Streptococcus pneumoniae drives specific and lasting Natural Killer cell memory

NK cells are important mediators of innate immunity and play an essential role for host protection against infection, although their responses to bacteria are poorly understood. Recently NK cells were shown to display memory properties, as characterized by an epigenetic signature leading to a stronger secondary response. Although NK cell memory could be a promising mechanism to fight against infection, it has not been described upon bacterial infection. Using a mouse model, we reveal that NK cells develop specific and long-term memory following sub-lethal infection with the extracellular pathogen Streptococcus pneumoniae. Memory NK cells display intrinsic sensing and response to bacteria in vitro, in a manner that is enhanced post-bacterial infection. In addition, their transfer into naïve mice confers protection from lethal infection for at least 12 weeks. Interestingly, NK cells display enhanced cytotoxic molecule production upon secondary stimulation and their protective role is dependent on Perforin and independent of IFNγ. Thus, our study identifies a new role for NK cells during bacterial infection, opening the possibility to harness innate immune memory for therapeutic purposes

Infection-mediated priming of phagocytes protects against lethal secondary Aspergillus fumigatus challenge

Phagocytes restrict the germination of Aspergillus fumigatus conidia and prevent the establishment of invasive pulmonary aspergillosis in immunecompetent mice. Here we report that immunecompetent mice recovering from a primary A. fumigatus challenge are protected against a secondary lethal challenge. Using RAGγc knock-out mice we show that this protection is independent of T, B and NK cells. In protected mice, lung phagocytes are recruited more rapidly and are more efficient in conidial phagocytosis and killing. Protection was also associated with an enhanced expression of CXCR2 and Dectin-1 on bone marrow phagocytes. We also show that protective lung cytokine and chemokine responses are induced more rapidly and with enhanced dynamics in protected mice. Our findings support the hypothesis that following a first encounter with a non-lethal dose of A. fumigatus conidia, the innate immune system is primed and can mediate protection against a secondary lethal infection

Enhanced Inflammatory Potential of CD4(+) T-Cells That Lack Proteasome Immunosubunit Expression, in a T-Cell Transfer-Based Colitis Model

Proteasomes play a fundamental role in intracellular protein degradation and therewith regulate a variety of cellular processes. Exposure of cells to (pro)inflammatory cytokines upregulates the expression of three inducible catalytic proteasome subunits, the immunosubunits, which incorporate into newly assembled proteasome complexes and alter the catalytic activity of the cellular proteasome population. Single gene-deficient mice lacking one of the three immunosubunits are resistant to dextran sulfate sodium (DSS)-induced colitis development and, likewise, inhibition of one single immunosubunit protects mice against the development of DSS-induced colitis. The observed diminished disease susceptibility has been attributed to altered cytokine production and CD4+ T-cell differentiation in the absence of immunosubunits. To further test whether the catalytic activity conferred by immunosubunits plays an essential role in CD4+ T-cell function and to distinguish between the role of immunosubunits in effector T-cells versus inflamed tissue, we used a T-cell transfer-induced colitis model. Naïve wt or immunosubunit-deficient CD4+ T-cells were adoptively transferred into RAG1-/- and immunosubunit-deficient RAG1-/- mice and colitis development was determined six weeks later. While immunosubunit expression in recipient mice had no effect on colitis development, transferred immunosubunit-deficient T- cells were more potent in inducing colitis and produced more proinflammatory IL17 than wt T-cells. Taken together, our data show that modifications in proteasome-mediated proteolysis in T-cells, conferred by lack of immunosubunit incorporation, do not attenuate but enhance CD4+ T-cell-induced inflammation

Cellules NK et inflammation systémique : compartimentalisation et réponse mémoire

L'inflammation systémique est une réaction qui implique l’ensemble de l’organisme suite une agression sévère, potentiellement mortelle, illustrée par le syndrome de réponse inflammatoire systémique (SIRS). De nombreux acteurs cellulaires et moléculaires contribuent au développement de cette cascade inflammatoire parmi lesquels les cellules NK jouent un rôle clé. Malgré l'accumulation de preuves sur l’existence de propriétés spécifiques à chaque organe en réponse à l'inflammation systémique, en termes de cellules NK, on sait peu de choses sur la dynamique compartimentalisée de l’activation des cellules NK pendant un SIRS. En outre, le statut immunitaire des cellules NK après la résolution d’un SIRS est également mal connu. Dans le présent travail, nous avons étudié les réponses des cellules NK provenant de différents organes en utilisant un modèle d’endotoxinémie murine. Nous avons caractérisé la réponse des cellules NK au sein de la rate, du poumon, de la moelle osseuse, de la cavité péritonéale, et dans la circulation. Nous avons trouvé que, malgré une dynamique similaire de la réponse dans les différents organes, les réponses des cellules NK sont compartimentalisées avec des seuils différent et spécifiques. A l’aide de transferts adoptifs, nous avons constaté que la réactivité des cellules NK spécifiques d'organes peut refléter le compartiment d’origine lors des phases initiales de l'inflammation. Cependant, les cellules NK ont la capacité de s’adapter rapidement à leur nouvel environnement et d'ajuster leurs niveaux de réponse à ceux des cellules NK résidentes. Ainsi, cette étude fournit une preuve de concept qui confirme la compartimentalisation de la réponse des cellules NK lors de l'inflammation systémique. Dans une deuxième partie, nous avons analysé le statut des cellules NK à différents moments après une endotoxinémie. Les réponses des cellules NK au sein d’une préparation de cellules de la rate sont fortement supprimées en réponse à une restimulation in vitro, 14 jours après l'endotoxinémie. Cependant, nous avons montré que la réactivité intrinsèque des cellules NK est en fait augmentée après l'injection d’endotoxine, aboutissant à des cellules NK présentant des caractéristiques de cellules NK mémoires. Des expériences de transfert adoptif ont confirmé les propriétés de mémoire des cellules NK après endotoxinémie. Nos résultats accroissent la connaissance concernant le rôle des cellules NK dans un contexte d'inflammation systémique, révélant des réponses compartimentalisés et l’induction d’une mémoire suite à l’endotoxinémie. L'observation selon laquelle les cellules NK développent des propriétés de mémoire après une inflammation systémique dans le contexte d'un environnement suppressif est d’une grande nouveauté et ce phénomène est rapporté pour la première fois.Systemic inflammation is whole-body reaction to a triggering insult that often results in life threatening illness like systemic inflammatory response syndrome (SIRS). Contributing to the development of this inflammatory cascade are numerous cellular and molecular players, among which, NK cells have been shown to play a key role. Despite accumulating evidence on the organ-specific properties of both systemic inflammation and NK cells, little is known about the compartmentalized dynamics of NK cell activation during SIRS. Furthermore, the status of NK cells after the resolution of SIRS is also poorly characterized. In the present work, we investigated NK responses in different organs using a mouse model of endotoxinemia and characterized the compartmentalized response of spleen, lung, bone marrow, peritoneal and circulating NK cells. We found that despite similar dynamics of response in different organs, NK cells responses, are compartmentalized with seemingly specific thresholds of maximum activation. Using a series of adoptive transfers, we found that while organ-specific NK cell responsiveness can affect the initial phases of inflammation, these cells have the capacity to quickly adapt to a new environment and adjust their response levels to that of resident NK cells. Thus, this study provides proof of concept data on the compartmentalization of the NK cell responses during systemic inflammation. In a second part, we assessed the status of NK cells at different times after endotoxemia. NK cells responses in the context of whole spleen preparations were severely suppressed in response to in vitro restimulation at 14 days after endotoxemia. However, intrinsic NK cell responsiveness was increased after endotoxemia, showing characteristics of NK cell memory. Adoptive transfer experiments confirmed memory properties of NK cells after endotoxemia. Overall, these results expand on the role of NK cells in the context of systemic inflammation revealing compartmentalized responses during and memory properties following endotoxemia. The observation that NK cells develop memory properties after systemic inflammation in the context of a suppressive environment is of the highest novelty and the first one to report such a phenomenon

Local Microenvironment Controls the Compartmentalization of NK Cell Responses during Systemic Inflammation in Mice.

International audienceSystemic inflammatory response syndrome is a whole-body reaction to a triggering insult that often results in life-threatening illness. Contributing to the development of this inflammatory cascade are numerous cellular partners, among which NK cells were shown to play a key role. Accumulating evidence points to organ-specific properties of systemic inflammation and NK cells. However, little is known about compartment-specific activation of NK cells during systemic inflammatory response syndrome or the relative contribution of NK cell-intrinsic properties and microenvironmental cues. In this study, we undertook a sequential characterization of NK responses in the spleen, lungs, bone marrow, peritoneum, and blood using a mouse model of endotoxemia. We report that, despite similar systemic dynamics of NK cell responses, expression of activation markers (CD69 and CD25) and effector molecules (IFN-γ, granzyme B, and IL-10) display organ-specific thresholds of maximum activation. Using adoptive transfers of spleen and lung NK cells, we found that these cells have the capacity to quickly adapt to a new environment and adjust their response levels to that of resident NK cells. This functional adaptation occurs without significant alterations in phenotype and independently of subpopulation-specific trafficking. Thus, using a dynamic in vivo-transfer system, to our knowledge our study is the first to report the compartmentalization of NK cells responses during systemic inflammation and to show that NK cell-intrinsic properties and microenvironmental cues are involved in this process, in a sequential manner

Streptococcus pneumoniae drives specific and lasting Natural Killer cell memory

NK cells are important mediators of innate immunity and play an essential role for host protection against infection, although their responses to bacteria are poorly understood. Recently NK cells were shown to display memory properties, as characterized by an epigenetic signature leading to a stronger secondary response. Although NK cell memory could be a promising mechanism to fight against infection, it has not been described upon bacterial infection. Here, we reveal that NK cells develop specific and long-term memory following sub-lethal infection with the extracellular pathogen Streptococcus pneumoniae . Memory NK cells display intrinsic sensing and response to bacteria in vitro , in a manner that is enhanced post-bacterial infection. In addition, their transfer into naïve mice confer protection from lethal infection for at least 12 weeks. Interestingly, NK cells display enhanced cytotoxic molecule production upon secondary stimulation and their protective role is dependent on Perforin and independent of IFNγ. Thus, our study identifies a new role for NK cells during bacterial infection, opening the possibility to harness innate immune memory for therapeutic purposes

Streptococcus pneumoniae Infection Promotes Histone H3 Dephosphorylation by Modulating Host PP1 Phosphatase

International audiencePathogenic bacteria can alter host gene expression through post-translational modifications of histones. We show that a natural colonizer, Streptococcus pneumoniae, induces specific histone modifications, including robust dephosphorylation of histone H3 on serine 10 (H3S10), during infection of respiratory epithelial cells. The bacterial pore-forming toxin pneumolysin (PLY), along with the pyruvate oxidase SpxB responsible for H2O2 production, play important roles in the induction of this modification. The combined effects of PLY and H2O2 trigger host signaling that culminates in H3S10 dephosphorylation, which is mediated by the host cell phosphatase PP1. Strikingly, S. pneumoniae infection induces dephosphorylation and subsequent activation of PP1 catalytic activity. Colonization of PP1 catalytically deficient cells results in impaired intracellular S. pneumoniae survival and infection. Interestingly, PP1 activation and H3S10 dephosphorylation are not restricted to S. pneumoniae and appear to be general epigenomic mechanisms favoring intracellular survival of pathogenic bacteria

H3K4me1 Supports Memory-like NK Cells Induced by Systemic Inflammation

International audienceNatural killer (NK) cells are unique players in innate immunity and, as such, an attractive target for immunotherapy. NK cells display immune memory properties in certain models, but the long-term status of NK cells following systemic inflammation is unknown. Here we show that following LPS-induced endotoxemia in mice, NK cells acquire cell-intrinsic memory-like properties, showing increased production of IFNγ upon specific secondary stimulation. The NK cell memory response is detectable for at least 9 weeks and contributes to protection from E. coli infection upon adoptive transfer. Importantly, we reveal a mechanism essential for NK cell memory, whereby an H3K4me1-marked latent enhancer is uncovered at the ifng locus. Chemical inhibition of histone methyltransferase activity erases the enhancer and abolishes NK cell memory. Thus, NK cell memory develops after endotoxemia in a histone methylation-dependent manner, ensuring a heightened response to secondary stimulation

Innate immune memory through TLR2 and NOD2 contributes to the control of Leptospira interrogans infection

International audienceLeptospira interrogans are pathogenic spirochetes responsible for leptospirosis, a worldwide reemerging zoonosis. Many Leptospira serovars have been described, and prophylaxis using inactivated bacteria provides only short-term serovar-specific protection. Therefore, alternative approaches to limit severe leptospirosis in humans and morbidity in cattle would be welcome. Innate immune cells, including macrophages, play a key role in fighting infection and pathogen clearance. Recently, it has been shown that functional reprograming of innate immune cells through the activation of pattern recognition receptors leads to enhanced nonspecific antimicrobial responses upon a subsequent microbial encounter. This mechanism is known as trained immunity or innate immune memory. We have previously shown that oral treatment with Lactobacillus plantarum confers a beneficial effect against acute leptospirosis. Here, using a macrophage depletion protocol and live imaging in mice, we established the role of peritoneal macrophages in limiting the initial dissemination of leptospires. We further showed that intraperitoneal priming of mice with CL429, a TLR2 and NOD2 agonist known to mimic the modulatory effect of Lactobacillus, alleviated acute leptospiral infection. The CL429 treatment was characterized as a training effect since i.) it was linked to peritoneal macrophages that produced ex vivo more pro-inflammatory cytokines and chemokines against 3 different pathogenic serovars of Leptospira, independently of the presence of B and T cells, ii.) it had systemic effects on splenic cells and bone marrow derived macrophages, and iii.) it was sustained for 3 months. Importantly, trained macrophages produced more nitric oxide, a potent antimicrobial compound, which has not been previously linked to trained immunity. Accordingly, trained macrophages better restrict leptospiral survival. Finally, we could use CL429 to train ex vivo human monocytes that produced more cytokines upon leptospiral stimulation. In conclusion, host-directed treatment using a TLR2/NOD2 agonist could be envisioned as a novel prophylactic strategy against acute leptospirosis

CD4 T cells and iTreg cells in mice with T-cell transfer-induced colitis.

<p>Splenocytes of mice with T-cell transfer-induced colitis, harvested six weeks after T-cell transfer, were stained for CD4 and FoxP3 expression and analyzed by flow cytometry. (A) absolute numbers of splenocytes; (B, D) percentages, and (C, E) numbers of CD4+ T-cells and CD4+FoxP3+ T-cells in the spleen. Results for individual mice and means+SEM (n = 3–6 per group) are depicted. *p<0.05.</p