Distinct patterns of leukocyte recruitment in the pulmonary microvasculature in response to local and systemic inflammation

Intravital Microscopy of Lipopolysaccharide-Induced Inflammatory Changes in Different Organ Systems-A Scoping Review

Intravital microscopy (IVM) is a powerful imaging tool that captures biological processes in real-time. IVM facilitates the observation of complex cellular interactions in vivo, where ex vivo and in vitro experiments lack the physiological environment. IVM has been used in a multitude of studies under healthy and pathological conditions in different organ systems. IVM has become essential in the characterization of the immune response through visualization of leukocyte-endothelial interactions and subsequent changes within the microcirculation. Lipopolysaccharide (LPS), a common inflammatory trigger, has been used to induce inflammatory changes in various studies utilizing IVM. In this review, we provide an overview of IVM imaging of LPS-induced inflammation in different models, such as the brain, intestines, bladder, and lungs.

Local immune dysregulation and subsequent inflammatory response contribute to pulmonary edema caused by Enterovirus infection in mice

Pulmonary edema that comes on suddenly is the leading cause of mortality in hand-foot-and-mouth disease (HFMD) patients; however, its pathogenesis is still largely unclear. A range of research suggest immunopathogenesis during the occurrence of pulmonary edema in severe HFMD patients. Herein, to investigate the potential mechanism of immune dysregulation in the development of pulmonary edema upon Enterovirus (EV) infection, we established mouse infection models for Enteroviruses (EVs) including Coxsackievirus (CV) A6, Enterovirus A71 (EVA71), and CVA2 exhibiting a high incidence of pulmonary edema. We found that EVs infection induced an immune system disorder by reducing the numbers of pulmonary and circulatory T cells, B cells, macrophages, and monocytes and increasing the numbers of lung neutrophils, myeloid-derived suppressor cells (MDSCs), and activated T cells. In addition, the concentrations of C-X-C motif chemokine ligand 1 (CXCL-1), tumor necrosis factor-alpha, monocyte chemoattractant protein-1, and interleukin 6 were increased in EV-infected lungs. Moreover, we found that EVs replication in mice lungs lead to apoptosis of lung cells and degradation of tight junction proteins. In conclusion, EVs infection likely triggered a complexed immune defense mechanism and caused dysregulation of innate immune cells (MDSCs, neutrophils, monocytes, and macrophages) and adaptive cellular immunity (B cells, T cells). This dysregulation increased the release of cytokines and other inflammatory factors from activated immune-related cells and caused lung barrier damage and pulmonary edema.

E3 Ubiquitin Ligase Midline 1 Regulates Endothelial Cell ICAM-1 Expression and Neutrophil Adhesion in Abdominal Sepsis

Septic lung damage is associated with endothelial cell and neutrophil activation. This study examines the role of the E3 ubiquitin ligase midline 1 (Mid1) in abdominal sepsis. Mid1 expression was increased in endothelial cells derived from post-capillary venules in septic mice and TNF-α challenge increased Mid1 levels in endothelial cells in vitro. The siRNA-mediated knockdown of Mid1 decreased TNF-α-induced upregulation of ICAM-1 and neutrophil adhesion to endothelial cells. Moreover, Mid1 silencing reduced leukocyte adhesion in post-capillary venules in septic lungs in vivo. The silencing of Mid1 not only decreased Mid1 expression but also attenuated expression of ICAM-1 in lungs from septic mice. Lastly, TNF-α stimulation decreased PP2Ac levels in endothelial cells in vitro, which was reversed in endothelial cells pretreated with siRNA directed against Mid1. Thus, our novel data show that Mid1 is an important regulator of ICAM-1 expression and neutrophil adhesion in vitro and septic lung injury in vivo. A possible target of Mid1 is PP2Ac in endothelial cells. Targeting the Mid1-PP2Ac axis may be a useful way to reduce pathological lung inflammation in abdominal sepsis.

Comparison of CD3e Antibody and CD3e-sZAP Immunotoxin Treatment in Mice Identifies sZAP as the Main Driver of Vascular Leakage

Anti-CD3-epsilon (CD3e) monoclonal antibodies (mAbs) and CD3e immunotoxins (ITs) are promising targeted therapy options for various T-cell disorders. Despite significant advances in mAb and IT engineering, vascular leakage syndrome (VLS) remains a major dose-limiting toxicity for ITs and has been poorly characterized for recent "engineered" mAbs. This study undertakes a direct comparison of non-mitogenic CD3e-mAb (145-2C11 with Fc-silentTM murine IgG1: S-CD3e-mAb) and a new murine-version CD3e-IT (saporin-streptavidin (sZAP) conjugated with S-CD3e-mAb: S-CD3e-IT) and identifies their distinct toxicity profiles in mice. As expected, the two agents showed different modes of action on T cells, with S-CD3e-mAb inducing nearly complete modulation of CD3e on the cell surface, while S-CD3e-IT depleted the cells. S-CD3e-IT significantly increased the infiltration of polymorphonuclear leukocytes (PMNs) into the tissue parenchyma of the spleen and lungs, a sign of increased vascular permeability. By contrast, S-CD3e-mAbs-treated mice showed no notable signs of vascular leakage. Treatment with control ITs (sZAP conjugated with Fc-silent isotype antibodies) induced significant vascular leakage without causing T-cell deaths. These results demonstrate that the toxin portion of S-CD3e-IT, not the CD3e-binding portion (S-CD3e-mAb), is the main driver of vascular leakage, thus clarifying the molecular target for improving safety profiles in CD3e-IT therapy.

Synthesis, Characterization, and In Vivo Cytokinome Profile of IL-12-Loaded PLGA Nanospheres

We report the successful encapsulation and elution of recombinant murine IL-12 (rmIL-12) from poly(lactide-co-glycolic) acid (PLGA) nanospheres (IL-12-NS) synthesized using the double emulsion/solvent evaporation (DESE) technique with microsphere depletion through ultracentrifugation. Images obtained with scanning electron microscopy (SEM) showcased a characteristic spherical shape with a mean particle diameter of 138.1 ± 10.8 nm and zeta potential of −15.1 ± 1.249 mV. These values suggest minimal flocculation when in solution, which was reflected in an in vivo biodistribution study that reported no observed morbidity/mortality. Encapsulation efficiency (EE) was determined to be 0.101 ± 0.009% with average particle concentration obtained per batch of 1.66 × 10⁹ ± 4.45 × 10⁸ particles/mL. Disparate zeta (ζ) potentials obtained from both protein-loaded and protein-unloaded batches suggested surface adsorption of protein, and confocal microscopy of BSA-FITC-loaded nanospheres confirmed the presence of protein within the polymeric shell. Furthermore, elution of rmIL-12 from IL-12-NS at a concentration of 500 million particles/mL was characterized using enzyme-linked immunosorbent assay (ELISA). When IL-12-NS was administered in vivo to female BALB/c mice through retroorbital injection, IL-12-NS produced a favorable systemic cytokine profile for tumoricidal activity within the peripheral blood. Whereas IFN-γ nadir occurred at 72 hours, levels recovered quickly and displayed positive correlations postburst out to 25 days postinjection. IL-12-NS administration induced proinflammatory changes while prompting minimal counterregulatory increases in anti-inflammatory IL-10 and IL-4 cytokine levels. Further, while IL-6 levels increased to 30 folds of the baseline during the burst phase, they normalized by 72 hours and trended negatively throughout the sill phase. Similar trends were observed with IL-1β and CXCL-1, suggesting a decreased likelihood of progression to a systemic inflammatory response syndrome-like state. As IL-12-NS delivers logarithmically lower amounts of IL-12 than previously administered during human clinical trials, our data reflect the importance of IL-12-NS which safely create a systemic immunostimulatory environment.

Actin-related protein 2/3 complex regulates neutrophil extracellular trap expulsion and lung damage in abdominal sepsis

Neutrophil extracellular trap (NET) formation is a key feature in sepsis. The aim of the present study was to examine the role of the actin cytoskeleton in regulating the expulsion of NETs. Actin-related protein 2/3 (Arp 2/3) complex is an important regulator of F-actin polymerization. Co-incubation with CK666, a specific Arp 2/3 inhibitor, decreased PMA-induced NET formation in vitro. CK666 not only abolished F-actin polymerization but also caused intracellular retention of NETs. Inhibition of Arp 2/3 reduced NET formation on circulating neutrophils and in the bronchoalveolar space in mice undergoing cecal ligation and puncture (CLP). Notably, treatment with CK666 attenuated CLP-induced neutrophil recruitment, edema formation and tissue damage in the lungs. Moreover, Arp 2/3 inhibition decreased levels of CXCL-1 and interleukin-6 in the lung and plasma of septic animals. Taken together, this study shows that expulsion of NETs is regulated by the actin cytoskeleton and that inhibition of Arp 2/3-dependent F-actin polymerization not only decrease NET formation but also protect against pathological inflammation and tissue damage in septic lung injury. Thus, we suggest that targeting NET release is a novel and useful way to ameliorate lung damage in abdominal sepsis.

Targeting S100A9 Reduces Neutrophil Recruitment, Inflammation and Lung Damage in Abdominal Sepsis

S100A9, a pro-inflammatory alarmin, is up-regulated in inflamed tissues. However, the role of S100A9 in regulating neutrophil activation, inflammation and lung damage in sepsis is not known. Herein, we hypothesized that blocking S100A9 function may attenuate neutrophil recruitment in septic lung injury. Male C57BL/6 mice were pretreated with the S100A9 inhibitor ABR-238901 (10 mg/kg), prior to cercal ligation and puncture (CLP). Bronchoalveolar lavage fluid (BALF) and lung tissue were harvested for analysis of neutrophil infiltration as well as edema and CXC chemokine production. Blood was collected for analysis of membrane-activated complex-1 (Mac-1) expression on neutrophils as well as CXC chemokines and IL-6 in plasma. Induction of CLP markedly increased plasma levels of S100A9. ABR-238901 decreased CLP-induced neutrophil infiltration and edema formation in the lung. In addition, inhibition of S100A9 decreased the CLP-induced up-regulation of Mac-1 on neutrophils. Administration of ABR-238901 also inhibited the CLP-induced increase of CXCL-1, CXCL-2 and IL-6 in plasma and lungs. Our results suggest that S100A9 promotes neutrophil activation and pulmonary accumulation in sepsis. Targeting S100A9 function decreased formation of CXC chemokines in circulation and lungs and attenuated sepsis-induced lung damage. These novel findings suggest that S100A9 plays an important pro-inflammatory role in sepsis and could be a useful target to protect against the excessive inflammation and lung damage associated with the disease.

Surfactant Lipidomics of Alveolar Lavage Fluid in Mice Based on Ultra-High-Performance Liquid Chromatography Coupled to Hybrid Quadrupole-Exactive Orbitrap Mass Spectrometry

Surfactant lipid metabolism is closely related to pulmonary diseases. Lipid metabolism disorder can cause lung diseases, vice versa. With this rationale, a useful method was established in this study to determine the lipidome in bronchoalveolar lavage fluid (BALF) of mice. The lipid components in BALF were extracted by liquid-liquid extraction (methanol and methyl tert-butyl ether, and water). Ultra-high-performance liquid chromatography coupled to hybrid Quadrupole-Exactive Orbitrap mass spectrometry was used to analyze the extracted samples, which showed a broad scanning range of 215-1800 m/z. With MS-DIAL software and built-in LipidBlast database, we identified 38 lipids in positive, and 31 lipids in negative, ion mode, including lysophosphatidylcholine (lysoPC), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), etc. Then, the changes of lipids in BALF of mice with acute lung injury (ALI) induced by lipopolysaccharide (LPS) was investigated, which may contribute to further exploration of the pathogenesis of ALI.

Neutrophil extracellular trap-microparticle complexes enhance thrombin generation via the intrinsic pathway of coagulation in mice

Abdominal sepsis is associated with dysfunctional hemostasis. Thrombin generation (TG) is a rate-limiting step in systemic coagulation. Neutrophils can expell neutrophil extracellular traps (NETs) and/or microparticles (MPs) although their role in pathological coagulation remains elusive. Cecal ligation and puncture (CLP)-induced TG in vivo was reflected by a reduced capacity of plasma from septic animals to generate thrombin. Depletion of neutrophils increased TG in plasma from CLP mice. Sepsis was associated with increased histone 3 citrullination in neutrophils and plasma levels of cell-free DNA and DNA-histone complexes and administration of DNAse not only eliminated NET formation but also elevated TG in sepsis. Isolated NETs increased TG and co-incubation with DNAse abolished NET-induced formation of thrombin. TG triggered by NETs was inhibited by blocking factor XII and abolished in factor XII-deficient plasma but intact in factor VII-deficient plasma. Activation of neutrophils simultaneously generated large amount of neutrophil-derived MPs, which were found to bind to NETs via histone-phosphatidylserine interactions. These findings show for the first time that NETs and MPs physically interact, and that NETs might constitute a functional assembly platform for MPs. We conclude that NET-MP complexes induce TG via the intrinsic pathway of coagulation and that neutrophil-derived MPs play a key role in NET-dependent coagulation.

Murine models of cardiovascular comorbidity in chronic obstructive pulmonary disease

Patients with chronic obstructive pulmonary disease (COPD) have an increased risk for cardiovascular disease (CVD). Currently, COPD patients with atherosclerosis (i.e., the most important underlying cause of CVD) receive COPD therapy complemented with standard CVD therapy. This may, however, not be the most optimal treatment. To investigate the link between COPD and atherosclerosis and to develop specific therapeutic strategies for COPD patients with atherosclerosis, a substantial number of preclinical studies using murine models have been performed. In this review, we summarize the currently used murine models of COPD and atherosclerosis, both individually and combined, and discuss the relevance of these models for studying the pathogenesis and development of new treatments for COPD patients with atherosclerosis. Murine and clinical studies have provided complementary information showing a prominent role for systemic inflammation and oxidative stress in the link between COPD and atherosclerosis. These and other studies showed that murine models for COPD and atherosclerosis are useful tools and can provide important insights relevant to understanding the link between COPD and CVD. More importantly, murine studies provide good platforms for studying the potential of promising (new) therapeutic strategies for COPD patients with CVD.

Rac1 regulates bacterial toxin-induced thrombin generation

OBJECTIVE

Systemic inflammatory response syndrome is associated with severe coagulopathy. The purpose of this study was to examine thrombin generation in systemic inflammation triggered by the endotoxin lipopolysaccharide (LPS) and the exotoxin streptococcal M1 protein.

METHODS

Thrombin generation, lung histology and myeloperoxidase (MPO) activity were determined 6 and 24 h after induction of systemic inflammation. Male C57BL/6 mice received the Rac1 inhibitor NSC23766 prior to challenge with bacterial toxins.

RESULTS

LPS and M1 protein challenge increased neutrophil infiltration and caused damage in the lung. Time to peak thrombin formation was increased and peak and total generation of thrombin were decreased in plasma from LPS- and M1 protein-treated mice. Coincubation of samples from mice exposed to bacterial toxins with platelet poor plasma from healthy mice completely reversed the inhibitory effect of LPS and M1 protein on thrombin generation, suggesting that bacterial toxins decreased levels of plasma factors explaining the reduction of thrombin generating capacity of plasma from septic animals. NSC23766 treatment not only decreased LPS- and M1 protein-induced neutrophil accumulation as well as levels of interleukin-6 and CXCL2 in the lung, but also abolished bacterial toxin-induced changes in thrombin generation. For example, NSC23766 increased peak formation by 57% and total thrombin generation by 48% in LPS-treated animals at 6 h.

CONCLUSIONS

Taken together, our novel findings show that bacterial toxins increase thrombin generation via consumption of plasma factors and that Rac1 signaling plays an important role in thrombin generation in response to bacterial toxins. Thus, targeting Rac1 activity might be a useful way not only to ameliorate pulmonary inflammation, but also inhibit pathological changes in coagulation in bacterial infections.

Dynamic changes in thrombin generation in abdominal sepsis in mice

Systemic inflammatory response syndrome and severe infections are associated with major derangements in the coagulation system. The purpose of this study was to examine the dynamic alterations in thrombin generation in abdominal sepsis. Abdominal sepsis was induced by cecal ligation and puncture (CLP) in C57/Bl6 mice. Cecal ligation and puncture caused a systemic inflammatory response, with neutrophil recruitment and tissue damage in the lung as well as thrombocytopenia and leukocytopenia. Thrombin generation, coagulation factors, lung histology, and myeloperoxidase activity was determined 1, 3, 6, and 24 h after induction of CLP. It was found that thrombin generation was increased 1 h after CLP and that thrombin generation started to decrease at 3 h and was markedly reduced 6 and 24 h after CLP induction. Platelet-poor plasma from healthy mice could completely reverse the inhibitory effect of CLP on thrombin generation, suggesting that sepsis caused a decrease in the levels of plasma factors regulating thrombin generation in septic animals. Indeed, it was found that CLP markedly decreased plasma levels of prothrombin, factor V, and factor X at 6 and 24 h. Moreover, we observed that CLP increased plasma levels of activated protein C at 6 h, which returned to baseline levels 24 h after CLP induction. Finally, pretreatment with imipenem/cilastatin attenuated the CLP-evoked decrease in thrombin generation and consumption of prothrombin 24 h after CLP induction. Our novel findings suggest that thrombin generation is initially increased and later decreased in abdominal sepsis. Sepsis-induced reduction in thrombin generation is correlated to changes in the plasma levels of coagulation factors and activated protein C. These findings help explain the dynamic changes in global hemostasis in abdominal sepsis.

Monocytes regulate systemic coagulation and inflammation in abdominal sepsis

Abdominal sepsis is associated with significant changes in systemic inflammation and coagulation. The purpose of the present study was to examine the role of peripheral blood monocytes for systemic coagulation, including thrombin generation and consumption of coagulation factors. Abdominal sepsis was induced by cecal ligation and puncture (CLP) in C57BL/6 mice. Plasma and lung levels of IL-6 and C-X-C motif (CXC) chemokines [chemokine CXC ligand (CXCL)1, CXCL2, and CXCL5], pulmonary activity of myeloperoxidase, thrombin generation, and coagulation factors were determined 6 h after CLP induction. Administration of clodronate liposomes decreased circulating levels of monocytes by 96%. Time to peak thrombin formation was increased and peak and total thrombin generation was decreased in plasma from CLP animals. Monocyte depletion decreased time to peak formation of thrombin and increased peak and total generation of thrombin in septic animals. In addition, monocyte depletion decreased the CLP-induced increase in the levels of thrombin-antithrombin complexes in plasma. Depletion of monocytes increased plasma levels of prothrombin, factor V, factor X, and protein C in septic mice. Moreover, depletion of monocytes decreased CLP-induced levels of IL-6 and CXC chemokines in the plasma and lung by >59% and 20%, respectively. CLP-induced myeloperoxidase activity in the lung was attenuated by 44% in animals depleted of monocytes. Taken together, our findings show, for the first time, that peripheral blood monocytes regulate systemic coagulation. The results of our study improve our understanding of the pathophysiology of sepsis and encourage further attempts to target innate immune cell functions in abdominal sepsis.

Proinflammatory role of neutrophil extracellular traps in abdominal sepsis

Excessive neutrophil activation is a major component in septic lung injury. Neutrophil-derived DNA may form extracellular traps in response to bacterial invasions. The aim of the present study was to investigate the potential role of neutrophil extracellular traps (NETs) in septic lung injury. Male C57BL/6 mice were treated with recombinant human (rh)DNAse (5 mg/kg) after cecal ligation and puncture (CLP). Extracellular DNA was stained by Sytox green, and NET formation was quantified by confocal microscopy and cell-free DNA in plasma, peritoneal cavity, and lung. Blood, peritoneal fluid, and lung tissue were harvested for analysis of neutrophil infiltration, NET levels, tissue injury, as well as CXC chemokine and cytokine formation. We observed that CLP caused increased formation of NETs in plasma, peritoneal cavity, and lung. Administration of rhDNAse not only eliminated NET formation in plasma, peritoneal cavity, and bronchoalveolar space but also reduced lung edema and tissue damage 24 h after CLP induction. Moreover, treatment with rhDNAse decreased CLP-induced formation of CXC chemokines, IL-6, and high-mobility group box 1 (HMGB1) in plasma, as well as CXC chemokines and IL-6 in the lung. In vitro, we found that neutrophil-derived NETs had the capacity to stimulate secretion of CXCL2, TNF-α, and HMGB1 from alveolar macrophages. Taken together, our findings show that NETs regulate pulmonary infiltration of neutrophils and tissue injury via formation of proinflammatory compounds in abdominal sepsis. Thus we conclude that NETs exert a proinflammatory role in septic lung injury.