Tissue Factor-Negative Cell-Derived Microparticles Play a Distinctive Role in Hemostasis: A Viewpoint Review.

Circulating cell-derived microparticles (MPs) exhibit procoagulant activity and have been investigated for a possible role in some human pathologies. However, their potential role in hemostasis has been neglected and often denied. This review brings to attention a specific body of direct clinical evidence supporting an important but distinctive role of MPs in hemostasis. Evidence for a role of MPs in hemostasis includes: (1) two congenital bleeding disorders attributed to impaired release of MPs; (2) two recent studies of trauma patients relating naturally elevated endogenous MPs at admission to reduced transfusion requirements and better outcomes; (3) a study of coronary surgery patients showing that elevated MP before surgery reduces transfusion requirements during surgery; and (4) a clinical study of patients with immune thrombocytopenia demonstrating that those with high circulating MP have reduced bleeding compared to patients with similar platelet counts but lower MP levels. Mechanisms involving potentiating the contact factor pathway are thought to play a key role and are probably synergistic with polyphosphate released from activated platelets at sites of endothelial injury. Hemostatic defect of patients with deficient MP-mediated coagulation resembles deficiency of FXI (hemophilia C), distinct from hemophilia A or B, so can be termed type C hemostasis. A better understanding of this proposed hemostatic pathway may lead to improved methods for controlling excessive bleeding in surgery, trauma, and other clinical settings.

Presurgical levels of circulating cell-derived microparticles discriminate between patients with and without transfusion in coronary artery bypass graft surgery.

OBJECTIVES: Improved understanding of presurgical risk factors for transfusions will lead to reduction in their number and related complications. The goal of this study is to identify these factors in coronary artery bypass graft (CABG) surgery. METHODS: Presented herein are results of analyses of data from an ongoing study of transfusion in CABG surgery. Of 122 patients, 81 received transfusion (Tx) and 41 did not (NoTx). In addition to routine tests, presurgical levels of microparticles from platelets (PMPs), red cells (RMPs), and other lineages were assayed. RESULTS: The Tx and NoTx groups were similar with respect to most presurgical variables but differed in distribution of gender, blood type, diabetes prevalence, activated partial thromboplastin time (aPTT), hemoglobin (HGB), and microparticle levels. Stepwise multiple logistic regression was used to evaluate presurgical variables and to develop a model to assess risk factors for transfusion. CD41(+) PMP and CD235(+) RMP levels were found to be the main risk factors for transfusion. The Model's discriminating ability was assessed using receiver operating characteristic curve analysis, which showed that the area under the model curve (± standard error) was 0.86 ± 0.04 (95% confidence interval, 0.77-0.94). According to the model, patients with higher presurgical levels of circulating CD41(+) PMP, CD235a(+) RMP, and HGB, as well as a shorter aPTT, are less likely to receive transfusion(s). CONCLUSIONS: Presurgical levels of CD41(+) PMPs and CD235a(+) RMPs are the main risk factors for transfusion in CABG, followed by HGB and aPTT.

Red cell-derived microparticles (RMP) as haemostatic agent.

Among circulating cell-derived microparticles, those derived from red cells (RMP) have been least well investigated. To exploit potential haemostatic benefit of RMP, we developed a method of producing them in quantity, and here report on their haemostatic properties. High-pressure extrusion of washed RBC was employed to generate RMP. RMP were identified and enumerated by flow cytometry. Their size distribution was assessed by Doppler electrophoretic light scattering analysis (DELSA). Interaction with platelets was studied by platelet aggregometry, and shear-dependent adhesion by Diamed IMPACT-R. Thrombin generation and tissue factor (TF) expression was also measured. The effect of RMP on blood samples of patients with bleeding disorders was investigated ex vivo by thromboelastography (TEG). Haemostatic efficacy in vivo was assessed by measuring reduction of blood loss and bleeding time in rats and rabbits. RMP have mean diameter of 0.45 µm and 50% of them exhibit annexin V binding, a proxy for procoagulant phospholipids (PL). No TF could be detected by flow cytometry. At saturating concentrations of MPs, RMP generated thrombin robustly but after longer delay compared to PMP and EMP. RMP enhanced platelet adhesion and aggregation induced by low-dose ADP or AA. In TEG study, RMP corrected or improved haemostatic defects in blood of patients with platelet and coagulation disorders. RMP reduced bleeding time and blood loss in thrombocytopenic rabbits (busulfan-treated) and in Plavix-treated rats. In conclusion, RMP has broad haemostatic activity, enhancing both primary (platelet) and secondary (coagulation) haemostasis, suggesting potential use as haemostatic agent for treatment of bleeding.

Complement in neurobiology.

The complement (C) system is a vital arm of innate immunity with many roles, including control of inflammation. This article examines the (C) system with emphasis on recent developments on complement relevant to neurobiology, in particular regarding our understanding and treatment of immune-mediated diseases. We will briefly outline the C system, and provide an updated review of its many receptors and regulatory factors. This section concludes with a listing of important roles of the C system, from recruitment of neural stem/progenitor cells, to its' relation to coagulation and adaptive immunity, and its lesser-known but beneficial roles in physiology. We also review evidence for C-mediated diseases, which include multiple sclerosis and Alzheimer's disease. Therapeutic approaches for C-mediated diseases, considers emphasizing modulators of the C system including several less widely studied approaches such as heparinoids, vitamin D, and intravenous IgM. Finally, we summarize cutting-edge work on the role of C-mediated natural antibodies in autoimmunity and treatment strategies based on those findings, e.g., for remyelination and post-ischemic stroke repair. Improved understanding of the C system may hold great promise for the treatment of neurodegenerative diseases.

Microparticle size and its relation to composition, functional activity, and clinical significance.

It is emerging that cell-derived microparticles (MP) have multiple functional activities in areas including hemostasis, thrombosis, inflammation, and as messengers in the transport of bioactive lipids, cytokines, complement, and immune signaling. Some of these activities may be performed by distinct phenotypic subsets of MP, even if derived from the same cell type. The focus of this article concerns the size classes of MP, covering methods of MP size measurement, differences in composition between size classes, and relation of size to functional (procoagulant) activity. Some of the issues considered remain to be resolved, such as whether the MP known as exosomes are truly a distinct class of MP, as well as the detailed mechanisms underlying the release of MP of different size ranges.

Role of platelets in neuroinflammation: a wide-angle perspective.

OBJECTIVES: This review summarizes recent developments in platelet biology relevant to neuroinflammatory disorders. Multiple sclerosis (MS) is taken as the "Poster Child" of these disorders but the implications are wide. The role of platelets in inflammation is well appreciated in the cardiovascular and cancer research communities but appears to be relatively neglected in neurological research. ORGANIZATION: After a brief introduction to platelets, topics covered include the matrix metalloproteinases, platelet chemokines, cytokines and growth factors, the recent finding of platelet PPAR receptors and Toll-like receptors, complement, bioactive lipids, and other agents/functions likely to be relevant in neuroinflammatory diseases. Each section cites literature linking the topic to areas of active research in MS or other disorders, including especially Alzheimer's disease. CONCLUSION: The final section summarizes evidence of platelet involvement in MS. The general conclusion is that platelets may be key players in MS and related disorders, and warrant more attention in neurological research.

Potential roles of cell-derived microparticles in ischemic brain disease.

PURPOSE: The objective of this study is to review the role of cell-derived microparticles in ischemic cerebrovascular diseases. MATERIALS AND METHODS: An extensive PubMed search of literature pertaining to this study was performed in April 2009 using specific keyword search terms related to cell-derived microparticles and ischemic stroke. Some references are not cited here as it is not possible to be all inclusive or due to space limitation. DISCUSSION: Cell-derived microparticles are small membranous vesicles released from the plasma membranes of platelets, leukocytes, red cells and endothelial cells in response to diverse biochemical agents or mechanical stresses. They are the main carriers of circulating tissue factor, the principal initiator of intravascular thrombosis, and are implicated in a variety of thrombotic and inflammatory disorders. This review outlines evidence suggesting that cell-derived microparticles are involved predominantly with microvascular, as opposed to macrovascular, thrombosis. More specifically, cell-derived microparticles may substantially contribute to ischemic brain disease in several settings, as well as to neuroinflammatory conditions. CONCLUSION: If further work confirms this hypothesis, novel therapeutic strategies for minimizing cell-derived microparticles-mediated ischemia are available or can be developed, as discussed.

Antiphospholipid antibodies: paradigm in transition.

OBJECTIVES: This is a critical review of anti-phospholipid antibodies (aPL). Most prior reviews focus on the aPL syndrome (APS), a thrombotic condition often marked by neurological disturbance. We bring to attention recent evidence that aPL may be equally relevant to non-thrombotic autoimmune conditions, notably, multiple sclerosis and ITP. ORGANIZATION: After a brief history, the recent proliferation of aPL target antigens is reviewed. The implication is that many more exist. Theories of aPL in thrombosis are then reviewed, concluding that all have merit but that aPL may have more diverse pathological consequences than now recognized. Next, conflicting results are explained by methodological differences. The lupus anticoagulant (LA) is then discussed. LA is the best predictor of thrombosis, but why this is true is not settled. Finally, aPL in non-thrombotic disorders is reviewed. CONCLUSION: The current paradigm of aPL holds that they are important in thrombosis, but they may have much wider clinical significance, possibly of special interest in neurology.

Evidence of platelet activation in multiple sclerosis.

OBJECTIVE: A fatality in one multiple sclerosis (MS) patient due to acute idiopathic thrombocytopenic purpura (ITP) and a near fatality in another stimulated our interest in platelet function abnormalities in MS. Previously, we presented evidence of platelet activation in a small cohort of treatment-naive MS patients. METHODS: In this report, 92 normal controls and 33 stable, untreated MS patients were studied. Platelet counts, measures of platelet activation [plasma platelet microparticles (PMP), P-selectin expression (CD62p), circulating platelet microaggragtes (PAg)], as well as platelet-associated IgG/IgM, were carried out. In addition, plasma protein S activity was measured. RESULTS: Compared to controls, PMP were significantly elevated in MS (p < 0.001) and CD62p expression was also markedly elevated (p < 0.001). Both are markers of platelet activation. Platelet-associated IgM, but not IgG, was marginally elevated in MS (p = 0.01). Protein S in MS patients did not differ significantly from normal values. CONCLUSION: Platelets are significantly activated in MS patients. The mechanisms underlying this activation and its significance to MS are unknown. Additional study of platelet activation and function in MS patients is warranted.

Transendothelial migration of leukocytes is promoted by plasma from a subgroup of immune thrombocytopenic purpura patients with small-vessel ischemic brain disease.

We previously described a subgroup of immune thrombocytopenic purpura (ITP) patients presenting with recurring transient ischemic attack-like symptoms and progressive cognitive impairment due to small vessel disease (SVD) seen in the brain. They presented minimal bleeding despite thrombocytopenia, and platelet activation was elevated compared to classic ITP. On the hypothesis that the blood-brain barrier (BBB) is compromised in this subgroup, we investigated the effect of plasma from SVD-ITP patients on the transendothelial migration of leukocytes (TEML). Brain microvascular endothelial cells (BMVEC) were grown to confluence on 6.5-microm pore filters and plasma from 10 healthy controls, 20 classic ITP, and 5 SVD-ITP were added and incubated 24 hr. Then 1 x 10(5) monocytes (U937) were added and the number migrated through the EC monolayer after 6 hr was measured by flow cytometry. The effect on TEML of danazol was also assessed. We found that plasma from SVD-ITP but not classic ITP induced 10-fold rise in EC activation marker CD62E and a sevenfold increase in TEML, to 38.5% +/- 12.5% of cells migrated, compared to normal controls (5.6% +/- 1.2%) or classic ITP (6.1% +/- 0.2%), P < 0.001. Preincubation of U937 with endothelial microparticles (EMP) increased TEML by 20.0% +/- 6.4% with SVD-ITP plasma, significantly more than with classic ITP or control plasmas, P = 0.003. Pretreatment of cultures with danazol (100 microg/mL) inhibited TEML by 25% in all wells tested, whether or not EMP were added. In summary, SVD-ITP plasma activates EC and augments TEML, suggesting plasma-mediated BBB dysfunction in this syndrome. Danazol modestly but significantly inhibited TEML.

Clinical and neuroimaging correlates of antiphospholipid antibodies in multiple sclerosis: a preliminary study.

BACKGROUND: The presence of antiphospholipid antibodies (APLA) in multiple sclerosis (MS) patients has been reported frequently but no clear relationship between APLA and the clinical and neuroimaging features of MS have heretofore been shown. We assessed the clinical and neuroimaging features of MS patients with plasma APLA. METHODS: A consecutive cohort of 24 subjects with relapsing-remitting (RR) MS were studied of whom 7 were in remission (Rem) and 17 in exacerbation (Exc). All subjects were examined and underwent MRI of brain. Patients' plasma was tested by standard ELISA for the presence of both IgM and IgG antibodies using a panel of 6 targets: cardiolipin (CL), beta2 glycoprotein I (beta2GPI), Factor VII/VIIa (FVIIa), phosphatidylcholine (PC), phosphatidylserine (PS) and phosphatidylethanolamine (PE). RESULTS: In exacerbation up to 80% of MS subjects had elevated titers of IgM antibodies directed against the above antigens. However, in remission, less than half of MS patients had elevated titers of IgM antibodies against one or more of the above antigens. This difference was significant, p < 0.01, for all 6 target antigens. Interestingly, none of the MS patients had elevated plasma titers of IgG against any of the target antigens tested. Correlation analysis between MRI enhancing lesions and plasma levels of APLA revealed high correlation for aPC, aPS and aFVIIa (p

Platelet activation rather than endothelial injury identifies risk of thrombosis in subjects positive for antiphospholipid antibodies.

BACKGROUND: Anti-phospholipid antibodies (APLA) are often associated with thrombosis, defining the antiphospholipid syndrome (APS) but it remains unclear why many subjects who are positive for APLA chiefly anti-cardiolipin (aCL) or anti-beta2GPI (abeta2GPI) do not develop thrombosis. A related question addressed in this study is whether the target of cellular injury in APS is predominately platelets or endothelial cells (EC). METHODS: aCL and abeta2GPI were determined by ELISA in 88 patients, 60 of whom were thrombotic and 28 non-thrombotic. Platelet activation was measured by CD62P and by concentration of platelet microparticles (PMP) and EC activation was assessed by endothelial microparticles (EMP), both by flow cytometry. Lupus anticoagulant (LAC) was measured in the hospital laboratory. RESULTS: There was no difference in frequency of aCL or abeta2GPI, neither IgG or IgM, between the thrombotic and non-thrombotic groups. Both groups showed elevated EMP compared to controls but this did not differ between thrombotic and non-thrombotic groups. In contrast, PMP were not significantly elevated in non-thrombotic but were elevated in thrombotic compared to non-thrombotic (p=0.03) and controls. CD62P, an independent marker of platelet activation, was also elevated in thrombotic vs. non-thrombotic. There was a trend for increased LAC in the thrombotic group but not significant. CONCLUSION: Although all subjects had evidence of endothelial activation, only platelet activation differed between thrombotic and non-thrombotic. This supports the hypothesis that platelet activation predisposes to thrombosis in the presence of chronic EC activation. These data also raise the possibility of distinguishing risk-prone APLA-positive individuals.

Cell-derived microparticles and exosomes in neuroinflammatory disorders.

All blood cells and the vascular endothelium shed microparticles (MP) from their plasma membranes when suitably stimulated, and assay of MP in patient blood has found increasing application to the monitoring of disease states. In addition, mounting evidence suggests that MP are not mere epiphenomena but play significant roles in the pathophysiology of thromboses, inflammation, and cancers. This chapter endeavors to summarize the limited number of studies thus far done on MP in neurological disorders such as multiple sclerosis (MS), transient ischemic attacks, and the neurological manifestations of antiphospholipid syndrome (APS). In addition, the chapter offers some plausible hypotheses on possible roles of MP in the pathophsyiology of these disorders, chiefly, the hypothesis that MP are indeed important participants in some neuropathologies, especially those which are ischemic in nature, but probably also inflammatory ones. The chapter also goes over the history and general principles of MP studies (e.g., assay methods and pitfalls), comparison with alternative methods (e.g., soluble markers of disease states), subclasses of MP (such as exosomes), and other topics aimed at helping readers to consider MP studies in their own clinical fields. Tables include a listing of bioactive agents known to be carried on MP, many of which were heretofore considered strictly soluble, and some of which can be transferred from cell to cell via MP vectors, for example certain cytokine receptors.

Interstitial lung disease (ILD) and severe ITP.

INTRODUCTION: Platelets play an important role in inflammatory and immune responses. We report interstitial lung disease (ILD) developing during the acute phase of severe thrombocytopenia in 3 patients with severe refractory ITP. METHODS AND RESULTS: We identified 3 cases with severe ITP who developed ILD in the course of refractory chronic ITP. The thrombocytopenia was severe in all cases. ILD was an incidental finding at the presentation and often misdiagnosed as lung infections. ILD was documented by lung biopsy in cases 1 and 2, supplemented by serial chest X-rays and/or CAT scan. As the ITP improved, ILD regressed in case 1, persisted in case 2, and progressed to advanced pulmonary fibrosis in case 3. CONCLUSION: We report an association of ILD with severe refractory ITP. ILD was detected in acute phase of platelet destruction, suggesting that platelet destruction may have triggered inflammation in the lung, leading to ILD.

Antiphospholipid antibodies (APLA) in immune thrombocytopenic purpura (ITP) and antiphospholipid syndrome (APS).

Antiphospholipid antibodies (APLA) are associated with anti-phospholipid syndrome (APS), a thrombotic disorder, but they are also frequently detected in immune thrombocytopenic purpura (ITP), a bleeding disorder. To investigate possible differences of APLA between these two disorders, we assayed IgG and IgM APLA by ELISA in 21 patients with ITP and 33 with APS. The APLA reacting against two protein target antigens, beta(2)-glycoprotein 1 (beta2GP1) and FVII/VIIa, and four phospholipids [cardiolipin (CL), phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylethanolamine (PE)] as well as lupus anticoagulant (LA) were analyzed. We made the following observations: (i) IgG and IgM antibodies to beta2GP1 and IgM antibodies to FVII/VIIa were more common in APS than ITP, P < 0.05, while IgG antibodies against the phospholipids (aCL, aPC, aPS, aPE) were more common in ITP than APS, P < 0.05; (ii) multiple APLA > or =3 antigens) were more frequent in APS than ITP, P < 0.05; (iii) LA was frequently associated with APS but was absent in ITP; (iv) APLA is quite common in ITP: two-thirds were positive for at least one APLA. In summary, APLA are prevalent in ITP but their profile differs from APS. In APS, antibodies were predominantly against beta2GP1 and 80% had positive LA, while in ITP the APLA reacted most often with the phospholipids without LA. The difference in APLA may result in opposite clinical manifestations in two disorders.

Antiphospholipid antibodies and platelet activation as risk factors for thrombosis in thrombocythaemia.

INTRODUCTION: Risk factors for thrombosis (TB) in thrombocythaemia (TC) associated with myeloproliferative disorder (MPD) are not well defined. METHODS: We measured antiphospholipid antibodies (APLA) in 35 patients with TC associated with MPD. Fourteen had TB and 21 did not. We assayed IgG and IgM APLA by ELISA for 6 antigens: beta2GP1, cardiolipin (CL), phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylethanolamine (PE) and FVII/VIIa, together with markers of activation of platelets (CD62P) and endothelium [endothelial microparticles (EMP)]. RESULTS: At least one positive APLA was detected in 66% of TC patients overall. The incidence was significantly higher in the TB subgroup (92.8%) than non-TB (47.6%, p < 0.05). Multiple APLA (positive for more than one antigen) were also more frequent in TB, for both IgG and IgM, for all 6 antigens tested (p < 0.05). However, IgM APLA predominated, being about 2-fold more frequently positive than IgG for all 6 antigens. Platelet CD62P was significantly higher in the TB group (p < 0.05). EMP did not differ between TB and non-TB. The most frequent thrombotic complication was recurring ischemic cerebral vascular accidents (ICVA), leading to progressive cognitive impairment. Venous TB often developed at unusual sites. Recurring and reversible TB were common features in TC. SUMMARY: This study suggests that APLA and platelet activation are risk factors for TB in TC. APLA are prevalent in TC, and IgM APLA predominated over IgG. Activation of platelets but not of endothelium may be consistent with the reversible and recurrent features of TB in TC.

Levels of endothelial and platelet microparticles and their interactions with leukocytes negatively correlate with organ dysfunction and predict mortality in severe sepsis.

OBJECTIVE: Mortality in sepsis is believed to be associated with exaggerated inflammatory responses, but recent evidence suggests that poor outcome is associated with reduced inflammation. To test this hypothesis, we measured several inflammatory markers to determine whether any of them or any combinations are associated with mortality or organ dysfunction. DESIGN: Clinical study. SETTING: School of medicine. PATIENTS: Thirty-five patients with severe sepsis. INTERVENTIONS: Markers of endothelial, platelet, and leukocyte activation were measured on days 1, 2, and 3 after enrollment. The markers were a) endothelial microparticles (EMPs) and their conjugates with monocytes (EMP/MONO); b) platelet microparticles (PMPs) and platelet activation marker CD62P; c) platelet-leukocyte conjugates (PLT/LEU) and leukocyte activation marker CD11b; and d) intracellular nitric oxide in leukocytes. MEASUREMENTS AND MAIN RESULTS: The 28-day mortality rate was 51% (18 of 35). Significant differences between survivors and nonsurvivors on day 1 were found in PLT/LEU (p = .001), CD11b (p = 0.02), and EMP/MONO (p = .02) groups. Using logistic regression to assess if these markers predict mortality on day 1, we found that PLT/LEU had the best predictive value among the markers used (area under receiver operating characteristics curve = 0.82). All markers of cell activation and inflammation were significantly higher among survivors on days 2 and 3, except nitric oxide, which was lower. This marker showed significant negative correlation with the Sequential Organ Failure Assessment score throughout the study. CONCLUSIONS: Our data support the hypothesis that early increased, not decreased, inflammatory response as measured by our markers is associated with improved survival rate. A high negative correlation was found between some of these markers and Sequential Organ Failure Assessment score.

Life-threatening hypercoagulable state following splenectomy in ITP: successful management with aggressive antithrombotic therapy and danazol.

A life-threatening hypercoagulable state (HCS) is reported that developed after splenectomy in idiopathic thrombocytopenic purpura (ITP). A 50-year-old active male was rejected for blood donation because of an incidental finding of low platelet counts, 40,000/uL. The diagnosis was ITP. Although asymptomatic, he underwent splenectomy because of poor response to steroids and intravenous (IV) gamma globulin. One month after splenectomy, he suffered pulmonary emboli without deep venous embolism (DVT), followed by bilateral DVT, threatening amputation of the legs. Emergency thrombolysis, insertion of stent, and IV heparin saved his legs. Extensive workup for HCS was negative. IV heparin was withheld for colonoscopy for possible gastrointestinal neoplasm, at which time DVT recurred, necessitating another thrombolysis and heparin infusion. He was discharged on enoxaparin, antiplatelet therapy, and danazol. Platelet hyperactivation, characterized by high platelet microparticles (PMP) and CD62P, was present throughout his course of active ITP, resolving when ITP went into remission with danazol therapy. ITP has remained in remission for 4 years after stopping enoxaparin and danazol. In vitro, his plasma in active ITP induced activation of normal platelets, generating PMP and inducing CD62p-positive platelets and platelet aggregates; his plasma from remission had no effect. This indicates the presence of a platelet activating factor, possibly anti-platelet antibodies. Splenectomy may have allowed procoagulant PMP to accumulate to high levels resulting in HCS. We advise awareness of thrombotic complications post-splenectomy in the subset of ITP patients who are largely asymptomatic and exhibit persisting platelet activation.

Elevated endothelial microparticle-monocyte complexes induced by multiple sclerosis plasma and the inhibitory effects of interferon-beta 1b on release of endothelial microparticles, formation and transendothelial migration of monocyte-endothelial microparticle complexes.

Monocyte migration through the disrupted cerebral endothelial cell (EC) junctions plays an essential role in formation of multiple sclerosis (MS) demyelinating lesions. During pathogenesis of MS, activated ECs release endothelial microparticles (EMP), which possibly facilitate transendothelial migration (TEMIG) of monocytes. To assess functional roles of EMP in MS, specifically, their (i) interaction with monocytes, (ii) effect on monocyte TEMIG in an in vitro model of the brain microvascular endothelial cells (BMVEC), (iii) phenotypic profiles of EMP elicited by MS plasma and (iv) the effects of IFN-beta 1b on release of EMP and on TEMIG of monocytes (mono) and monocytes:EMP complexes (mono:EMP) through the BMVEC. The effect of IFN-beta 1b on the release of EMP and the TEMIG of mono and mono:EMP was assessed by preincubating BMVEC cultures of IFN-beta 1b prior to addition of plasma. Three EMP phenotypes, CD54, CD62E and CD31 were assayed. Plasma specimens from 20 patients with relapsing remitting MS (11 in exacerbation, MS-E, and 9 in remission, ME-R) and 10 healthy controls were studied. Incubation of BMVEC with MS-E plasma yielded elevated levels of EMPCD54, EMP62E and EMPCD31 relative to MS-R and control plasmas. MS-E but not MS-R or control plasma also augmented TEMIG of monocytes, respectively. Mono:EMP complexes further augmented TEMIG relative to mono alone, but only in the presence of MS-E plasma; there was no significant effect with MS-R or control plasmas. The presence of IFN-beta 1b inhibited TEMIG of mono and mono:EMP by 20% and 30%, respectively. MS-E but not MS-R plasma elicited release of activation-derived EMP and enhanced TEMIG of mono and mono:EMP. IFN-beta 1b inhibited TEMIG and release of EMP, suggesting a role of EMP and a novel therapeutic mechanism for IFN-beta 1b in MS.