Comparison of leukotriene B4-induced neutrophil migration through different cellular barriers

Role of anti-human leucocyte antigen class II alloantibody and monocytes in development of transfusion-related acute lung injury

Recently, evidence implicating the roles of the anti-human leucocyte antigen (HLA) class II antibody in the development of transfusion-related acute lung injury (TRALI), which is one of the most serious possible side effects of transfusion, has been accumulating. The aim of this study is to clarify the roles of the anti-HLA DR alloantibody in TRALI development. Cultured human lung microvascular endothelial (LME) cells were incubated with either HLA-DR15-positive or HLA-DR15-negative monocytes together with serum from a single multiparous donor previously implicated in a clinical case of TRALI and known to contain anti-HLA DR15 antibody. Production of soluble leukotriene B(4) (LTB(4)) was measured in the supernatant and found to be markedly increased in the presence of HLA-DR15-positive monocytes but not with the HLA-DR15-negative monocytes or in the absence of LME cells. The vascular cell adhesion molecule-1 expression in LME cells and leucocyte-function-associated molecule-1 (LFA-1) expression in HLA-DR15-positive monocytes were notably enhanced after combined culture of LME cells, HLA-DR15-positive monocytes and TRALI-inducing anti-HLA DR15 antibody-positive serum. In conclusion, anti-HLA DR alloantibodies may be implicated in LME dysfunction that leads to TRALI, in a monocyte-dependent manner.

A taurine-supplemented vegan diet may blunt the contribution of neutrophil activation to acute coronary events

Neutrophils are activated in the coronary circulation during acute coronary events (unstable angina and myocardial infarction), often prior to the onset of ischemic damage. Moreover, neutrophils infiltrate coronary plaque in these circumstances, and may contribute to the rupture or erosion of this plaque, triggering thrombosis. Activated neutrophils secrete proteolytic enzymes in latent forms which are activated by the hypochlorous acid (HOCl) generated by myeloperoxidase. These phenomena may help to explain why an elevated white cell count has been found to be an independent coronary risk factor. Low-fat vegan diets can decrease circulating leukocytes--neutrophils and monocytes--possibly owing to down-regulation of systemic IGF-I activity. Thus, a relative neutropenia may contribute to the coronary protection afforded by such diets. However, vegetarian diets are devoid of taurine - the physiological antagonist of HOCl--and tissue levels of this nutrient are relatively low in vegetarians. Taurine has anti-atherosclerotic activity in animal models, possibly reflecting a role for macrophage-derived myeloperoxidase in the atherogenic process. Taurine also has platelet-stabilizing and anti-hypertensive effects that presumably could reduce coronary risk. Thus, it is proposed that a taurine-supplemented low-fat vegan diet represents a rational strategy for diminishing the contribution of activated neutrophils to acute coronary events; moreover, such a regimen would work in a number of other complementary ways to promote cardiovascular health. Moderate alcohol consumption, the well-tolerated drug pentoxifylline, and 5-lipoxygenase inhibitors--zileuton, boswellic acids, fish oil--may also have potential in this regard.

Tools for anti-inflammatory drug design:In vitro models of leukocyte migration

Inhibiting leukocyte recruitment is now a major focus in the design of novel anti-inflammatory drugs. Following the identification of lead compounds from conventional high-throughput screens using appropriate receptors or enzymes, it is important to validate the action of the compounds in a suitable in vitro model of leukocyte migration. Here, we review a range of different experimental approaches to modelling leukocyte migration, and identify the multi-well filter migration assay as the best compromise between the amount of resources required to screen multiple compounds and the amount of information gained about the effects of the compounds on cell movement behavior. However, there are pitfalls in the interpretation of data obtained using the multi-well filter migration assay, which arise from the imperfect correlation between the number of cells undergoing migration and the inhibitory activity of the test substances. We examine a number of such pitfalls and provide practical approaches to mitigate these problems as far as possible. We recommend a general strategy for screening inhibitors of cell migration using in vitro functional assays. While being more resource intensive than surrogate measures such as calcium flux, functional approaches nevertheless provide superior correlations with anti-inflammatory activity in vivo.

Human endothelial cells cultured on microporous filters used for leukocyte transmigration studies form monolayers on both sides of the filter

A growing number of studies on the mechanism of leukocyte transendothelial migration use endothelial cells grown on microporous filters as an in vitro model of endothelium. Ultrastructural examination of such a model system previously demonstrated that human pulmonary artery endothelial cells (HPAEC) formed confluent monolayers on both sides of the 3-microm-pore filter (Mackarel et al., 1999). To determine whether this was a characteristic specific to pulmonary artery endothelial cells, the growth characteristics of a human pulmonary microvascular endothelial cell type (HMVEC-L) and the widely used human umbilical vein endothelial cells (HUVEC) on 3-microm microporous filters were examined by transmission electron microscopy (TEM). Similar to HPAEC, HMVEC-L and HUVEC were also found to grow on both sides of the filter. All three endothelial cell types were capable of migrating through the 3 microm pores of the filter to form a monolayer on the filter underside. The endothelial cells on the underside were orientated in an inverted position with the luminal surface facing away from the filter. Such 'bilayer' formation was observed at a range of seeding densities and in different culture media. Despite the presence of a bilayer of endothelial cells, TEM demonstrated that neutrophils migrated successfully across the cell-filter-cell system. Previous transmigration reports in which an in vitro model similar to ours was used have often assumed only one layer of endothelial cells. The observations reported here indicate that while endothelial cells on microporous filters are useful models for examining leukocyte-endothelial interactions, they are not appropriate for studies examining endothelial cell 'sidedness.'

Promoting detachment of neutrophils adherent to murine postcapillary venules to control inflammation: effect of lipocortin 1

In this study we investigated, using intravital microscopy, how neutrophil extravasation across mouse mesenteric postcapillary venules is inhibited by the glucocorticoid-regulated protein lipocortin (LC; also termed annexin) 1. Intraperitoneal injection of 1 mg of zymosan into mice induced neutrophil rolling on the activated mesenteric endothelium followed by adhesion (maximal at 2 hr: 5-6 cells per 100-micrometers of vessel length) and emigration (maximal at 4 hr: 8-10 cells per high-powered field). Treatment of mice with human recombinant LC1 (2 mg/kg s.c.) or its mimetic peptide Ac2-26 (13 mg/kg s.c.) did not modify cell rolling but markedly reduced (>/=50%) the degree of neutrophil adhesion and emigration (P < 0.05). Intravenous treatment with peptide Ac2-26 (13 mg/kg) or recombinant human LC1 (0.7-2 mg/kg) promoted detachment of neutrophils adherent to the endothelium 2 hr after zymosan administration, with adherent cells detaching within 4.12 +/- 0.75 min and 2.36 +/- 0.31 min, respectively (n = 20-25 cells). Recruitment of newly adherent cells to the endothelium was unaffected. The structurally related protein LC5 was inactive in this assay, whereas a chimeric molecule constructed from the N terminus of LC1 (49 aa) attached to the core region of LC5 produced cell detachment with kinetics similar to LC1. Removal of adherent neutrophils from activated postcapillary endothelium is a novel pharmacological action, and it is at this site where LC1 and its mimetics operate to down-regulate this aspect of the host inflammatory response.

The sequential migration of neutrophils through endothelium and epithelium: a new model system

To better understand the mechanisms by which neutrophils migrate into the airways, we constructed a novel in vitro model system with human umbilical vein endothelial cell (HUVE) monolayers grown on top of permeable filters and human lung Type II-like alveolar epithelial cell (A549) monolayers grown on the undersurface of the filters. The sequential migration of human neutrophils through the endothelium (apical to basal movement) and subsequently through the epithelium (basal to apical movement) in response to a stimulus located basally to the epithelium was measured. We found that the neutrophil chemoattractants, formylmethionylleucylphenylalanine (FMLP), leukotriene B4 (LTB4), and interleukin-8 (IL-8), induced dose-responsive migration through the double monolayer-filter complex. The pattern of migration was similar to that observed through either a naked filter or single monolayer-filter complex. Maximal chemotaxis through the double monolayer-filter complex was observed by 3 hours. Thus, we have established an in vitro model system to examine the sequential migration of neutrophils through endothelium and the respiratory epithelium in a manner analogous to that occurring with an in vivo airway stimulus causing neutrophil-rich airway inflammatory responses.

Lipocortin 1 and chemokine modulation of granulocyte and monocyte accumulation in experimental inflammation

1. Migration of blood-derived leukocytes to tissue sites of inflammation is a hallmark of the response that the host organizes to counteract an insult or a trauma or an infection. A cascade of events is then activated to allow interaction between the leukocyte and the endothelium of postcapillary venule, and this cascade is finely regulated such that mechanisms of negative control are operating side by side with pathways that promote and sustain the extravasation process. Examples of both these positive and negative regulatory systems are discussed here. 2. In vivo accumulation of specific subtypes of leukocytes in response to application of selective chemokines operates through an indirect mechanism that includes the perivenular mast cell and, in particular, the mast cell-derived amines, such as histamine and serotonin. In fact, treatments of animals with (1) histamine H1 or serotonin antagonists or with (2) the mast cell stabilizer cromolyn or with (3) prior depletion of intact mast cells are maneuvers that successfully reduce eosinophil, neutrophil and monocyte extravasation in response to eotaxin, interleukin-8 or monocyte chemoattractant protein-1, respectively. A model in which histamine provides a P-selectin-dependent rolling phenomenon is then postulated. 3. The discovery that neutrophil-derived lipocortin 1 acts as an autocrine mediator with an inhibitory action on the emigration (diapedesis) process confirms the growing body of experimental data that showed that exogenously administered lipocortin 1 and lipocortin 1 mimetics (peptide Ac2-26) potently inhibit neutrophil extravasation in response to different stimuli. Externalization of lipocortin 1 on the plasma membrane of adherent neutrophils reduces their rate of passage through the endothelial gaps. Because cell-associated lipocortin 1 levels are under the partial control of corticosterone (endogenous circulating glucocorticoid hormone in rodents) and dexamethasone (a synthetic glucocorticoid hormone with a potent anti-inflammatory profile), a model is proposed in which a balance between anti-inflammatory (lipocortin 1, etc.) and pro-inflammatory (adhesion molecules, cytokines and chemokines) mediators explains the difference in the rate of leukocyte accumulation during the different stages of the host inflammatory response. 4. In conclusion, this review emphasizes the importance of in vivo experimental systems as a valid way of obtaining pertinent observations and reiterates the importance of negative regulatory mechanisms on the leukocyte extravasation process operating within the host.

IL-8 is one of the major chemokines produced by monkey airway epithelium after ozone-induced injury

A rhesus monkey interleukin (IL)-8 cDNA clone with >94% homology to the human IL-8 gene was isolated by differential hybridization from a cDNA library of distal airways after ozone inhalation. In situ hybridization and immunohistochemistry showed increased IL-8 mRNA and protein levels in epithelial cells at 1 h but not at 24 h after inhalation of ozone. The appearance of IL-8 in airway epithelial cells correlated well with neutrophil influx into airway epithelia and lumens. Air-liquid interface cultures of tracheobronchial epithelial cells were exposed to ozone in vitro. We observed a transient increase in IL-8 secretion in culture medium immediately after ozone exposure and a dose-dependent increase in IL-8 secretion and mRNA production. In vitro neutrophil chemotaxis showed a parallel dose and time profile to epithelial cell secretion of IL-8. Treatment with anti-IL-8 neutralizing antibody blocked >80% of the neutrophil chemotaxis in vitro. These results suggest that IL-8 is a key chemokine in acute ozone-induced airway inflammation in primates.

Human and bovine endothelial cell monolayers are differentially activated for neutrophil transmigration by human plasma

Endothelial cells used in transendothelial migration assays have been derived from different sources including human umbilical vein and bovine pulmonary artery. As plasma-induced activation of endothelial cells for enhanced transmigration of leukocytes may be pathophysiologically relevant, the role of species differences between plasma and endothelial cells was studied. The effects of human plasma on human umbilical vein and bovine pulmonary artery endothelial cells with regard to transmigration of neutrophils were compared. Transendothelial migration of neutrophils was tested employing endothelial cell-covered Transwell cell culture chamber inserts with micropore filters of 5 microns pore size. Results showed that human plasma induces neutrophil transmigration of both human umbilical vein and bovine pulmonary artery endothelial cell monolayers. Plasma samples from 50 to 69 year old men with and without carotid arteriosclerosis (N = 152) stimulated endothelial cells of human origin significantly stronger for transmigration of neutrophils than endothelial cells of bovine origin. Analyses of limits of agreement and of correlation of the two methods indicated that bovine pulmonary artery and human umbilical vein endothelial cells cannot replace each other in assays of plasma-induced activation of transmigration. Plasma levels of soluble adhesion molecule P-selectin, which are elevated in patients with arteriosclerotic diseases, are inversely related to plasma-induced activation of neutrophil transmigration of endothelial monolayers of human origin but not of bovine origin (N = 65). As rates of transmigration that were induced by plasma from subjects without carotid arteriosclerosis (N = 73) were significantly related between human and bovine endothelium, elevated plasma levels of soluble P-selectin may thus affect results of assays for plasma-induced activation of neutrophil transmigration of endothelial monolayers in a species-specific manner.

Characterization of transendothelial chemotaxis of T lymphocytes

We have adapted a chemotaxis assay using human umbilical vein endothelial cell (HUVEC) monolayers on microporous membranes for studying lymphocyte transendothelial chemotaxis in vitro. Supernatants of peripheral blood mononuclear cells stimulated with phytohemagglutinin (PHA) were identified as an excellent source of lymphocyte chemoattractant activity. The activity in PHA supernatant typically caused 2-6% of peripheral blood lymphocytes (PBL) to transmigrate compared to 0.1-0.3% to media control. Checkerboard analysis demonstrated that transmigration was directional and not attributable to random locomotion. Purified T lymphocytes also underwent transendothelial chemotaxis to PHA supernatant. Using monoclonal antibodies to several human adhesion receptors, we found that the interaction between LFA-1 and ICAM-1/ICAM-2 was more important for transendothelial lymphocyte chemotaxis than the interaction between VLA-4 and VCAM-1. A monoclonal antibody to the beta 1 integrin subunit inhibited chemotaxis more than antibodies to the VLA alpha 2, alpha 3, alpha 4, or alpha 5 subunits. The transendothelial assay was used to guide purification of the lymphocyte chemoattractant activity, which we reported previously to be monocyte chemoattractant protein-1 (MCP-1) (Carr et al., Proc. Natl. Acad. Sci. USA (1994) 91, 3652). The adhesion molecules required for chemotaxis to MCP-1 were similar to those with PHA supernatant. The use of HUVEC in the assay enhances the signal-to-background ratio of chemotaxis and provides a model that is physiologically relevant to lymphocyte emigration from the bloodstream into sites of inflammation.

Allergic models and cytokines

Cytokines are proinflammatory protein mediators produced by many cells, including mast cells, T lymphocytes, eosinophils, airway epithelial cells, and macrophages. There are numerous in vitro and in vivo animal and human studies showing that cytokines are released as a result of allergic reactions. Cytokines mediate allergic inflammation by activating eosinophils, promoting mast cell development, regulating immunoglobulin isotype switching to immunoglobulin E, modulating adhesion molecule regulation, and promoting both neutrophil and eosinophil chemotaxis. Furthermore, there are data that show the pro-inflammatory effects of cytokines may be blocked by cytokine antagonists. This report reviews the in vitro and in vivo animal and human studies of allergic models of cytokine production and regulation. It also discusses the specific roles of cytokines in the allergic inflammatory response and asthma.

Polymorphonuclear leukocyte transmigration promotes invasion of colonic epithelial monolayer by Shigella flexneri

In vivo and in vitro, Shigella flexneri, an invasive pathogen of the human colon, cannot invade epithelial cells through their apical pole. To identify ways by which it may reach the cellular basolateral domain in order to invade, we have established an assay using the human colonic T-84 cell line grown on permeable filters. Human PMN were added to the basal pole of the cells, and invasive shigellae to their apical pole. Apical addition of bacteria induced strong transmigration of PMN, reaching a maximum after 1 h of incubation. Transmigration depended on a receptor-specific interaction since it was inhibited by an anti-CD18 monoclonal antibody that antagonizes binding of MAC1 on its putative epithelial cell receptor. After 1 h of PMN transmigration, shigellae started to invade the monolayer in areas of intense PMN infiltration. Invasion was clearly dependant on PMN transmigration since it was also inhibited by addition of an anti-CD18 monoclonal antibody. This in vitro assay is consistent with in vivo observations showing early PMN efflux within colonic crypts in the course of shigellosis. PMN transmigration may therefore allow invasion in the colon by opening the paracellular pathway to invasive microorganisms.

Leukocyte/endothelial interactions and blood-brain barrier permeability in rats during cerebral superfusion with LTB4

The experimental study analyses the vasomotor response (change of diameter of pial arterioles and venules), and blood-brain barrier function of the pia-arachnoidea at the rat brain surface before, during and after cerebral superfusion with 1.5 or 15.0 nM LTB4 in mock CSF. Leukocyte dynamics were studied by assessment of their centerline velocity, of rolling along ("roller") and attachment to ("sticker") the venular wall of white blood cells intravitally stained by Rhodamin 6G. Superfusion of the brain with LTB4 at both dose levels led to dilation of arterioles to 130% (p < 0.001), while of venules to 117% (p < 0.001) of control. The centerline velocity of leukocytes increased from 0.7 to 0.9 mm/s, however, only after superfusion with LTB4 at the high dose level. LTB4 induced a dose-dependent rolling (p < 0.01) and sticking of leukocytes (p < 0.001). Yet, a delay of about 60 min between cerebral administration of LTB4 and the maximal response of leukocyte rolling and sticking was observed. Whereas the blood-brain barrier was not opened by cerebral superfusion with 1.5 or 15.0 nM LTB4, for i.v. Na(+)-fluorescein, barrier leakage was promptly induced by 30.0 nM. The present findings demonstrate that cerebral administration of LTB4 by superfusion of the exposed brain surface is eliciting a pronounced vasomotor response, whereas the induction of leukocyte/endothelial interactions is less impressive.

Degree of neutrophil chemotaxis is dependent upon the chemoattractant and barrier

Stimulated neutrophil migration across lung endothelial and epithelial barriers is important in lung inflammatory processes. To better understand the interaction between chemoattractants, neutrophils, and endothelium and epithelium, we compared the ability of leukotriene B4 (LTB4), formylmethionylleucylphenylalanine (FMLP), and platelet-activating factor (PAF) to induce human neutrophil migration across 3-microns-pore filters alone and human umbilical vein endothelial (HUVE) cells and two different epithelial cell types, Madin-Darby canine kidney (MDCK) cells and human lung A549 cells, cultured in monolayers on these filters. LTB4, FMLP, and PAF induced neutrophil migration through naked filters, endothelial cells, and epithelial cells in a dose-related fashion. At optimal chemoattractant doses, LTB4, FMLP, and PAF induced relatively equivalent neutrophil migration through filters and endothelial and epithelial monolayers. However, the doses at which optimal neutrophil migration was observed to occur as well as the degree of neutrophil migration through the three barriers varied depending upon the chemoattractant. Based on dose-response experiments, the relative rank order of potency for the three chemoattractants was: LTB4 = FMLP greater than PAF for filter alone barrier; LTB4 greater than FMLP greater than PAF for HUVE cell barrier; and FMLP greater than LTB4 greater than PAF for MDCK and A549 epithelial cell barriers. Our data suggest that neutrophil chemotactic and subsequent lung inflammatory responses are interrelatedly influenced by both the quantity and type of chemoattractant present and the barrier through which the neutrophil must migrate.

Neutrophil migration across a cultured epithelial monolayer elicits a biphasic resistance response representing sequential effects on transcellular and paracellular pathways

Migration of polymorphonuclear leukocytes across epithelia is a hallmark of many inflammatory disease states. Neutrophils traverse epithelia by migrating through the paracellular space and crossing intercellular tight junctions. We have previously shown (Nash, S., J. Stafford, and J.L. Madara. 1987. J. Clin. Invest. 80:1104-1113), that leukocyte migration across T84 monolayers, a model human intestinal epithelium, results in enhanced tight junction permeability--an effect quantitated by the use of a simple, standard electrical assay of transepithelial resistance. Here we show that detailed time course studies of the transmigration-elicited decline in resistance has two components, one of which is unrelated to junctional permeability. The initial decrease in resistance, maximal 5-13 min after initiation of transmigration, occurs despite inhibition of transmigration by an antibody to the common beta subunit of neutrophil beta 2 integrins, and is paralleled by an increase in transepithelial short-circuit current. Chloride ion substitution and inhibitor studies indicate that the early-phase resistance decline is not attributable to an increase in tight junction permeability but is due to decreased resistance across epithelial cells resulting from chloride secretion. Since T84 cells are accepted models for studies of the regulation of Cl- and water secretion, our results suggest that neutrophil transmigration across mucosal surfaces (for example, respiratory and intestinal tracts) may initially activate flushing of the surface by salt and water. Equally important, these studies, by providing a concrete example of sequential transcellular and paracellular effects on transepithelial resistance, highlight the fact that this widely used assay cannot simply be viewed as a direct functional probe of tight junction permeability.

Role of reactive oxygen species in intestinal diseases

It is well known that reactive oxygen metabolites are generated during several pathologies, and that they are able to disturb many cellular processes and eventually lead to cellular injury. After intestinal ischemia, reactive oxygen species are produced when the ischemic tissue is reperfused. The enzyme xanthine oxidase is thought to play a key role in this process. As a result of this oxygen radical production, the permeability of the endothelium and the mucosa increases, allowing infiltration of inflammatory leukocytes into the ischemic area. Moreover, reactive oxygen species are also indirectly involved in leukocyte activation. In turn, these inflammatory cells respond with the production of oxygen radicals, which play an important role in the development of tissue injury. Thus, intestinal ischemia and reperfusion evokes an inflammatory response. Also during chronic intestinal inflammatory diseases, reactive oxygen metabolites are proposed to play an important role in the pathology. Scavenging of reactive oxygen species will thus be beneficial in these disorders.