The Triggering Receptor Expressed on Myeloid Cells 2 Inhibits Complement Component 1q Effector Mechanisms and Exerts Detrimental Effects during Pneumococcal Pneumonia

Phagocytosis and inflammation within the lungs is crucial for host defense during bacterial pneumonia. Triggering receptor expressed on myeloid cells (TREM)-2 was proposed to negatively regulate TLR-mediated responses and enhance phagocytosis by macrophages, but the role of TREM-2 in respiratory tract infections is unknown. Here, we established the presence of TREM-2 on alveolar macrophages (AM) and explored the function of TREM-2 in the innate immune response to pneumococcal infection in vivo. Unexpectedly, we found Trem-2(-/-) AM to display augmented bacterial phagocytosis in vitro and in vivo compared to WT AM. Mechanistically, we detected that in the absence of TREM-2, pulmonary macrophages selectively produced elevated complement component 1q (C1q) levels. We found that these increased C1q levels depended on peroxisome proliferator-activated receptor-δ (PPAR-δ) activity and were responsible for the enhanced phagocytosis of bacteria. Upon infection with S. pneumoniae, Trem-2(-/-) mice exhibited an augmented bacterial clearance from lungs, decreased bacteremia and improved survival compared to their WT counterparts. This work is the first to disclose a role for TREM-2 in clinically relevant respiratory tract infections and demonstrates a previously unknown link between TREM-2 and opsonin production within the lungs

The role of Lipocalin 2 in macrophage polarization and the host defense against Streptococcus pneumoniae

Trotz des Einsatzes von Antibiotika und Impfprogrammen ist die bakterielle Pneumonie, meist verursacht durch Streptococcus pneumoniae, auch heute noch die weltweit häufigste Todesursache von Kindern. In der Lunge residierende Makrophagen, als Teil des angeborenen Immunsystems, spielen bei der Abwehr von Streptococcus pneumoniae eine kritische Rolle. Sie sind die ersten Zellen, die auf die Infektion reagieren und essentiell für die Induktion der Entzündung. Bei Aktivierung produzieren die Makrophagen Zytokine und Chemokine, die zur Rekrutierung von Neutrophilen und im Weiteren zur Eliminierung der Bakterien führen. Je stärker und schneller diese frühe Entzündungsreaktion induziert wird, umso effizienter funktioniert die Beseitigung der Pneumokokken und umso besser ist auch der Verlauf der Erkrankung. Demnach ist die Aktivierung und Polarisierung von Lungenmakrophagen ein kritischer Faktor in der Abwehr von Streptococcus pneumoniae. Im Zuge dieser Studie wurde die bronchoalveolare Lavage (BAL) Flüssigkeit von Patienten mit schwerer, beatmungspflichtiger Pneumonie auf das Vorhandensein von verschiedenen Entzündungsmediatoren untersucht. Besonders auffallend waren deutlich erhöhte Konzentrationen von Lipocalin 2 (LCN2), einem antimikrobiellen Glykoprotein das vorwiegend von Zellen des angeborenen Immunsystems, wie Makrophagen, Neutrophilen und Epithelzellen, produziert wird. LCN2 war bis jetzt hauptsächlich für seine Aktivität gegen Escherichia coli und Klebsiella pneumoniae bekannt, wobei die antimikrobielle Wirkung auf der Fähigkeit von LCN2 beruht bakterielle Siderophoren zu binden und den Bakterien auf diesem Wege Eisen zu entziehen. Obwohl Streptococcus pneumoniae bis dato als Siderophor-unabhängiger Keim gilt, fanden wir sehr hohe LCN2 Konzentrationen in Patienten mit Pneumokokken Pneumonie und beschlossen daher die Funktion von LCN2 in der Abwehr von Streptococcus pneumoniae genauer zu untersuchen. Es ist bekannt, dass die LCN2 Expression von immunsuppressiven Substanzen induziert wird. Basierend darauf, stellten wir die Hypothese auf, dass LCN2 direkt an der Regulation der Makrophagenaktivierung und -funktion beteiligt ist und damit eine wichtige Rolle während der Pneumokokken Pneumonie spielt. Mit Hilfe diverser zellbiologischer Techniken konnten wir zeigen, dass LCN2 i) vor allem von deaktivierten Makrophagen produziert wird und ii), dass die Präsenz von LCN2 auch essentiell für den Vorgang der Makrophagendeaktivierung ist. Mechanistisch weisen unsere Daten darauf hin, dass die antiinflammatorischen Effekte von LCN2 von IL-10, einem wichtigen antiinflammatorischen Zytokin, vermittelt werden. Diese, auf in vitro Versuchen basierenden Erkenntnisse, werden auch in vivo reflektiert, was anhand eines Pneumokokken Mausmodells untersucht wurde. Während der Infektion induziertes LCN2 führte in Mäusen zu einer verzögerten frühen Immunantwort und damit zu einer schnelleren Vermehrung der Bakterien. Im Gegensatz dazu zeigten LCN2 defizienten Mäuse eine verstärkte frühe Zytokinproduktion, vermehrte Einwanderung von Neutrophilen in die Lunge und als Konsequenz einen Überlebensvorteil während der Pneumokokken Pneumonie. Im Einklang damit korreliert eine starke LCN2 Induktion mit einer höheren Sterberate bei Patienten mit durch Gram-positive Keime verursachter Lungenentzündung. Unsere Daten weisen erstmals auf eine schädliche Rolle von LCN2 bei Infektionen mit Streptococcus pneumoniae hin und identifizieren LCN2 als potentiellen Biomarker für die Prognose von Pneumokokken Pneumonien.Despite advances in antimicrobial therapies and vaccination protocols, pneumonia remains the most common cause of death of children worldwide. Among the causative pathogens of bacterial pneumonia in humans, Streptococcus pneumoniae is the most relevant one. Innate immunity is the first line of defense against invading lung pathogens. In the course of pneumonia activated macrophages elicit an inflammatory response, leading to the recruitment of neutrophils and clearance of bacteria. The successful elimination of pneumococci requires the immediate induction of this inflammatory response, which ultimately determines the outcome. Thus, the activation and polarization of lung macrophages is considered a crucial factor for the successful defense against S. pneumoniae. We studied the presence of inflammatory molecules in the bronchoalveolar lavage (BAL) fluid of patients suffering from severe pneumonia requiring mechanical ventilation and discovered substantially elevated concentrations of Lipocalin 2 (LCN2). LCN2 is a glycoprotein expressed mainly by innate immune cells such as macrophages, neutrophils and epithelial cells. It is known for its antimicrobial activity against bacteria such as Escherichia coli or Klebsiella pneumoniae, which is based on LCN2's ability to scavenge a subset of bacterial siderophores, thereby preventing bacterial iron acquisition. Strikingly, although Streptococcus pneumoniae is considered as a siderophore-independent pathogen, infection with this bacterium strongly induced LCN2 in humans - and the biological role of this finding was unclear. We therefore decided to investigate the potential function of LCN2 in the inflammatory response to this bacterium. Considering reports indicating the involvement of deactivating agents in the regulation of LCN2 expression, we hypothesized that LCN2 might be involved in determining the functional properties of macrophages. Using a variety of molecular techniques, we discovered that LCN2 was released by deactivated macrophages - and that LCN2 itself had the capacity to deactivate macrophages in the presence of bacteria. We further revealed that the anti-inflammatory cytokine IL-10 mediated the anti-inflammatory effects in the presence of LCN2. Using a murine pneumococcal pneumoniae model, we were able to reproduce the deactivating properties of LCN2 in the lungs upon infection, which led to a delayed immune response and consequently enhanced bacterial outgrowth. Mice deficient in LCN2 therefore exhibited an improved immune response and survival from pneumococcal infections. In agreement with data from mouse studies, we further discovered that higher LCN2 levels in the BAL of patients suffering from pneumonia caused by Gram positive bacteria correlated with a bad outcome of the infection. Our data reveal for the first time a detrimental role for Lcn 2 during severe infections caused by Streptococcus pneumoniae and indicate that LCN2 could potentially serve as a biomarker of severe lung infections.submitted by Joanna Maria WarszawskaAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersWien, Med. Univ., Diss., 2014OeBB(VLID)188355

Storage of bronchoalveolar lavage fluid and accuracy of microbiologic diagnostics in the ICU: a prospective observational study

Introduction: Early initiation of appropriate antimicrobial treatment is a cornerstone in managing pneumonia. Because microbiologic processing may not be available around the clock, optimal storage of specimens is essential for accurate microbiologic identification of pathogenetic bacteria. The aim of our study was to determine the accuracy of two commonly used storage approaches for delayed processing of bronchoalveolar lavage in critically ill patients with suspected pneumonia. Methods: This study included 132 patients with clinically suspected pneumonia at two medical intensive care units of a tertiary care hospital. Bronchoalveolar lavage samples were obtained and divided into three aliquots: one was used for immediate culture, and two, for delayed culture (DC) after storage for 24 hours at 4 degrees C (DC4) and -80 degrees C (DC-80), respectively. Results: Of 259 bronchoalveolar lavage samples, 84 (32.4\%) were positive after immediate culture with 115 relevant culture counts (>= 10(4) colony-forming units/ml). Reduced (<10(4) colony-forming units/ml) or no growth of four and 57 of these isolates was observed in DC4 and DC-80, respectively. The difference between mean bias of immediate culture and DC4 (-0.035; limits of agreement, -0.977 to 0.906) and immediate culture and DC-80 (-1.832; limits of agreement, -4.914 to 1.267) was -1.788 +/- 1.682 (P < 0.0001). Sensitivity and negative predictive value were 96.5\% and 97.8\% for DC4 and 50.4\% and 75.4\% for DC-80, respectively; the differences were statistically significant (P < 0.0001). Conclusions: Bronchoalveolar lavage samples can be processed for culture when stored up to 24 hours at 4 degrees C without loss of diagnostic accuracy. Delayed culturing after storage at -80 degrees C may not be reliable, in particular with regard to Gram-negative bacteria

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