Immunology
Abstract
Vanin-1 is a membrane-anchored pantetheinase highly expressed in the gut and liver. It hydrolyzes pantetheine to pantothenic acid (vitamin B5) and the low-molecular-weight thiol cysteamine. The latter is believed to be a key regulating factor of several essential metabolic pathways, acting through sulfhydryl-disulfide exchange reactions between sulfhydryl groups of the enzymes and the oxidized form, cystamine. Its physiological importance remains to be elucidated, however. To explore this point, we developed Vanin-1–deficient mice that lack free cysteamine. We examined the susceptibility of deficient mice to intestinal inflammation, either acute (NSAID administration) or chronic (Schistosoma infection). We found that Vanin-1–/– mice better controlled inflammatory reaction and intestinal injury in both experiments. This protection was associated with increased γ-glutamylcysteine synthetase activity and increased stores of reduced glutathione, as well as reduced inflammatory cell activation in inflamed tissues. Oral administration of cystamine reversed all aspects of the deficient phenotype. These findings suggest that one cysteamine function is to upregulate inflammation. Consequently, the pantetheinase activity of Vanin-1 molecule could be a target for a new anti-inflammatory strategy.
Authors
Florent Martin, Marie-France Penet, Fabrice Malergue, Hubert Lepidi, Alain Dessein, Franck Galland, Max de Reggi, Philippe Naquet, Bouchra Gharib
Abstract
Glucocorticoids have potent immunosuppressive properties, but their effects are often modulated by the conditions prevailing in the local immune milieu. In this study we determined whether the action of glucocorticoids is influenced by the degree of signaling during T cell activation. We found that dexamethasone (Dex) effectively suppressed T cell receptor–induced (TCR-induced) proliferation of naive CD4+ T cells, through a mechanism involving downregulation of c-Fos expression and inhibition of activator protein-1 (AP-1), nuclear factor of activated T cells (NF-AT), and NF-κB transcriptional activity. However, enhancement of TCR signaling by CD28- or IL-2–mediated costimulation abrogated the suppressive effect of Dex on c-Fos expression and AP-1 function and restored cellular proliferation. The amount of signaling through the MAPK pathway was critical in determining the effect of Dex on T cell activation. In particular, costimulatory signaling via MAPK kinase (MEK) and extracellular signal–regulated kinase (ERK) was essential for the development of T cell resistance to Dex. Selective blockade of MEK/ERK signal transduction abolished the costimulation-induced resistance. In contrast, transmission of IL-2 signals via STAT5 and CD28 signals via NF-κB remained inhibited by Dex. These results imply that the immune system, by regulating the degree of local costimulation through MEK/ERK, can modify the effect of glucocorticoids on T cells. Moreover, these findings suggest that MAPK inhibitors may offer a therapeutic solution for glucocorticoid resistance.
Authors
Daphne C. Tsitoura, Paul B. Rothman
Abstract
Sepsis is a common, life-threatening disease for which there is little treatment. The cysteine protease dipeptidyl peptidase I (DPPI) activates granule-associated serine proteases, several of which play important roles in host responses to bacterial infection. To examine DPPI’s role in sepsis, we compared DPPI–/– and DPPI+/+ mice using the cecal ligation and puncture (CLP) model of septic peritonitis, finding that DPPI–/– mice are far more likely to survive sepsis. Outcomes of CLP in mice lacking mast cell DPPI reveal that the absence of DPPI in mast cells, rather than in other cell types, is responsible for the survival advantage. Among several cytokines surveyed in peritoneal fluid and serum, IL-6 is highly and differentially expressed in DPPI–/– mice compared with DPPI+/+ mice. Remarkably, deleting IL-6 expression in DPPI–/– mice eliminates the survival advantage. The increase in IL-6 in septic DPPI–/– mice, which appears to protect these mice from death, may be related to reduced DPPI-mediated activation of mast cell tryptase and other peptidases, which we show cleave IL-6 in vitro. These results indicate that mast cell DPPI harms the septic host and that DPPI is a novel potential therapeutic target for treatment of sepsis.
Authors
Jon Mallen–St. Clair, Christine T.N. Pham, S. Armando Villalta, George H. Caughey, Paul J. Wolters
Abstract
Authors
Guillermina Girardi, Jessica Berman, Patricia Redecha, Lynn Spruce, Joshua M. Thurman, Damian Kraus, Travis J. Hollmann, Paolo Casali, Michael C. Caroll, Rick A. Wetsel, John D. Lambris, V. Michael Holers, Jane E. Salmon
Abstract
Most of the human tumor-associated antigens (TAAs) characterized thus far are derived from nonmutated “self”-proteins. Numerous strategies have been developed to break tolerance to TAAs, combining various forms of antigens with different vectors and adjuvants. However, no study has yet determined how to select epitopes within a given TAA to induce the highest antitumor effector response. We addressed this question by evaluating in HLA-A*0201-transgenic HHD mice the antitumor vaccination efficacy of high- and low-affinity epitopes from the naturally expressed murine telomerase reverse transcriptase (mTERT). Immunity against low-affinity epitopes was induced with heteroclitical variants. We show here that the CTL repertoire against high-affinity epitopes is partially tolerized, while that against low-affinity epitopes is composed of frequent CTLs with high avidity. The high-affinity p797 and p545 mTERT epitopes are not able to protect mice from a lethal challenge with the mTERT-expressing EL4-HHD tumor. In contrast, mice developing CTL responses against the p572 and p988 low-affinity epitopes exhibit potent antitumor immunity and no sign of autoimmune reactivity against TERT-expressing normal tissues. Our results strongly argue for new TAA epitope selection and modification strategies in antitumor immunotherapy applications in humans.
Authors
David-Alexandre Gross, Stéphanie Graff-Dubois, Paule Opolon, Sébastien Cornet, Pedro Alves, Annelise Bennaceur-Griscelli, Olivier Faure, Philippe Guillaume, Hüseyin Firat, Salem Chouaib, François A. Lemonnier, Jean Davoust, Isabelle Miconnet, Robert H. Vonderheide, Kostas Kosmatopoulos
Abstract
According to the quality of response they mediate, autoreactive T cells recognizing islet β cell peptides could represent both disease effectors in the development of type 1 diabetes (T1DM) and directors of tolerance in nondiabetic individuals or those undergoing preventative immunotherapy. A combination of the rarity of these cells, inadequate technology, and poorly defined epitopes, however, has hampered examination of this paradigm. We have identified a panel of naturally processed islet epitopes by direct elution from APCs bearing HLA-DR4. Employing these epitopes in a sensitive, novel cytokine enzyme-linked immunosorbent spot assay, we show that the quality of autoreactive T cells in patients with T1DM exhibits extreme polarization toward a proinflammatory Th1 phenotype. Furthermore, we demonstrate that rather than being unresponsive, the majority of nondiabetic, HLA-matched control subjects also manifest a response against islet peptides, but one that shows extreme T regulatory cell (Treg, IL-10–secreting) bias. We conclude that development of T1DM depends on the balance of autoreactive Th1 and Treg cells, which may be open to favorable manipulation by immune intervention.
Authors
Sefina Arif, Timothy I. Tree, Thomas P. Astill, Jennifer M. Tremble, Amanda J. Bishop, Colin M. Dayan, Bart O. Roep, Mark Peakman
Abstract
Immunological synapses are organized cell-cell junctions between T lymphocytes and APCs composed of an adhesion ring, the peripheral supramolecular activation cluster (pSMAC), and a central T cell receptor cluster, the central supramolecular activation cluster (cSMAC). In CD8+ cytotoxic T lymphocytes, the immunological synapse is thought to facilitate specific killing by confining cytotoxic agents to the synaptic cleft. We have investigated the interaction of human CTLs and helper T cells with supported planar bilayers containing ICAM-1. This artificial substrate provides identical ligands to CD4+ and CD8+ T cells, allowing a quantitative comparison. We found that cytotoxic T lymphocytes form a ring junction similar to a pSMAC in response to high surface densities of ICAM-1 in the planar bilayer. MICA, a ligand for NKG2D, facilitated the ring junction formation at lower surface densities of ICAM-1. ICAM-1 and MICA are upregulated in tissues by inflammation- and stress-associated signaling, respectively. Activated CD8+ T cells formed fivefold more ring junctions than did activated CD4+ T cells. The ring junction contained lymphocyte function associated antigen-1 and talin, but did not trigger polarization and granule translocation to the interface. This result has specific implications for the mechanism of effective CTL hunting for antigen in tissues. Abnormalities in this process may alter CTL reactivity.
Authors
Kristina Somersalo, Nadja Anikeeva, Tasha N. Sims, V. Kaye Thomas, Roland K. Strong, Thomas Spies, Tatiana Lebedeva, Yuri Sykulev, Michael L. Dustin
Abstract
The TNF-related apoptosis-inducing ligand (TRAIL) induces apoptosis of tumor cells but not most normal cells. Its role in hepatic cell death and hepatic diseases is not clear. In vitro studies suggest that murine hepatocytes are not sensitive to TRAIL-induced apoptosis, indicating that TRAIL may not mediate hepatic cell death. Using two experimental models of hepatitis, we found that hepatic cell death in vivo was dramatically reduced in TRAIL-deficient mice and mice treated with a blocking TRAIL receptor. Although both TRAIL and its death receptor 5 were constitutively expressed in the liver, TRAIL expression by immune cells alone was sufficient to restore the sensitivity of TRAIL-deficient mice to hepatitis. Thus, TRAIL plays a crucial role in hepatic cell death and hepatic inflammation.
Authors
Shi-Jun Zheng, Pu Wang, Galit Tsabary, Youhai H. Chen
Abstract
Antiphospholipid syndrome (APS) is defined by recurrent pregnancy loss and thrombosis in the presence of antiphospholipid (aPL) Ab’s. Currently, therapy for pregnant women with APS is focused on preventing thrombosis, but anticoagulation is only partially successful in averting miscarriage. We hypothesized that complement activation is a central mechanism of pregnancy loss in APS and tested this in a model in which pregnant mice receive human IgG containing aPL Ab’s. Here we identify complement component C5 (and particularly its cleavage product C5a) and neutrophils as key mediators of fetal injury, and we show that Ab’s or peptides that block C5a–C5a receptor interactions prevent pregnancy complications. The fact that F(ab)′2 fragments of aPL Ab’s do not mediate fetal injury and that C4-deficient mice are protected from fetal injury suggests that activation of the complement cascade is initiated via the classical pathway. Studies in factor B–deficient mice, however, indicate that alternative pathway activation is required and amplifies complement activation. In contrast, activating FcγRs do not play an important role in mediating aPL Ab–induced fetal injury. Our findings identify the key innate immune effectors engaged by pathogenic autoantibodies that mediate poor pregnancy outcomes in APS and provide novel and important targets for prevention of pregnancy loss in APS.
Authors
Guillermina Girardi, Jessica Berman, Patricia Redecha, Lynn Spruce, Joshua M. Thurman, Damian Kraus, Travis J. Hollmann, Paolo Casali, Michael C. Caroll, Rick A. Wetsel, John D. Lambris, V. Michael Holers, Jane E. Salmon
Abstract
Gastrointestinal allergic disorders represent a diverse spectrum of inflammatory diseases that are occurring with increasing incidence and severity. An essential question concerning these disorders is to determine the specific cells and mediators responsible for specific clinical manifestations. With this in mind, we developed a murine model of oral allergen–induced intestinal inflammation accompanied by strong Th2-associated humoral and cellular responses and focused on the immunopathogenesis of allergic diarrhea. Exposure of OVA/alum–sensitized mice to repeated doses of intragastric OVA induced genetically restricted, dose-dependent, acute diarrhea associated with increased intestinal permeability, eosinophilia, and mastocytosis. Mice developed limited systemic manifestations of anaphylaxis, even though they developed marked intestinal mucosal mast cell degranulation. Notably, experiments involving mast cell depletion (with anti–c-kit mAb), anti-IgE treatment, and FcεRI-deficient mice indicated a critical effector role for mast cells in mediating allergic diarrhea. Furthermore, allergic diarrhea was dependent upon synergistic signaling induced by serotonin and platelet-activating factor (PAF), but not histamine. These results demonstrate that oral allergen–induced diarrhea associated with experimental Th2 intestinal inflammation is largely mast cell, IgE, serotonin, and PAF dependent.
Authors
Eric B. Brandt, Richard T. Strait, Dan Hershko, Quan Wang, Emily E. Muntel, Troy A. Scribner, Nives Zimmermann, Fred D. Finkelman, Marc E. Rothenberg
Copyright © 2025 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)