Immune status in sepsis: the bug, the site of infection and the severity can make the difference

Studying a large number of patients with sepsis, the Hellenic sepsis study group led by Evangello Giamarellos-Bourboulis emphasizes that the nature of the bacterial infection, its origin (community or nosocomial), its site, and its severity exert different pressures on the immune system. Their study illustrates the heterogeneity of patients with sepsis and points out that numerous key parameters of severe infection influence immune status

In vivo bioluminescence imaging and histopathopathologic analysis reveal distinct roles for resident and recruited immune effector cells in defense against invasive aspergillosis

BACKGROUND: Invasive aspergillosis (IA) is a major cause of infectious morbidity and mortality in immune compromised patients. Studies on the pathogenesis of IA have been limited by the difficulty to monitor disease progression in real-time. For real-time monitoring of the infection, we recently engineered a bioluminescent A. fumigatus strain. RESULTS: In this study, we demonstrate that bioluminescence imaging can track the progression of IA at different anatomic locations in a murine model of disease that recapitulates the natural route of infection. To define the temporal and functional requirements of distinct innate immune cellular subsets in host defense against respiratory A. fumigatus infection, we examined the development and progression of IA using bioluminescence imaging and histopathologic analysis in mice with four different types of pharmacologic or numeric defects in innate immune function that target resident and recruited phagocyte subsets. While bioluminescence imaging can track the progression and location of invasive disease in vivo, signals can be attenuated by severe inflammation and associated tissue hypoxia. However, especially under non-inflammatory conditions, such as cyclophosphamide treatment, an increasing bioluminescence signal reflects the increasing biomass of alive fungal cells. CONCLUSIONS: Imaging studies allowed an in vivo correlation between the onset, peak, and kinetics of hyphal tissue invasion from the lung under conditions of functional or numeric inactivation of phagocytes and sheds light on the germination speed of conidia under the different immunosuppression regimens. Conditions of high inflammation -either mediated by neutrophil influx under corticosteroid treatment or by monocytes recruited during antibody-mediated depletion of neutrophils- were associated with rapid conidial germination and caused an early rise in bioluminescence post-infection. In contrast, 80% alveolar macrophage depletion failed to trigger a bioluminescent signal, consistent with the notion that neutrophil recruitment is essential for early host defense, while alveolar macrophage depletion can be functionally compensated

Interferon-gamma and granulocyte/monocyte colony-stimulating factor production by natural killer cells involves different signaling pathways and the adaptor stimulator of interferon genes (STING)

Natural killer (NK) cells are important for innate immunity in particular through the production of IFN-gamma and GM-CSF. Both cytokines are important in restoration of immune function of tolerized leukocytes under inflammatory events. The expression of TLRs in NK cells has been widely studied by analyzing the mRNA of these receptors, rarely seeking their protein expression. We previously showed that murine spleen NK cells express TLR9 intracellularly and respond to CpG oligodeoxynucleotide (CpG-ODN) by producing IFN-gamma and GM-CSF. However, to get such production the presence of accessory cytokines (such as IL-15 and IL-18) was required, whereas CpG-ODN or accessory cytokines alone did not induce IFN-gamma or GM-CSF. We show here that TLR9 overlaps with the Golgi apparatus in NK cells. Furthermore, CpG-ODN stimulation in the presence of accessory cytokines induces the phosphorylation of c-Jun, STAT3, and IkappaBalpha. IFN-gamma and GM-CSF production requires NF-kappaB and STAT3 activation as well as Erk-dependent mechanisms for IFN-gamma and p38 signaling for GM-CSF. Using knock-out-mice, we show that UNC93b1 and IL-12 (produced by NK cells themselves) are also necessary for IFN-gamma and GM-CSF production. IFN-gamma production was found to be MyD88- and TLR9-dependent, whereas GM-CSF was TLR9-independent but dependent on STING (stimulator of interferon genes), a cytosolic adaptor recently described for DNA sensing. Our study thereby allows us to gain insight into the mechanisms of synergy between accessory cytokines and CpG-ODN in NK cells. It also identifies a new and alternative signaling pathway for CpG-ODN in murine NK cells

Circulating biomarkers may be unable to detect infection at the early phase of sepsis in ICU patients: the CAPTAIN prospective multicenter cohort study.

PURPOSE: Sepsis and non-septic systemic inflammatory response syndrome (SIRS) are the same syndromes, differing by their cause, sepsis being secondary to microbial infection. Microbiological tests are not enough to detect infection early. While more than 50 biomarkers have been proposed to detect infection, none have been repeatedly validated. AIM: To assess the accuracy of circulating biomarkers to discriminate between sepsis and non-septic SIRS. METHODS: The CAPTAIN study was a prospective observational multicenter cohort of 279 ICU patients with hypo- or hyperthermia and criteria of SIRS, included at the time the attending physician considered antimicrobial therapy. Investigators collected blood at inclusion to measure 29 plasma compounds and ten whole blood RNAs, and-for those patients included within working hours-14 leukocyte surface markers. Patients were classified as having sepsis or non-septic SIRS blindly to the biomarkers results. We used the LASSO method as the technique of multivariate analysis, because of the large number of biomarkers. RESULTS: During the study period, 363 patients with SIRS were screened, 84 having exclusion criteria. Ninety-one patients were classified as having non-septic SIRS and 188 as having sepsis. Eight biomarkers had an area under the receiver operating curve (ROC-AUC) over 0.6 with a 95% confidence interval over 0.5. LASSO regression identified CRP and HLA-DRA mRNA as being repeatedly associated with sepsis, and no model performed better than CRP alone (ROC-AUC 0.76 [0.68-0.84]). CONCLUSIONS: The circulating biomarkers tested were found to discriminate poorly between sepsis and non-septic SIRS, and no combination performed better than CRP alone

Rôle de la voie Toll-Like Receptor 2 et de la phagocytose dans la production de cytokines par les cellules mononuclées phagocytaires en réponse à Staphylococcus aureus

Staphylococcus aureus est une bactérie à Gram positif responsable d'un nombre croissant de pathologies humaines. Notre étude a comme objectif d'étudier la production de cytokines par les cellules mononucléées phagocytaires (monocytes, macrophages péritonéaux et alvéolaires) en réponse à S. aureus. Nous avons confirmé que la présence de TLR2 n'était pas indispensable pour la reconnaissance de S. aureus par les macrophages péritonéaux. En revanche, l'activation du TLR2 et la phagocytose de la bactérie étaient requises simultanément pour les monocytes et les macrophages alvéolaires, afin d'obtenir une production optimale de cytokines. De plus, à l'aide d'inhibiteurs spécifiques, nous avons observé que p38 et la Pi3K avaient un rôle central dans ces deux voies d'activauon. Au contraire, Racl et ERK étaient important spécifiquement pour l'activation de la voie intracellulaire chez les macrophages péritonéaux ou alvéolaires. Nous avons cherché à identifier le récepteur intracellulaire permettant la détection de S. aureus après phagocytose. La transfection d'un dominant-négatif de NOD2 dans la lignée macrophagique RAW 264.7 inhibait fortement l'activation de NF-KB en réponse à S. aureus. Mais en utilisant des cellules primaires ne possédant pas NOD2, nous avons observé que l'absence de ce récepteur n'avait pas d'incidence sur la production de cytokines. Enfin, l'injection en intra-nasal d'une souche de S.aureus, n'a pas montré de différence entre les souris NOD2 déficientes et leurs congénères sauvages. Toutefois, les souris NOD2 déficientes semblaient se remettre plus rapidement de l'infection, que ce soit au niveau de la perte du poids que des lésions pulmonaires. En conclusion, nos travaux mettent en évidence une voie d'activauon des macrophages autre que le TLR2 et dépendante de la phagocytose. NOD2 ne semble pas jouer un rôle critique, lors de la réponse à S. aureus, que ce soit in vitro ou in vivo. Enfin, nous avons pu observer qu'au sein même de la population mononucléée phagocytaire, il existe de grandes différences quant au rôle de la phagocytose dans la réponse à S. aureus. Ceci souligne l'hétérogénéité de la réponse de ces phagocytes professionnels selon le compartiment dont ils proviennent.Staphylococcus aureus is a Gram positive bacteria leading to an increasing number of human pathologies. The goal of our work was to study the S. aureus-induced cytokine production by phagocytic mononuclear cells (i.e monocytes, peritoneal and alveolar macrophages). We confirmed that TLR2 was dispensable for peritoneal macrophage response to S. aureus. In contrast, TLR2 activation and phagocytosis were both required to obtain a full cytokine production in monocytes and alveolar macrophages. Furthermore, with specific inhibitors, we observed that p38 and Pi3K had a key role in both activation pathways. On the contrary, Racl and ERK were important for macrophages intracellular pathway. We then investigated which receptor was detecting S. aureus after phagocytosis. Transfection of a dominant-negative form of NOD2 in RAW 264.7 macrophagic cell line inhibited strongly NF-KB activation in response to S. aureus. However, using NOD2-deficient primary cells, we observed that the absence of NOD2 did not alter cytokine production. Finally, NOD2-/- animals responses were comparable to wild-type after intra-nasal injection of S. aureus. Nevertheless, NOD2-/- mice recovered faster than wild-type (weigh gain and pulmonary lesions). In conclusion, our work shows the existence of a TLR2-independant activation pathway that relies on phagocytosis. NOD2 does not play a critical role in S. aureus response, both in vivo and in vitro. Finally, we show that, in phagocytic mononuclear cells, there is a great discrepancy in the role of phagocytosis in the response to S. aureus. This work underlines the heterogeneity in the phagocytic cells response depending on the compartment they are derived from.PARIS5-BU Méd.Cochin (751142101) / SudocSudocFranceF

Natural killer cells responsiveness to Toll-like receptor agonists during bacterial sepsis

Au cours d une infection, les cellules de l immunité innée sont capables de reconnaître via les Toll-like receptors (TLR) des motifs appelés pathogen-associated molecular patterns. Les cellules natural killer (NK) contribuent au processus inflammatoire en produisant de nombreuses cytokines. Chez la souris, nous avons montré que l expression du TLR2 et du TLR4 dans les cellules NK spléniques est intracellulaire, comme pour le TLR9. La réponse des NK aux agonistes des TLR2, 4 et 9 nécessite la présence de cytokines accessoires (IL-15 et IL-18), afin d obtenir une production significative des cytokines pro-inflammatoires IFN- et GM-CSF. En revanche, dans un modèle de sepsis polymicrobial, les NK spléniques de souris présentent une diminution dramatique de leur production d IFN- et de GM-CSF en réponse aux agonistes des TLR. Cette diminution est sous le contrôle des cellules T régulatrices (Treg) et due au TGF- 1. L analyse des voies de signalisation nous a permis de montrer que la production de GM-CSF est abolie chez les cellules NK de souris déficientes pour STING en réponse au CpG-DNA. Ces résultats mettent en lumière une voie alternative et cytoplasmique pour la détection de l ADN bactérien dans les cellules NK, différente de la voie classique TLR9-MyD88 dépendante. De plus, nous avons montré un trafic du récepteur TLR2 depuis l intérieur vers la surface des cellules NK. La migration du TLR2 à la surface des NK nécessite la molécule UNC93B1, précédemment décrite comme transporteur endosomal de TLR.Chez les cellules NK humaines circulantes (sous-populations CD3-CD56bright et CD3-CD56dim), nous avons montré que l expression des TLR2 et 4 est majoritairement intracellulaire, comme pour le TLR9 et comme chez la souris. La production d IFN- par les NK de sujets sains en réponse aux agonistes des TLR nécessite également la présence de cytokines accessoires. Nous montrons que cette production est fortement altérée pour les NK des patients admis en soins intensifs et ayant un sepsis ou un syndrome de réponse inflammatoire systémique (SIRS). De même nous avons trouvé des différences entre les patients et les sujets sains dans l expression du CD69 (marqueur d activation précoce) et des TLR eux-mêmes. Cette étude indique que les NK des patients sepsis et SIRS deviennent tolérants aux agonistes des TLR en terme de production d IFN- , de manière similaire à ce qui a été décrit pour d autres cellules comme les monocytesAs sensors of infection, innate immune cells are able to recognize pathogen-associated molecular patterns by receptors such as Toll-like receptors (TLR). NK cells contribute to inflammatory processes by the production of numerous cytokines. In mice, we have shown that the protein expression of TLR2 and TLR4 in naive NK cells from spleen is predominantly intracellular, similarly to TLR9. The responsiveness of purified NK cells to TLR2, 4 or 9 agonists in vitro requires the presence of accessory cytokines (IL-15 and 18) to trigger a significant production of IFN- and GM-CSF. In contrast, NK cells purified from a model of in vivo polymicrobial sepsis, showed a dramatic reduction in their capacity to respond to TLR agonists in terms of IFN- and GM-CSF release due an inhibitory cross talk with Treg cells mediated by TGF- 1. Analyzing the signaling pathways involved in cytokine production in response to CpG-DNA, we found that GM-CSF production was abolished in NK cells from STING-deficient mice, revealing that this intracytoplasmic receptor acts as a TLR9/MyD88-independent alternative sensor to bacterial DNA in NK cells. Additionally we show that intracellularly expressed TLR2 traffics to the cell surface of NK cells, by a mechanism involving UNC93B1, a protein previous described as an endosomal TLR carrier.In human peripheral blood NK cells (CD3-CD56bright and CD3-CD56dim subsets), we show that TLR2 and 4 protein expression is primarily intracellular, similar to TLR9, and similar to our findings in murine NK cells. The ex vivo responsiveness of human blood NK cells to TLR2, 4 or 9 agonists also requires accessory cytokines, to promote secretion of IFN- . In intensive care patients diagnosed with systemic inflammatory response syndrome (SIRS) and sepsis, IFN- production was significantly decreased. We also discovered modulations in the expression of CD69 (early activation marker) and in that of TLR themselves. This study indicates that NK cells undergo tolerance in response to TLR agonists during SIRS or sepsis, similarly to other cells, such as monocytes.PARIS5-Bibliotheque electronique (751069902) / SudocSudocFranceF

Bench-to-bedside review: natural killer cells in sepsis - guilty or not guilty?

Bacterial sepsis and septic shock are complex inflammatory disorders associated with a systemic inflammatory response syndrome. In the most severe cases of infection, an overzealous release of pro-inflammatory cytokines and inflammatory mediators by activated leukocytes, epithelial cells and endothelial cells, known as a 'cytokine storm', leads to deleterious effects such as organ dysfunction and even death. By the end of the 20th century, natural killer (NK) cells were for the first time identified as important players during sepsis. The role of this cell type was, however, double-edged, either 'angel' or 'devil' depending upon the bacterial infection model under study. Bacterial sensors (such as Toll-like receptors) have recently been shown to be expressed at the protein level in these cells. In addition, NK cells are important sources of interferon-γ and granulocyte-macrophage colony-stimulating factor, which are pro-inflammatory cytokines necessary to fight infection but can contribute to deleterious inflammation as well. Interestingly, an adaptative response occurs aimed to silence them, similar to the well-known phenomenon of endotoxin reprogramming