapy.

CD4+Foxp3+ regulatory T cell differentiation mediated by endometrial stromal cell-derived TECK promotes the growth and invasion of endometriotic lesions

Endometriosis is associated with an abnormal immune response to endometrial cells, which can facilitate the implantation and proliferation of ectopic endometrial tissue. The proportion of CD4(+)Foxp3(+) regulatory T cells (Tregs) is significantly increased in the peritoneal fluid of women with endometriosis. The thymus-expressed chemokine TECK/CCL25 directly promotes the invasiveness of endometrial stromal cells (ESCs). The aim of this study was to investigate the effects of ESC-derived TECK on the crosstalk between Tregs and ESCs in the progress of endometriosis. We determined that the percentage of Tregs and the concentration of TECK increased in the peritoneal fluid with the progression of endometriosis. The supernatant from co-cultured human ESCs and macrophages not only induced Treg differentiation and increased Treg expression of interleukin-10 (IL-10), transforming growth factor-β (TGF-β) and CD73 by activating the AKT/STAT3 signaling pathway but also repressed Treg apoptosis by downregulating Fas and FasL expression and enhanced the Treg-mediated suppression of CD4(+)CD25(-) T cells. In addition, in vitro and in vivo trials confirmed that these effects could be inhibited by anti-TECK neutralizing Abs. The secretion of IL-10 and TGF-β by Tregs increased MMP2 expression and decreased TIMP1 expression and further stimulated the proliferation and invasion of ESCs and the growth of ectopic lesions. These results indicate that TECK derived from ESCs and macrophages upregulates the number and function of Tregs in the ectopic milieu, which contributes to endometriotic immunotolerance and high levels of ESC proliferation and invasion, thereby facilitating the progression of endometriosis.

Transplantation of SHED prevents bone loss in the early phase of ovariectomy-induced osteoporosis

Stem cells from human exfoliated deciduous teeth (SHED) are a unique postnatal stem cell population, possessing multipotent differentiation capacity and immunomodulatory properties. However, the mechanism by which SHED treat immune diseases is not fully understood. Here we show that systemic transplantation of SHED via the tail vein ameliorates ovariectomy (OVX)-induced osteopenia by reducing T-helper 1 (Th1) and T-helper 17 (Th17) cell numbers in the recipient OVX mice. Mechanistically, SHED transplantation induces activated T-cell apoptosis in OVX mice via Fas ligand (FasL)-mediated Fas pathway activation, leading to up-regulation of regulatory T-cells (Tregs) and down-regulation of Th1 and Th17 cells. This SHED-mediated immunomodulation rescues OVX-induced impairment of bone marrow mesenchymal stem cells (BMMSCs) and activation of osteoclastogenesis, resulting in increased bone mass. In summary, SHED-mediated T-cell apoptosis via a FasL/Fas pathway results in immune tolerance and ameliorates the osteopenia phenotype in OVX mice.

Telomerase governs immunomodulatory properties of mesenchymal stem cells by regulating FAS ligand expression

Bone marrow mesenchymal stem cells (BMMSCs) are capable of differentiating into multiple cell types and regulating immune cell response. However, the mechanisms that govern the immunomodulatory properties of BMMSCs are still not fully elucidated. Here we show that telomerase-deficient BMMSCs lose their capacity to inhibit T cells and ameliorate the disease phenotype in systemic sclerosis mice. Restoration of telomerase activity by telomerase reverse transcriptase (TERT) transfection in TERT^−/− BMMSCs rescues their immunomodulatory functions. Mechanistically, we reveal that TERT, combined with β-catenin and BRG1, serves as a transcriptional complex, which binds the FAS ligand (FASL) promoter to upregulate FASL expression, leading to an elevated immunomodulatory function. To test the translational value of these findings in the context of potential clinical therapy, we used aspirin treatment to upregulate telomerase activity in BMMSCs, and found a significant improvement in the immunomodulatory capacity of BMMSCs. Taken together, these findings identify a previously unrecognized role of TERT in improving the immunomodulatory capacity of BMMSCs, suggesting that aspirin treatment is a practical approach to significantly reduce cell dosage in BMMSC-based immunotherapies.

Subject Categories Stem Cells; Immunology

PMA and ionomycin induce glioblastoma cell death: activation-induced cell-death-like phenomena occur in glioma cells

Phorbol myristate acetate (PMA) and ionomycin (Io) can induce T cell activation and proliferation. Furthermore, they stimulate activation-induced cell death (AICD) in mature lymphocytes via Fas/Fas ligand (FasL) up-regulation. In this study, we explored the influence of PMA/Io treatment on glioblastoma cells, and found that AICD-like phenomena may also occur in glioma. Using the MTT assay and cell counting, we demonstrated that treatment of PMA/Io significantly inhibited the proliferation of glioma cell lines, U87 and U251. TUNEL assays and transmission electron microscopy revealed that PMA/Io markedly induced U87 and U251 cell apoptosis. Propidium iodide staining and flow cytometry showed that treatment with PMA/Io resulted in an arrestment of cell cycle and an increase in cell death. Using real-time PCR and western blot, we found that PMA/Io up-regulated the expression of Fas and FasL at both mRNA and protein level, which confirmed that PMA/Io induced glioma cell death. Specific knockdown of NFAT1 expression by small hairpin RNA greatly reduced the PMA/Io induced cell death and apoptosis by inhibition of FasL expression. Microarray analysis showed that the expression of NFAT1 significantly correlated with the expression of Fas. The coexistence of Fas with NFAT1 in vivo provides the background for AICD-like phenomena to occur in glioma. These findings demonstrate that PMA/Io can induce glioblastoma cell death through the NFAT1-Fas/FasL pathway. Glioma-related AICD-like phenomena may provide a novel avenue for glioma treatment.

Mechanisms underlying antigen-specific tolerance of stable and convertible Th17 cells during suppression of autoimmune diabetes

Type 1 diabetes involves both T helper (Th)1 and Th17 cells. While the mechanisms underlying the control of Th1 cells are relatively well defined, those operating modulation of Th17 cells remain unknown. Moreover, given that Th17 cells are plastic and can drive disease as stable or convertible T cells, effective approaches to counter type 1 diabetes would have to alter Th17 function under both circumstances. Herein, we genetically incorporated the BDC2.5-reactive p79 mimotope into an Ig molecule, and the resulting Ig-p79 was used to investigate Th17 tolerance. Accordingly, diabetogenic BDC2.5 Th17 cells were transferred into NOD mice under convertible or stable conditions and their fate was evaluated upon induction of tolerance and disease suppression by Ig-p79. The findings show that convertible (Th17 to Th1) cells display downregulation of the chemokine (C-X-C motif) receptor 3 that was associated with diminished T-box transcription factor T-bet expression, retention in the spleen, and inhibition of trafficking to the pancreas. In contrast, stable Th17 cells downregulated orphan nuclear receptor ROR-γt but increased Fas ligand expression and died by apoptosis. Thus, the final signature transcription factor shapes the mechanism of tolerance in plastic Th17 cells. These findings suggest that effective strategies against type 1 diabetes will require regimens that could drive both mechanisms of tolerance to overcome the disease.

Mesenchymal-stem-cell-induced immunoregulation involves FAS-ligand-/FAS-mediated T cell apoptosis

Systemic infusion of bone marrow mesenchymal stem cells (BMMSCs) yields therapeutic benefit for a variety of autoimmune diseases, but the underlying mechanisms are poorly understood. Here we show that in mice systemic infusion of BMMSCs induced transient T cell apoptosis via the FAS ligand (FASL)-dependent FAS pathway and could ameliorate disease phenotypes in fibrillin-1 mutated systemic sclerosis (SS) and dextran-sulfate-sodium-induced experimental colitis. FASL(-/-) BMMSCs did not induce T cell apoptosis in recipients, and could not ameliorate SS and colitis. Mechanistic analysis revealed that FAS-regulated monocyte chemotactic protein 1 (MCP-1) secretion by BMMSCs recruited T cells for FASL-mediated apoptosis. The apoptotic T cells subsequently triggered macrophages to produce high levels of TGFβ, which in turn led to the upregulation of CD4(+)CD25(+)Foxp3(+) regulatory T cells and, ultimately, immune tolerance. These data therefore demonstrate a previously unrecognized mechanism underlying BMMSC-based immunotherapy involving coupling via FAS/FASL to induce T cell apoptosis.

Inflammatory cytokines determine the susceptibility of human CD8 T cells to Fas-mediated activation-induced cell death through modulation of FasL and c-FLIP(S) expression

The nature of inflammatory signals determines the outcome of T cell responses. However, little is known about how inflammatory cytokines provided to human CD8 T cells during activation affects their susceptibility to post-activation cell death. We have examined and compared the effects of the inflammatory cytokine IL-12, as well as the combination of IL-1, IL-6, and IL-23 (IL-1/6/23) on the susceptibility of primary human CD8 T cells to post-activation cell death. Human CD8 T cells activated in the presence of IL-1/6/23 underwent significantly less cell death after activation as compared with those activated in IL-12. This was due to reduced susceptibility to Fas-mediated activation-induced cell death (AICD). Mechanistically, the reduced level of cell death in CD8 T cells activated in IL-1/6/23 was a result of a low level of FasL expression and high level of c-FLIP(S) expression. When the effect of IL-1, IL-6, and IL-23 individually was examined, IL-1 or IL-6 alone was sufficient to inhibit CD8 T cell death that occurs after activation in IL-12. IL-1, but not IL-6, inhibited expression of FasL, whereas IL-6, but not IL-1, increased c-FLIP(S) expression. Our findings show that the presence of IL-1 and/or IL-6 during activation of human CD8 T cells attenuates Fas-mediated AICD, whereas IL-12 increases the susceptibility of activated CD8 T cells to this form of cell death.

The power and the promise of restimulation-induced cell death in human immune diseases

Controlled expansion and contraction of lymphocytes both during and after an adaptive immune response are imperative to sustain a healthy immune system. Both extrinsic and intrinsic pathways of lymphocyte apoptosis are programmed to eliminate cells at the proper time to ensure immune homeostasis. Genetic disorders of apoptosis described in mice and humans have established Fas and Bim as critical pro-apoptotic molecules responsible for T-cell death in response to T-cell receptor restimulation and cytokine withdrawal, respectively. Emerging evidence prompts revision of this classic paradigm, especially for our understanding of restimulation-induced cell death (RICD) and its physiological purpose. Recent work indicates that RICD employs both Fas and Bim for T-cell deletion, dispelling the notion that these molecules are assigned to mutually exclusive apoptotic pathways. Furthermore, new mouse model data combined with our discovery of defective RICD in X-linked lymphoproliferative disease (XLP) patient T cells suggest that RICD is essential for precluding excess T-cell accumulation and associated immunopathology during the course of certain infections. Here, we review how these advances offer a refreshing new perspective on the phenomenon of T-cell apoptosis induced through antigen restimulation, including its relevance to immune homeostasis and potential for therapeutic interventions.

Sphingosine-1-phosphate Signaling in Human Submandibular Cells

Sphingosine-1-phosphate (S1P) is a significant lipid messenger modulating many physiological responses. S1P plays a critical role in autoimmune disease and is suggested to be involved in Sjögren’s syndrome pathology. However, the mechanism of S1P signaling in salivary glands is unclear. Here we studied the effects of S1P on normal human submandibular gland cells. S1P increased levels of the intracellular Ca2+ concentration ([Ca2+]i), which was inhibited by pre-treatment with U73122 or 2-aminoethoxydiphenyl borate (2-APB). Pre-treated S1P did not inhibit subsequent carbachol-induced [Ca2+]i increase, which suggests that S1P and muscarinic signaling are independent of each other. S1P1, S1P2, and S1P3 receptors SphK1 and SphK2 were commonly expressed in human salivary gland cells. S1P, but not carbachol, induces the expression of interleukin-6 and Fas. Our results suggest that S1P triggers Ca2+ signaling and the apoptotic pathway in normal submandibular gland cells, which suggests in turn that S1P affects the progression of Sjögren’s syndrome.

Comparison of sensitivity of Th1, Th2, and Th17 cells to Fas-mediated apoptosis

Following activation through the TCR, CD4+ T cells can differentiate into three major subsets: Th1, Th2, and Th17 cells. IL-17-secreting Th17 cells play an important role in the pathogenesis of several autoimmune diseases and in immune responses to pathogens, but little is known about the regulation of apoptosis in Th17 cells. In this study, the sensitivity of in vitro-polarized Th1, Th2, and Th17 cells to Fas-mediated apoptosis was compared directly by different methods. The order of sensitivity of T cell subsets to Fas-mediated apoptosis is: Th1 > Th17 > Th2. The greater sensitivity of Th17 cells to Fas-mediated apoptosis compared with Th2 cells correlated with their higher expression of FasL and comparable expression of the antiapoptotic molecule FLIP. The decreased sensitivity of Th17 compared with Th1 cells correlated with the higher expression of FLIP by Th17 cells. Transgenic overexpression of FLIP in T cells protected all three subsets from Fas-mediated apoptosis. These findings provide new knowledge for understanding how survival of different subsets of T cells is regulated.

Melatonin protects CD4+ T cells from activation-induced cell death by blocking NFAT-mediated CD95 ligand upregulation

Over the past 20 y, the hormone melatonin was found to be produced in extrapineal sites, including cells of the immune system. Despite the increasing data regarding the biological effects of melatonin on the regulation of the immune system, the effect of this molecule on T cell survival remains largely unknown. Activation-induced cell death plays a critical role in the maintenance of the homeostasis of the immune system by eliminating self-reactive or chronically stimulated T cells. Because activated T cells not only synthesize melatonin but also respond to it, we investigated whether melatonin could modulate activation-induced cell death. We found that melatonin protects human and murine CD4(+) T cells from apoptosis by inhibiting CD95 ligand mRNA and protein upregulation in response to TCR/CD3 stimulation. This inhibition is a result of the interference with calmodulin/calcineurin activation of NFAT that prevents the translocation of NFAT to the nucleus. Accordingly, melatonin has no effect on T cells transfected with a constitutively active form of NFAT capable of migrating to the nucleus and transactivating target genes in the absence of calcineurin activity. Our results revealed a novel biochemical pathway that regulates the expression of CD95 ligand and potentially other downstream targets of NFAT activation.

Unlike Th1, Th17 cells mediate sustained autoimmune inflammation and are highly resistant to restimulation-induced cell death

Both Th1 and Th17 T cell subsets can mediate inflammation, but the kinetics of the pathogenic processes mediated by these two subsets have not been investigated. Using an experimental system in which TCR-transgenic Th1 or Th17 cells specific for hen egg lysozyme induce ocular inflammation in recipient mice expressing eye-restricted hen egg lysozyme, we found important differences in the in vivo behavior of these two subsets. Th1 cells initially proliferated considerably faster and invaded the eye more quickly than their Th17 counterparts, but then disappeared rapidly. By contrast, Th17 cells accumulated and remained the majority of the infiltrating CD4(+) cells in the eye for as long as 25 days after transfer, mediating more long-lasting pathological changes. Unlike Th1, Th17 cells were highly resistant to restimulation-induced apoptosis, a major pathway by which autoimmune and chronically restimulated Th1 cells are eliminated. Th17 cells had reduced Fas ligand production and resistance to Fas-induced apoptosis, relative to Th1 cells, despite similar surface expression of Fas. Th17-induced ocular inflammation also differed from Th1-induced inflammation by consisting of more neutrophils, whereas Th1-induced disease had higher proportions of CD8 cells. Taken together, our data show that pathogenic processes triggered by Th17 lag behind those induced by Th1, but then persist remarkably longer, apparently due to the relative resistance of Th17 cells to restimulation-induced cell death. The long-lasting inflammation induced by Th17 cells is in accord with these cells being involved in chronic conditions in humans.