Lymphoid procoagulant response to bacterial endotoxin in the rat

The gut microbiota - a modulator of endothelial cell function and a contributing environmental factor to arterial thrombosis

Introduction: There is emerging evidence linking the commensal gut microbiota with the development of cardiovascular disease and arterial thrombosis. In immunothrombosis, the host clotting system protects against the dissemination of invading microbes, not considering the huge number of microbes that interact with host physiology in a mutualistic fashion. Areas covered: Interestingly, recent research revealed that colonizing gut microbes profoundly influence host innate immune pathways that support arterial thrombus growth. The gut microbiota promotes arterial thrombus formation by enhancing the pro-adhesive capacity of the vascular endothelium, triggering hepatic von Willebrand factor synthesis and its release by Weibel-Palade body exocytosis, resulting in elevated von Willebrand factor levels and enhancing FVIII stability in plasma. Furthermore, the metabolic capacity of gut resident microbes promotes agonist-induced platelet activation and deposition. Here, we give an overview, with a focus on the vascular endothelium, on how this gut-resident microbial ecosystem contributes to arterial thrombus formation. Expert opinion: The gut microbiota and its metabolites not only act on agonist-induced platelet reactivity, but also influence the hepatic endothelial phenotype via remote signaling, facilitating arterial thrombus growth at the arterial injury site.

In Vitro Assessment of Nanoparticle Effects on Blood Coagulation

Blood clotting is a complex process which involves both cellular and biochemical components. The key cellular players in the blood clotting process are thrombocytes or platelets. Other cells, including leukocytes and endothelial cells, contribute to clotting by expressing the so-called pro-coagulant activity (PCA) complex on their surface. The biochemical component of blood clotting is represented by the plasma coagulation cascade, which includes plasma proteins also known as coagulation factors. The coordinated interaction between platelets, leukocytes, endothelial cells, and plasma coagulation factors is necessary for maintaining hemostasis and for preventing excessive bleeding. Undesirable activation of all or some of these components may lead to pathological blood coagulation and life-threatening conditions such as consumptive coagulopathy or disseminated intravascular coagulation (DIC). In contrast, unintended inhibition of the coagulation pathways may lead to hemorrhage. Thrombogenicity is the property of a test material to induce blood coagulation by affecting one or more elements of the clotting process. Anticoagulant activity refers to the property of a test material to inhibit coagulation. The tendency to cause platelet aggregation, perturb plasma coagulation, and induce leukocyte PCA can serve as an in vitro measure of a nanomaterial's likelihood to be pro- or anticoagulant in vivo. This chapter describes three procedures for in vitro analyses of platelet aggregation, plasma coagulation time, and activation of leukocyte PCA. Platelet aggregation and plasma coagulation procedures have been described earlier. The revision here includes updated details about nanoparticle sample preparation, selection of nanoparticle concentration for the in vitro study, and updated details about assay controls. The chapter is expanded to describe a method for the leukocyte PCA analysis and case studies demonstrating the performance of these in vitro assays.

Dendrimer-induced leukocyte procoagulant activity depends on particle size and surface charge

Aims: Thrombogenicity associated with the induction of leukocyte procoagulant activity (PCA) is a common complication in sepsis and cancer. Since nanoparticles are increasingly used for drug delivery, their interaction with coagulation systems is an important part of the safety assessment. The purpose of this study was to investigate the effects of nanoparticle physicochemical properties on leukocyte PCA, and to get insight into the mechanism of PCA induction. Materials & Methods: A total of 12 formulations of polyamidoamine (PAMAM) dendrimers, varying in size and surface charge, were studied in vitro using recalcification time assay. Results: Irrespective of their size, anionic and neutral dendrimers did not induce leukocyte PCA in vitro. Cationic particles induced PCA in a size- and charge-dependent manner. The mechanism of PCA induction was similar to that of doxorubicin. Cationic dendrimers were also found to exacerbate endotoxin-induced PCA. Conclusion: PAMAM dendrimer-induced leukocyte PCA depends on particle size, charge and density of surface groups.

The role of tyrosine phosphorylation in lipopolysaccharide- and zymosan-induced procoagulant activity and tissue factor expression in macrophages

The expression of surface procoagulants by exudative macrophages represents an important mechanism underlying local fibrin deposition at sites of extravascular inflammation. The present studies investigated the contribution of tyrosine phosphorylation to the generation of macrophage procoagulant activity (PCA) and tissue factor expression in response to proinflammatory stimuli. Both lipopolysaccharide (LPS) and zymosan rapidly stimulated tyrosine phosphorylation in elicited murine peritoneal macrophages. This effect was prevented by the tyrosine kinase inhibitors genistein and herbimycin and augmented by the addition of the phosphotyrosine phosphatase inhibitor vanadate. The vanadate-mediated rise in phosphotyrosine accumulation was abrogated by the use of diphenylene iodonium, an inhibitor of the respiratory burst oxidase, suggesting a role for peroxides of vanadate as contributors to the tyrosine phosphorylation. This notion was supported by the finding that vanadyl hydroperoxide markedly increased the accumulation of phosphotyrosine residues. To define the role of tyrosine phosphorylation in the induction of macrophage PCA by LPS, the effects of tyrosine kinase inhibition by genistein and herbimycin were investigated. Both agents inhibited the expression of macrophage PCA. Further, Northern blot analysis with the cDNA probe for murine tissue factor indicated that the inhibition occurred at the mRNA level or earlier. Since vanadate augmented phosphotyrosine accumulation, it was hypothesized that it might enhance generation of macrophage products. However, vanadate reduced induction of PCA in response to LPS. By contrast, vanadate augmented basal prostaglandin E2 (PGE2) release and stimulated PGE2 release by macrophages. Indomethacin prevented the increase in PGE2 but only partially restored normal levels of PCA. The effect of vanadate on tissue factor expression appeared to be posttranscriptional. These studies thus demonstrate, by functional Western blotting and Northern blotting techniques, that tyrosine phosphorylation plays a role in the regulation of macrophage PCA and tissue factor expression in response to proinflammatory stimuli.

Cellular mechanisms of abscess formation: macrophage procoagulant activity and major histocompatibility complex recognition

BACKGROUND

Macrophage procoagulant activity (PCA) has been proposed as a key mediator of abscess formation. Experimentally, transient systemic bacterial infection lead to increased numbers of intraabdominal abscesses after a subsequent episode of peritonitis. We tested the hypothesis that these events were regulated by classic major histocompatibility complex (MHC)-restricted antigen processing and presentation to lymphocytes followed by lymphocyte-mediated up-regulation of macrophage PCA.

METHODS

In vitro, macrophages and lymphocytes from BALB/c or C57BL/6 mice either untreated or preexposed to Escherichia coli were coincubated with bacteria or lipopolysaccharide. Cell lysates were tested for PCA in a one-step dotting assay. In vivo, mice were either preexposed to E. coli or received passive transfer of lymphocytes from MHC-compatible or MHC-incompatible and naive or preexposed donors; peritonitis and intraabdominal abscesses were afterwards induced with E. coli, Bacteroides fragilis, and a sterile fecal adjuvant. Mice were killed after 10 days and were studied for abscess number and bacterial composition.

RESULTS

The presence of lymphocytes consistently increased macrophage PCA; lymphocytes from preexposed donors induced twice as much PCA as lymphocytes from naive donors regardless of MHC background. Both bacterial preexposure and passive transfer of lymphocytes from preexposed donors increased later intraabdominal abscess number in an MHC-restricted fashion.

CONCLUSIONS

Transient infections enhance subsequent lymphocyte-mediated macrophage PCA, correlating with increases in abscess formation after peritonitis. The need for MHC identity to reproduce these results via passive transfer in vivo is consistent with classic T-cell receptor-mediated antigen presentation and lymphocyte activation before enhancement of PCA during peritonitis.

Nosocomial bacteremia-induced increases in abscess formation correlate with in vitro upregulation of macrophage procoagulant activity

OBJECTIVE

To evaluate the hypothesis that sublethal exposure to common nosocomial pathogens can alter the host response to a later, distant infectious insult (peritonitis and intraperitoneal abscess formation), and that these changes are related to the induction of macrophage procoagulant activity.

DESIGN

A multiexperiment, randomized, controlled trial.

SETTING

Animal research laboratory of a university medical center.

SUBJECTS

One hundred sixty-five Balb/c mice, weighing 20 to 25 g, were used for in vivo experiments and as the source of peritoneal macrophages for in vitro experiments.

INTERVENTIONS

Nine groups of mice (n = 10 to 18 per group) were twice systemically preexposed to sublethal amounts of live Escherichia coli, Enterobacter cloacae, Pseudomonas aeruginosa, Staphylococcus epidermidis, Enterococcus faecalis, or Candida albicans, or to 2.5 or 5.0 micrograms E. coli lipopolysaccharide O26:B6. One week later, mice underwent the induction of mixed E. coli/Bacteroides fragilis peritonitis, leading to abscess formation. In parallel experiments in vitro, 10(6) mouse peritoneal macrophages were incubated with similar amounts of nosocomial pathogens or lipopolysaccharide to determine the induction of macrophage procoagulant activity.

MEASUREMENTS AND MAIN RESULTS

The three Gram-negative bacilli tested significantly upregulated both abscess formation and macrophage procoagulant activity, with a strong linear correlation between abscess formation and procoagulant activity. These effects were not seen with the Gram-positive cocci or with C. albicans. Pre-exposure of mice to endotoxin alone did not alter later abscess formation, but did increase macrophage procoagulant activity.

CONCLUSIONS

Sublethal exposure to some Gram-negative nosocomial pathogens can significantly alter a host's response to a later, distant, infection, even when caused by different bacteria. In the case of peritonitis and intraperitoneal abscess formation, these changes may be mediated by the upregulation of macrophage procoagulant activity. The presence of endotoxin alone does not completely explain these phenomena.

Pasteurella haemolytica A1 and bovine respiratory disease: pathogenesis

The severe fibrinonecrotic pneumonia associated with pneumonic pasteurellosis usually results from colonization of the lower respiratory tract by Pasteurella haemolytica biotype A, serotype 1(A1). Despite recent research efforts, the authors lack a detailed understanding of the interactions and host response to P. haemolytica in the respiratory tract. The authors hypothesize that management and environmental stress factors or viral infection alters the upper respiratory tract (URT) epithelium allowing P. haemolytica to colonize the epithelium. Once the URT is colonized, large numbers of organisms enter the lung where they interact with alveolar macrophages. Endotoxin, released from the bacteria, crosses the alveolar wall where it activates pulmonary intravascular macrophages, endothelium, neutrophils, lymphocytes, platelets, complement, and Hageman factor leading to complex interactions of cells and mediators. It is the progression of this inflammatory response with neutrophil influx that is ultimately responsible for the pulmonary injury. Leukotoxin is a major virulence factor of P. haemolytica that allows it to survive by destroying phagocytic cells. At subcytolytic concentrations it may also enhance the inflammatory response by activating cells to produce mediators and release reactive oxygen metabolites and proteases.

Spontaneous and lipopolysaccharide-induced expression of procoagulant activity by equine lung macrophages in comparison with blood monocytes and blood neutrophils

The procoagulant activity (PCA) associated with equine bronchoalveolar lavage cells was determined and compared with that expressed by peripheral blood mononuclear cells and neutrophils. Lung cell preparations from horses affected with chronic pulmonary disease were included in all experiments and there was no difference in the qualitative type of response compared with lung cells which were obtained from healthy horses. Significant amounts of PCA were expressed by cells freshly procured from bronchoalveolar lavages of healthy and diseased horses. When adherent lung cells were kept in culture for some time, cell-associated PCA slightly decreased within 4 h, reached its lowest point after approximately 24 h and rose again during the second week of culture. In contrast, freshly isolated blood mononuclear cells or neutrophils expressed little PCA. Following culture for 24 h, mononuclear cells began to express increased PCA levels. Both cultivated lung cells (comprised mainly on alveolar macrophages) and blood mononuclear cells responded to LPS by dramatically increased PCA expression, whereas neutrophils showed a small augmentation of PCA on LPS stimulation. Fresh mononuclear cells and cultivated lung cells differed in their PCA response to LPS in several respects. Blood mononuclear cells were more sensitive to LPS than lung macrophages and responded to a 100-fold lower LPS concentration than the latter. Mononuclear cell-associated PCA peaked 4 h after stimulation whereas that of cultured macrophages continued to increase up to 24 h after stimulation. Lung macrophages cultured in adherence responded to LPS stimulation with a much higher PCA increase than macrophages cultured in suspension, in teflon containers. However, the culture vessel did not influence the PCA expressed by unstimulated cells. PCA expression depended to a large extent on transcription and translation, as evidenced by a 60-85% reduction of PCA in cycloheximide- or actinomycin D-treated, LPS-stimulated lung macrophages. PCA was largely cell-associated; only a small proportion of cell-associated PCA was shed into the medium. The PCA associated with mononuclear cells and with lung macrophages was tissue factor because of its dependence on clotting factor VII and its independence from clotting factor VIII. The expression of PCA by freshly isolated cells, the lower sensitivity to LPS, and the loss of PCA in the first 24 h of cultivation are indicative of in vivo activation of lung macrophages.

Alterations in pulmonary morphology and peripheral coagulation profiles caused by intratracheal inoculation of live and ultraviolet light-killed Pasteurella haemolytica A1 in calves

Eighteen male Holstein calves were divided into groups of three and inoculated intratracheally with 5 x 10(9) logarithmic phase or ultraviolet light-killed Pasteurella haemolytica biotype A serotype 1. Serial coagulation profiles were done on one calf from each group during the first 24 hours after inoculation. One calf from each group was necropsied at 4, 12, and 24 hours after inoculation and lesions were characterized with light and transmission electron microscopy. We found that 1) the pulmonary intravascular macrophage may have an important role in the early intravascular inflammatory events; 2) there was morphologic evidence for local initiation of the coagulation cascade in the lung early in the disease process but it was not a consumptive process; and 3) killed-bacteria were capable of causing fibrin exudation, platelet aggregation and alveolar epithelial damage similar to live bacteria, but the degenerative changes in neutrophils, endothelial cells and intravascular fibrin formation that occur with live bacteria were not seen.

Platelet-activating factor primes endotoxin-stimulated macrophage procoagulant activity

Macrophage procoagulant activity (PCA) at the site of inflammation may be induced by several stimuli including bacteria and endotoxin (LPS). The local factors controlling PCA induction are poorly defined. The lipid mediator platelet-activating factor (PAF) is ubiquitous to inflammatory sites. To determine the effect of PAF on LPS-induced PCA, thioglycolate-elicited murine peritoneal macrophages were exposed to PAF (10(-7) M) or control medium for 30 min and then stimulated with LPS (10 micrograms/ml) for 2, 4, or 6 hr. The ability of macrophages to shorten the clotting time of plasma (ie., PCA) was then measured and clotting times were converted to PCA units using a thromboplastin standard. Cytosolic calcium ([Ca2+]i) measurements were made using the calcium-sensitive fluorescent dye indo-1. PAF alone did not induce a rise in PCA expression (medium alone, 47 +/- 11 mU/10(6) cells; PAF alone, 49 +/- 12 mU/10(6) cells at t = 4 hr), but PAF treatment prior to LPS exposure resulted in a significant increase in the LPS-stimulated expression of PCA (LPS alone, 190 +/- 29 mU/10(6) cells; PAF/LPS, 329 +/- 57 mU/10(6) cells at t = 4 hr, P less than 0.05). This priming effect was reversed by the PAF antagonist WEB 2086 (WEB/PAF/LPS, 196 +/- 31 mU/2 x 10(6) cells). Stimulation of cells with PAF alone resulted in a rapid rise in [Ca2+]i (resting, 213 +/- 19 nmole; peak, 577 +/- 35 nmole). This effect was also inhibited by WEB 2086. These data suggest that PAF plays an important role in the modulation of PCA production by macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)

Disparate mechanisms of induction of procoagulant activity by live and inactivated bacteria and viruses

This study describes the dose response, time course, and lymphocyte requirements of procoagulant activity (PCA) induction following stimulation of thioglycolate-elicited BALB/c peritoneal macrophages with live and inactivated bacteria (Bacteroides fragilis, Escherichia coli, and Staphylococcus aureus) and murine hepatitis virus type 3 (MHV-3). Induction of PCA by MHV-3 was significantly more rapid and the maximal PCA achieved was significantly greater than by the three bacterial species studied. In relation to induction of PCA by bacteria, the PCA response was more rapid and of greater magnitude with S. aureus and E. coli than with B. fragilis. MHV-3 induced an augmented PCA response at all concentrations of virus studied in a dose-dependent fashion, whereas higher titers of live bacteria (greater than 10(7) CFU/ml) inhibited PCA, suggesting the production of an inhibitory factor. Significant PCA induction was observed when macrophages were incubated with bacteria or virus in the absence of lymphocytes. At low titers of B. fragilis (10(3) CFU/ml), addition of lymphocytes greatly augmented PCA production, whereas at higher titers (10(7) CFU/ml), the addition of lymphocytes only slightly augmented the PCA response. In contrast, MHV-3 induction of PCA was enhanced by the addition of lymphocytes at all concentrations of virus studied, suggesting a lymphocyte-dependent process. Heat-inactivated bacteria were as effective as live bacteria in inducing PCA, suggesting that induction of PCA by bacteria requires only a bacterial surface component. In contrast, UV-inactivated MHV-3 did not induce PCA, suggesting that viral replication is a necessary step in PCA induction. These results suggest that the cellular and metabolic requirements for induction of PCA differ among viral and bacterial pathogens and may partly explain their differences in pathogenicity.

A prothrombinase complex of mouse peritoneal macrophages

Addition of prothrombin to mouse peritoneal macrophages in vitro resulted in the formation of a thrombin-like enzyme, as demonstrated by use of the luminogenic peptide substrate S-2621. The prothrombinase activity was sedimented by high-speed centrifugation following homogenization of the cells and was abolished by treatment of the cells with the nonionic detergent Triton X-100 at 0.02% concentration. Moreover, the activity was drastically reduced by maintaining cultures in the presence of warfarin and, presumably due to competitive substrate inhibition, by adding S-2222, a chromogenic peptide substrate for Factor Xa. These findings suggest that prothrombin cleavage is catalyzed by Factor Xa at the macrophage surface. The generated thrombin was inhibited by antithrombin, and this reaction was accelerated by heparin with high affinity for antithrombin but not by the corresponding oligosaccharides composed of 8-14 monosaccharide units. Such oligosaccharides which are capable of accelerating the inactivation of Factor Xa by antithrombin, inhibited thrombin formation from prothrombin in the macrophage cultures, presumably by promoting inactivation by antithrombin of Factor Xa in a prothrombinase complex. Activation of the macrophage coagulation system, as proposed to occur in certain inflammatory conditions, thus may be modulated at various levels by heparin, or heparin oligosaccharides, released from mast cells.

Induction of macrophage procoagulant activity by Bacteroides fragilis

Fibrin deposition in the peritoneal cavity during acute peritonitis appears to predispose the host to abscess formation by providing an environment for bacterial proliferation protected from host defenses. The purpose of the present study was to determine whether the potent abscess-inducing anaerobe Bacteroides fragilis could promote fibrin deposition by inducing mononuclear cells to express procoagulant activity (PCA). B. fragilis stimulated PCA in a dose-dependent fashion, achieving a maximum at 10(7) CFU/ml. Heat-killed B. fragilis induced comparable levels of PCA, while a nonspecific phagocytic stimulus, latex beads, was not stimulatory. B. fragilis was capable of inducing PCA even when phagocytosis was blocked by preexposure of cells to latex beads. The results suggested that phagocytosis was neither necessary nor sufficient for the generation of PCA. Cell separation studies showed that PCA was solely produced by macrophages and that lymphocytes did not augment its production. These studies suggest one potential mechanism by which B. fragilis might initiate abscess formation.

Amidolytic assay for procoagulant activity of lymphoid and tumor cells

Among the effector molecules induced in monocytes by the cellular immune response is tissue factor (TF), the initiating receptor/cofactor of the extrinsic coagulation protease cascade that is also frequently observed on human tumor cells. Other cellular activators have also been described on monocytes and tumor cells. Analyses of the cellular immune procoagulant response would be aided by a simple and efficient form of quantitation. An assay for cellular procoagulant activity (PCA) induction and expression was developed utilizing the chromogenic thrombin substrate tosyl-Gly-Pro-Arg-p-nitroanilide acetate. The constitutive or induced PCA of a variety of cells was analyzed. Peripheral blood mononuclear cells, peritoneal exudate cells, 13762 Mat B (III) mammary carcinoma cells, 1591-RE fibrosarcoma cells, the macrophage cell line WEHI-265, a detector of PCA inducing lymphokines, or mixtures of these cells were incubated with or without stimuli, e.g., endotoxin, in 96-well microplates. After incubation the cells were assayed for PCA by addition of the chromogenic substrate for thrombin using fibrinogen depleted plasma as a source of the coagulation proteins factors VII, X, V and prothrombin. The absorbance at 405 nm was determined. Spontaneous cleavage of the chromogenic substrate restricted the assay to total analysis times of less than 14 min. The 13762 Mat B (III) rat tumor which constitutively expressed tissue factor-like procoagulant activity induced measurable substrate hydrolysis with as few as 100 cells/well. It was observed that the chromogenic substrate assay was approximately twice as sensitive as conventional clotting assays for procoagulant activity. Endotoxin stimulated human peripheral blood mononuclear cells and mouse peritoneal exudate cells were readily analyzed. The procoagulant activity of approximately 280 LPS-stimulated human monocytes generated sufficient thrombin to provide a significant measurable signal within 10 min. Also supernatants from mixed lymphocyte cultures as well as from immune lymphocyte responses to syngeneic tumor cell cultures induced procoagulant activity in the macrophage like cell line WEHI-265 as determined with the assay for thrombin generation. The hydrolysis of the substrate was attributed to thrombin formation since the induced cleavage was abolished by hirudin, the highly specific active site inhibitor of thrombin. This chromogenic thrombin assay can be used for measuring induction of viable cell expression or total cellular procoagulant activity rapidly and efficiently in large replicate numbers suitable for a variety of analyses of cellular immune responses including clonal analyses of gene induction.