Factor XI deficiency enhances the pulmonary allergic response to house dust mite in mice independent of factor XII.

Asthma is associated with activation of coagulation in the airways. The coagulation system can be initiated via the extrinsic tissue factor-dependent pathway or via the intrinsic pathway, in which the central player factor XI (FXI) can be either activated via active factor XII (FXIIa) or via thrombin. We aimed to determine the role of the intrinsic coagulation system and its possible route of activation in allergic lung inflammation induced by the clinically relevant human allergen house dust mite (HDM). Wild-type (WT), FXI knockout (KO), and FXII KO mice were subjected to repeated exposure to HDM via the airways, and inflammatory responses were compared. FXI KO mice showed increased influx of eosinophils into lung tissue, accompanied by elevated local levels of the main eosinophil chemoattractant eotaxin. Although gross lung pathology and airway mucus production did not differ between groups, FXI KO mice displayed an impaired endothelial/epithelial barrier function, as reflected by elevated levels of total protein and IgM in bronchoalveolar lavage fluid. FXI KO mice had a stronger systemic IgE response with an almost completely absent HDM-specific IgG1 response. The phenotype of FXII KO mice was, except for a higher HDM-specific IgG1 response, similar to that of WT mice. In conclusion, FXI attenuates part of the allergic response to repeated administration of HDM in the airways by a mechanism that is independent of activation via FXII.

The gut microbiota plays a protective role in the host defence against pneumococcal pneumonia.

OBJECTIVE: Pneumonia accounts for more deaths than any other infectious disease worldwide. The intestinal microbiota supports local mucosal immunity and is increasingly recognised as an important modulator of the systemic immune system. The precise role of the gut microbiota in bacterial pneumonia, however, is unknown. Here, we investigate the function of the gut microbiota in the host defence against Streptococcus pneumoniae infections. DESIGN: We depleted the gut microbiota in C57BL/6 mice and subsequently infected them intranasally with S. pneumoniae. We then performed survival and faecal microbiota transplantation (FMT) experiments and measured parameters of inflammation and alveolar macrophage whole-genome responses. RESULTS: We found that the gut microbiota protects the host during pneumococcal pneumonia, as reflected by increased bacterial dissemination, inflammation, organ damage and mortality in microbiota-depleted mice compared with controls. FMT in gut microbiota-depleted mice led to a normalisation of pulmonary bacterial counts and tumour necrosis factor-α and interleukin-10 levels 6 h after pneumococcal infection. Whole-genome mapping of alveolar macrophages showed upregulation of metabolic pathways in the absence of a healthy gut microbiota. This upregulation correlated with an altered cellular responsiveness, reflected by a reduced responsiveness to lipopolysaccharide and lipoteichoic acid. Compared with controls, alveolar macrophages derived from gut microbiota-depleted mice showed a diminished capacity to phagocytose S. pneumoniae. CONCLUSIONS: This study identifies the intestinal microbiota as a protective mediator during pneumococcal pneumonia. The gut microbiota enhances primary alveolar macrophage function. Novel therapeutic strategies could exploit the gut-lung axis in bacterial infections.

Activated protein C inhibits neutrophil migration in allergic asthma: a randomised trial.

Asthma patients show evidence of a procoagulant state in their airways, accompanied by an impaired function of the anticoagulant protein C system. We aimed to study the effect of recombinant human activated protein C (rhAPC) in allergic asthma patients.We conducted a randomised, double-blind, placebo-controlled, proof-of-concept study in house dust mite (HDM) allergic asthma patients. Patients were randomised to receive intravenous rhAPC (24 µg·kg(-1)·h(-1); n=12) or placebo (n=12) for 11 h. 4 h after the start of infusion, a first bronchoscopy was performed to challenge one lung segment with saline (control) and a contralateral segment with a combination of HDM extract and lipopolysaccharide (HDM+LPS), thereby mimicking environmental house dust exposure. A second bronchoscopy was conducted 8 h after intrabronchial challenge to obtain bronchoalveolar lavage fluid (BALF).rhAPC did not influence HDM+LPS induced procoagulant changes in the lung. In contrast, rhAPC reduced BALF leukocyte counts by 43% relative to placebo, caused by an inhibitory effect on neutrophil influx (64% reduction), while leaving eosinophil influx unaltered. rhAPC also reduced neutrophil degranulation products in the airways.Intravenous rhAPC attenuates HDM+LPS-induced neutrophil migration and protein release in allergic asthma patients by an effect that does not rely on coagulation inhibition.

Asthma and coagulation.

Asthma is a chronic airway disease characterized by paroxysmal airflow obstruction evoked by irritative stimuli on a background of allergic lung inflammation. Currently, there is no cure for asthma, only symptomatic treatment. In recent years, our understanding of the involvement of coagulation and anticoagulant pathways, the fibrinolytic system, and platelets in the pathophysiology of asthma has increased considerably. Asthma is associated with a procoagulant state in the bronchoalveolar space, further aggravated by impaired local activities of the anticoagulant protein C system and fibrinolysis. Protease-activated receptors have been implicated as the molecular link between coagulation and allergic inflammation in asthma. This review summarizes current knowledge of the impact of the disturbed hemostatic balance in the lungs on asthma severity and manifestations and identifies new possible targets for asthma treatment.

Intrabronchial activated protein C enhances lipopolysaccharide-induced pulmonary responses.

Intravenous administration of activated protein C (APC) inhibits coagulation and inflammation in the lungs of humans and animals. Investigations in rodents demonstrated that direct intrapulmonary delivery of APC also exerts anticoagulant and anti-inflammatory effects. The effect of intrabronchial administration of recombinant human (rh)APC on lipopolysaccharide (LPS)-induced haemostatic and inflammatory alterations in the bronchoalveolar space of humans was studied. Eight subjects received rhAPC via intrabronchial instillation by bronchoscope, while in a contralateral subsegment subjects received saline; all subjects were challenged bilaterally with LPS in the same lung subsegments. Four additional subjects received rhAPC (75 µg), with saline as a control in the contralateral subsegment, while they were bilaterally "challenged" with saline. After 6 h a bronchoalveolar lavage was performed and coagulation and inflammatory parameters were measured. rhAPC enhanced LPS-induced coagulation activation in the bronchoalveolar space, when compared with the control side. In addition, rhAPC amplified LPS-induced pro-inflammatory responses, as indicated by higher concentrations of cytokines and chemokines. rhAPC alone did not have procoagulant or pro-inflammatory effects. Locally administered rhAPC has unexpected procoagulant and pro-inflammatory effects in LPS-challenged lung subsegments. These data argue against a role for intrapulmonary delivery of rhAPC as a treatment strategy for lung inflammatory disorders in humans.

The lectin-like domain of thrombomodulin hampers host defence in pneumococcal pneumonia.

The lectin-like domain of thrombomodulin (TM) plays an important regulatory role in sterile inflammatory conditions, but its role in severe Gram-positive infectious disease is unknown. Streptococcus pneumoniae is the most common cause of community-acquired pneumonia. The aim of this study was to determine the role of the lectin-like domain of TM in murine pneumococcal pneumonia. Wild-type (WT) mice and mice lacking the lectin-like domain of TM (TM(LeD/LeD)) were infected intranasally with viable S. pneumoniae and either observed in a survival study or euthanised 6, 24 or 48 h after infection. TM(LeD/LeD) mice had a markedly better survival in pneumococcal pneumonia when compared with WT mice. At 48 h post-infection with S. pneumoniae, TM(LeD/LeD) mice had lower bacterial loads in blood and liver, and exhibited less pulmonary inflammation, as shown by having less lung histopathology, less neutrophil influx and lower cytokine and chemokine levels. Plasma levels of pro-inflammatory cytokines were also reduced in TM(LeD/LeD) mice after exposure to the infection. Deletion of the lectin-like domain of TM improves the host defence in pneumococcal pneumonia. The lectin-like domain of TM may have a differential role in response to Gram-positive or Gram-negative bacteria.

Loss of suppression of tumorigenicity 2 (ST2) gene reverses sepsis-induced inhibition of lung host defense in mice.

RATIONALE: After surviving the initial hyperinflammatory phase, patients with sepsis display features consistent with immunosuppression, which renders the host susceptible to nosocomial infections, in particular bacterial pneumonia. Suppression of tumorigenicity 2 (ST2) is a negative regulator of Toll-like receptor signaling implicated in endotoxin tolerance. OBJECTIVES: The present study sought to determine the role of ST2 in modulating host defense in the lung during sepsis, using a murine model of cecal ligation and puncture (CLP)-induced sepsis followed by a secondary infection with Pseudomonas aeruginosa via the airways. METHODS: CLP or sham surgery was performed on BALB/c wild-type (WT) and ST2 knockout (KO) mice, and 24 hours later animals were challenged with 10(8) live P. aeruginosa. MEASUREMENTS AND MAIN RESULTS: CLP mice demonstrated impaired clearance of Pseudomonas from their lungs and reduced pulmonary levels of tumor necrosis factor-α and IL-6 compared with sham mice. After CLP, ST2KO mice with secondary pneumonia displayed a strongly improved survival and a better bacterial clearance compared with WT mice, which was accompanied by enhanced lung inflammation. CLP did not influence the responsiveness of alveolar macrophages toward P. aeruginosa ex vivo irrespective of the st2 genotype. In contrast, CLP resulted in a reduced capacity of WT CD4(+) and CD8(+) T cells to produce IFN-γ and tumor necrosis factor-α, an immune suppressive effect that was not seen in ST2KO mice. CONCLUSIONS: These findings indicate that gene products of ST2 contribute to the immune-compromised state during sepsis and the ensuing disturbed homeostasis of lung host defense.

Impact of endogenous protein C on pulmonary coagulation and injury during lethal H1N1 influenza in mice.

Influenza accounts for 5-10% of community-acquired pneumonia cases, and is a major cause of mortality. Sterile and bacterial lung injury are associated with procoagulant and inflammatory derangements in the lungs and down-regulation of the protein C (PC) pathway has been correlated with disease severity and mortality in severe bacterial pneumonia and sepsis. In addition, during lethal influenza pneumonia, pulmonary and systemic coagulation are activated, which can be attenuated by the administration of recombinant activated (A) PC. We here determined the role of endogenous PC in lethal H1N1 influenza A infection. Male C57BL/6 mice pretreated with an inhibitory monoclonal antibody directed against murine PC or a control antibody were intranasally infected with a lethal dose of a mouse-adapted H1N1 influenza A strain. Mice were killed at 48 or 96 hours after infection, after which lungs and bronchoalveolar lavage fluid were harvested, or observed for up to 9 days. Anti-PC antibody treatment aggravated pulmonary activation of coagulation as compared with control antibody treatment, as reflected by increased lung concentrations of thrombin-antithrombin complexes and fibrin degradation products, as well as intravascular thrombus formation. Anti-PC antibody treatment aggravated lung histopathology, but lowered bronchoalveolar neutrophil influx and total protein levels, and delayed mortality. In conclusion, endogenous PC has strong effects on the host response to lethal influenza A infection, inhibiting pulmonary coagulopathy and inflammation on the one hand, but facilitating neutrophil influx and protein leak and accelerating mortality on the other hand.

Human plasma-derived C1 esterase inhibitor concentrate has limited effect on house dust mite-induced allergic lung inflammation in mice.

C1 esterase inhibitor (C1-INH) can inhibit multiple pathways (complement, contact-kinin, coagulation, and fibrinolysis) that are all implicated in the pathophysiology of asthma. We explored the effect of human plasma-derived C1-INH on allergic lung inflammation in a house dust mite (HDM) induced asthma mouse model by daily administration of C1-INH (15 U) during the challenge phase. NaCl and HDM exposed mice had comparable plasma C1-INH levels, while bronchoalveolar lavage fluid (BALF) levels were increased in HDM exposed mice coinciding with slightly reduced activation of complement (C5a). C1-INH treatment reduced Th2 response and enhanced HDM-specific IgG1. Influx of eosinophils in BALF or lung, pulmonary damage, mucus production, procoagulant response or plasma leakage in BALF was similar in both groups. In conclusion, C1-INH dampens Th2 responses during HDM induced allergic lung inflammation.

The endothelial protein C receptor impairs the antibacterial response in murine pneumococcal pneumonia and sepsis.

Pneumococcal pneumonia is a frequent cause of gram-positive sepsis and has a high mortality. The endothelial protein C receptor (EPCR) has been implicated in both the activation of protein C (PC) and the anti-inflammatory actions of activated (A)PC. The aim of this study was to determine the role of the EPCR in murine pneumococcal pneumonia and sepsis. Wild-type (WT), EPCR knockout (KO) and Tie2-EPCR mice, which overexpress EPCR on the endothelium, were infected intranasally (pneumonia) or intravenously (sepsis) with viable Streptococcus pneumoniae and euthanised at 24 or 48 hours after initiation of the infection for analyses. Pneumonia did not alter constitutive EPCR expression on pulmonary endothelium but was associated with an influx of EPCR positive neutrophils into lung tissue. In pneumococcal pneumonia EPCR KO mice demonstrated diminished bacterial growth in the lungs and dissemination to spleen and liver, reduced neutrophil recruitment to the lungs and a mitigated inflammatory response. Moreover, EPCR KO mice displayed enhanced activation of coagulation in the early phase of disease. Correspondingly, in pneumococcal sepsis EPCR KO mice showed reduced bacterial growth in lung and liver and attenuated cytokine release. Conversely, EPCR-overexpressing mice displayed higher bacterial outgrowth in lung, blood, spleen and liver in pneumococcal sepsis. In conclusion, EPCR impairs antibacterial defense in both pneumococcal pneumonia and sepsis, which is associated with an enhanced pro-inflammatory response.

Mast cell-deficient kit mice develop house dust mite-induced lung inflammation despite impaired eosinophil recruitment.

BACKGROUND: Mast cells are implicated in allergic and innate immune responses in asthma, although their role in models using an allergen relevant for human disease is incompletely understood. House dust mite (HDM) allergy is common in asthma patients. Our aim was to investigate the role of mast cells in HDM-induced allergic lung inflammation. METHODS: Wild-type (Wt) and mast cell-deficient Kit(w-sh) mice on a C57BL/6 background were repetitively exposed to HDM via the airways. RESULTS: HDM challenge resulted in a rise in tryptase activity in bronchoalveolar lavage fluid (BALF) of Wt mice, indicative of mast cell activation. Kit(w-sh) mice showed a strongly attenuated HDM- induced recruitment of eosinophils in BALF and lung tissue, accompanied by reduced pulmonary levels of the eosinophil chemoattractant eotaxin. Remarkably, Kit(w-sh) mice demonstrated an unaltered capacity to develop lung pathology and increased mucus production in response to HDM. The increased plasma IgE in response to HDM in Wt mice was absent in Kit(w-sh) mice. CONCLUSION: These data contrast with previous reports on the role of mast cells in models using ovalbumin as allergen in that C57BL/6 Kit(w-sh) mice display a selective impairment of eosinophil recruitment without differences in other features of allergic inflammation.

Protease-activated receptor-2 deficient mice have reduced house dust mite-evoked allergic lung inflammation.

Protease-activated receptor-2 (PAR2) is abundantly expressed in the pulmonary compartment. House dust mite (HDM) is a common cause of allergic asthma and contains multiple PAR2 agonistic proteases. The aim of this study was to determine the role of PAR2 in HDM-induced allergic lung inflammation. For this, the extent of allergic lung inflammation was studied in wild type (Wt) and PAR2 knockout (KO) mice after repeated airway exposure to HDM. HDM exposure of Wt mice resulted in a profound influx of eosinophils in bronchoalveolar lavage fluid (BALF) and accumulation of eosinophils in lung tissue, which both were strongly reduced in PAR2 KO mice. PAR2 KO mice demonstrated attenuated lung pathology and protein leak in the bronchoalveolar space, accompanied by lower BALF levels of the anaphylatoxins C3a and C5a. This study reveals, for the first time, an important role for PAR2 in allergic lung inflammation induced by the clinically relevant allergens contained in HDM.

Overexpression of the endothelial protein C receptor is detrimental during pneumonia-derived gram-negative sepsis (Melioidosis).

BACKGROUND: The endothelial protein C receptor (EPCR) enhances anticoagulation by accelerating activation of protein C to activated protein C (APC) and mediates anti-inflammatory effects by facilitating APC-mediated signaling via protease activated receptor-1. We studied the role of EPCR in the host response during pneumonia-derived sepsis instigated by Burkholderia (B.) pseudomallei, the causative agent of melioidosis, a common form of community-acquired Gram-negative (pneumo)sepsis in South-East Asia. METHODOLOGY/PRINCIPAL FINDINGS: Soluble EPCR was measured in plasma of patients with septic culture-proven melioidosis and healthy controls. Experimental melioidosis was induced by intranasal inoculation of B. pseudomallei in wild-type (WT) mice and mice with either EPCR-overexpression (Tie2-EPCR) or EPCR-deficiency (EPCR(-/-)). Mice were sacrificed after 24, 48 or 72 hours. Organs and plasma were harvested to measure colony forming units, cellular influxes, cytokine levels and coagulation parameters. Plasma EPCR-levels were higher in melioidosis patients than in healthy controls and associated with an increased mortality. Tie2-EPCR mice demonstrated enhanced bacterial growth and dissemination to distant organs during experimental melioidosis, accompanied by increased lung damage, neutrophil influx and cytokine production, and attenuated coagulation activation. EPCR(-/-) mice had an unremarkable response to B. pseudomallei infection as compared to WT mice, except for a difference in coagulation activation in plasma. CONCLUSION/SIGNIFICANCE: Increased EPCR-levels correlate with accelerated mortality in patients with melioidosis. In mice, transgenic overexpression of EPCR aggravates outcome during Gram-negative pneumonia-derived sepsis caused by B. pseudomallei, while endogenous EPCR does not impact on the host response. These results add to a better understanding of the regulation of coagulation during severe (pneumo)sepsis.