Anita de Boer

Hapten‐induced colitis associated with maintained Th1 and inflammatory responses in IFN‐γ receptor‐deficient mice

IFN‐γ is a potent pro‐inflammatory cytokine thought to be involved in the pathogenesis of Crohns disease. To further define the role of IFN‐γ in intestinal inflammation, we studied the effects of intra‐colonic 2,4,6‐trinitrobenzene sulfonic acid (TNBS) instillation in mice with a functionally inactivated IFN‐γ receptor 1 (IFN‐γR1– / –). Our results indicate that IFN‐γ is not necessary for the induction of hapten‐induced colitis: after TNBS administration both wild‐type and IFN‐γR1– / – mice lost body weight, and the histological features of TNBS‐induced colitis were comparable. Colons of IFN‐γR1– / – mice contained a greater number of cells, represented by macrophages and CD4+ T cells; caudal lymph node cells produced more IFN‐γ and TNF‐α upon stimulation in vitro. Moreover, IL‐18 and IL‐12 p40 RNA levels were comparably up‐regulated after TNBS treatment in IFN‐γR1– / – wild‐type mice. These findings demonstrate that IFN‐γ is dispensable for the development of TNBS‐induced colitis. Importantly, the production of Th1 cytokines (e. g. IFN‐γ and TNF‐α) by caudal lymph node T lymphocytes was enhanced rather than decreased in IFNγR1– / – mice with no evidence for default Th2 development.

Lung Inflammation Induced by Lipoteichoic Acid or Lipopolysaccharide in Humans

RATIONALE Recognition of pathogen-associated molecular patterns by Toll-like receptors (TLRs) is considered to be important for an appropriate immune response against pathogens that enter the lower airways. OBJECTIVES We studied the effects of two different TLR agonists relevant for respiratory infections in the human lung: lipoteichoic acid (LTA; TLR2 agonist, component of gram-positive bacteria) and lipopolysaccharide (LPS; TLR4-agonist, component of gram-negative bacteria). METHODS Fifteen healthy subjects were given LPS or LTA: by bronchoscope, sterile saline was instilled into a lung segment followed by instillation of LTA or LPS into the contralateral lung. After 6 hours, a bronchoalveolar lavage was performed and inflammatory parameters were determined. Isolated RNA from purified alveolar macrophages was analyzed by multiplex ligation-dependent probe amplification. In addition, spontaneous cytokine release by alveolar macrophages was measured. MEASUREMENTS AND MAIN RESULTS Marked differences were detected between LTA- and LPS-induced lung inflammation. Whereas both elicited neutrophil recruitment, only LPS instillation was associated with activation of neutrophils (CD11b surface expression, degranulation product levels) and consistent rises of chemo-/cytokine levels. Moreover, LPS but not LTA activated alveolar macrophages, as reflected by enhanced expression of 10 different mRNAs encoding proinflammatory mediators and increased spontaneous cytokine release upon incubation ex vivo. Remarkably, only LTA induced C5a release. CONCLUSIONS This is the first study to report the in vivo effects of LTA in men and to compare inflammation induced by LTA and LPS in the human lung. Our data suggest that stimulation of TLR2 or TLR4 results in differential pulmonary inflammation, which may be of relevance for understanding pathogenic mechanisms at play during gram-positive and gram-negative respiratory tract infection.

Tissue-Type Plasminogen Activator Modulates Inflammatory Responses and Renal Function in Ischemia Reperfusion Injury

Acute renal failure is often the result of ischemia-reperfusion (I/R) injury. Neutrophil influx is an important damaging event in I/R. Tissue-type plasminogen activator (tPA) not only is a major fibrinolytic agent but also is involved in inflammatory processes. A distinct upregulation of tPA after I/R, with de novo tPA production by proximal renal tubules, was found. For investigating the role of tPA in I/R, renal ischemia was induced in tPA-/- and wild-type (WT) mice by clamping both renal arteries for 35 min followed by reperfusion. Mice were killed 1, 5, and 10 d after reperfusion. After 1 d, tPA-/- mice displayed significantly less neutrophil influx into the interstitial area compared with WT mice. In addition, tPA-/- mice showed quicker recovery of renal function than WT mice. The protocol was repeated after injection of tPA-antisense oligonucleotides into WT mice, leading to even more explicit results: Antisense-treated mice showed less histologic damage, better renal function, and less neutrophil influx than control mice. Surprising, complement C3 concentration, levels of proinflammatory cytokines and chemokines, intercellular adhesion molecule-1 expression, and matrix metalloproteinase activity were similar in WT and tPA-/- mice. Plasmin activity levels in WT and tPA-/- kidneys were also comparable, indicating that tPA influences neutrophil influx into ischemic renal tissue independent from plasmin generation. This study shows that targeting tPA could be of therapeutic importance in treating I/R injury by diminishing neutrophil influx and preserving renal function.

Endogenous Interleukin-18 Improves the Early Antimicrobial Host Response in Severe Melioidosis

ABSTRACT Melioidosis is caused by the soil saprophyte Burkholderia pseudomallei and is endemic in Southeast Asia. The pathogenesis of melioidosis is still largely unknown, although gamma interferon (IFN-γ) seems to play an obligatory role in host defense. Previously, we have shown that IFN-γ production in melioidosis is controlled in part by interleukin-18 (IL-18). The aim of the present study was to determine the role of IL-18 in the immune response to B. pseudomallei. For this the following investigations were performed. (i) Plasma IL-18 and blood monocyte IL-18 mRNA levels were elevated in 34 patients with culture-proven melioidosis compared to the levels in 32 local healthy controls; in addition, IL-18 binding protein levels were markedly elevated in patients, strongly correlating with mortality. (ii) IL-18 gene-deficient (IL-18 knockout [KO]) mice showed accelerated mortality after intranasal infection with a lethal dose of B. pseudomallei, which was accompanied by enhanced bacterial growth in their lungs, livers, spleens, kidneys, and blood at 24 and 48 h postinfection, compared to wild-type mice. In addition, IL-18 KO mice displayed evidence of enhanced hepatocellular injury and renal insufficiency. Together, these data indicate that the enhanced production of IL-18 in melioidosis is an essential part of a protective immune response to this severe infection.

Priming of alveolar macrophages upon instillation of lipopolysaccharide in the human lung.

The airways are continuously exposed to respiratory pathogens, which may result in bacterial pneumonia, one of the most common infectious diseases and the leading cause of sepsis. Considering that recurrent exposure to microbial products can lead to tolerance of immune cells, and that this might contribute to the susceptibility to nosocomial infection, we investigated the effect of in vivo lipopolysaccharide (LPS) instillation on the responsiveness of alveolar macrophages. In eight healthy humans, sterile saline was instilled into a lung segment by bronchoscope, followed by instillation of LPS into the contralateral lung; 6 hours later, a bilateral bronchoalveolar lavage was performed, and purified alveolar macrophages were ex vivo stimulated with LPS or lipoteichoic acid (LTA), triggering Toll-like receptor (TLR)-4 and -2, respectively. In vivo LPS-exposed alveolar macrophages were primed, as reflected by increased ex vivo LPS- and LTA-induced IL-1 beta and IL-6 gene expression and production compared with in vivo saline-exposed alveolar macrophages. LPS instillation did not influence the surface expression of TLR4 or TLR2. Furthermore, LPS instillation did not impact on the expression of a number of extracellular and intracellular regulators of TLR signaling. However, p38 mitogen-activated protein kinase remained phosphorylated in alveolar macrophages upon LPS instillation. The current data demonstrate that LPS instillation in the human lung primes alveolar macrophages for further stimulation with either LPS or LTA, possibly by sustained p38 mitogen-activated protein kinase activation.

Soluble urokinase-type plasminogen activator receptor levels in patients with burn injuries and inhalation trauma requiring mechanical ventilation: an observational cohort study

IntroductionSoluble urokinase-type plasminogen activator receptor (suPAR) has been proposed as a biologic marker of fibrinolysis and inflammation. The aim of this study was to investigate the diagnostic and prognostic value of systemic and pulmonary levels of suPAR in burn patients with inhalation trauma who need mechanical ventilation.MethodssuPAR was measured in plasma and nondirected lung-lavage fluid of mechanically ventilated burn patients with inhalation trauma. The samples were obtained on the day of inhalation trauma and on alternate days thereafter until patients were completely weaned from the mechanical ventilator. Mechanically ventilated patients without burns and without pulmonary disease served as controls.ResultsSystemic levels of suPAR in burn patients with inhalation trauma were not different from those in control patients. On admission and follow up, pulmonary levels of suPAR in patients with inhalation trauma were significantly higher compared with controls. Pulmonary levels of suPAR highly correlated with pulmonary levels of interleukin 6, a marker of inflammation, and thrombin-antithrombin complexes, markers of coagulation, but not plasminogen activator activity, a marker of fibrinolysis. Systemic levels of suPAR were predictive of the duration of mechanical ventilation and length of intensive care unit (ICU) stay. Duration of mechanical ventilation and length of ICU stay were significantly longer in burn-injury patients with systemic suPAR levels > 9.5 ng/ml.ConclusionsPulmonary levels of suPAR are elevated in burn patients with inhalation trauma, and they correlate with pulmonary inflammation and coagulation. Although pulmonary levels of suPAR may have diagnostic value in burn-injury patients, systemic levels of suPAR have prognostic value.

Cardiac arrest patients have an impaired immune response, which is not influenced by induced hypothermia

IntroductionInduced hypothermia is increasingly applied as a therapeutic intervention in ICUs. One of the underlying mechanisms of the beneficial effects of hypothermia is proposed to be reduction of the inflammatory response. However, a fear of reducing the inflammatory response is an increased infection risk. Therefore, we studied the effect of induced hypothermia on immune response after cardiac arrest.MethodsA prospective observational cohort study in a mixed surgical-medical ICU. Patients admitted at the ICU after surviving cardiac arrest were included and during 24 hours body temperature was strictly regulated at 33°C or 36°C. Blood was drawn at three time points: after reaching target temperature, at the end of the target temperature protocol and after rewarming to 37°C. Plasma cytokine levels and response of blood leucocytes to stimulation with toll-like receptor (TLR) ligands lipopolysaccharide (LPS) from Gram-negative bacteria and lipoteicoic acid (LTA) from Gram-positive bacteria were measured. Also, monocyte HLA-DR expression was determined.ResultsIn total, 20 patients were enrolled in the study. Compared to healthy controls, cardiac arrest patients kept at 36°C (n = 9) had increased plasma cytokines levels, which was not apparent in patients kept at 33°C (n = 11). Immune response to TLR ligands in patients after cardiac arrest was generally reduced and associated with lower HLA-DR expression. Patients kept at 33°C had preserved ability of immune cells to respond to LPS and LTA compared to patients kept at 36°C. These differences disappeared over time. HLA-DR expression did not differ between 33°C and 36°C.ConclusionsPatients after cardiac arrest have a modest systemic inflammatory response compared to healthy controls, associated with lower HLA-DR expression and attenuated immune response to Gram-negative and Gram-positive antigens, the latter indicative of an impaired immune response to bacteria. Patients with a body temperature of 33°C did not differ from patients with a body temperature of 36°C, suggesting induced hypothermia does not affect immune response in patients with cardiac arrest.Trial registrationClinicalTrials.gov NCT01020916, registered 25 November 2009

Lung-protective mechanical ventilation does not protect against acute kidney injury in patients without lung injury at onset of mechanical ventilation

INTRODUCTION Preclinical and clinical studies suggest that mechanical ventilation contributes to the development of acute kidney injury (AKI), particularly in the setting of lung-injurious ventilator strategies. OBJECTIVE To determine whether ventilator settings in critically ill patients without acute lung injury (ALI) at onset of mechanical ventilation affect the development of AKI. DESIGN, SETTING, AND PATIENTS Secondary analysis of a randomized controlled trial (N = 150), comparing conventional tidal volume (V(T), 10 mL/kg) with low tidal volume (V(T), 6 mL/kg) mechanical ventilation in critically ill patients without ALI at randomization. During the first 5 days of mechanical ventilation, the RIFLE class was determined daily, whereas neutrophil gelatinase-associated lipocalin and cystatin C levels were measured in plasma collected on days 0, 2, and 4. RESULTS Eighty-six patients had no AKI at inclusion, and 18 patients (21%) subsequently developed AKI, but without significant difference between ventilation strategies. (Cumulative hazard, 0.26 vs 0.23; P = .88.) The courses of neutrophil gelatinase-associated lipocalin and cystatin C plasma levels did not differ significantly between randomization groups. CONCLUSION In the present study in critically patients without ALI at onset of mechanical ventilation, lower tidal volume ventilation did not reduce the development or worsening of AKI compared with conventional tidal volume ventilation.

Gene Expression Profiling of Apoptosis Regulators in Patients with Sepsis

Introduction: Sepsis is associated with a dysregulation of apoptosis in immune cells, which has been implicated in both immunosuppression and multiple organ failure. We describe the expression profiles of genes encoding key regulators of apoptosis in highly purified monocytes, granulocytes and CD4+ T lymphocytes. Methods: Sixteen patients with sepsis were recruited from the intensive care unit and were compared with 24 healthy controls. RNA was isolated from highly purified monocyte, granulocyte and CD4+ T-lymphocyte populations. Gene expression profiles were determined using multiplex ligation-dependent probe amplification for the simultaneous detection of 30 pro- and anti-apoptotic target genes. Results: Relative to healthy controls, patients with sepsis showed increased transcription of both pro- and anti-apoptotic genes in peripheral blood leukocytes. Specific monocyte, granulocyte and CD4+ T-lymphocyte mRNA profiles were identified. Anti-apoptotic profiles were found in monocytes and granulocytes, while CD4+ T lymphocytes displayed a foremost pro-apoptotic mRNA profile. Conclusions: These data indicate that in patients with sepsis, the alterations in apoptosis of circulating leukocytes occur in a cell-specific manner.

Serum levels of N-terminal proB-type natriuretic peptide in mechanically ventilated critically ill patients--relation to tidal volume size and development of acute respiratory distress syndrome.

BackgroundSerum levels of N–terminal proB–type natriuretic peptide (NT–proBNP) are elevated in patients acute respiratory distress syndrome (ARDS). Recent studies showed a lower incidence of acute cor pulmonale in ARDS patients ventilated with lower tidal volumes. Consequently, serum levels of NT–proBNP may be lower in these patients.We investigated the relation between serum levels of NT–proBNP and tidal volumes in critically ill patients without ARDS at the onset of mechanical ventilation.MethodsSecondary analysis of a randomized controlled trial of lower versus conventional tidal volumes in patients without ARDS. NT–pro BNP were measured in stored serum samples. Serial serum levels of NT–pro BNP were analyzed controlling for acute kidney injury, cumulative fluid balance and presence of brain injury. The primary outcome was the effect of tidal volume size on serum levels of NT–proBNP. Secondary outcome was the association with development of ARDS.ResultsSamples from 150 patients were analyzed. No relation was found between serum levels of NT–pro BNP and tidal volume size. However, NT-proBNP levels were increasing in patients who developed ARDS. In addition, higher levels were observed in patients with acute kidney injury, and in patients with a more positive cumulative fluid balance.ConclusionSerum levels of NT–proBNP are independent of tidal volume size, but are increasing in patients who develop ARDS.