Polyfunctional HCV-specific T-cell responses are associated with effective control of HCV replication.

HCV infection has a severe course of disease in HIV/HCV co-infection and in liver transplant recipients. However, the mechanisms involved remain unclear. Here, we evaluated functional profiles of HCV-specific T-cell responses in 86 HCV mono-infected patients, 48 HIV/HCV co-infected patients and 42 liver transplant recipients. IFN-gamma and IL-2 production and ability of CD4 and CD8 T cells to proliferate were assessed after stimulation with HCV-derived peptides. We observed that HCV-specific T-cell responses were polyfunctional in HCV mono-infected patients, with presence of proliferating single IL-2-, dual IL-2/IFN-gamma and single IFN-gamma-producing CD4+ and dual IL-2/IFN-gamma and single IFN-gamma-producing CD8+ cells. In contrast, HCV-specific T-cell responses had an effector profile in HIV/HCV co-infected individuals and liver transplant recipients with absence of single IL-2-producing HCV-specific CD4+ and dual IL-2/IFN-gamma-producing CD8+ T cells. In addition, HCV-specific proliferation of CD4+ and CD8+ T cells was severely impaired in HIV/HCV co-infected patients and liver transplant recipients. Importantly, "only effector" T-cell responses were associated with significantly higher HCV viral load and more severe liver fibrosis scores. Therefore, the present results suggest that immune-based mechanisms may contribute to explain the accelerated course of HCV infection in conditions of HIV-1 co-infection and liver transplantation.

Delayed mortality and attenuated thrombocytopenia associated with severe malaria in urokinase- and urokinase receptor-deficient mice.

We explored the role of urokinase and tissue-type plasminogen activators (uPA and tPA), as well as the uPA receptor (uPAR; CD87) in mouse severe malaria (SM), using genetically deficient (-/-) mice. The mortality resulting from Plasmodium berghei ANKA infection was delayed in uPA(-/-) and uPAR(-/-) mice but was similar to that of the wild type (+/+) in tPA(-/-) mice. Parasitemia levels were similar in uPA(-/-), uPAR(-/-), and +/+ mice. Production of tumor necrosis factor, as judged from the plasma level and the mRNA levels in brain and lung, was markedly increased by infection in both +/+ and uPAR(-/-) mice. Breakdown of the blood-brain barrier, as evidenced by the leakage of Evans Blue, was similar in +/+ and uPAR(-/-) mice. SM was associated with a profound thrombocytopenia, which was attenuated in uPA(-/-) and uPAR(-/-) mice. Administration of aprotinin, a plasmin antagonist, also delayed mortality and attenuated thrombocytopenia. Platelet trapping in cerebral venules or alveolar capillaries was evident in +/+ mice but absent in uPAR(-/-) mice. In contrast, macrophage sequestration in cerebral venules or alveolar capillaries was evident in both +/+ and uPAR(-/-) mice. Polymorphonuclear leukocyte sequestration in alveolar capillaries was similar in +/+ and uPAR(-/-) mice. These results demonstrate that the uPAR deficiency attenuates the severity of SM, probably by its important role in platelet kinetics and trapping. These results therefore suggest that platelet sequestration contributes to the pathogenesis of SM.

CD8 beta increases CD8 coreceptor function and participation in TCR-ligand binding.

To study the role of CD8 beta in T cell function, we derived a CD8 alpha/beta-(CD8-/-) T cell hybridoma of the H-2Kd-restricted N9 cytotoxic T lymphocyte clone specific for a photoreactive derivative of the Plasmodium berghei circumsporozoite peptide PbCS 252-260. This hybridoma was transfected either with CD8 alpha alone or together with CD8 beta. All three hybridomas released interleukin 2 upon incubation with L cells expressing Kd-peptide derivative complexes, though CD8 alpha/beta cells did so more efficiently than CD8 alpha/alpha and especially CD8-/- cells. More strikingly, only CD8 alpha/beta cells were able to recognize a weak agonist peptide derivative variant. This recognition was abolished by Fab' fragments of the anti-Kd alpha 3 monoclonal antibody SF1-1.1.1 or substitution of Kd D-227 with K, both conditions known to impair CD8 coreceptor function. T cell receptor (TCR) photoaffinity labeling indicated that TCR-ligand binding on CD8 alpha/beta cells was approximately 5- and 20-fold more avid than on CD8 alpha/a and CD8-/- cells, respectively. SF1-1.1.1 Fab' or Kd mutation D227K reduced the TCR photoaffinity labeling on CD8 alpha/beta cells to approximately the same low levels observed on CD8-/- cells. These results indicate that CD8 alpha/beta is a more efficient coreceptor than CD8alpha/alpha, because it more avidly strengthens TCR-ligand binding.

Destruction of conditional insulinoma cell lines in NOD mice: a role for autoimmunity.

AIMS/HYPOTHESIS: betaTC-tet (H2(k)) is a conditional insulinoma cell line derived from transgenic mice expressing a tetracycline-regulated oncogene. Transgenic expression of several proteins implicated in the apoptotic pathways increase the resistance of betaTC-tet cells in vitro. We tested in vivo the sensitivity of the cells to rejection and the protective effect of genetic alterations in NOD mice. METHODS: betaTC-tet cells and genetically engineered lines expressing Bcl-2 (CDM3D), a dominant negative mutant of MyD88 or SOCS-1 were transplanted in diabetic female NOD mice or in male NOD mice with diabetes induced by high-dose streptozotocin. Survival of functional cell grafts in NOD-scid mice was also analyzed after transfer of splenocytes from diabetic NOD mice. Autoreactive T-cell hybridomas and splenocytes from diabetic NOD mice were stimulated by betaTC-tet cells. RESULTS: betaTC-tet cells and genetically engineered cell lines were all similarly rejected in diabetic NOD mice and in NOD-scid mice after splenocyte transfer. In 3- to 6-week-old male NOD mice treated with high-dose streptozotocin, the cells temporarily survived, in contrast with C57BL/6 mice treated with high-dose streptozotocin (indefinite survival) and untreated 3- to 6-week-old male NOD mice (rejection). The protective effect of high-dose streptozotocin was lost in older male NOD mice. betaTC-tet cells did not stimulate autoreactive T-cell hybridomas, but induced IL-2 secretion by splenocytes from diabetic NOD mice. CONCLUSION/INTERPRETATION: The autoimmune process seems to play an important role in the destruction of betaTC-tet cells in NOD mice. Genetic manipulations intended at increasing the resistance of beta cells were inefficient. Similar approaches should be tested in vivo as well as in vitro. High dose streptozotocin influences immune rejection and should be used with caution.

Danger signaling through the inflammasome acts as a master switch between tolerance and sensitization.

Efficient priming of adaptive immunity depends on danger signals provided by innate immune pathways. As an example, inflammasome-mediated activation of caspase-1 and IL-1beta is crucial for the development of reactive T cells targeting sensitizers like dinitrofluorobenzene (DNFB). Surprisingly, DNFB and dinitrothiocyanobenzene provide cross-reactive Ags yet drive opposing, sensitizing vs tolerizing, T cell responses. In this study, we show that, in mice, inflammasome-signaling levels can be modulated to turn dinitrothiocyanobenzene into a sensitizer and DNFB into a tolerizer, and that it correlates with the IL-6 and IL-12 secretion levels, affecting Th1, Th17, and regulatory T cell development. Hence, our data provide the first evidence that the inflammasome can define the type of adaptive immune response elicited by an Ag, and hint at new strategies to modulate T cell responses in vivo.

Less mortality but more relapses in experimental allergic encephalomyelitis in CD8-/- mice.

Mice lacking in CD8 were generated from homologous recombination in embryonal stem cells at the CD8 locus and bred with the experimental allergic encephalomyelitis (EAE)-susceptible PL/JH-2u through four backcross generations to investigate the role of CD8+ T cells in this model of multiple sclerosis. The disease onset and susceptibility were similar to those of wild-type mice. However, the mutant mice had a milder acute EAE, reflected by fewer deaths, but more chronic EAE, reflected by a higher frequency of relapse. This suggests that CD8+ T lymphocytes may participate as both effectors and regulators in this animal model.

Functional heterogeneity of memory CD4 T cell responses in different conditions of antigen exposure and persistence.

Memory CD4 T cell responses are functionally and phenotypically heterogeneous. In the present study, memory CD4 T cell responses were analyzed in different models of Ag-specific immune responses differing on Ag exposure and/or persistence. Ag-specific CD4 T cell responses for tetanus toxoid, HSV, EBV, CMV, and HIV-1 were compared. Three distinct patterns of T cell response were observed. A dominant single IL-2 CD4 T cell response was associated with the model in which the Ag can be cleared. Polyfunctional (single IL-2 plus IL-2/IFN-gamma plus single IFN-gamma) CD4 T cell responses were associated with Ag persistence and low Ag levels. A dominant single IFN-gamma CD4 T cell response was associated with the model of Ag persistence and high Ag levels. The results obtained supported the hypothesis that the different patterns observed were substantially influenced by different conditions of Ag exposure and persistence.

Successes and limitations of targeted therapies in renal cell carcinoma.

Until recently, the standard treatment for metastatic renal cell carcinoma (RCC) was nonspecific immunotherapy based on interleukin-2 or interferon-α. This was associated with a modest survival benefit and with significant clinical toxicities. The understanding of numerous molecular pathways in RCC, including HIF, VEGF, mTOR, and the consecutive use of targeted therapies since the beginning of 2005 have significantly improved outcomes for patients with metastatic RCC with an overall survival greater than 2 years. At present, at least 7 targeted agents are approved for first and consecutive lines of treatment of clear cell metastatic RCC. Long-term benefit and extended survival may be achieved through the optimal use of targeted therapies: optimal dosing, adverse event management and treatment duration and compliance. Advances in the finding of prognostic factors highlight the potential for personalizing treatment for patients with metastatic RCC. Data regarding the best sequencing of targeted therapies, predictive biomarkers, best timing of surgery, patient risk profiles, understanding of resistance mechanisms and safety of targeted therapies are growing and will provide a further step ahead in the management of advanced RCC. In parallel, a new class of therapeutics is emerging in RCC: immunotherapy; in particular check-point blockade antibodies are showing very promising results.

Intestinal gluconeogenesis is a key factor for early metabolic changes after gastric bypass but not after gastric lap-band in mice.

Unlike the adjustable gastric banding procedure (AGB), Roux-en-Y gastric bypass surgery (RYGBP) in humans has an intriguing effect: a rapid and substantial control of type 2 diabetes mellitus (T2DM). We performed gastric lap-band (GLB) and entero-gastro anastomosis (EGA) procedures in C57Bl6 mice that were fed a high-fat diet. The EGA procedure specifically reduced food intake and increased insulin sensitivity as measured by endogenous glucose production. Intestinal gluconeogenesis increased after the EGA procedure, but not after gastric banding. All EGA effects were abolished in GLUT-2 knockout mice and in mice with portal vein denervation. We thus provide mechanistic evidence that the beneficial effects of the EGA procedure on food intake and glucose homeostasis involve intestinal gluconeogenesis and its detection via a GLUT-2 and hepatoportal sensor pathway.

Evidence from glut2-null mice that glucose is a critical physiological regulator of feeding.

A role for glucose in the control of feeding has been proposed, but its precise physiological importance is unknown. Here, we evaluated feeding behavior in glut2-null mice, which express a transgenic glucose transporter in their beta-cells to rescue insulin secretion (ripglut1;glut2-/- mice). We showed that in the absence of GLUT2, daily food intake was increased and feeding initiation and termination following a fasting period were abnormal. This was accompanied by suppressed regulation of hypothalamic orexigenic and anorexigenic neuropeptides expression during the fast-to-refed transition. In these conditions, however, there was normal regulation of the circulating levels of insulin, leptin, or glucose but a loss of regulation of plasma ghrelin concentrations. To evaluate whether the abnormal feeding behavior was due to suppressed glucose sensing, we evaluated feeding in response to intraperitoneal or intracerebroventricular glucose or 2-deoxy-D-glucose injections. We showed that in GLUT2-null mice, feeding was no longer inhibited by glucose or activated by 2-deoxy-D-glucose injections and the regulation of hypothalamic neuropeptide expression by intracerebroventricular glucose administration was lost. Together, these data demonstrate that absence of GLUT2 suppressed the function of central glucose sensors, which control feeding probably by regulating the hypothalamic melanocortin pathway. Furthermore, inactivation of these glucose sensors causes overeating.

Bystander activation of CD4+ T cells.

Bystander activation of T cells, i.e. the stimulation of unrelated (heterologous) T cells by cytokines during an Ag-specific T-cell response, has been best described for CD8(+) T cells. In the CD8(+) compartment, the release of IFN and IFN-inducers leads to the production of IL-15, which mediates the proliferation of CD8(+) T cells, notably memory-phenotype CD8(+) T cells. CD4(+) T cells also undergo bystander activation, however, the signals inducing this Ag-nonspecific stimulation of CD4(+) T cells are less well known. A study in this issue of the European Journal of Immunology sheds light on this aspect, suggesting that common gamma-chain cytokines including IL-2 might be involved in bystander activation of CD4(+) T cells.

Monoubiquitination and Activity of the Paracaspase MALT1 Requires Glutamate 549 in the Dimerization Interface.

The mucosa-associated lymphoid tissue protein-1 (MALT1, also known as paracaspase) is a protease whose activity is essential for the activation of lymphocytes and the growth of cells derived from human diffuse large B-cell lymphomas of the activated B-cell subtype (ABC DLBCL). Crystallographic approaches have shown that MALT1 can form dimers via its protease domain, but why dimerization is relevant for the biological activity of MALT1 remains largely unknown. Using a molecular modeling approach, we predicted Glu 549 (E549) to be localized within the MALT1 dimer interface and thus potentially relevant. Experimental mutation of this residue into alanine (E549A) led to a complete impairment of MALT1 proteolytic activity. This correlated with an impaired capacity of the mutant to form dimers of the protease domain in vitro, and a reduced capacity to promote NF-κB activation and transcription of the growth-promoting cytokine interleukin-2 in antigen receptor-stimulated lymphocytes. Moreover, this mutant could not rescue the growth of ABC DLBCL cell lines upon MALT1 silencing. Interestingly, the MALT1 mutant E549A was unable to undergo monoubiquitination, which we identified previously as a critical step in MALT1 activation. Collectively, these findings suggest a model in which E549 at the dimerization interface is required for the formation of the enzymatically active, monoubiquitinated form of MALT1.

n-3 PUFAs modulate T-cell activation via protein kinase C-alpha and -epsilon and the NF-kappaB signaling pathway.

We elucidated the mechanisms of action of two n-3 PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), in Jurkat T-cells. Both DHA and EPA were principally incorporated into phospholipids in the following order: phosphatidylcholine < phosphatidylethanolamine < phosphatidylinositol/phosphatidylserine. Furthermore, two isoforms of phospholipase A(2) (i.e., calcium-dependent and calcium-independent) were implicated in the release of DHA and EPA, respectively, during activation of these cells. The two fatty acids inhibited the phorbol 12-myristate 13-acetate (PMA)-induced plasma membrane translocation of protein kinase C (PKC)-alpha and -epsilon. The two n-3 PUFAs also inhibited the nuclear translocation of nuclear factor kappaB (NF-kappaB) and the transcription of the interleukin-2 (IL-2) gene in PMA-activated Jurkat T-cells. Together, these results demonstrate that DHA and EPA, being released by two isoforms of phospholipase A(2), modulate IL-2 gene expression by exerting their action on two PKC isoforms and NF-kappaB in Jurkat T-cells.

Study of the proteolytic activity of the paracaspase MALT1 in T cell activation

Summary : Several signalling cascades are initiated through the triggering of the T cell receptor (TCR) by an antigenic peptide expressed at the surface of an antigen presenting cell. These pathways lead to morphological changes controlling T cell adhesiveness and migration to the site of infection, and to the activation of transcription factors that regulate key genes for the proper development of the immune response. Amongst them, the nuclear factor xB (NF-κB) is the subject of intense research since more than twenty years because deregulated NF-κB signalling in lymphocytes can lead to immunodeficiency, autoimmunity or lymphomas. Therefore, the understanding of the molecular mechanisms regulating NF-κB activation is important for the development of new therapeutics aimed at treating various diseases. In T lymphocytes, a complex composed of CARMAI, BCL10 and MALT1 relays signals from TCR proximal events to NF-κB activation. Gene translocations of the BCL10 or MALTI genes or oncogenic mutations affecting CARNA 1 result in constitutive NF-κB activation and are related to the development of certain forms of lymphomas. MALT1 contains acaspase-like domain, but it is unknown whether this domain is proteolytically active. In this study, we found that MALT1 has arginine-directed proteolytic activity. We showed that the proteolytic activity of MALT 1 is key to TCR-induced NF-κB activation and production of interleukin 2. We identified BCL 10 as a MALT 1 substrate, and we showed that its cleavage regulates T cell adhesion to the extracellular matrix protein fibronectin. Furthermore, we identified caspase 10 as another substrate of MALT1. caspase 10 is a close homologue of caspase 8 and is known to be involved in the induction of apoptosis upon Fast or TRAIL stimulation. We showed that caspase 10 is important for TCR-induced NF-κB activation and interleukin 2 production, identifying for the first time a non apoptotic function for caspase 10. These data provide evidence for previously uncharacterized roles of MALT 1 and BCL 10 in the regulation of T cell adhesion and of caspase 10 in the activation of lymphocytes, and allow a better understanding of the molecular mechanisms of T lymphocyte activation. Since the proteolytic activity of MALT1 is essential to T cell activation, it suggests that the targeting of this activity may be relevant for the development of immunomodulatory or anticancer drugs. Résumé : De nombreuses voies de signalisation sont initiées via la stimulation des récepteurs des cellules T (TCR) par un peptide antigénique exprimé à la surface d'une cellule présentatrice d'antigènes. Ces cascades de signalisation produisent des changements morphologiques qui contrôlent l'adhésion des cellules T et leur migration vers le site d'infection. Elles contrôlent également l'activation de facteurs de transcription qui régulent la transcription de gènes importants pour la réponse immunitaire. Parmi ces derniers, le facteur nucléaire KB (NF-κB) joue un rôle essentiel, puisqu'une régulation aberrante de son activité dans les lymphocytes peut causer des immunodéficiences, des maladies autoimmunes ou des lymphomes. C'est pour cela que la compréhension des mécanismes moléculaires qui contrôlent l'activation de NF-κB est donc importante pour le développement de nouvelles thérapies. Un complexe contenant les protéines CAIZMAI, BCL10 et MALT1 transmet, dans les lymphocytes T, le signal du TCR vers l'activation de NF-κB. Des translocations des gènes qui codent pour BCL10 et MALTI et des mutations affectant la fonction de CARNAI ont été liées au développement de certaines formes de lymphomes. MALTI contient un domaine qui ressemble au domaine catalytique présent dans les caspases, mais il n'est pas connu si ce domaine a une activité protéolytique. Dans cette étude, nous avons découvert que MALTI est une protéase qui a une spécificité pour les acides aminés basiques comme l'arginine. Nous montrons que l'activité protéolytique de MALTI est importante pour l'activation de NF-κB et la production d'interleukine 2 après stimulation du TCR. Nous avons observé que BCL10 est clivé par MALTI pendant l'activation des lymphocytes T, et que ce clivage est impliqué dans la régulation de l'adhésion des lymphocytes T à la fibronectin, une protéine de la matrice extracellulaire. De plus, nous avons identifié que la caspase 10, qui a une grande homologie avec la caspase 8 et qui jusqu'à maintenant est connue pour son rôle dans l'induction de la mort cellulaire en réponse à une stimulation par Fast ou par TRAIL, est également un substrat de MALT 1. En montrant que la caspase 10 est nécessaire à l' activation de NF-icB et à la production de l'interleukine 2 après stimulation du TCR, nous décrivons pour la première fois une fonction non apoptotique de la caspase 10. Ces résultats décrivent de nouveaux rôles pour MALT1 et BCL10 dans le contrôle de l'adhésion des lymphocytes T et de la caspase 10 pour l'activation des lymphocytes T. Puisque l'activité protéolytique de MALT1 est essentielle pour l'activation des lymphocytes T, nous suggérons que cibler cette activité protéolytique de MALT 1 pourrait amener de nouvelles possibilités de traitement de maladies où une activation aberrante des lymphocytes est impliquée.

The proteolytic activity of the paracaspase MALT1 is key in T cell activation

The paracaspase MALT1 is pivotal in antigen receptor-mediated lymphocyte activation and lymphomagenesis. MALT1 contains a caspase-like domain, but it is unknown whether this domain is proteolytically active. Here we report that MALT1 had arginine-directed proteolytic activity that was activated after T cell stimulation, and we identify the signaling protein Bcl-10 as a MALT1 substrate. Processing of Bcl-10 after Arg228 was required for T cell receptor-induced cell adhesion to fibronectin. In contrast, MALT1 activity but not Bcl-10 cleavage was essential for optimal activation of transcription factor NF-kappaB and production of interleukin 2. Thus, the proteolytic activity of MALT1 is central to T cell activation, which suggests a possible target for the development of immunomodulatory or anticancer drugs