Expression Of Procoagulant Activity Research Articles

Effects of interleukin-1, lipopolysaccharide, and streptococci on procoagulant activity of cultured human cardiac valve endothelial and stromal cells

Fibrin is the primary constituent of the vegetation in infective endocarditis, and tissue factor expression is a major mechanism of coagulation activation on infected valves. To determine which cells may participate in coagulation activation in this setting, expression of procoagulant activity (PCA; shown to be tissue factor) was studied in cultured endothelial and stromal cells derived from human cardiac valves. Endothelial cells had negligible PCA (99 +/- 50 mU/10(5) cells, mean +/- 1 standard deviation) unless stimulated by lipopolysaccharide or interleukin-1, which increased PCA to 5,592 +/- 1,482 and 5,901 +/- 1,497 mU/10(5) cells, respectively, in 6 h. Incubation of cells with viable enterococci or viridans streptococci or with an enterococcal cell wall preparation did not induce PCA. Cultured valve stromal cells constitutively expressed high levels of PCA (14,276 +/- 8,738 mU/10(5) cells) which was not changed with exposure to interleukin-1. PCAs of stromal or stimulated endothelial cells from valves of both right and left sides of the heart were comparable. The results suggest that endothelial cells may contribute to fibrin deposition during infection if stimulated, but PCA is not directly induced by bacteria. Stromal cells could contribute PCA if exposed to blood in the course of valve injury.

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.

Synergistic Effect of Low Doses of Tumor Necrosis Factor and Sera from Patients with Systemic Lupus Erythematosus on the Expression of Procoagulant Activity by Cultured Endothelial Cells

The effect of 15 antiphospholipid antibody (APA) positive SLE sera, 13 APA negative SLE sera, 10 APA negative sera from patients with other connective tissue diseases (CTD) and 15 control sera on the expression of endothelial procoagulant activity (PCA) was studied. Endothelial cells (EC) were stimulated with tumor necrosis factor (TNF) and 20% serum for 4 hr and the surface PCA expression was measured. Without TNF, none of the sera stimulated PCA expression. With suboptimal TNF stimulation, 14/15 APA positive SLE sera, 7/13 APA negative SLE sera, 2/10 CTD sera and 2/15 control sera enhanced PCA expression. This stimulating effect resided in the IgG fraction and was associated with the presence of APA, but not with a history of thrombosis. Purified APA had no PCA stimulating activity. PCA expression was inhibited by cycloheximide and heat treatment (30 min, 56 degrees C) of serum. In conclusion, 21/28 (75%) SLE sera increase the TNF-induced endothelial PCA expression. Although this effect predominantly occurs with APA positive serum, a causative role of APA was not demonstrated.

Induction of Endothelial Cell/Macrophage Procoagulant Activity: Synergistic Stimulation by Gamma Interferon and Granulocyte-Macrophage Colony Stimulating Factor

Inflammatory mediators such as endotoxin can stimulate the expression of procoagulant activity on both endothelial cells and macrophages while the monokines Interleukin 1, IL-1, and Tumor Necrosis Factor, TNF, induce procoagulant activity on endothelial cells. Incubation of murine peritoneal macrophages with suboptimal concentrations of endotoxin results in a two fold increase in procoagulant activity. Macrophages incubated with gamma interferon, IFN gamma, or Granulocyte-Macrophage Colony Stimulating Factor, GM-CSF, for 16 hours prior to endotoxin stimulation demonstrated a synergistic increase in procoagulant activity. A synergistic increase in procoagulant activity was also observed with primary cultures of human umbilical cord endothelial cells incubated with recombinant human IFN gamma for 16 hours prior to endotoxin, TNF, or IL-1 stimulation. Human GM-CSF had no stimulatory effect on endotoxin or monokine induced endothelial cell procoagulant activity. The augmentation of macrophage and endothelial cell procoagulant activity by IFN gamma and GM-CSF may provide a novel explanation for the role of these cytokines in acute and chronic inflammation.

Procoagulant induction by human lymphokine and interferon gamma/PMA on a myelomonocytic cell line, RC2a.

The human myelomonocytic cell line RC2a expressed procoagulant activity following stimulation with human lymphokine (LK) prepared by stimulating peripheral blood mononuclear cells with either mitogens (Concanavalin A, phytohaemagglutinin or antigen (tuberculin). Induction was rapid, with optimal activity observed between 6 and 8 h, was decreased in cultures containing serum and was not inhibited by actinomycin D or cycloheximide. The LK activity was not inhibited by an anti-interferon gamma (IFN gamma) antibody. IFN gamma and phorbol myristate acetate (PMA) had no activity but acted in synergy to induce procoagulant expression; interferon alpha plus PMA were without effect. In contrast to the LK-induced response, procoagulant induced by IFN gamma/PMA was not detected for up to 8 h and steadily rose over 24-48 h culture and was dependent on new protein and RNA synthesis. Bacterial lipopolysaccharide, a potent inducer of thromboplastin on normal human monocytes, failed, either alone or in combination with LK, IFN gamma, PMA or IFN gamma plus PMA, to activate procoagulant expression on RC2a cells. Both LK and IFN gamma/PMA-induced procoagulant had properties of thromboplastin expressed both intracellularly and on intact, viable cells. This study shows that RC2a cells are responsive to factors produced as the result of an activated cell-mediated immune response which may therefore contribute to the coagulopathies common to this form of malignancy.

Recombinant IFN-gamma synergizes with lipopolysaccharide to induce macrophage membrane procoagulants.

Fibrin deposition is an important histopathologic feature of inflammation and is mediated, in part, by monocyte/macrophage procoagulants. rIFN gamma acted in synergy with suboptimal levels of bacterial LPS by priming thioglycollate-induced mouse peritoneal exudate cells (TG-PEC) to express high levels of surface procoagulant. TFN-alpha beta, TFN-alpha, IL-1, either alone or in combination with LPS or IFN-gamma, had no effect on macrophage procoagulant activity expression. In contrast to the dramatic increases of macrophage procoagulant activity induced by IFN-gamma/LPS, on exudate macrophages, normal peritoneal macrophages, or peripheral blood monocytes were unresponsive suggesting that the state of activation of the macrophage determines reactivity. IFN-gamma induced a Factor VIIa-like activity detected only after cell disruption. Synergy between LPS and IFN-gamma-induced procoagulants may occur as the result of the assembly of the thromboplastin (induced by LPS), Factor VII/VIIa complex on the macrophage surface. RNA synthesis was required for procoagulant induction. Procoagulant expression may, as for other cytokines involved in inflammatory responses, be regulated by short lived repressor proteins as low dose cycloheximide superinduced procoagulant responses to both LPS and IFN-gamma and caused the extracellular expression of procoagulant in response to IFN-gamma. This study suggests an important role for IFN-gamma in the assembly of components of the extrinsic coagulant cascade on the macrophage surface. The synergy between IFN-gamma and LPS may moderate macrophage-initiated fibrin deposition characteristic of inflammatory responses.

Effects of the Lupus Anticoagulant in Patients with Systemic lupus Erythematosus on Endothelial Cell Prostacyclin Release and Procoagulant Activity

A disturbance in endothelial cell (EC) function may be pathogenetic in the thrombotic tendency of patients with the lupus anticoagulant (LA). The ability of serum from normal subjects and patients with systemic lupus erythematosus (SLE), with and without the LA, to modulate the release of prostacyclin (PGI2) and the expression of procoagulant activity by cultured human EC was investigated. Only the 10% and 20% serum concentrations from patients with SLE-LA produced a significantly greater inhibition of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) release (the stable metabolite of PGI2) than control serum. However, when patients with SLE-LA having Raynaud's phenomenon were excluded from this group, there was then no significant difference between the effect of the patient and control serum. Serum from patients with SLE +/- LA caused a significant increase in EC procoagulant activity compared to healthy controls. The two-stage partial thromboplastin time expressed in seconds decreased from 66 (normal) to 34 (SLE - LA) and 31 (SLE + LA), but there was no significant difference between the patients with and without the LA. The significantly increased EC procoagulant activity induced by serum from patients with SLE +/- LA may account for the observed increased incidence of thrombotic events in patients with SLE. Our data suggest that factors other than decreased prostacyclin release are responsible for the altered hemostasis observed in patients with SLE + LA.

Different expression of procoagulant activity in macrophages associated with experimental and human tumors.

Mononuclear phagocytes, an integral part of the lymphoreticular infiltrate of human and experimental tumors, might contribute to fibrin deposition within malignant tissues through the production of procoagulant activity (PCA). Recent studies in different types of experimental tumors and in some cancer patients indicate that the functional status in terms of PCA of mononuclear phagocytes at 'peripheral' sites is not the same as that of macrophages at the tumor site (tumor-associated macrophages, TAM). Peripheral blood monocytes and/or peritoneal macrophages from V2-carcinoma-bearing rabbits and from mice bearing different types of tumors, like cells from normal animals, have low levels of basal PCA and are able to respond with a marked increase in PCA to in vitro stimulation. Likewise, in patients with primary lung cancer, pulmonary alveolar macrophages (PAM) obtained from the contralateral side of the neoplasm and blood monocytes behave essentially as cells from normal individuals. In contrast, profound changes in PCA have been found in TAM. In some experimental tumors and in a number of the patients, macrophages taken at the tumor site express high levels of basal PCA, which most probably reflect in vivo activation. Local activation of macrophages for PCA production might contribute to fibrin deposition at the tumor site. In the other experimental tumors studied and in the remaining patients, not only have macrophages low basal PCA but they also fail to respond to various stimulants in vitro. Although the mechanisms underlying these changes and their pathophysiological significance remain to be established, it is apparent that neoplastic growth may modulate the expression of macrophage PCA at the tumor site.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional and Immunological Assays of F VIII in 133 Haemophiliacs - Characterization of a Subgroup of Patients with Mild Haemophilia A and Discrepancy in 1- and 2-Stage Assays

A systematic study of the levels of FVIII antigen and activity was done in 133 haemophiliacs. No measurable antigen was demonstrated in the 60 severe haemophiliacs, with the exception of 3 patients with levels ranging between 1.5 and 4.5 U/dl, which corresponded to a dramatic FVIII deficiency. The situation was more complex with the 73 moderate and mild haemophiliacs: 39 of them (53.4%) had a partial, concordant deficiency of both the antigen and the procoagulant activity (1- and 2-stage methods), likely corresponding to a decrease in the synthesis of normal FVIII. The conclusion for the other 34 patients, was a qualitative abnormality of FVIII, the levels of antigen in comparison with the procoagulant activity (1-stage method) appearing to be either very reduced (n = 6) or even nil (n = 8), or on the contrary very much higher (n = 20) or normal. For 11 patients in this last category, we found a clear discrepancy between the procoagulant activity levels obtained with the 2 different techniques, the 1-stage levels being higher than the 2-stage levels. This discrepancy which was stable with restudy on multiple occasions and found in different members of the same families was remedied when vWF was absent in one-stage assay. This suggests that we have identified a variant of haemophilia A with an inherited abnormality of FVIII characterized by an in vitro vWF-dependent expression of procoagulant activity.

T-lymphocyte requirement for the induction of mouse macrophage procoagulant activity by Trypanosoma brucei.

We have previously shown that peritoneal macrophages from Trypanosoma brucei infected mice, but not from uninfected mice, expressed high levels of procoagulant activity that could not be produced in vitro by incubation of unstimulated macrophages with bloodstream forms of trypanosomes. In the present study we demonstrate that trypanosome-induced macrophage activation can be achieved in vitro by providing either sensitized (day 7 of infection) lymphocytes and trypanosomes or the supernatant fluid from this interaction. The ability of lymphocytes to secrete macrophage-activating lymphokines is enhanced up to day 12 of infection but was absent in the later stages. Although enhancement of the procoagulant activity occurred in infected nude mice, it seems that macrophage function in African trypanosomiasis, as regards the expression of procoagulant activity, is regulated by T-lymphocytes.

Dipyridamole stimulates urokinase production and suppresses procoagulant activity of rabbit alveolar macrophages: a possible mechanism of antithrombotic action

Dipyridamole, an inhibitor of platelet aggregation, has been shown to have beneficial effects in disorders characterized by extravascular fibrin deposition. Mononuclear phagocytes are present in extravascular sites and are capable of expressing both plasminogen activator and procoagulant activities, which suggests these cells play a central role in extravascular fibrin turnover. We therefore sought to determine whether dipyridamole affects the expression of plasminogen activator and procoagulant activities by rabbit alveolar macrophages cultured in vitro. We found that dipyridamole (10 to 100 mumol/L) caused increases in both cell-associated and released plasminogen activator activity, which reached levels of 240% (P less than .05) and 543% (P less than .01) of controls, respectively. In contrast, dipyridamole decreased the cell-associated procoagulant activity of alveolar macrophages to as little as 21.3% of controls (P less than .01). Similar effects were seen in cells cotreated with lymphokines. The procoagulant activity expressed by these cells functioned as a tissue thromboplastin. The plasminogen activator of control and treated cells was a urokinase as determined by molecular weight characteristics (50 kilodaltons) and by antibody neutralization profiles using polyclonal antibodies against human urokinase and tissue plasminogen activator. These effects of dipyridamole could not be duplicated by structurally dissimilar agents sharing some of the pharmacological actions of dipyridamole; however, two pyrimidopyrimidine compounds structurally similar to dipyridamole effectively mimicked the effects on both procoagulant and plasminogen activator activities. We conclude that dipyridamole may have antithrombotic effects by directly modulating the role of mononuclear phagocytes in fibrin turnover. Thus, dipyridamole may be useful in situations where extravascular fibrin deposition is important to the pathogenesis of tissue injury and repair.

Dipyridamole Stimulates Urokinase Production and Suppresses Procoagulant Activity of Rabbit Alveolar Macrophages: A Possible Mechanism of Antithrombotic Action

Abstract Dipyridamole, an inhibitor of platelet aggregation, has been shown to have beneficial effects in disorders characterized by extravascular fibrin deposition. Mononuclear phagocytes are present in extravascular sites and are capable of expressing both plasminogen activator and procoagulant activities, which suggests these cells play a central role in extravascular fibrin turnover. We therefore sought to determine whether dipyridamole affects the expression of plasminogen activator and procoagulant activities by rabbit alveolar macrophages cultured in vitro. We found that dipyridamole (10 to 100 mumol/L) caused increases in both cell-associated and released plasminogen activator activity, which reached levels of 240% (P less than .05) and 543% (P less than .01) of controls, respectively. In contrast, dipyridamole decreased the cell-associated procoagulant activity of alveolar macrophages to as little as 21.3% of controls (P less than .01). Similar effects were seen in cells cotreated with lymphokines. The procoagulant activity expressed by these cells functioned as a tissue thromboplastin. The plasminogen activator of control and treated cells was a urokinase as determined by molecular weight characteristics (50 kilodaltons) and by antibody neutralization profiles using polyclonal antibodies against human urokinase and tissue plasminogen activator. These effects of dipyridamole could not be duplicated by structurally dissimilar agents sharing some of the pharmacological actions of dipyridamole; however, two pyrimidopyrimidine compounds structurally similar to dipyridamole effectively mimicked the effects on both procoagulant and plasminogen activator activities. We conclude that dipyridamole may have antithrombotic effects by directly modulating the role of mononuclear phagocytes in fibrin turnover. Thus, dipyridamole may be useful in situations where extravascular fibrin deposition is important to the pathogenesis of tissue injury and repair.

Antibody and immune complexes induce tissue factor production by human endothelial cells.

Patients with systemic lupus erythematosus (SLE) have an increased incidence of arterial and venous thromboses. The mechanism by which thromboses develop in these patients is unknown. We had previously observed that the sera of patients with SLE contain antibodies and immune complexes that can bind to endothelial cells. Because endothelial cells can synthesize tissue factor, a potent activator of coagulation, we studied the effect of IgG complexes and sera from patients with SLE on the production of tissue factor by these cells. Human umbilical venous endothelial cells incubated with heat-aggregated IgG (HA-IgG) (0.5 to 4.0 mg) elaborate procoagulant activity in a dose-dependent manner. All procoagulant activity was found in the particulate cell fraction, and none was secreted into the medium. Maximum expression of procoagulant activity required 6 to 8 hr, and its production was totally inhibited by the addition of cyclohexamide or actinomycin D. The presence of gel-filtered platelets augmented production of procoagulant activity by endothelial cells stimulated by HA-IgG. Endothelial cell procoagulant activity was not inactivated by diisofluoropropylphosphate, required the presence of Factor VII for its expression, and was neutralized by a specific anti-tissue factor antibody. Endothelial cells incubated with sera from 14 of 16 patients with SLE produced increased amounts of tissue factor compared with 21 normal sera (p less than 0.025). Fractions of two SLE sera containing monomeric IgG, IgA, or IgM, as well as fractions containing IgG complexes, each stimulated endothelial cells to produce more tissue factor than similar fractions prepared from two normal sera. These studies demonstrate that endothelial cells will produce the procoagulant tissue factor after exposure to anti-endothelial cell antibodies or IgG-containing immune complexes. The production of tissue factor by endothelial cells at sites of immune vascular injury may play a role in the development of thromboses in patients with SLE.

Production and characterization of a monoclonal antibody (A1-3) that binds selectively to activated monocytes and inhibits monocyte procoagulant activity.

We describe the generation and characterization of a new monoclonal antibody, A1-3, which possesses two unique properties. First, A1-3 binds selectively to stimulated human monocytes. Secondly, A1-3 inhibits the procoagulant activity expressed by stimulated monocytes and by human brain tissue factor. Unstimulated human peripheral blood cells (granulocytes, lymphocytes, monocytes, red blood cells, and platelets), prepared in the absence of detectable endotoxin, express no procoagulant activity and fail to bind A1-3. Stimulation of peripheral blood monocytes. alveolar macrophages, or the monocyte-like cell line U937, however, results in the expression of procoagulant activity and the binding of A1-3. The surface antigen recognized by A1-3 was recovered from endotoxin-stimulated human monocyte vesicles by immune precipitation and demonstrated an apparent m.w. of approximately 52,000. It is proposed that the monoclonal antibody A1-3 detects a differentiation antigen on human monocytes that is expressed in response to stimuli for monocyte activation.

Tissue factor induction in human monocytes. Two distinct mechanisms displayed by different alloantigen-responsive T cell clones.

One component of the cellular immune response to antigens is the expression of procoagulant activity (PCA) by monocytes and macrophages. Induction of human monocyte PCA in response to alloantigenic stimulation requires the collaboration of HLA-DR-responsive T cells. In mixed lymphocyte cultures (MLCs), the induction of monocyte tissue factor appears to be mediated exclusively by a T cell-derived lymphokine. We have used a soft agar cloning method to generate alloantigen-responsive T cell clones from MLCs between irradiated Daudi lymphoblastoid cells and human peripheral blood mononuclear cells. Developing clones were screened for the ability to induce PCA in fresh autologous monocytes in response to Daudi stimulator cells. PCA induction was observed with some, but not all, proliferating T cell clones and two modes of induction were apparent. Some T cell clones mediated PCA induction exclusively by lymphokine production, whereas other clones delivered induction signals by direct cellular collaboration with the monocyte effector cells. These two inductive pathways were represented in distinct, non-inclusive functional subsets of T cell clones. Constitutive production of soluble inducer signals was not observed in T inducer clones. The magnitude of the monocyte PCA response increased in response to an increase in the allogeneic stimulator/T clone responder ratio, and third-party allogeneic cells were unable to elicit the PCA-inducing lymphokine signals from T inducer clones. Both modes of induction were shown to generate tissue factor protein activity in monocytes. Collectively, these results suggest that PCA induction can be initiated in response to alloantigens through collaboration with certain OKT3+, OKT4+, OKT8-, OKM1- T inducer clones, and that induction can be mediated by at least two different functional subsets of human T cells. Stimulation with the appropriate alloantigen may elicit both lymphokine and T cell-contact pathways of induction of tissue factor in human monocytes.

The immune response to mouse hepatitis virus: expression of monocyte procoagulant activity and plasminogen activator during infection in vivo.

After infection with 10(3) plaque-forming units of mouse hepatitis virus strain 3 (MHV-3) in vivo, peripheral blood mononuclear cells and splenic cells expressed procoagulant activity (PCA) in a pattern directly correlating with susceptibility to disease. Mononuclear cells from BALB/cJ mice, a strain which is fully susceptible to MHV-3, expressed a greater than 500-fold increase in PCA. PCA was first detected within 12 hr of infection; prior to histologic evidence of disease and viral replication, it reached maximal levels 48 hr post-infection (p.i.) and persisted until the death of the animals 5 to 7 days p.i. Mononuclear cells from C3HeB/FeJ mice expressed a significant but lesser titer of PCA, with elevated PCA persisting throughout the chronically infected state until death of the animals 4 to 6 mo p.i. Basal levels of PCA were detected in mononuclear cells from fully resistant A/J mice despite the presence of large amounts of virus in livers, spleens, and sera from these animals. When mononuclear cells expressing high PCA were subfractionated, monocytes were found to be the cellular source of greater than 96% of the PCA activity. Increased plasminogen activator activity was found in monocytes from resistant A/J mice at the time when PCA was markedly elevated in BALB/cJ and C3HeB/FeJ mice. This activity persisted for 5 to 7 days p.i., but was undetectable 10 days p.i. at a time when the mice had cleared the virus from their blood streams. These observations suggest that monocyte PCA may be important in the pathogenesis of MHV-3 disease, whereas the production of monocyte plasminogen activators may contribute to resistance of A/J mice to MHV-3-induced liver disease.

Macrophage-induced glomerular fibrin deposition in experimental glomerulonephritis in the rabbit.

Glomerular fibrin deposition is important in the pathogenesis of renal failure and crescent formation in glomerulonephritis. The mechanisms of glomerular fibrin deposition are unknown. The current studies explored the role of macrophages in this process. Methods were developed for measuring glomerular fibrin deposition and glomerular procoagulant activity in a passive model of the autologous phase of antiglomerular basement membrane antibody-induced glomerulonephritis in rabbits. Significant fibrin deposition was observed to be associated with glomerular macrophage accumulation. Leukocyte ablation with mustine hydrochloride prevented both glomerular macrophage accumulation and fibrin deposition without affecting the coagulation system or the deposition of disease-inducing antibodies and complement. Repletion with mononuclear inflammatory cells produced significant fibrin deposition. To examine the role of tissue injury per se in glomerular fibrin deposition, a macrophage-independent model of glomerular injury (heterologous phase glomerulonephritis) was also studied. Although a similar degree of glomerular injury occurred, there was no significant fibrin deposition. This suggests that macrophages, rather than injury alone, are responsible for fibrin deposition. Lysates of isolated glomeruli containing macrophages demonstrated greatly enhanced procoagulant activity compared with lysates of glomeruli without macrophages. Thus macrophages appear to be directly responsible for glomerular fibrin deposition in antiglomerular basement membrane antibody-induced glomerulonephritis, and this appears to be due to their ability to express procoagulant activity rather than their propensity to cause glomerular injury.

Antigen-induced monocyte procoagulant activity. Requirement for antigen presentation and histocompatibility leukocyte antigen-DR molecules.

The present study explores the interactions between lymphocytes and monocytes that are required for expression of procoagulant activity (PCA) by monocytes in response to purified protein derivative of the tubercle bacillus (PPD) or tularemia antigen. The PCA response was antigen specific: peripheral blood mononuclear cells (PBM) from donors sensitive to PPD or tularemia showed an increase in PCA only in response to the sensitizing antigen. The PCA was tissue factorlike in that Factors VII and X were required for expression of the activity, whereas Factor VIII was not. Maximum PCA developed only after 36 to 72 h. Fractionation of PBM into lymphocytes and monocytes after antigenic stimulation demonstrated that greater than 90% of the PCA was associated with monocytes. Isolated monocytes or lymphocytes incubated with sensitizing antigen had the same PCA as control cells. Purified lymphocytes that had been pulsed with antigen were unable to elicit a PCA response from monocytes to which they were added. However, adherent monocytes incubated with antigen, then washed free of unbound protein, were able to trigger lymphocytes to become stimulatory for PCA toward responding monocytes. The development of antigen-specific PCA in PBM could be blocked by including a monoclonal antibody to HLA-DR antigen in the incubation. The antibody had no effect on the clotting assay, on preformed PCA, cell viability, or on stimulatory antigen itself. These results indicate that elaboration of PCA by mononuclear cells may be an intrinsic part of the classical immune response to antigen, and may explain the presence of fibrin in immune lesions, as well as the occurrence of thrombotic complications in many immune disorders.

Studies on rat mammary adenocarcinomas: a model for metastasis.

Studies carried out by the authors on the rat mammary adenocarcinoma cell lines MAT 13762 and DMBA-8 are summarized. A series of variants and somatic cell hybrids have been prepared and partially characterized in terms of phenotypic properties which may correlate with metastatic potential. These include measurement of in vitro migration, lectin binding properties, expression of procoagulant activity and shedding of cell surface components. Particular emphasis has been placed on the production of enzymically-active plasminogen activator, as this seems to correlate with the ability of cells to metastasize. The finding has also been made that several of the cell types studied produce, in vitro, an inhibitor of plasminogen activator which may influence the metastatic behaviour of tumor cells. Results obtained are discussed in the context of the usefulness of these tumor systems for the study of spontaneous and experimental metastasis and the factors involved in these processes. Preliminary results of cloning and fluctuation analysis of metastatic potential together with discussion of the role of the metastatic heterogeneity and the formation of metastatic variants by mutation events are included.

Interleukin 1 (IL-1) induces biosynthesis and cell surface expression of procoagulant activity in human vascular endothelial cells.

Human monocyte-derived interleukin 1 (IL-1) was found to be a potent inducer of procoagulant activity in cultured human vascular endothelium. IL-1-induced human umbilical vein endothelial cell procoagulant activity (HEC-PCA) was transiently expressed, manifest in intact cell monolayers, and required protein synthesis. Data obtained with coagulation factor-deficient plasma and a goat anti-human apoprotein III antiserum suggested that most, if not all, of IL-1-induced endothelial cell procoagulant activity is tissue factor-like. IL-1 induction of HEC-PCA may be important in the pathogenesis of intravascular coagulation in a variety of immunological and inflammatory conditions.