From birth to adult life: Innate lymphoid cells type-2 shape the lung immune environment

Bei der Geburt wird das Lungengewebe plötzlich der äußeren Umgebung ausgesetzt, durch Lufteinstrom entfaltet und dadurch dramatischen vaskulären und anatomischen Veränderungen unterworfen. Über die immunologische Umgebung in diesem heiklen Moment des Lebens und über den Phänotyp und die Funktion lungenresidenter Immunzellen ist wenig bekannt. Da einige Spieler des angeborenen Immunsystems bereits bei der Embryogenese in der Lunge vorhanden sind, stellten wir die Hypothese auf, dass die Geburt eine orchestrierte und spezifische Immunreaktion in der Lunge auslöst. Wir untersuchten daher die Rolle eines der bekanntesten von Epithelzellen produzierten Zytokine, Interleukin- 33 (IL-33), das als Antwort auf mechanischen Stress gebildet wird. Bei der Arbeit mit neugeborenen Mäusen entdeckten wir die sofortige Hochregulation von IL-33 vom ersten Lebenstag an, gefolgt von einer Welle von IL-13 produzierenden und im Gewebe proliferierenden angeborenen Typ-2-Lymphozyten (ILC2s), die die ersten drei Wochen nach der Geburt andauerte. Der Beginn der ILC2-Expansion fiel mit dem Auftreten von Alveolarmakrophagen (AMs) am postnatalen Tag 3 zusammen und induzierte ihre frühe in situ Polarisation zu einem IL-13-abhängigen, entzündungshemmenden M2-Phänotyp. Am postnatalen Tag 14 waren neugeborene AMs von WT-Mäusen weniger imstande, eine entzündliche Immunantwort gegen den Erreger Streptokokkus pneumoniae (S. pneumoniae) zu erzeugen, im Vergleich mit AMs, die aus IL-13- oder ILC2-defizienten Mäusen extrahiert wurden. Der perinatal erworbene ILC2- und IL-13-abhängige Phänotyp, wurde später im Leben durch die IL-33/ILC2s-Achse aktiv homöostatisch aufrechterhalten. Tatsächlich behielten Monozyten einen intrinsischen M1-Phänotyp, wenn sie in eine ILC2-defiziente oder IL-13-defiziente Empfänger-Maus übertragen wurden, was die homöostatische Rolle von ILC2s und IL-13 in der Aufrechterhaltung der Polarisierung von AMs auch in der erwachsenen Lunge untermauert. Diese homöostatisch gesteuerte Typ-2-Umgebung ging auf Kosten einer verzögerten Reaktion auf S. pneumoniae-Infektion. Tatsächlich zeigten ILC2- und IL-13-defiziente Mäuse eine erhöhte bakterielle Clearance von S. pneumoniae und Staphylokokkus aureus. Unsere Arbeit liefert eine neue homöostatische Rolle von ILC2s bei der Einstellung der Schwelle der Immunaktivierung gegen bakterielle Lungeninfektionen. Darüber hinaus beschreiben wir zum ersten Mal das Vorhandensein einer aktiven Immunantwort als Reaktion auf die Geburt, die durch IL-33-Hochregulation und ILC2- Aktivierung in der neugeborenen Lunge charakterisiert ist. Dieser Signalweg kann dabei helfen, die Anfälligkeit von Neugeborenen für Allergien und Lungeninfektionen zu erklären.At the moment of birth, the lung tissue is suddenly exposed to the external environment, inflated with air and subjected to dramatic vascular and anatomical changes. Little is known about the immunological environment at this delicate moment of life and its consequence on the phenotype and function of lung immune cells. Since a few players of the innate immune system already reside in the lung during embryogenesis, we hypothesized the existence of an orchestrated immune response at birth that would create a specific birth-induced immune environment in the lung and regulate the massive perinatal immune cell infiltration. We therefore investigated the role of one of the most potent epithelium-derived cytokine known in the lung, the alarmin interleukin-33 (IL-33), which is able to respond to mechanical stress. Working with newborn mice, we discovered a wave of IL-33 upregulation starting at birth, which activated tissue resident embryonic type 2 innate lymphoid cells (ILC2s), and lasted for the first three weeks of life. The beginning of ILC2 expansion coincided with the appearance of alveolar macrophages (AMs) on postnatal day 3. ILC2-derived IL-13 induced their early in-tissue polarization to an anti-inflammatory M2 phenotype. By postnatal day 14, newborn AMs from WT mice were less able to mount an inflammatory immune response against the pathogen Streptococcus pneumoniae (S. pneumoniae) when compared to AMs extracted from IL-13 or ILC2 deficient mice. The ILC2 and IL-13 dependent phenotype acquired perinatally was actively maintained at homeostasis later in life by the IL-33/ILC2s axis. In fact, monocyte progenitors maintained an intrinsic M1 phenotype when transferred to an ILC2 deficient or IL-13 deficient mouse recipient, proving the role of ILC2s and IL-13 in inducing a homeostatic polarization of AMs also in the adult lung at steady state. This homeostatically driven type-2 environment comes at the cost of a delayed response to S. pneumoniae infection. In fact, ILC2s and IL-13 deficient mice presented an increased bacterial clearance of S. pneumoniae and Staphylococcus aureus. Our work provides a new homeostatic role of ILC2s in the adult lung and its role in setting the threshold of immune activation against bacterial lung infections. Moreover, it describes for the first time the presence of an active immune response to birth, characterized by IL-33 upregulation and ILC2 activation in the newborn lung. This pathway could help explaining the susceptibility of newborns to allergy and lung infections.submitted by Simona SaluzzoAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersMedizinische Universität Wien, Diss., 2018(VLID)271075

Interleukin-33 improves local immunity during Gram-negative pneumonia by a combined effect on neutrophils and inflammatory monocytes

Pneumonia represents a major health care burden and Gram-negative bacteria provide an increasing therapeutic challenge at least in part through the emergence of multidrug-resistant strains. IL-33 is a multifunctional cytokine belonging to the IL-1 family that can affect many different cell types. We sought here to determine the effect of recombinant IL-33 on the host response during murine pneumonia caused by the common Gram-negative pathogen Klebsiella pneumoniae. IL-33 pretreatment prolonged survival for more than 1 day during lethal airway infection and decreased bacterial loads at the primary site of infection and distant organs. Postponed treatment with IL-33 (3 h) also reduced bacterial growth and dissemination. IL-33-mediated protection was not observed in mice deficient for the IL-33 receptor component IL-1 receptor-like 1. IL-33 induced a brisk type 2 response, characterized by recruitment of type 2 innate lymphoid cells to the lungs and enhanced release of IL-5 and IL-13. However, neither absence of innate lymphoid cells or IL-13, nor blocking of IL-5 impacted on IL-33 effects in mice infected with Klebsiella. Likewise, IL-33 remained effective in reducing bacterial loads in mice lacking B, T, and natural killer T cells. Experiments using antibody-mediated cell depletion indicated that neutrophils and inflammatory monocytes were of importance for antibacterial defense. The capacity of IL-33 to restrict bacterial growth in the lungs was strongly reduced in mice depleted of both neutrophils and inflammatory monocytes, but not in mice selectively depleted of either one of these cell types. These results suggest that IL-33 boosts host defense during bacterial pneumonia by a combined effect on neutrophils and inflammatory monocytes

First-Breath-Induced Type 2 Pathways Shape the Lung Immune Environment

From birth onward, the lungs are exposed to the external environment and therefore harbor a complex immunological milieu to protect this organ from damage and infection. We investigated the homeostatic role of the epithelium-derived alarmin interleukin-33 (IL-33) in newborn mice and discovered the immediate upregulation of IL-33 from the first day of life, closely followed by a wave of IL-13producing type 2 innate lymphoid cells (ILC2s), which coincided with the appearance of alveolar macrophages (AMs) and their early polarization to an IL-13-dependent anti-inflammatory M2 phenotype. ILC2s contributed to lung quiescence in homeostasis by polarizing tissue resident AMs and induced an M2 phenotype in transplanted macrophage progenitors. ILC2s continued to maintain the M2 AM phenotype during adult life at the cost of a delayed response to Streptococcus pneumoniae infection in mice. These data highlight the homeostatic role of ILC2s in setting the activation threshold in the lung and underline their implications in anti-bacterial defenses.(VLID)456113

Genetic barriers more than environmental associations explain Serratia marcescens population structure.

Bacterial species often comprise well-separated lineages, likely emerged and maintained by genetic isolation and/or ecological divergence. How these two evolutionary actors interact in the shaping of bacterial population structure is currently not fully understood. In this study, we investigate the genetic and ecological drivers underlying the evolution of Serratia marcescens, an opportunistic pathogen with high genomic flexibility and able to colonise diverse environments. Comparative genomic analyses reveal a population structure composed of five deeply-demarcated genetic clusters with open pan-genome but limited inter-cluster gene flow, partially explained by Restriction-Modification (R-M) systems incompatibility. Furthermore, a large-scale research on hundred-thousands metagenomic datasets reveals only a partial habitat separation of the clusters. Globally, two clusters only show a separate gene composition coherent with ecological adaptations. These results suggest that genetic isolation has preceded ecological adaptations in the shaping of the species diversity, an evolutionary scenario coherent with the Evolutionary Extended Synthesis

Heme drives hemolysis-induced susceptibility to infection via disruption of phagocyte functions

International audienceHemolysis drives susceptibility to bacterial infections and predicts poor outcome from sepsis. These detrimental effects are commonly considered to be a consequence of heme-iron serving as a nutrient for bacteria. We employed a Gram-negative sepsis model and found that elevated heme levels impaired the control of bacterial proliferation independently of heme-iron acquisition by pathogens. Heme strongly inhibited phagocytosis and the migration of human and mouse phagocytes by disrupting actin cytoskeletal dynamics via activation of the GTP-binding Rho family protein Cdc42 by the guanine nucleotide exchange factor DOCK8. A chemical screening approach revealed that quinine effectively prevented heme effects on the cytoskeleton, restored phagocytosis and improved survival in sepsis. These mechanistic insights provide potential therapeutic targets for patients with sepsis or hemolytic disorders

N-3 fatty acids in patients with multiple cardiovascular risk factors

BACKGROUND: Trials have shown a beneficial effect of n-3 polyunsaturated fatty acids in patients with a previous myocardial infarction or heart failure. We evaluated the potential benefit of such therapy in patients with multiple cardiovascular risk factors or atherosclerotic vascular disease who had not had a myocardial infarction. METHODS: In this double-blind, placebo-controlled clinical trial, we enrolled a cohort of patients who were followed by a network of 860 general practitioners in Italy. Eligible patients were men and women with multiple cardiovascular risk factors or atherosclerotic vascular disease but not myocardial infarction. Patients were randomly assigned to n-3 fatty acids (1 g daily) or placebo (olive oil). The initially specified primary end point was the cumulative rate of death, nonfatal myocardial infarction, and nonfatal stroke. At 1 year, after the event rate was found to be lower than anticipated, the primary end point was revised as time to death from cardiovascular causes or admission to the hospital for cardiovascular causes. RESULTS: Of the 12,513 patients enrolled, 6244 were randomly assigned to n-3 fatty acids and 6269 to placebo. With a median of 5 years of follow-up, the primary end point occurred in 1478 of 12,505 patients included in the analysis (11.8%), of whom 733 of 6239 (11.7%) had received n-3 fatty acids and 745 of 6266 (11.9%) had received placebo (adjusted hazard ratio with n-3 fatty acids, 0.97; 95% confidence interval, 0.88 to 1.08; P=0.58). The same null results were observed for all the secondary end points. CONCLUSIONS: In a large general-practice cohort of patients with multiple cardiovascular risk factors, daily treatment with n-3 fatty acids did not reduce cardiovascular mortality and morbidity. Copyright © 2013 Massachusetts Medical Society