Tumor necrosis factor receptor 2 contributes to ozone-induced airway hyperresponsiveness in mice.

UNLABELLED: The purpose of this study was to determine whether tumor necrosis factor (TNF) contributes to airway hyperresponsiveness (AHR) and migration of polymorphonuclear leukocytes (PMN) into the airways following exposure to ozone (O(3)). Wild-type mice, TNF p55 or p75 receptor knockout mice (p55 TNFR -/- and p75 TNFR -/-), as well as double receptor knockout mice (p55/p75 TNFR -/-), were exposed to O(3). Three hours after cessation of O(3), airway responses to inhaled methacholine were determined by whole body plethysmography using changes in enhanced pause (Penh) as an index of airway narrowing. In wild-type mice, O(3) exposure (0.5 ppm, 3 h) caused a significant increase in airway responsiveness as indicated by a 1.2 log leftward shift in the methacholine dose- response curve. In contrast, in p55/p75 TNFR -/- mice, O(3) caused only a 0.5 log shift in the dose-response curve (p < 0.05 compared with wild-type). Similar results were obtained in p75 TNFR -/- mice. In contrast, O(3)-induced airway hyperresponsiveness was not different in WT and p55 TNFR -/- mice. During O(3) exposure (1 pm, 3 h), minute ventilation (V E) decreased by 64 +/- 4% in wild-type, but only 24 +/- 5% in p55/p75 TNFR -/- mice, indicating that despite their reduced O(3)-induced AHR, the TNFR-deficient mice actually inhaled a greater dose of O(3). Similar results were obtained in p75 -/- mice, whereas changes in V E induced by O(3) were the same in wild-type and p55 -/- mice. PMN numbers in bronchoalveolar lavage fluid recovered 21 h after cessation of exposure to O(3) (2 ppm, 3 h) were significantly increased compared with after air exposure but were not different in wild-type and p55/p75 TNFR -/- mice. Our results indicate that TNF contributes to the AHR but not the PMN emigration induced by acute O(3) exposure. KEYWORDS: whole body plethysmography; polymorphonuclear leukocytes; minute ventilation; knockout mice; methacholine

Targeted mutation of TNF receptor I rescues the RelA-deficient mouse and reveals a critical role for NF-kappa B in leukocyte recruitment.

NF-kappaB binding sites are present in the promoter regions of many acute phase and inflammatory response genes, suggesting that NF-kappaB plays an important role in the initiation of innate immune responses. However, targeted mutations of the various NF-kappaB family members have yet to identify members responsible for this critical role. RelA-deficient mice die on embryonic day 15 from TNF-alpha-induced liver degeneration. To investigate the importance of RelA in innate immunity, we genetically suppressed this embryonic lethality by breeding the RelA deficiency onto a TNFR type 1 (TNFR1)-deficient background. TNFR1/RelA-deficient mice were born healthy, but were susceptible to bacterial infections and bacteremia and died within a few weeks after birth. Hemopoiesis was intact in TNFR1/RelA-deficient newborns, but neutrophil emigration to alveoli during LPS-induced pneumonia was severely reduced relative to that in wild-type or TNFR1-deficient mice. In contrast, radiation chimeras reconstituted with RelA or TNFR1/RelA-deficient hemopoietic cells were healthy and demonstrated no defect in neutrophil emigration during LPS-induced pneumonia. Analysis of RNA harvested from the lungs of mice 4 h after LPS insufflation revealed that the induction of several genes important for neutrophil recruitment to the lung was significantly reduced in TNFR1/RelA-deficient mice relative to that in wild-type or TNFR1-deficient mice. These results suggest that TNFR1-independent activation of RelA is essential in cells of nonhemopoietic origin during the initiation of an innate immune response.

The p38 mitogen-activated protein kinase mediates cytoskeletal remodeling in pulmonary microvascular endothelial cells upon intracellular adhesion molecule-1 ligation.

Changes in the cytoskeleton of endothelial cells (ECs) play important roles in mediating neutrophil migration during inflammation. Previous studies demonstrated that neutrophil adherence to TNF-alpha-treated pulmonary microvascular ECs induced cytoskeletal remodeling in ECs that required ICAM-1 ligation and oxidant production and was mimicked by cross-linking ICAM-1. In this study, we examined the role of ICAM-1-induced signaling pathways in mediating actin cytoskeletal remodeling. Cross-linking ICAM-1 induced alterations in ICAM-1 distribution, as well as the filamentous actin rearrangements and stiffening of ECs shown previously. ICAM-1 cross-linking induced phosphorylation of the p38 mitogen-activated protein kinase (MAPK) that was inhibited by allopurinol and also induced an increase in the activity of the p38 MAPK that was inhibited by SB203580. However, SB203580 had no effect on oxidant production in ECs or ICAM-1 clustering. ICAM-1 cross-linking also induced phosphorylation of heat shock protein 27, an actin-binding protein that may be involved in filamentous actin polymerization. The time course of heat shock protein 27 phosphorylation paralleled that of p38 MAPK phosphorylation and was completely inhibited by SB203580. In addition, SB203580 blocked the EC stiffening response induced by either neutrophil adherence or ICAM-1 cross-linking. Moreover, pretreatment of ECs with SB203580 reduced neutrophil migration toward EC junctions. Taken together, these data demonstrate that activation of p38 MAPK, mediated by xanthine oxidase-generated oxidant production, is required for cytoskeletal remodeling in ECs induced by ICAM-1 cross-linking or neutrophil adherence. These cytoskeletal changes in ECs may in turn modulate neutrophil migration toward EC junctions.

Mechanisms of leukocyte sequestration in inflamed lungs.

The lungs are an important site of host defense. The capillary blood contains an increased concentration of neutrophils and other leukocytes compared with large vessels, due to the structure of the pulmonary capillary bed, the diameter of spherical leukocytes, and their poor deformability compared with erythrocytes. During inflammation within the distal airways, neutrophils sequester within the pulmonary capillaries and emigrate into the parenchyma. This sequential process involves complex events regulating interactions between mechanical and adhesive properties of both neutrophils and endothelial cells. Initial changes in the cytoskeleton may stiffen the neutrophils and prevent them from deforming, while subsequent dynamic cytoskeletal remodeling of neutrophils and endothelial cells results in crawling and transendothelial migration. Emigration of neutrophils can occur through at least two adhesion pathways: one that requires the CD11/CD18 adhesion complex and one that does not. Which pathway is selected is determined by the stimulus and the signaling pathways that are initiated. Migration through the alveolo-capillary wall is also highly regulated. Neutrophils released from the bone marrow traffic first through the pulmonary microvasculature, and the phenotype of these newly released neutrophils impacts pulmonary host defense. The many recent studies underline the complexity of neutrophil responses and host defense and the uncertainties of our knowledge.

Polar production of interleukin-8 by mesothelial cells promotes the transmesothelial migration of neutrophils: role of intercellular adhesion molecule-1.

Migration of polymorphonuclear neutrophils (PMNL) from the vascular compartment into the pleural space occurs rapidly during the development of parapneumonic effusions. This study investigated the polarized secretion of interleukin (IL)-8 in activated pleural mesothelial cells (PMC) and the migration of PMNL across resting, activated PMC monolayers. Results show that PMC produce IL-8 in a polar manner. When PMC were stimulated with Staphylococcus aureus or IL-1beta at the basal or at the apical surface, significantly (P< .05) more IL-8 was released toward the apical surface. This polarized production of IL-8 was confirmed by in situ hybridization. PMNL migration was higher from the basilar to apical than from the apical to basilar surface of PMC. Neutralizing antibodies against IL-8 and intercellular adhesion molecule (ICAM)-1 significantly (P< .001) blocked PMNL migration across activated monolayers. Thus, during pleural inflammation, PMC regulate the influx of PMNL into the pleural space by polar production of IL-8 and expression of ICAM-1.

Mechanisms of granulocytosis in the absence of CD18.

Genetic deficiency in CD18 leads to disease characterized by myeloid hyperplasia, including profound granulocytosis and splenomegaly. Myeloid hyperplasia could directly result from the disruption of CD18 functions essential to granulopoiesis or basal leukocyte trafficking. Alternatively, myeloid hyperplasia could be reactive in nature, due to disruption of essential roles of CD18 in leukocyte responses to microbial challenge. To distinguish between these mechanisms, the hematopoietic systems of lethally irradiated wild-type (WT) mice were reconstituted with either WT fetal liver cells or CD18-deficient fetal liver cells, or an equal mixture of both types of cells. Granulocytosis and splenomegaly developed in mice that received CD18-deficient fetal liver cells. Splenomegaly was prevented and granulocytosis was inhibited by more than 95% in mice that had received both CD18-deficient and WT fetal liver cells, suggesting that myeloid hyperplasia was largely reactive in nature. Consistent with this postulate, the circulating life spans in the blood and the fraction of neutrophils that incorporated BrdU in the bone marrow were not increased for CD18-deficient neutrophils compared with the WT. However, these animals did develop mild granulocytosis compared with mice reconstituted with WT cells alone, and a higher percentage of CD18-deficient leukocytes were neutrophils compared with the WT leukocytes. These observations suggest that the granulocytosis observed in the absence of CD18 occurs through at least 2 mechanisms: one that is dramatically improved by the presence of WT cells, likely reactive in nature, and a second that is independent of the WT hematopoietic cells, involving an alteration in the lineage distribution of blood leukocytes.

Early response cytokines and innate immunity: essential roles for TNF receptor 1 and type I IL-1 receptor during Escherichia coli pneumonia in mice.

The early response cytokines, TNF and IL-1, have overlapping biologic effects that may function to propagate, amplify, and coordinate host responses to microbial challenges. To determine whether signaling from these early response cytokines is essential to orchestrating innate immune responses to intrapulmonary bacteria, the early inflammatory events induced by instillation of Escherichia coli into the lungs were compared in wild-type (WT) mice and mice deficient in both TNF receptor 1 (TNFR1) and the type I IL-1 receptor (IL1R1). Neutrophil emigration and edema accumulation induced by E. coli were significantly compromised by TNFR1/IL1R1 deficiency. Neutrophil numbers in the circulation and within alveolar septae did not differ between WT and TNFR1/IL1R1 mice, suggesting that decreased neutrophil emigration did not result from decreased sequestration or delivery of intravascular neutrophils. The nuclear translocation of NF-kappa B and the expression of the chemokine macrophage inflammatory protein-2 did not differ between WT and TNFR1/IL1R1 lungs. However, the concentration of the chemokine KC was significantly decreased in the bronchoalveolar lavage fluids of TNFR1/IL1R1 mice compared with that in WT mice. Thus, while many of the molecular and cellular responses to E. coli in the lungs did not require signaling by either TNFR1 or IL1R1, early response cytokine signaling was critical to KC expression in the pulmonary air spaces and neutrophil emigration from the alveolar septae.

Changes in the biomechanical properties of neutrophils and endothelial cells during adhesion.

This study examined changes in the biomechanical properties of cultured pulmonary microvascular endothelial cells (ECs) and neutrophils induced by adhesion of neutrophils to these ECs. The biomechanical properties of cells were evaluated using magnetic twisting cytometry, which measures the angular rotation of ferromagnetic beads bound to cells through antibody ligation on application of a specified magnetic torque. Adhesion of neutrophils to 24-hour tumor necrosis factor-alpha (TNF-alpha)-treated ECs, but not to untreated ECs, induced an increase in EC stiffness within 2 minutes, which was accompanied by an increase and a reorganization of F-actin in ECs. A cell-permeant, phosphoinositide-binding peptide attenuated the EC stiffening response, suggesting that intracellular phosphoinositides are required. The stiffening response was not inhibited by ML-7, a myosin light-chain kinase inhibitor, or BAPTA, an intracellular Ca2+ chelator. Moreover, the phosphorylation pattern of the regulatory myosin light chains was unaltered within 15 minutes of neutrophil adherence. These data suggested that the EC stiffening response appeared not to be mediated by myosin light-chain-dependent mechanisms. Concomitantly, neutrophil adhesion to 24-hour TNF-alpha-treated ECs also induced changes in the biomechanical properties of neutrophils compared to neutrophils bound to untreated ECs. Taken together, these results demonstrated that neutrophil adhesion to TNF-alpha-treated ECs induces changes in the biomechanical properties of both cell types through actin cytoskeletal remodeling. These changes may modulate neutrophil transmigration across the endothelium during inflammation.

Computational modeling of RBC and neutrophil transit through the pulmonary capillaries.

A computational model of the pulmonary microcirculation is developed and used to examine blood flow from arteriole to venule through a realistically complex alveolar capillary bed. Distributions of flow, hematocrit, and pressure are presented, showing the existence of preferential pathways through the system and of large segment-to-segment differences in all parameters, confirming and extending previous work. Red blood cell (RBC) and neutrophil transit are also analyzed, the latter drawing from previous studies of leukocyte aspiration into micropipettes. Transit time distributions are in good agreement with in vivo experiments, in particular showing that neutrophils are dramatically slowed relative to the flow of RBCs because of the need to contract and elongate to fit through narrower capillaries. Predicted neutrophil transit times depend on how the effective capillary diameter is defined. Transient blockage by a neutrophil can increase the local pressure drop across a segment by 100--300%, leading to temporal variations in flow and pressure as seen by videomicroscopy. All of these effects are modulated by changes in transpulmonary pressure and arteriolar pressure, although RBCs, neutrophils, and rigid microspheres all behave differently.

Neutrophil-induced changes in the biomechanical properties of endothelial cells: roles of ICAM-1 and reactive oxygen species.

This study evaluated the changes in the biomechanical properties of endothelial cells (ECs) induced by neutrophil adhesion and the roles of ICAM-1 and reactive oxygen species (ROS) in modulating these changes. Neutrophil adherence to 24-h TNF-alpha-activated pulmonary microvascular ECs induced an increase in the apparent stiffness of ECs within 2 min, measured with magnetic twisting cytometry. An anti-ICAM-1 Ab blocked the EC stiffening response without inhibiting neutrophil adherence. Moreover, cross-linking ICAM-1 mimicked the stiffening response induced by neutrophils. The neutrophil-induced increase in the apparent stiffness of ECs was inhibited with 1% DMSO (a hydroxyl radical scavenger), allopurinol (a xanthine oxidase inhibitor), or deferoxamine (an iron chelator), suggesting that ROS may be involved in mediating the EC stiffening response. The cellular sources of ROS were determined by measuring the oxidation of dichlorofluorescein. Neutrophil adherence to TNF-alpha-activated ECs induced ROS production only in ECs, and not in neutrophils. This ROS production in ECs was completely prevented by the anti-ICAM-1 Ab and partially inhibited by allopurinol. These results suggest that ICAM-1-mediated signaling events during neutrophil adherence may activate xanthine oxidase, which in turn mediates the ROS production in ECs that leads to stiffening. ROS generated in ECs on neutrophil adherence appear to mediate cytoskeletal remodeling, which may modulate subsequent inflammatory responses.

The accumulation of dendritic cells in the lung is impaired in CD18-/- but not in ICAM-1-/- mutant mice.

Bone marrow-derived dendritic cell (DC) precursors migrate via the blood stream to peripheral tissues to adopt their sentinel function. To identify factors facilitating their emigration to the lung, mutant mice deficient in E-selectin, P-selectin, E/P-selectin, ICAM-1, or CD18 and their respective controls were examined. DCs and monocytes/macrophages were immunolabeled with M5/114 and MOMA-2 mAbs, respectively, and quantified morphometrically. Of these genotypes, the numbers of DC and MOMA-2+ cells were significantly less only in the lungs of CD18-/- mice by 68 and 35% in alveolar walls and by 28 and 26% in venous walls, respectively. DCs were reduced by 30 and 41% around large and small airways, respectively, but the number of MOMA-2+ cells in these locations was not significantly different from controls. Ablation of a single gene may be associated with augmented expression of other, related gene products. Therefore, we examined the expression of VCAM-1. Increased numbers of arteries exhibited continuous luminal VCAM-1 staining in both CD18-/- and ICAM-1-/- mutants. VCAM-1 expression was absent in pulmonary capillaries and unchanged in veins. These data suggest that under nonperturbing conditions, CD18-mediated adhesion is required for the full complement of DC precursors to accumulate in the lungs. However, the defect in CD18-/- mice is partial, suggesting that CD18-independent adhesion occurs. The alternative pathway may involve VLA-4/VCAM-1 in arteries and venules but not in capillaries. The smaller defect in ICAM-1-/- mice suggests that the CD11/CD18 complex recognizes ligands other than ICAM-1 at some sites.

Endotoxin-induced mortality is related to increased oxidative stress and end-organ dysfunction, not refractory hypotension, in heme oxygenase-1-deficient mice.

BACKGROUND: Heme oxygenase (HO)-1 is an enzyme that degrades heme to generate CO (a vasodilatory gas), iron, and the potent antioxidant bilirubin. A disease process characterized by decreases in vascular tone and increases in oxidative stress is endotoxic shock. Moreover, HO-1 is markedly induced in multiple organs after the administration of endotoxin (lipopolysaccharide [LPS]) to mice. METHODS AND RESULTS: To determine the role of HO-1 in endotoxemia, we administered LPS to mice that were wild-type (+/+), heterozygous (+/-), or homozygous null (-/-) for targeted disruption of HO-1. LPS produced a similar induction of HO-1 mRNA and protein in HO-1(+/+) and HO-1(+/-) mice, whereas HO-1(-/-) mice showed no HO-1 expression. Four hours after LPS, systolic blood pressure (SBP) decreased in all the groups. However, SBP was significantly higher in HO-1(-/-) mice (121+/-5 mm Hg) after 24 hours, compared with HO-1(+/+) (96+/-7 mm Hg) and HO-1(+/-) (89+/-13 mm Hg) mice. A sustained increase in endothelin-1 contributed to this SBP response. Even though SBP was higher, mortality was increased in HO-1(-/-) mice, and they exhibited hepatic and renal dysfunction that was not present in HO-1(+/+) and HO-1(+/-) mice. The end-organ damage and death in HO-1(-/-) mice was related to increased oxidative stress. CONCLUSIONS: These data suggest that the increased mortality during endotoxemia in HO-1(-/-) mice is related to increased oxidative stress and end-organ (renal and hepatic) damage, not to refractory hypotension.

Roles of tumor necrosis factor receptor signaling during murine Escherichia coli pneumonia.

We hypothesized that tumor necrosis factor (TNF)-alpha signaling is essential to inflammation and host defense during Escherichia coli pneumonia. We tested this hypothesis by instilling E. coli into the lungs of wild-type (WT) mice and gene-targeted mice that lack both p55 and p75 receptors for TNF-alpha. The emigration of neutrophils 6 h after instillation of E. coli was not decreased, but rather was significantly increased (167% of WT), in TNF receptor (TNFR)-deficient mice. This increased neutrophil emigration did not result from peripheral blood neutrophilia or enhanced neutrophil sequestration, inasmuch as the numbers of neutrophils in the circulating blood and in the pulmonary capillaries did not differ between TNFR-deficient and WT mice. The accumulation of pulmonary edema fluid was not inhibited in TNFR-deficient compared with WT mice. Nuclear factor-kappaB (NF-kappaB) translocation in the lungs was not prevented in TNFR-deficient mice. Thus, signaling pathways independent of TNFRs can mediate the acute inflammatory response during E. coli pneumonia. However, despite this inflammatory response, bacterial clearance was impaired in TNFR-deficient mice (109 +/- 8% versus 51 +/- 14% of the original inoculum viable after 6 h in TNFR-deficient and WT mice, respectively). Increased neutrophil emigration during E. coli pneumonia in TNFR-deficient mice may thus result from an increased bacterial burden in the lungs. During acute E. coli pneumonia, the absence of TNFR signaling compromised bacterial killing, but did not prevent inflammation, as measured by the accumulation of edema fluid and neutrophils.

Leukocyte trafficking in alveoli and airway passages.

Many pulmonary diseases preferentially affect the large airways or the alveoli. Although the mechanisms are often particular to each disease process, site-specific differences in leukocyte trafficking and the regulation of inflammation also occur. Differences in the process of margination, sequestration, adhesion, and migration occur that can be attributed to differences in anatomy, hemodynamics, and the expression of proteins. The large airways are nourished by the bronchial circulation, whereas the pulmonary circulation feeds the distal lung parenchyma. The presence of different cell types in large airways from those in alveoli might contribute to site-specific differences in the molecular regulation of the inflammatory process.

Signaling functions of L-selectin in neutrophils: alterations in the cytoskeleton and colocalization with CD18.

Ligation and clustering of L-selectin by Ab ("cross-linking") or physiologic ligands results in activation of diverse responses that favor enhanced microvascular sequestration and emigration of neutrophils. The earliest responses include a rise in intracellular calcium, enhanced tyrosine phosphorylation, and activation of extracellular signal-regulated kinases. Additionally, cross-linking of L-selectin induces sustained shape change and activation of beta2 integrins, leading to neutrophil arrest under conditions of shear flow. In this report, we examined several possible mechanisms whereby transmembrane signals from L-selectin might contribute to an increase in the microvascular retention of neutrophils and enhanced efficiency of emigration. In human peripheral blood neutrophils, cross-linking of L-selectin induced alterations in cellular biophysical properties, including a decrease in cell deformability associated with F-actin assembly and redistribution, as well as enhanced adhesion of microspheres bound to beta2 integrins. L-selectin and the beta2 integrin became spatially colocalized as determined by confocal immunofluorescence microscopy and fluorescence resonance energy transfer. We conclude that intracellular signals from L-selectin may enhance the microvascular sequestration of neutrophils at sites of inflammation through a combination of cytoskeletal alterations leading to cell stiffening and an increase in adhesiveness mediated through alterations in beta2 integrins.

Effects of CD18 deficiency on the emigration of murine neutrophils during pneumonia.

We hypothesized that CD18 deficiency would impair the ability of neutrophils to emigrate from pulmonary blood vessels during certain pneumonias. To directly compare the abilities of wild-type (WT) and CD18-deficient neutrophils to emigrate, mice with both types of leukocytes in their blood were generated by reconstituting the hemopoietic systems of lethally irradiated C57BL/6 mice with mixtures of fetal liver cells from WT and CD18-deficient mice. Percentages of CD18-deficient neutrophils in the circulating and emigrated pools were compared during experimental pneumonias. Similar percentages were observed in the blood and bronchoalveolar lavage fluid 6 or 24 h after intratracheal instillation of Streptococcus pneumoniae, demonstrating that no site on the CD18 molecule was required for either its adhesive or its signaling functions during neutrophil emigration. However, 6 h after instillation of Escherichia coli LPS or Pseudomonas aeruginosa, the percentage of CD18-deficient neutrophils in the bronchoalveolar lavage fluid was only about one-fourth of that observed in the blood. This difference persisted for at least 24 h after instillation of E. coli LPS. Thus, neutrophil emigration elicited by the Gram-negative stimuli E. coli LPS or P. aeruginosa was compromised by deficiency of CD18. These data, based on comparing WT and gene-targeted CD18-deficient neutrophils within the same animals, provide evidence for molecular pathways regulating neutrophil emigration, which could not be appreciated in previous studies with pharmacological blockade or genetic deficiency of CD18.