Cleavage of roquin and regnase-1 by the paracaspase MALT1 releases their cooperatively repressed targets to promote T(H)17 differentiation.

Humoral autoimmunity paralleled by the accumulation of follicular helper T cells (T(FH) cells) is linked to mutation of the gene encoding the RNA-binding protein roquin-1. Here we found that T cells lacking roquin caused pathology in the lung and accumulated as cells of the T(H)17 subset of helper T cells in the lungs. Roquin inhibited T(H)17 cell differentiation and acted together with the endoribonuclease regnase-1 to repress target mRNA encoding the T(H)17 cell-promoting factors IL-6, ICOS, c-Rel, IRF4, IκBNS and IκBζ. This cooperation required binding of RNA by roquin and the nuclease activity of regnase-1. Upon recognition of antigen by the T cell antigen receptor (TCR), roquin and regnase-1 proteins were cleaved by the paracaspase MALT1. Thus, this pathway acts as a 'rheostat' by translating TCR signal strength via graded inactivation of post-transcriptional repressors and differential derepression of targets to enhance T(H)17 differentiation.

Unrestrained cleavage of Roquin-1 by MALT1 induces spontaneous T cell activation and the development of autoimmunity.

Constitutive activation of the MALT1 paracaspase in conventional T cells of Malt1TBM/TBM (TRAF6 Binding Mutant = TBM) mice causes fatal inflammation and autoimmunity, but the involved targets and underlying molecular mechanisms are unknown. We genetically rendered a single MALT1 substrate, the RNA-binding protein (RBP) Roquin-1, insensitive to MALT1 cleavage. These Rc3h1Mins/Mins mice showed normal immune homeostasis. Combining Rc3h1Mins/Mins alleles with those encoding for constitutively active MALT1 (TBM) prevented spontaneous T cell activation and restored viability of Malt1TBM/TBM mice. Mechanistically, we show how antigen/MHC recognition is translated by MALT1 into Roquin cleavage and derepression of Roquin targets. Increasing T cell receptor (TCR) signals inactivated Roquin more effectively, and only high TCR strength enabled derepression of high-affinity targets to promote Th17 differentiation. Induction of experimental autoimmune encephalomyelitis (EAE) revealed increased cleavage of Roquin-1 in disease-associated Th17 compared to Th1 cells in the CNS. T cells from Rc3h1Mins/Mins mice did not efficiently induce the high-affinity Roquin-1 target IκBNS in response to TCR stimulation, showed reduced Th17 differentiation, and Rc3h1Mins/Mins mice were protected from EAE. These data demonstrate how TCR signaling and MALT1 activation utilize graded cleavage of Roquin to differentially regulate target mRNAs that control T cell activation and differentiation as well as the development of autoimmunity.

Nfkbid Overexpression in Nonobese Diabetic Mice Elicits Complete Type 1 Diabetes Resistance in Part Associated with Enhanced Thymic Deletion of Pathogenic CD8 T Cells and Increased Numbers and Activity of Regulatory T Cells.

Type 1 diabetes (T1D) in both humans and NOD mice is caused by T cell-mediated autoimmune destruction of pancreatic ß cells. Increased frequency or activity of autoreactive T cells and failures of regulatory T cells (Tregs) to control these pathogenic effectors have both been implicated in T1D etiology. Due to the expression of MHC class I molecules on ß cells, CD8 T cells represent the ultimate effector population mediating T1D. Developing autoreactive CD8 T cells normally undergo extensive thymic negative selection, but this process is impaired in NOD mice and also likely T1D patients. Previous studies identified an allelic variant of Nfkbid, a NF-κB signal modulator, as a gene strongly contributing to defective thymic deletion of autoreactive CD8 T cells in NOD mice. These previous studies found ablation of Nfkbid in NOD mice using the clustered regularly interspaced short palindromic repeats system resulted in greater thymic deletion of pathogenic CD8 AI4 and NY8.3 TCR transgenic T cells but an unexpected acceleration of T1D onset. This acceleration was associated with reductions in the frequency of peripheral Tregs. In this article, we report transgenic overexpression of Nfkbid in NOD mice also paradoxically results in enhanced thymic deletion of autoreactive CD8 AI4 T cells. However, transgenic elevation of Nfkbid expression also increased the frequency and functional capacity of peripheral Tregs, in part contributing to the induction of complete T1D resistance. Thus, future identification of a pharmaceutical means to enhance Nfkbid expression might ultimately provide an effective T1D intervention approach.

Emission Spectroscopy-Based Sensor System to Correlate the In-Cylinder Combustion Temperature of a Diesel Engine to NOx Emissions.

Due to a rising importance of the reduction of pollutant, produced by conventional energy technologies, the knowledge of pollutant forming processes during a combustion is of great interest. In this study the in-cylinder temperature, of a near series diesel engine, is examined with a minimal invasive emission spectroscopy sensor. The soot, nearly a black body radiator, emits light, which is spectrally detected and evaluated with a modified function of Planck's law. The results show a good correlation between the determined temperatures and the NOx concentration, measured in the exhaust gas of the engine, during a variety of engine operating points. A standard deviation between 25 K and 49 K was obtained for the in-cylinder temperature measurements.

Immunophenotyping of Monocyte Migration Markers and Therapeutic Effects of Selenium on IL-6 and IL-1ß Cytokine Axes of Blood Mononuclear Cells in Preoperative and Postoperative Coronary Artery Disease Patients.

Multivessel coronary artery disease (CAD) is characterized by underlying chronic vascular inflammation and occlusion in the coronary arteries, where these patients undergo coronary artery bypass grafting (CABG). Since post-cardiotomy inflammation is a well known phenomenon after CABG, attenuation of this inflammation is required to reduce perioperative morbidity and mortality. In this study, we aimed to phenotype circulating frequencies and intensities of monocyte subsets and monocyte migration markers, respectively, and to investigate the plasma level of inflammatory cytokines and chemokines between preoperative and postoperative CAD patients and later, to intervene the inflammation with sodium selenite. We found a higher amplitude of inflammation, postoperatively, in terms of CCR1high monocytes and significantly increased pro-inflammatory cytokines, IL-6, IL-8, and IL-1RA. Further, in vitro intervention with selenium displayed mitigating effects on the IL-6/STAT-3 axis of mononuclear cells derived from postoperative CAD patients. In addition, in vitro selenium intervention significantly reduced IL-1ß production as well as decreased cleaved caspase-1 (p20) activity by preoperative (when stimulated) as well as postoperative CAD mononuclear cells. Though TNF-α exhibited a positive correlation with blood troponin levels in postoperative CAD patients, there was no obvious effect of selenium on the TNF-α/NF-κB axis. In conclusion, anti-inflammatory selenium might be utilized to impede systemic inflammatory cytokine axes to circumvent aggravating atherosclerosis and further damage to the autologous bypass grafts during the post-surgical period.

Gadd45 Proteins in Immunity 2.0.

To protect the host against invading pathogens such as viruses, bacteria, and parasites as well as against tumor cells, the immune system of vertebrates has to distinguish between self and non-self, but also between harmless and dangerous. To do so, the immune system developed an innate and an adaptive branch that provide immediate and long-lasting protection, respectively. Furthermore, the immune system is composed of different cell types, which are specialized to combat different threats, and it is located at strategic locations to manage surveillance of the whole body. Therefore, immune cells need to communicate with each other. Growth arrest and DNA damage-inducible 45 (Gadd45) proteins are important components of intracellular signaling networks that convey messages from other cells in the receiving cell into biological responses. Within the 7 years that have passed since my first overview about Gadd45 proteins in the immune system, substantial progress has been made in our understanding of the immune system and with respect to Gadd45 proteins. Therefore, it is time for an update-Gadd45 proteins in immunity 2.0. In order to put Gadd45 proteins into the context of the immune system, I will first give a brief introduction into the immune system. Afterwards, I will give a brief introduction into Gadd45 proteins. For deeper insight, I refer to the other chapters of this book. The third section discusses the role of Gadd45 proteins in myeloid and lymphoid cells. The last two sections will be on the function of Gadd45 proteins in infection, autoimmunity, and tumor immunology.

Regulating T-cell differentiation through the polyamine spermidine.

BACKGROUND: The cross-talk between the host and its microbiota plays a key role in the promotion of health. The production of metabolites such as polyamines by intestinal-resident bacteria is part of this symbiosis shaping host immunity. The polyamines putrescine, spermine, and spermidine are abundant within the gastrointestinal tract and might substantially contribute to gut immunity. OBJECTIVE: We aimed to characterize the polyamine spermidine as a modulator of T-cell differentiation and function. METHODS: Naive T cells were isolated from wild-type mice or cord blood from healthy donors and submitted to polarizing cytokines, with and without spermidine treatment, to evaluate CD4+ T-cell differentiation in vitro. Moreover, mice were subjected to oral supplementation of spermidine, or its precursor l-arginine, to assess the frequency and total numbers of regulatory T (Treg) cells in vivo. RESULTS: Spermidine modulates CD4+ T-cell differentiation in vitro, preferentially committing naive T cells to a regulatory phenotype. After spermidine treatment, activated T cells lacking the autophagy gene Atg5 fail to upregulate Foxp3 to the same extent as wild-type cells. These results indicate that spermidine's polarizing effect requires an intact autophagic machinery. Furthermore, dietary supplementation with spermidine promotes homeostatic differentiation of Treg cells within the gut and reduces pathology in a model of T-cell transfer-induced colitis. CONCLUSION: Altogether, our results highlight the beneficial effects of spermidine, or l-arginine, on gut immunity by promoting Treg cell development.

Type of PaperY192 within the SH2 Domain of Lck Regulates TCR Signaling Downstream of PLC-γ1 and Thymic Selection.

Signaling via the TCR, which is initiated by the Src-family tyrosine kinase Lck, is crucial for the determination of cell fates in the thymus. Because of its pivotal role, ablation of Lck results in a profound block of T-cell development. Here, we show that, in addition to its well-known function in the initiation of TCR signaling, Lck also acts at a more downstream level. This novel function of Lck is determined by the tyrosine residue (Y192) located in its SH2 domain. Thymocytes from knock-in mice expressing a phosphomimetic Y192E mutant of Lck initiate TCR signaling upon CD3 cross-linking up to the level of PLC-γ1 phosphorylation. However, the activation of downstream pathways including Ca2+ influx and phosphorylation of Erk1/2 are impaired. Accordingly, positive and negative selections are blocked in LckY192E knock-in mice. Collectively, our data indicate that Lck has a novel function downstream of PLCγ-1 in the regulation of thymocyte differentiation and selection.

The NF-κB transcription factor c-Rel controls host defense against Citrobacter rodentium.

Mice lacking CD4+ T cells or B cells are highly susceptible to Citrobacter rodentium infection. In this study, we show that the activity of the transcription factor c-Rel in lymphocytes is crucial for clearance of C. rodentium. Mice deficient for c-Rel fail to generate protective antibodies and to eradicate the pathogen.

IκB(NS) protein mediates regulatory T cell development via induction of the Foxp3 transcription factor.

Forkhead box P3 positive (Foxp3(+)) regulatory T (Treg) cells suppress immune responses and regulate peripheral tolerance. Here we show that the atypical inhibitor of NFκB (IκB) IκB(NS) drives Foxp3 expression via association with the promoter and the conserved noncoding sequence 3 (CNS3) of the Foxp3 locus. Consequently, IκB(NS) deficiency leads to a substantial reduction of Foxp3(+) Treg cells in vivo and impaired Foxp3 induction upon transforming growth factor-ß (TGF-ß) treatment in vitro. Moreover, fewer Foxp3(+) Treg cells developed from IκB(NS)-deficient CD25(-)CD4(+) T cells adoptively transferred into immunodeficient recipients. Importantly, IκB(NS) was required for the transition of immature GITR(+)CD25(+)Foxp3(-) thymic Treg cell precursors into Foxp3(+) cells. In contrast to mice lacking c-Rel or Carma1, IκB(NS)-deficient mice do not show reduced Treg precursor cells. Our results demonstrate that IκB(NS) critically regulates Treg cell development in the thymus and during gut inflammation, indicating that strategies targeting IκB(NS) could modulate the Treg cell compartment.

Essential role of IκBNS for in vivo CD4+ T-cell activation, proliferation, and Th1-cell differentiation during Listeria monocytogenes infection in mice.

Acquisition of effector functions in T cells is guided by transcription factors, including NF-κB, that itself is tightly controlled by inhibitory proteins. The atypical NF-κB inhibitor, IκBNS, is involved in the development of Th1, Th17, and regulatory T (Treg) cells. However, it remained unclear to which extend IκBNS contributed to the acquisition of effector function in T cells specifically responding to a pathogen during in vivo infection. Tracking of adoptively transferred T cells in Listeria monocytogenes infected mice antigen-specific activation of CD4+ T cells following in vivo pathogen encounter to strongly rely on IκBNS . While IκBNS was largely dispensable for the acquisition of cytotoxic effector function in CD8+ T cells, IκBNS -deficient Th1 effector cells exhibited significantly reduced proliferation, marked changes in the pattern of activation marker expression, and reduced production of the Th1-cell cytokines IFN-γ, IL-2, and TNF-α. Complementary in vitro analyses using cells from novel reporter and inducible knockout mice revealed that IκBNS predominantly affects the early phase of Th1-cell differentiation while its function in terminally differentiated cells appears to be negligible. Our data suggest IκBNS as a potential target to modulate specifically CD4+ T-cell responses.

A Hypermorphic Nfkbid Allele Contributes to Impaired Thymic Deletion of Autoreactive Diabetogenic CD8+ T Cells in NOD Mice.

In both NOD mice and humans, the development of type 1 diabetes (T1D) is dependent in part on autoreactive CD8+ T cells recognizing pancreatic ß cell peptides presented by often quite common MHC class I variants. Studies in NOD mice previously revealed that the common H2-Kd and/or H2-Db class I molecules expressed by this strain aberrantly lose the ability to mediate the thymic deletion of pathogenic CD8+ T cell responses through interactions with T1D susceptibility genes outside the MHC. A gene(s) mapping to proximal chromosome 7 was previously shown to be an important contributor to the failure of the common class I molecules expressed by NOD mice to mediate the normal thymic negative selection of diabetogenic CD8+ T cells. Using an inducible model of thymic negative selection and mRNA transcript analyses, we initially identified an elevated Nfkbid expression variant as a likely NOD-proximal chromosome 7 region gene contributing to impaired thymic deletion of diabetogenic CD8+ T cells. CRISPR/Cas9-mediated genetic attenuation of Nfkbid expression in NOD mice resulted in improved negative selection of autoreactive diabetogenic AI4 and NY8.3 CD8+ T cells. These results indicated that allelic variants of Nfkbid contribute to the efficiency of intrathymic deletion of diabetogenic CD8+ T cells. However, although enhancing thymic deletion of pathogenic CD8+ T cells, ablating Nfkbid expression surprisingly accelerated T1D onset that was associated with numeric decreases in both regulatory T and B lymphocytes in NOD mice.

Memantine potentiates cytarabine-induced cell death of acute leukemia correlating with inhibition of Kv1.3 potassium channels, AKT and ERK1/2 signaling.

BACKGROUND: Treatment of acute leukemia is challenging and long-lasting remissions are difficult to induce. Innovative therapy approaches aim to complement standard chemotherapy to improve drug efficacy and decrease toxicity. Promising new therapeutic targets in cancer therapy include voltage-gated Kv1.3 potassium channels, but their role in acute leukemia is unclear. We reported that Kv1.3 channels of lymphocytes are blocked by memantine, which is known as an antagonist of neuronal N-methyl-D-aspartate type glutamate receptors and clinically applied in therapy of advanced Alzheimer disease. Here we evaluated whether pharmacological targeting of Kv1.3 channels by memantine promotes cell death of acute leukemia cells induced by chemotherapeutic cytarabine. METHODS: We analyzed acute lymphoid (Jurkat, CEM) and myeloid (HL-60, Molm-13, OCI-AML-3) leukemia cell lines and patients' acute leukemic blasts after treatment with either drug alone or the combination of cytarabine and memantine. Patch-clamp analysis was performed to evaluate inhibition of Kv1.3 channels and membrane depolarization by memantine. Cell death was determined with propidium iodide, Annexin V and SYTOX staining and cytochrome C release assay. Molecular effects of memantine co-treatment on activation of Caspases, AKT, ERK1/2, and JNK signaling were analysed by Western blot. Kv1.3 channel expression in Jurkat cells was downregulated by shRNA. RESULTS: Our study demonstrates that memantine inhibits Kv1.3 channels of acute leukemia cells and in combination with cytarabine potentiates cell death of acute lymphoid and myeloid leukemia cell lines as well as primary leukemic blasts from acute leukemia patients. At molecular level, memantine co-application fosters concurrent inhibition of AKT, S6 and ERK1/2 and reinforces nuclear down-regulation of MYC, a common target of AKT and ERK1/2 signaling. In addition, it augments mitochondrial dysfunction resulting in enhanced cytochrome C release and activation of Caspase-9 and Caspase-3 leading to amplified apoptosis. CONCLUSIONS: Our study underlines inhibition of Kv1.3 channels as a therapeutic strategy in acute leukemia and proposes co-treatment with memantine, a licensed and safe drug, as a potential approach to promote cytarabine-based cell death of various subtypes of acute leukemia.

c-REL and IκBNS Govern Common and Independent Steps of Regulatory T Cell Development from Novel CD122-Expressing Pre-Precursors.

Foxp3-expressing regulatory T cells (Tregs) are essential regulators of immune homeostasis and, thus, are prime targets for therapeutic interventions of diseases such as cancer and autoimmunity. c-REL and IκBNS are important regulators of Foxp3 induction in Treg precursors upon γ-chain cytokine stimulation. In c-REL/IκBNS double-deficient mice, Treg numbers were dramatically reduced, indicating that together, c-REL and IκBNS are pivotal for Treg development. However, despite the highly reduced Treg compartment, double-deficient mice did not develop autoimmunity even when aged to more than 1 y, suggesting that c-REL and IκBNS are required for T cell effector function as well. Analyzing Treg development in more detail, we identified a CD122+ subset within the CD25-Foxp3- precursor population, which gave rise to classical CD25+Foxp3- Treg precursors. Importantly, c-REL, but not IκBNS, controlled the generation of classical CD25+Foxp3- precursors via direct binding to the Cd25 locus. Thus, we propose that CD4+GITR+CD122+CD25-Foxp3- cells represent a Treg pre-precursor population, whose transition into Treg precursors is mediated via c-REL.

IκBNS regulates murine Th17 differentiation during gut inflammation and infection.

IL-17-producing Th17 cells mediate immune responses against a variety of fungal and bacterial infections. Signaling via NF-κB has been linked to the development and maintenance of Th17 cells. We analyzed the role of the unusual inhibitor of NF-κB, IκBNS, in the proliferation and effector cytokine production of murine Th17 cells. Our study demonstrates that nuclear IκBNS is crucial for murine Th17 cell generation. IκBNS is highly expressed in Th17 cells; in the absence of IκBNS, the frequencies of IL-17A-producing cells are drastically reduced. This was measured in vitro under Th17-polarizing conditions and confirmed in two colitis models. Mechanistically, murine IκBNS (-/-) Th17 cells were less proliferative and expressed markedly reduced levels of IL-2, IL-10, MIP-1α, and GM-CSF. Citrobacter rodentium was used as a Th17-inducing infection model, in which IκBNS (-/-) mice displayed an increased bacterial burden and diminished tissue damage. These results demonstrate the important function of Th17 cells in pathogen clearance, as well as in inflammation-associated pathology. We identified IκBNS to be crucial for the generation and function of murine Th17 cells upon inflammation and infection. Our findings may have implications for the therapy of autoimmune conditions, such as inflammatory bowel disease, and for the treatment of gut-tropic infections.

Autophagy in T-cell development, activation and differentiation.

Autophagy is a vital catabolic process for degrading bulky cytosolic contents, which cannot be resorbed via the proteasome. First described as a survival mechanism during nutrient starvation conditions, recent reports have demonstrated that autophagy supports metabolic functions of T cells at various stages of maturation and effector function. Autophagy is crucial for T-cell development at the precursor stage as self-renewability and quiescence of hematopoietic stem cells depend on autophagy of the mitochondria and the endoplasmic reticulum. Later, during development in the thymus, autophagy regulates peptide presentation in stromal cells and professional antigen-presenting cells, which mediate thymocyte selection. Furthermore, the metabolic changes when mature T cells enter the periphery and when they are activated are both dependent on autophagy. Lastly, autophagy prevents early aging and, thus, ensures maintenance of memory T cells.

IκBζ is a transcriptional key regulator of CCL2/MCP-1.

CCL2, also referred to as MCP-1, is critically involved in directing the migration of blood monocytes to sites of inflammation. Consequently, excessive CCL2 secretion has been linked to many inflammatory diseases, whereas a lack of expression severely impairs immune responsiveness. We demonstrate that IκBζ, an atypical IκB family member and transcriptional coactivator required for the selective expression of a subset of NF-κB target genes, is a key activator of the Ccl2 gene. IκBζ-deficient macrophages exhibited impaired secretion of CCL2 when challenged with diverse inflammatory stimuli, such as LPS or peptidoglycan. These findings were reflected at the level of Ccl2 gene expression, which was tightly coupled to the presence of IκBζ. Moreover, mechanistic insights acquired by chromatin immunoprecipitation demonstrate that IκBζ is directly recruited to the proximal promoter region of the Ccl2 gene and is required for transcription-enhancing histone H3 at lysine-4 trimethylation. Finally, IκBζ-deficient mice showed significantly impaired CCL2 secretion and monocyte infiltration in an experimental model of peritonitis. Together, these findings suggest a distinguished role of IκBζ in mediating the targeted recruitment of monocytes in response to local inflammatory events.

Glutathione depletion regulates both extrinsic and intrinsic apoptotic signaling cascades independent from multidrug resistance protein 1.

Glutathione (GSH) depletion is an important hallmark of apoptosis. We previously demonstrated that GSH depletion, by its efflux, regulates apoptosis by modulation of executioner caspase activity. However, both the molecular identity of the GSH transporter(s) involved and the signaling cascades regulating GSH loss remain obscure. We sought to determine the role of multidrug resistance protein 1 (MRP1) in GSH depletion and its regulatory role on extrinsic and intrinsic pathways of apoptosis. In human lymphoma cells, GSH depletion was stimulated rather than inhibited by pharmacological blockage of MRP1 with MK571. GSH loss was dependent on initiator caspases 8 and 9 activity. Genetic knock-down (>60 %) of MRP1 by stable transfection with short hairpin small interfering RNA significantly reduced MRP1 protein levels, which correlated directly with the loss of MRP1-mediated anion transport. However, GSH depletion and apoptosis induced by both extrinsic and intrinsic pathways were not affected by MRP1 knock-down. Interestingly, stimulation of GSH loss by MK571 also enhanced the initiator phase of apoptosis by stimulating initiator caspase 8 and 9 activity and pro-apoptotic BCL-2 interacting domain cleavage. Our results clearly show that caspase-dependent GSH loss and apoptosis are not mediated by MRP1 proteins and that GSH depletion stimulates the initiation phase of apoptosis in lymphoid cells.

Cellular-FLIP, Raji isoform (c-FLIP R) modulates cell death induction upon T-cell activation and infection.

Dysregulation of apoptosis caused by an imbalance of pro- and anti-apoptotic protein expression can lead to cancer, neurodegenerative, and autoimmune diseases. Cellular-FLIP (c-FLIP) proteins inhibit apoptosis directly at the death-inducing signaling complex of death receptors, such as CD95, and have been linked to apoptosis regulation during immune responses. While the isoforms c-FLIPL and c-FLIPS are well characterized, the function of c-FLIPR remains poorly understood. Here, we demonstrate the induction of endogenous murine c-FLIPR in activated lymphocytes for the first time. To analyze c-FLIPR function in vivo, we generated transgenic mice expressing murine c-FLIPR specifically in hematopoietic cells. As expected, lymphocytes from c-FLIPR transgenic mice were protected against CD95-induced apoptosis in vitro. In the steady state, transgenic mice had normal cell numbers and unaltered frequencies of B cells and T-cell subsets in lymphoid organs. However, when challenged with Listeria monocytogenes, c-FLIPR transgenic mice showed less liver necrosis and better bacterial clearance compared with infected wild-type mice. We conclude that c-FLIPR expression in hematopoietic cells supports an efficient immune response against bacterial infections.