Activation of coagulation and fibrinolysis during dengue virus infection

Role of auto-antibodies in the mechanisms of dengue pathogenesis and its progression: a comprehensive review

A complex interaction among virulence factors, host-genes and host immune system is considered to be responsible for dengue virus (DENV) infection and disease progression. Generation of auto-antibodies during DENV infection is a major phenomenon that plays a role in the pathophysiology of dengue hemorrhagic fever and dengue shock syndrome. Hemostasis, thrombocytopenia, hepatic endothelial dysfunction, and autoimmune blistering skin disease (pemphigus) are different clinical manifestations of dengue pathogenesis; produced due to the molecular mimicry of DENV proteins with self-antigens like coagulation factors, platelets and endothelial cell proteins. This review elaborately describes the current advancements in auto-antibody-mediated immunopathogenesis which inhibits coagulation cascade and promotes hyperfibrinolysis. Auto-antibodies like anti-endothelial cell antibodies-mediated hepatic inflammation during severe DENV infection have also been discussed. Overall, this comprehensive review provides insight to target auto-antibodies that may act as potential biomarkers for disease severity, and a ground for the development of therapeutic strategy against DENV.

Cardiovascular and haematological pathology in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS): A role for viruses

ME/CFS is a debilitating chronic condition that often develops after viral or bacterial infection. Insight from the study of Long COVID/Post Acute Sequelae of COVID-19 (PASC), the post-viral syndrome associated with SARS-CoV-2 infection, might prove to be useful for understanding pathophysiological mechanisms of ME/CFS. Disease presentation is similar between the two conditions, and a subset of Long COVID patients meet the diagnostic criteria for ME/CFS. Since Long COVID is characterized by significant vascular pathology - including endothelial dysfunction, coagulopathy, and vascular dysregulation - the question of whether or not the same biological abnormalities are of significance in ME/CFS arises. Cardiac abnormalities have for a while now been documented in ME/CFS cohorts, with recent studies demonstrating major deficits in cerebral blood flow, and hence vascular dysregulation. A growing body of research is demonstrating that ME/CFS is accompanied by platelet hyperactivation, anomalous clotting, a procoagulant phenotype, and endothelial dysfunction. Endothelial damage and dysregulated clotting can impair substance exchange between blood and tissues, and result in hypoperfusion, which may contribute to the manifestation of certain ME/CFS symptoms. Here we review the ME/CFS literature to summarize cardiovascular and haematological findings documented in patients with the condition, and, in this context, briefly discuss the potential role of previously-implicated pathogens. Overall, cardiac and haematological abnormalities are present within ME/CFS cohorts. While atherosclerotic heart disease is not significantly associated with ME/CFS, suboptimal cardiovascular function defined by reduced cardiac output, impaired cerebral blood flow, and vascular dysregulation are, and these abnormalities do not appear to be influenced by deconditioning. Rather, these cardiac abnormalities may result from dysfunction in the (autonomic) nervous system. Plenty of recently published studies are demonstrating significant platelet hyperactivity and endothelial dysfunction in ME/CFS, as well as anomalous clotting processes. It is of particular importance to determine to what extent these cardiovascular and haematological abnormalities contribute to symptom severity, and if these two systems can be targeted for therapeutic purposes. Viral reservoirs of herpesviruses exist in ME/CFS, and most likely contribute to cardiovascular and haematological dysfunction directly or indirectly. This review highlights the potential of studying cardiac functioning, the vasculature, and coagulation system in ME/CFS.

Tissue factor in COVID-19-associated coagulopathy

Evidence of micro- and macro-thrombi in the arteries and veins of critically ill COVID-19 patients and in autopsies highlight the occurrence of COVID-19-associated coagulopathy (CAC). Clinical findings of critically ill COVID-19 patients point to various mechanisms for CAC; however, the definitive underlying cause is unclear. Multiple factors may contribute to the prothrombotic state in patients with COVID-19. Aberrant expression of tissue factor (TF), an initiator of the extrinsic coagulation pathway, leads to thrombotic complications during injury, inflammation, and infections. Clinical evidence suggests that TF-dependent coagulation activation likely plays a role in CAC. Multiple factors could trigger abnormal TF expression and coagulation activation in patients with severe COVID-19 infection. Proinflammatory cytokines that are highly elevated in COVID-19 (IL-1β, IL-6 and TNF-α) are known induce TF expression on leukocytes (e.g. monocytes, macrophages) and non-immune cells (e.g. endothelium, epithelium) in other conditions. Antiphospholipid antibodies, TF-positive extracellular vesicles, pattern recognition receptor (PRR) pathways and complement activation are all candidate factors that could trigger TF-dependent procoagulant activity. In addition, coagulation factors, such as thrombin, may further potentiate the induction of TF via protease-activated receptors on cells. In this systematic review, with other viral infections, we discuss potential mechanisms and cell-type-specific expressions of TF during SARS-CoV-2 infection and its role in the development of CAC.

Beyond cuts and scrapes: plasmin in malaria and other vector-borne diseases

Plasmodium and other vector-borne pathogens have evolved mechanisms to hijack the mammalian fibrinolytic system to facilitate infection of the human host and the invertebrate vector. Plasmin, the effector protease of fibrinolysis, maintains homeostasis in the blood vasculature by degrading the fibrin that forms blood clots. Plasmin also degrades proteins from extracellular matrices, the complement system, and immunoglobulins. Here, we review some of the mechanisms by which vector-borne pathogens interact with components of the fibrinolytic system and co-opt its functions to facilitate transmission and infection in the host and the vector. Further, we discuss innovative strategies beyond conventional therapeutics that could be developed to target the interaction of vector-borne pathogens with the fibrinolytic proteins and prevent their transmission.

Predictors and Clinical Outcomes of Poor Platelet Recovery in Adult Dengue With Thrombocytopenia: A Multicenter, Prospective Study

BACKGROUND

Platelet transfusion is common in dengue patients with thrombocytopenia. We previously showed in a randomized clinical trial that prophylactic platelet transfusion did not reduce clinical bleeding. In this study, we aimed to characterize the predictors and clinical outcomes of poor platelet recovery in transfused and nontransfused participants.

METHODS

We analyzed patients from the Adult Dengue Platelet Study with laboratory-confirmed dengue with ≤20 000 platelets/μL and without persistent mild bleeding or any severe bleeding in a post hoc analysis. Poor platelet recovery was defined as a platelet count of ≤20 000/μL on Day 2. We recruited 372 participants from 5 acute care hospitals located in Singapore and Malaysia between 29 April 2010 and 9 December 2014. Of these, 188 were randomly assigned to the transfusion group and 184 to the control group.

RESULTS

Of 360 patients, 158 had poor platelet recovery. Age, white cell count, and day of illness at study enrollment were significant predictors of poor platelet recovery after adjustment for baseline characteristics and platelet transfusion. Patients with poor platelet recovery had longer hospitalizations but no significant difference in other clinical outcomes, regardless of transfusion. We found a significant interaction between platelet recovery and transfusion; patients with poor platelet recovery were more likely to bleed if given a prophylactic platelet transfusion (odds ratio 2.34, 95% confidence interval 1.18-4.63).

CONCLUSIONS

Dengue patients with thrombocytopenia who were older or presented earlier and with lower white cell counts were more likely to have poor platelet recovery. In patients with poor platelet recovery, platelet transfusion does not improve outcomes and may actually increase the risk of bleeding. The mechanisms of poor platelet recovery need to be determined.

CLINICAL TRIALS REGISTRATION

NCT01030211.

Multivariate time-series analysis of biomarkers from a dengue cohort offers new approaches for diagnosis and prognosis

Dengue is a major public health problem worldwide with distinct clinical manifestations: an acute presentation (dengue fever, DF) similar to other febrile illnesses (OFI) and a more severe, life-threatening form (severe dengue, SD). Due to nonspecific clinical presentation during the early phase of dengue infection, differentiating DF from OFI has remained a challenge, and current methods to determine severity of dengue remain poor early predictors. We present a prospective clinical cohort study conducted in Caracas, Venezuela from 2001-2005, designed to determine whether clinical and hematological parameters could distinguish DF from OFI, and identify early prognostic biomarkers of SD. From 204 enrolled suspected dengue patients, there were 111 confirmed dengue cases. Piecewise mixed effects regression and nonparametric statistics were used to analyze longitudinal records. Decreased serum albumin and fibrinogen along with increased D-dimer, thrombin-antithrombin complex, activated partial thromboplastin time and thrombin time were prognostic of SD on the day of defervescence. In the febrile phase, the day-to-day rates of change in serum albumin and fibrinogen concentration, along with platelet counts, were significantly decreased in dengue patients compared to OFI, while the day-to-day rates of change of lymphocytes (%) and thrombin time were increased. In dengue patients, the absolute lymphocytes to neutrophils ratio showed specific temporal increase, enabling classification of dengue patients entering the critical phase with an area under the ROC curve of 0.79. Secondary dengue patients had elongation of Thrombin time compared to primary cases while the D-dimer formation (fibrinolysis marker) remained always lower for secondary compared to primary cases. Based on partial analysis of 31 viral complete genomes, a high frequency of C-to-T transitions located at the third codon position was observed, suggesting deamination events with five major hot spots of amino acid polymorphic sites outside in non-structural proteins. No association of severe outcome was statistically significant for any of the five major polymorphic sites found. This study offers an improved understanding of dengue hemostasis and a novel way of approaching dengue diagnosis and disease prognosis using piecewise mixed effect regression modeling. It also suggests that a better discrimination of the day of disease can improve the diagnostic and prognostic classification power of clinical variables using ROC curve analysis. The piecewise mixed effect regression model corroborated key early clinical determinants of disease, and offers a time-series approach for future vaccine and pathogenesis clinical studies.

Dynamic changes of soluble ST2 levels predicted fatality and were involved in coagulopathy in dengue fever in the elderly

Background

Severe dengue virus (DENV) infection involves plasma leakage and vascular collapse, and leads to significant morbidity and death. Serum soluble ST2 (sST2 [interleukin (IL)-1 receptor like-1 protein: IL-1-RL-1]) levels are high in pediatric cases of DENV infection, and the disease progresses. However, the correlation between serum sST2 levels and the outcomes of DENV infection in the elderly (≥65 years) is unclear. We thus explored the mechanisms of serial sST2 level changes involved in the coagulopathy and bloodstream infections of elderly patients in Taiwan’s 2015 DENV outbreak.

Methods

This retrospective study was done in a tertiary medical center in southern Taiwan during the outbreak. All DENV-infected patients who, between July 1, 2015, and December 31, 2015, provided a written informed consent for at least two blood sample analyses were enrolled and reviewed. The serum levels of sST2 were quantified. ΔsST2 is defined as the “changes of sST2 levels in serially paired samples”. Receiver operating characteristic (ROC) curve and area under the ROC curve (AUC) analyses were used to evaluate the prognostic ability of ΔsST2.

Results

Forty-three patients with DENV infection were enrolled. Mean patient age was 75.0 ± 12.2 years and the case fatality rate was 44.2% (19/43). Significantly more non-survivors than survivors had increased ST2 level (78.9% vs. 12.5%, p < 0.001). The AUC value for serum ΔsST2 level was 0.857 for predicting DENV fatality. Moreover, patients given frozen fresh plasma (FFP) transfusions were significantly (p = 0.025) more likely to have higher serum ST2 level changes than were those who had not. DENV-infected patients with early bloodstream infections (BSIs) seemed to have higher ST2 levels than those who did not have BSIs.

Conclusions

Serum ST2 levels increased in the elderly (≥ 65 years of age) with DENV infection. The changes in serum sST2 levels might be a critical indicator of DENV infection severity for the elderly; sST2 is an important modulator of coagulopathy in severe DENV infections.

Dengue virus (DENV) infection is a mosquito-borne disease that annually affects at least 50 million people worldwide. The cytokine response during DENV infection is mercurial and abstruse. IL-1 receptor-like-1 (IL-1R-L-1 [aka ST2]) protein is associated with the severity of DENV infection, and elevated cytokine levels are important early predictors of dengue hemorrhagic fever and dengue shock syndrome. ST2, a member of the interleukin-1-receptor/toll-like receptor (TLR) superfamily, is an important biomarker of severe forms of pediatric DENV infection. We first confirmed a similar trend in the elderly cohort. Serial changes of soluble ST2 (sST2) levels were a more reliable predictor for dengue fatality than a single measurement was. Patients given fresh frozen plasma (FFP) transfusions had significantly higher serum ST2 levels than those who had not been given FFP transfusions. SerumsST2 might be necessary for modulating coagulopathy in severe DENV infections. The exact molecular mechanism and the optimal timing for sST2 testing need further investigation.

Coagulation abnormalities in dengue and dengue haemorrhagic fever patients

OBJECTIVE

The aim of this study was to assess abnormality of coagulation and anticoagulation parameters in dengue fever patients and the impact of these tests on the management of patients.

BACKGROUND

Dengue fever is endemic in Pakistan with seasonal rise in cases. Morbidities and mortalities are proportionately reported to be increasing and associated with disseminated intravascular coagulation resulting in haemorrhagic or thrombotic manifestations in patients having deranged coagulation profiles.

METHODS/MATERIALS

This observational and descriptive study was conducted on confirmed Dengue patients at the National Institute of Blood Diseases during the years 2013 to 2016. Patients of all age groups were included in this study. Results were analysed by SPSS version 23.

RESULTS

A total of 200 patients were selected with the mean age being 28.68 years (±13.28) and male predominance (147/200). The mean platelet count, haemoglobin and haematocrit at base line for bleeders and non-bleeders showed significant results, where platelet count at baseline for bleeders was 24 000, whereas for non-bleeders it was 29 000 and it showed significant correlation with bleeding (P-value .027). Platelets were transfused to 76 (38%) patients. However, none of the specialised haemostasis parameters beside the platelet count correlated with bleeding, requiring platelet transfusions.

CONCLUSION

Our study showed a significant association of platelet counts, haemoglobin and haematocrit with bleeding. It can be concluded that coagulation and anticoagulation profiles will not benefit the management of dengue patients and in countries like Pakistan, it will only add to the economic burden on the patients.

Increased Mosquito Midgut Infection by Dengue Virus Recruitment of Plasmin Is Blocked by an Endogenous Kazal-type Inhibitor

Dengue symptoms include alteration of blood coagulation and fibrinolysis, causing severe hemorrhage and death. Here, we demonstrate that higher concentration of plasmin, the human fibrinolytic factor, in blood meal enhances dengue virus (DENV) infection in mosquito midgut and dissemination in mosquitoes. We also show that mosquitoes express a plasmin-selective Kazal-type inhibitor (AaTI) in the midgut to inhibit plasmin proteolysis and revert the enhanced infection. Using bio-layer interferometry, we show that DENV, plasmin, and AaTI interact to form a tripartite complex. Eventually, plasmin increases midgut internalization of dextran molecules and this is reverted by AaTI. Our study demonstrates that (1) DENV recruits plasmin to increase local proteolytic activity in the midgut, thus degrading the glycocalyx and enhancing DENV internalization and (2) AaTI can act as a transmission-blocking agent by inhibiting plasmin proteolysis. Our results indicate that dengue pathogenesis enhances DENV fitness by increasing its infectivity to mosquitoes.

Targeted Interventions in Critically Ill Children with Severe Dengue

Background:

The World Health Organization guidelines provide suggestions on early recognition and treatment of severe dengue (SD); however, mortality in this group can be high and is related both to disease severity and the treatment complications.

Subjects and Methods:

In this prospective observational study, we report our results where standard therapy (ST) was enhanced by Intensive Care Unit (ICU) supportive measures that have proven beneficial in other conditions that share similar pathophysiology of capillary leak and fluid overload. These include early albumin for crystalloid-refractory shock, proactive monitoring for symptomatic abdominal compartment syndrome (ACS), application of a high-risk intubation management protocol, and other therapies. We compared outcomes in a matched retrospective cohort who received ST.

Results:

We found improved outcomes using these interventions in patients with the most devastating forms of dengue (ST+ group). We could demonstrate decreased positive fluid balance on days 1–3 and less symptomatic ACS that necessitated invasive percutaneous drainage (7.7% in ST+ group vs. 30% in ST group, P = 0.025). Other benefits in ST+ group included lower intubation and positive pressure ventilation requirements (18.4% in ST+ vs. 53.3% in ST, P = 0.003), lower incidence of major hemorrhage and acute kidney injury, and reduced pediatric ICU stays and mortality (2.6% in ST+ group vs. 26% in ST group, P = 0.004).

Conclusion:

Children with SD with refractory shock are at extremely high mortality risk. We describe the proactive application of several targeted ICU supportive interventions in addition to ST and could show that these interventions resulted in decreased resuscitation morbidity and improved outcomes in SD.

Thromboelastographic Analysis of Hemostatic Abnormalities in Dengue Patients Admitted in a Multidisciplinary Intensive Care Unit: A Cross-sectional Study

Background

Dengue fever is an important tropical infection causing significant mortality. The pathophysiology of hematological abnormalities in dengue remains poorly studied. In this study, we analyzed the hematological abnormalities by thromboelastography (TEG).

Methods

This cross-sectional study evaluated complicated dengue patients with TEG. Thromboelastographic variables were categorized into six patterns: factor deficiency, platelet dysfunction, enzymatic hypercoagulability, combined enzymatic and platelet hypercoagulability, primary fibrinolysis, and secondary hyperfibrinolysis.

Results

Twenty-five patients were analyzed for coagulation abnormalities by TEG. Coagulation factor deficiency pattern was noted in 11 patients (44%) whereas 3 patients (12%) were found to have low fibrinogen level pattern. Low platelet function was noted in 4 (16%) patients. Enzymatic hypercoagulability and combined enzymatic and platelet hypercoagulability were noted in one patient each (4.5%). Secondary fibrinolysis was noted in 1 patient (5%) and primary fibrinolysis in 3 (15.8%) patients. Factor deficiency pattern and low fibrinogen pattern were not significantly associated with hepatitis (P > 0.05). Activated partial thromboplastin time (aPTT) was not found to be significantly associated with factor deficiency pattern (P = 0.10) and low fibrinogen pattern (P = 0.20). Platelet count was not found to be significantly associated with platelet function (P = 0.54).

Conclusion

Factor deficiency pattern was the major abnormality noted in dengue patients followed by platelet dysfunction and primary fibrinolysis. Platelet count did not show significant association with platelet function. aPTT did not show significant association with factor deficiency and low fibrinogen patterns. Factor deficiency pattern and low fibrinogen pattern did not show significant association with hepatitis.

Prothrombin Time Prolongation was the Most Important Indicator of Severe Bleeding in Children with Severe Dengue Viral Infection

To determine the indicators of severe bleeding in children with severe dengue viral infection (DVI), the medical records of patients aged <15 years admitted to Songklanagarind Hospital in southern Thailand during 1989-2011 were reviewed. Severe-bleeding DVI was defined as needing blood products transfusion owing to DVI-caused bleeding. Of the 238 children with severe DVI according to the World Health Organization 2009 criteria, 44 (18.5%) had severe bleeding, of whom 28 (63.6%) died. The international normalized ratio (INR) had high correlations with both transaminase enzymes (Spearman correlation, rs = 0.67-0.69, p <0.01). Multivariate analysis found that patients who had dengue haemorrhagic fever (DHF) grade IV, platelets <20 000/mm3 and INR ≥ 1.5 had increased risk of severe bleeding with odds ratios (95% confidence intervals) of 3.4 (1.4, 8.6), 2.6 (1.1, 6.2) and 10.6 (4.0, 28.4), respectively. Blood products should be at hand in severe DHF children with high risk of severe bleeding.

Transient Monocytosis Subjugates Low Platelet Count in Adult Dengue Patients

Background

Dengue is one of the most important vector-borne human viral diseases globally. The kinetic changes of hematological parameters of dengue in adult Taiwanese patients have seldomly been systematically investigated and characterized.

Methodology/Principal Findings

Serial laboratory data of 1,015 adult patients who were diagnosed with dengue virus serotype 2 (DENV2) and 3 (DENV3) infections in southern Taiwan were retrospectively examined. Prominent parameters were verified with specimens from a 2015 dengue outbreak. Higher absolute monocyte counts on day 5 in severe patients than mild fever subjects after the onset of fever was seen. The absolute number of monocytes was significantly greater in those with DENV2 than DENV3 infections in spite of subtle differences in laboratory tests. Platelet counts were lowest and activated partial thromboplastin time was highest on day 5 in patients with severe conditions. In addition, sudden downward platelet counts corresponding to a transient surge of monocytes on day 4 onward was observed. Fluorescence-activated cell sorting analysis of peripheral blood mononuclear cells obtained from acute dengue patients and experimental investigations revealed that phagocytic effects of innate immune cells contribute to thrombocytopenia in dengue patients.

Conclusion

Innate phagocytic cells play an essential role in low platelet counts in adult patients with dengue virus infections.

A Cohort Study of Adult Patients with Severe Dengue in Taiwanese Intensive Care Units: The Elderly and APTT Prolongation Matter for Prognosis

Background

There was a large dengue outbreak in Taiwan in 2015, in which the ages of the affected individuals were higher than those in other countries. The aim of this study was to explore the characteristics and prognostic factors for adults with severe dengue in intensive care units (ICUs).

Methods

All adults admitted to ICUs with dengue virus infection (DENV) at a medical center from July 1, 2015 to December 31, 2015 were enrolled. DENV was diagnosed by the presence of serum NS1 antigen, IgM antibodies to dengue virus, or dengue virus RNA by real-time reverse transcriptase polymerase chain reaction. Demographic data, clinical features, and lab data were collected, and a multivariate Cox model was used to identify the predictive factors for in-hospital mortality.

Results

Seventy-five patients admitted to ICUs with laboratory-confirmed DENV were enrolled (mean age 72.3±9.3 years). The most common comorbidities included hypertension (72.0%), diabetes (43.7%), and chronic kidney disease (22.7%). The in-hospital case fatality rate (CFR) was 41.3%. The patients who died were predominantly female, had higher disease severity at ICU admission, shorter ICU/hospital stay, longer initial activated partial thromboplastin time (APTT), and higher initial serum aspartate transaminase levels. Cardiac arrest before ICU admission (hazard ratio [HR]: 6.26 [1.91–20.54]), prolonged APTT (>48 seconds; HR: 3.91 [1.69–9.07]), and the presence of acute kidney injury on admission (HR: 2.48 [1.07–5.74]), were independently associated with in-hospital fatality in the Cox multivariate analysis.

Conclusion

During the 2015 dengue outbreak in Taiwan, the patients with severe dengue in ICUs were characterized by old age, multiple comorbidities, and a high CFR. Organ failure (including cardiac failure, and renal failure) and coagulation disturbance (prolongation of initial APTT) were independent predictive factors for in-hospital fatality.

Severe forms of dengue fever (DF) are usually considered as a pediatric disease in southern Asia and are graded from dengue hemorrhagic fever (DHF) to dengue with shock syndrome (DSS). However, the age of affected individuals is increasing in Singapore, Thailand, Mainland China, Taiwan and many other countries. Limited data are available on the elderly with DF in intensive care units (ICUs). DF in the elderly is an emerging infectious disease and poses a new clinical challenge to physicians. We enrolled the patients with laboratory-confirmed dengue in our ICU during the 2015 dengue outbreak in Taiwan. These patients were characterized by old age, multiple comorbidities, and a high case fatality rate (CFR). All of the patients were classified as severe dengue, and the in-hospital CFR was 41.3%. Renal failure and cardiac arrest were associated with fatality. In addition to organ failure, initial prolonged activated partial thromboplastin time (APTT) in our study was consistent with an independent predictive factor for in-hospital fatality. Previous studies have also reported that prolongation of APTT is a clinical predictor of dengue virus infection (DENV) or DHF. Our results highlight that APTT prolongation may be a prognostic factor in critically ill adults with severe dengue.

Dengue Virus Nonstructural Protein 1-Induced Antibodies Cross-React with Human Plasminogen and Enhance Its Activation

Dengue virus (DENV) infection is the most common mosquito-borne viral disease, and it can cause life-threatening dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Abnormal activation of the coagulation and fibrinolysis system is one of the hallmarks of DHF/DSS. However, the mechanism underlying hemorrhage in DHF/DSS remains elusive. In previous studies, plasminogen (Plg) cross-reactive Abs, which can recognize DENV nonstructural protein (NS) 1, have been found in dengue patients. However, it is unclear whether these Abs are indeed induced by DENV NS1. Thus, we immunized mice with recombinant NS1 from both bacteria and drosophila to determine whether NS1 can induce Plg cross-reactive Abs. The results from the NS1-immunized mouse sera indicated that NS1 immunization induced Abs that could cross-react with Plg. To study the effects of these NS1-induced Plg cross-reactive Abs on fibrinolysis, we isolated several Plg cross-reactive anti-NS1 mAbs from these mice and found that some of them could enhance Plg activation. In addition, epitope mapping with a phage-displayed random peptide library revealed that one of these mAbs (2A5) could recognize NS1 C-terminal residues 305-311, which share sequence homology with Plg residues 590-597. A synthetic peptide of NS1 residues 305-311 could inhibit the binding of both 2A5 and its Fab to Plg and its enhanced activation. Thus, our results suggest that DENV NS1 can induce Plg cross-reactive Abs through molecular mimicry, which can enhance Plg activation and may contribute to the pathogenesis of DHF/DSS.

Evaluation of Prognostic Values of Tissue Plasminogen Activator and Plasminogen Activator Inhibitor-1 in Crimean-Congo Hemorrhagic Fever Patients

Background:

Crimean-Congo hemorrhagic fever (CCHF) is a widespread disease in Turkey, and was responsible for many deaths in endemic regions during the last decade. The pathogenesis of the disease is not fully understood yet.

Objectives:

In this study we aimed to determine the levels of tissue plasminogen activator (tPA) and Plasminogen activator inhibitor-1 (PAI-1) as predictors of prognosis in CCHF.

Patients and Methods:

Patients who were diagnosed by the polymerase chain reaction (PCR) and IgM positivity in the reference laboratory were included in this study. Tissue Plasminogen activator and PAI-1 levels were measured by the enzyme linked immunosorbent assay (ELISA) using a commercial kit (human t-PA ELISA and human PAL-1 ELISA; BioVendor research and diagnostic products, BioVendor-Laboratorni medicina a.s., Brno, Czech Republic).

Results:

A total of 46 patients participated in this study. The significant differences between recovering patients and the patients who died, regarding Aspartate aminotransferase (AST), Creatine Phosphokinase (CPK), Lactate Dehydrogenase (LDH), Prothrombin Time (PT), activated Partial Thromboplastin time (aPTT), and thrombocyte and fibrinogen levels, were consistent with many clinical studies in the literature. The fatal cases were found to have higher tPA and PAI-1 levels in contrast to the patients who completely recovered.

Conclusions:

We think that these findings may help the progress of understanding of CCHF pathogenesis.

Host biomarkers are associated with progression to dengue haemorrhagic fever: a nested case-control study

OBJECTIVES

Dengue represents the most important arboviral infection worldwide. Onset of circulatory collapse can be unpredictable. Biomarkers that can identify individuals at risk of plasma leakage may facilitate better triage and clinical management.

DESIGN

Using a nested case-control design, we randomly selected subjects from a prospective cohort study of dengue in Colombia (n=1582). Using serum collected within 96 hours of fever onset, we tested 19 biomarkers by ELISA in cases (developed dengue hemorrhagic fever or dengue shock syndrome (DHF/DSS); n=46), and controls (uncomplicated dengue fever (DF); n=65) and healthy controls (HC); n=15.

RESULTS

Ang-1 levels were lower and angptl3, sKDR, sEng, sICAM-1, CRP, CXCL10/IP-10, IL-18 binding protein, CHI3L1, C5a and Factor D levels were increased in dengue compared to HC. sICAM-1, sEng and CXCL10/IP-10 were further elevated in subjects who subsequently developed DHF/DSS (p=0.008, p=0.028 and p=0.025, respectively). In a logistic regression model, age (odds ratio (OR) (95% CI): 0.95 (0.92-0.98), p=0.001), hyperesthesia/hyperalgesia (OR; 3.8 (1.4-10.4), p=0.008) and elevated sICAM-1 (>298ng/mL: OR; 6.3 (1.5-25.7), p=0.011) at presentation were independently associated with progression to DHF/DSS.

CONCLUSIONS

These results suggest that inflammation and endothelial activation are important pathways in the pathogenesis of dengue and sICAM-1 levels may identify individuals at risk of plasma leakage.

Early indicators of severity and construction of a risk model for prognosis based upon laboratory parameters in patients with hemorrhagic fever with renal syndrome

BACKGROUND

The objective of this study was to explore the role of laboratory parameters as early indicators of severity and as effective predictors of prognosis in patients with hemorrhagic fever with renal syndrome (HFRS).

METHODS

A total of 356 patients were enrolled in this study and were divided into mild, moderate, severe and critical types according to the clinical classification of HFRS. The levels of 12 routinely tested laboratory parameters during the acute stage among the four types were compared. The predictive values of the laboratory parameters for prognosis were analyzed, and a risk model for prognosis based upon the parameters was constructed.

RESULTS

The levels of white blood counts (WBC), platelets (PLT), aspartate aminotransferase (AST), albumin (ALB), blood urea nitrogen (BUN), serum creatinine (Scr), prothrombin time (PT) and activated partial thromboplastin time (APTT) demonstrated significant differences among the four types (p<0.001); WBC, AST, PT and fibrinogen (Fib) were major independent risk factors for death; WBC, AST, PT and Fib used in combination were better for predicting prognosis than single parameters used alone (p<0.001).

CONCLUSIONS

Some routinely tested laboratory parameters can be beneficial as early indicators of severity of HFRS. Using a combination of WBC, AST, PT and Fib to predict the outcome in patients with HFRS exhibited acceptable diagnostic capability.

Thrombocytopenia in Dengue: Interrelationship between Virus and the Imbalance between Coagulation and Fibrinolysis and Inflammatory Mediators

Dengue is an infectious disease caused by dengue virus (DENV). In general, dengue is a self-limiting acute febrile illness followed by a phase of critical defervescence, in which patients may improve or progress to a severe form. Severe illness is characterized by hemodynamic disturbances, increased vascular permeability, hypovolemia, hypotension, and shock. Thrombocytopenia and platelet dysfunction are common in both cases and are related to the clinical outcome. Different mechanisms have been hypothesized to explain DENV-associated thrombocytopenia, including the suppression of bone marrow and the peripheral destruction of platelets. Studies have shown DENV-infected hematopoietic progenitors or bone marrow stromal cells. Moreover, anti-platelet antibodies would be involved in peripheral platelet destruction as platelets interact with endothelial cells, immune cells, and/or DENV. It is not yet clear whether platelets play a role in the viral spread. Here, we focus on the mechanisms of thrombocytopenia and platelet dysfunction in DENV infection. Because platelets participate in the inflammatory and immune response by promoting cytokine, chemokine, and inflammatory mediator secretion, their relevance as "immune-like effector cells" will be discussed. Finally, an implication for platelets in plasma leakage will be also regarded, as thrombocytopenia is associated with clinical outcome and higher mortality.

Endothelial dysfunction in dengue virus pathology

Dengue virus (DENV) is a leading cause of illness and death, mainly in the (sub)tropics, where it causes dengue fever and/or the more serious diseases dengue hemorrhagic fever and dengue shock syndrome that are associated with changes in vascular permeability. Despite extensive research, the pathogenesis of DENV is still poorly understood and, although endothelial cells represent the primary fluid barrier of the blood vessels, the extent to which these cells contribute to DENV pathology is still under debate. The primary target cells for DENV are dendritic cells and monocytes/macrophages that release various chemokines and cytokines upon infection, which can activate the endothelium and are thought to play a major role in DENV-induced vascular permeability. However, recent studies indicate that DENV also replicates in endothelial cells and that DENV-infected endothelial cells may directly contribute to viremia, immune activation, vascular permeability and immune targeting of the endothelium. Also, the viral non-structural protein-1 and antibodies directed against this secreted protein have been reported to be involved in endothelial cell dysfunction. This review provides an extensive overview of the effects of DENV infection on endothelial cell physiology and barrier function.

Molecular mimicry between dengue virus and coagulation factors induces antibodies to inhibit thrombin activity and enhance fibrinolysis

Dengue virus (DENV) is the most common cause of viral hemorrhagic fever, and it may lead to life-threating dengue hemorrhagic fever and shock syndrome (DHF/DSS). Because most cases of DHF/DSS occur in patients with secondary DENV infection, anti-DENV antibodies are generally considered to play a role in the pathogenesis of DHF/DSS. Previously, we have found that antithrombin antibodies (ATAs) with both antithrombotic and profibrinolytic activities are present in the sera of dengue patients. However, the mechanism by which these autoantibodies are induced is unclear. In this study, we demonstrated that antibodies induced by DENV immunization in mice and rabbits could bind to DENV antigens as well as to human thrombin and plasminogen (Plg). The binding of anti-DENV antibodies to thrombin and Plg was inhibited by preadsorption with DENV nonstructural protein 1. In addition, affinity-purified ATAs from DENV-immunized rabbit sera could inhibit thrombin activity and enhance Plg activation both in vitro and in vivo. Taken together, our results suggest that molecular mimicry between DENV and coagulation factors can induce the production of autoantibodies with biological effects similar to those of ATAs found in dengue patients. These coagulation-factor cross-reactive anti-DENV antibodies can interfere with the balance of coagulation and fibrinolysis, which may lead to the tendency of DHF/DSS patients to bleed.

IMPORTANCE

Dengue virus (DENV) infection is the most common mosquito-borne viral disease in tropical and subtropical areas. Over 50 million DENV infection cases develop each year, and more than 2.5 billion people are at risk of dengue-induced hemorrhagic fever and shock syndrome. Currently, there is no vaccine or drug treatment for DENV. In the present study, we demonstrated that DENV immunization could induce thrombin and plasminogen (Plg) cross-reactive antibodies, which were able to inhibit thrombin activity and enhance Plg activation. These results suggest that molecular mimicry between DENV antigens, thrombin, and Plg may elicit antibodies that disturb hemostasis. The selection of appropriate candidate antigens for use in DENV vaccines should prevent these potentially dangerous autoimmune responses.

Modulation of α-enolase post-translational modifications by dengue virus: increased secretion of the basic isoforms in infected hepatic cells

Hepatic cells are major sites of dengue virus (DENV) replication and liver injury constitutes a characteristic of severe forms of dengue. The role of hepatic cells in dengue pathogenesis is not well established, but since hepatocytes are the major source of plasma proteins, changes in protein secretion by these cells during infection might contribute to disease progression. Previously, we showed that DENV infection alters the secretion pattern of hepatic HepG2 cells, with α-enolase appearing as one of the major proteins secreted in higher levels by infected cells. ELISA analysis demonstrated that DENV infection modulates α-enolase secretion in HepG2 cells in a dose-dependent manner, but has no effect on its gene expression and on the intracellular content of the protein as assessed by PCR and western blot analyses, respectively. Two-dimensional western blots showed that both intracellular and secreted forms of α-enolase appear as five spots, revealing α-enolase isoforms with similar molecular weights but distinct isoeletric points. Remarkably, quantification of each spot content revealed that DENV infection shifts the isoform distribution pattern of secreted α-enolase towards the basic isoforms, whereas the intracellular protein remains unaltered, suggesting that post-translational modifications might be involved in α-enolase secretion by infected cells. These findings provide new insights into the mechanisms underlying α-enolase secretion by hepatic cells and its relationship with the role of liver in dengue pathogenesis. In addition, preliminary results obtained with plasma samples from DENV-infected patients suggest an association between plasma levels of α-enolase and disease severity. Since α-enolase binds plasminogen and modulates its activation, it is plausible to speculate the association of the increase in α-enolase secretion by infected hepatic cells with the haemostatic dysfunction observed in dengue patients including the promotion of fibrinolysis and vascular permeability alterations.

Clinical characteristics and outcomes in critical patients with hemorrhagic fever with renal syndrome

Background

Hemorrhagic fever with renal syndrome (HFRS) has become an important public health concern because of the high incidence and mortality rates, and limited treatment and vaccination. Until now, clinical studies on characteristics and outcomes in critical patients with HFRS have been limited. The aim of this study was to observe the clinical characteristics and cumulative proportions surviving and explore the predictive effects and risk factors for prognosis.

Methods

A detailed retrospective analysis of clinical records for critical HFRS patients was conducted. The patients enrolled were treated in the centre for infectious diseases, Tangdu Hospital, between January 2008 and August 2012. The clinical characteristics between the survivors and non-survivors were compared by Student’s t-test or Chi-square test. The risk clinical factors for prognosis were explored by logistic regression analysis. The predictive effects of prognosis in clinical and laboratory parameters were analyzed by receiver operating characteristic (ROC) curves. The cumulative proportions surviving at certain intervals in the critical patients were observed by Kaplan-Meier survival analysis.

Results

Of the 75 patients enrolled, the cumulative proportion surviving was 70.7% at the second week interval, with a 28-day mortality rate of 36.3%. The non-survivors tended to have higher frequencies of agitation, dyspnea, conjunctival hemorrhage, coma, cardiac failure, acute respiratory distress syndrome (ARDS) and encephalopathy (P < .05). ARDS, conjunctival hemorrhage and coma were risk factors for death in the critical patients with HFRS. The non-survivors were found to have lower serum creatinine (Scr) levels (P < .001) and higher incidences of prolonged prothrombin time (PT) (P = .006), activated partial thromboplastin time (APTT) (P = .003) and elevated white blood cells (WBC) levels (P = .005), and the laboratory parameters mentioned above reached statistical significance for predicting prognosis (P < .05).

Conclusion

The high fatality in critical patients with HFRS underscores the importance of clinicians’ alertness to the occurrence of potentially fatal complications and changes in biochemical status to ensure that timely and systematically supportive treatment can be initiated when necessary.

Infection of epithelial cells with dengue virus promotes the expression of proteins favoring the replication of certain viral strains

Dengue virus (DENV) is the causative agent of dengue and severe dengue. To understand better the dengue virus-host interaction, it is important to determine how the expression of cellular proteins is modified due to infection. Therefore, a comparison of protein expression was conducted in Vero cells infected with two different DENV strains, both serotype 2: DENV-2/NG (associated with dengue) and DENV-2/16681 (associated with severe dengue). The viability of the infected cells was determined, and neither strain induced cell death at 48 hr. In addition, the viral genomes and infectious viral particles were quantified, and the genome of the DENV-2/16681 strain was determined to have a higher replication rate compared with the DENV-2/NG strain. Finally, the proteins from infected and uninfected cultures were separated using two-dimensional gel electrophoresis, and the differentially expressed proteins were identified by mass spectrometry. Compared with the uninfected controls, the DENV-2/NG- and DENV-2/16681-infected cultures had five and six differentially expressed proteins, respectively. The most important results were observed when the infected cultures were compared to each other (DENV-2/NG vs. DENV-2/16681), and 18 differentially expressed proteins were identified. Based on their cellular functions, many of these proteins were linked to the increase in the replication efficiency of DENV. Among the proteins were calreticulin, acetyl coenzyme A, acetyl transferase, and fatty acid-binding protein. It was concluded that the infection of Vero cells with DENV-2/NG or DENV-2/16681 differentially modifies the expression of certain proteins, which can, in turn, facilitate infection.

The usefulness of clinical-practice-based laboratory data in facilitating the diagnosis of dengue illness

Alertness to dengue and making a timely diagnosis is extremely important in the treatment of dengue and containment of dengue epidemics. We evaluated the complementary role of clinical-practice-based laboratory data in facilitating suspicion/diagnosis of dengue. One hundred overall dengue (57 dengue fever [DF] and 43 dengue hemorrhagic fever [DHF]) cases and another 100 nondengue cases (78 viral infections other than dengue, 6 bacterial sepsis, and 16 miscellaneous diseases) were analyzed. We separately compared individual laboratory variables (platelet count [PC] , prothrombin time [PT], activated partial thromboplastin time [APTT], alanine aminotransferase [ALT], and aspartate aminotransferase [AST]) and varied combined variables of DF and/or DHF cases with the corresponding ones of nondengue cases. The sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) in the diagnosis of DF and/or DHF were measured based on these laboratory variables. While trade-off between sensitivity and specificity, and/or suboptimal PPV/NPV was found at measurements using these variables, prolonged APTT + normal PT + PC < 100 × 10⁹ cells/L had a favorable sensitivity, specificity, PPV, and NPV in diagnosis of DF and/or DHF. In conclusion, these data suggested that prolonged APTT + normal PT + PC < 100 × 10⁹ cells/L is useful in evaluating the likelihood of DF and/or DHF.

Reduced thrombin formation and excessive fibrinolysis are associated with bleeding complications in patients with dengue fever: a case-control study comparing dengue fever patients with and without bleeding manifestations

Background

Dengue cases have been classified according to disease severity into dengue fever (DF) and dengue hemorrhagic fever (DHF). Although DF is considered a non-severe manifestation of dengue, it has been recently demonstrated that DF represents a heterogeneous group of patients with varied clinical complications and grades of severity. Particularly, bleeding complications, commonly associated to DHF, can be detected in half of the patients with DF. Although a frequent complication, the causes of bleedings in DF have not been fully addressed. Thus, the aim of this study was to perform a comprehensive evaluation of possible pathophysiological mechanisms that could contribute to the bleeding tendency observed in patients with DF.

Methods

This is a case–control study that enrolled adults with DF without bleeding and adults with DF and bleeding complications during the defervescence period. Healthy controls were also included. Peripheral blood counts, inflammatory, fibrinolysis and endothelial cell activation markers, and thrombin generation were evaluated in patients and controls.

Results

We included 33 adults with DF without complications, 26 adults with DF and bleeding and 67 healthy controls. Bleeding episodes were mild in 15 (57.6%) and moderate in 11 (42.4%) patients, 8 (30.7%) patients had bleedings in multiple sites. Patients with DF and bleedings had lower platelet counts than DF without bleeding (median = 19,500 vs. 203,500/mm3, P < 0,0001). Levels of TNF-α, thrombomodulin and VWF were significantly increased in the two dengue groups than in healthy controls, but similar between patients with and without bleedings. Plasma levels of tPA and D-dimer were significantly increased in patients with bleedings (median tPA levels were 4.5, 5.2, 11.7 ng/ml, P < 0.0001 and median D-dimer levels were 515.5, 1028 and 1927 ng/ml, P < 0.0001). The thrombin generation test showed that patients with bleeding complications had reduced thrombin formation (total thrombin generated were 3753.4 in controls, 3367.5 in non-bleeding and 2274.5nM in bleeding patients, P < 0.002).

Conclusions

DF can manifest with spontaneous bleedings, which are associated with specific coagulation and fibrinolysis profiles that are not significantly present in DF without this complication. Particularly, thrombocytopenia, excessive fibrinolysis and reduced thrombin formation may contribute to the bleeding manifestations in DF.

Platelet activation and platelet-monocyte aggregate formation contribute to decreased platelet count during acute simian immunodeficiency virus infection in pig-tailed macaques

Platelets are key participants in innate immune responses to pathogens. As a decrease in circulating platelet count is one of the initial hematologic indicators of human immunodeficiency virus (HIV) infection, we sought to determine whether decline in platelet number during acute infection results from decreased production, increased antibody-mediated destruction, or increased platelet activation in a simian immunodeficiency virus (SIV)/macaque model. During acute SIV infection, circulating platelets were activated with increased surface expression of P-selection, CD40L and major histocompatibility complex class I. Platelet production was maintained and platelet autoantibodies were not detected during acute infection. Concurrent with a decrease in platelet numbers and an increase in circulating monocytes, platelets were found sequestered in platelet-monocyte aggregates, thereby contributing to the decline in platelet counts. Because the majority of circulating CD16(+) monocytes formed complexes with platelets during acute SIV infection, a decreased platelet count may represent platelet participation in the innate immune response to HIV.

Re-evaluation of the pathogenic roles of nonstructural protein 1 and its antibodies during dengue virus infection

Dengue virus (DENV) infection can cause life-threatening dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Vascular leakage and abnormal hemorrhage are the two major pathogenic changes found in these patients. From previous studies, it is known that both antibodies and cytokines induced in response to DENV infection are involved in the immunopathogenesis of DHF/DSS. However, the role of viral factors during DENV infection remains unclear. Nonstructural protein 1 (NS1), which is secreted in the sera of patients, is a useful diagnostic marker for acute DENV infection. Nevertheless, the roles of NS1 and its antibodies in the pathogenesis of DHF/DSS are unclear. The focus of this review is to evaluate the possible contributions of NS1 and the antibodies it induces to vascular leakage and abnormal hemorrhage during DENV infection, which may provide clues to better understanding the pathogenesis of DHF/DSS.

Antibodies against thrombin in dengue patients contain both anti-thrombotic and pro-fibrinolytic activities

Dengue virus (DENV) infection may result in severe life-threatening Dengue haemorrhagic fever (DHF). The mechanisms causing haemorrhage in those with DHF are unclear. In this study, we demonstrated that antibodies against human thrombin were increased in the sera of Dengue patients but not in that of patients infected with other viruses. To further characterise the properties of these antibodies, affinity-purified anti-thrombin antibodies (ATAs) were collected from Dengue patient sera by thrombin and protein A/L affinity columns. Most of the ATAs belonged to the IgG class and recognized DENV nonstructural protein 1 (NS1). In addition, we found that dengue patient ATAs also cross-reacted with human plasminogen (Plg). Functional studies in vitro indicated that Dengue patient ATAs could inhibit thrombin activity and enhance Plg activation. Taken together, these results suggest that DENV NS1-induced thrombin and Plg cross-reactive antibodies may contribute to the development of haemorrhage in patients with DHF by interfering with coagulation and fibrinolysis.

Coagulation factors, fibrinogen and plasminogen activator inhibitor-1, are differentially regulated by yellow fever virus infection of hepatocytes

Yellow fever virus (YFV) infection poses a great risk to un-vaccinated individuals living or traveling in the endemic regions of Africa and South America. It is estimated that approximately 30,000 people die each year of this disease. The liver is the main target of YFV, where as many as 80% of the hepatocytes may become involved in the infection. The overwhelming infection of the liver is associated with the observed hemorrhagic disease manifestations such as petechiae, ecchymoses, and hematemesis which are all thought to be linked with the observed coagulation abnormalities that include prolonged clotting times, reduction in clotting factors, fibrin-split products (D-dimers) and elevated prothrombin times. Many factors involved in the coagulation pathway are produced by hepatocytes, such as fibrinogen (FBG) and plasminogen activator inhibitor-1 (PAI-1). Both of these proteins have been indicated in another flavivirus related disease, dengue, as having roles related to the bleeding abnormalities observed and overall outcome of infection. In this study we wanted to determine if FBG and PAI-1 expression levels by human hepatocytes was disrupted or altered by infection with either wild-type Asibi or vaccine strain17-D YFVs. Our findings indicate that YFV infection does affect the transcriptional and translational expression of FBG and PAI-1 in human hepatocytes and that these results are further affected by IL-6 during early stages of infection. These results may lead to further understanding of the molecular mechanism associated with bleeding abnormalities observed during late stage YFV infection.

Dengue virus enhances thrombomodulin and ICAM-1 expression through the macrophage migration inhibitory factor induction of the MAPK and PI3K signaling pathways

Dengue virus (DV) infections cause mild dengue fever (DF) or severe life-threatening dengue hemorrhagic fever (DHF). The mechanisms that cause hemorrhage in DV infections remain poorly understood. Thrombomodulin (TM) is a glycoprotein expressed on the surface of vascular endothelial cells that plays an important role in the thrombin-mediated activation of protein C. Prior studies have shown that the serum levels of soluble TM (sTM) and macrophage migration inhibitory factor (MIF) are significantly increased in DHF patients compared to levels in DF patients or normal controls. In this study, we investigated how MIF and sTM concentrations are enhanced in the plasma of DHF patients and the potential effect of MIF on coagulation through its influence on two factors: thrombomodulin (TM) and intercellular adhesion molecule-1 (ICAM-1) in endothelial cells and monocytes. Recombinant human macrophage migration inhibitory factor (rMIF) was used to treat monocytic THP-1 cells and endothelial HMEC-1 cells or primary HUVEC cells. The subsequent expression of TM and ICAM-1 was assessed by immunofluorescent staining and flow cytometry analysis. Additionally, the co-incubation of THP-1 cells with various cell signaling pathway inhibitors was used to determine the pathways through which MIF mediated its effect. The data provided evidence that severe DV infections induce MIF expression, which in turn stimulates monocytes or endothelial cells to express TM and ICAM-1 via the Erk, JNK MAPK and the PI3K signaling pathways, supporting the idea that MIF may play an important role as a regulator of coagulation.

Review: Viral infections and mechanisms of thrombosis and bleeding

Viral infections are associated with coagulation disorders. All aspects of the coagulation cascade, primary hemostasis, coagulation, and fibrinolysis, can be affected. As a consequence, thrombosis and disseminated intravascular coagulation, hemorrhage, or both, may occur. Investigation of coagulation disorders as a consequence of different viral infections have not been performed uniformly. Common pathways are therefore not fully elucidated. In many severe viral infections there is no treatment other than supportive measures. A better understanding of the pathophysiology behind the association of viral infections and coagulation disorders is crucial for developing therapeutic strategies. This is of special importance in case of severe complications, such as those seen in hemorrhagic viral infections, the incidence of which is increasing worldwide. To date, only a few promising targets have been discovered, meaning the implementation in a clinical context is still hampered. This review discusses non‐hemorrhagic and hemorrhagic viruses for which sufficient data on the association with hemostasis and related clinical features is available. This will enable clinicians to interpret research data and place them into a perspective. J. Med. Virol. 84:1680–1696, 2012. © 2012 Wiley Periodicals, Inc.

Autoimmunity in dengue pathogenesis

Dengue is one of the most important vector-borne viral diseases. With climate change and the convenience of travel, dengue is spreading beyond its usual tropical and subtropical boundaries. Infection with dengue virus (DENV) causes diseases ranging widely in severity, from self-limited dengue fever to life-threatening dengue hemorrhagic fever and dengue shock syndrome. Vascular leakage, thrombocytopenia, and hemorrhage are the major clinical manifestations associated with severe DENV infection, yet the mechanisms remain unclear. Besides the direct effects of the virus, immunopathogenesis is also involved in the development of dengue disease. Antibody-dependent enhancement increases the efficiency of virus infection and may suppress type I interferon-mediated antiviral responses. Aberrant activation of T cells and overproduction of soluble factors cause an increase in vascular permeability. DENV-induced autoantibodies against endothelial cells, platelets, and coagulatory molecules lead to their abnormal activation or dysfunction. Molecular mimicry between DENV proteins and host proteins may explain the cross-reactivity of DENV-induced autoantibodies. Although no licensed dengue vaccine is yet available, several vaccine candidates are under development. For the development of a safe and effective dengue vaccine, the immunopathogenic complications of dengue disease need to be considered.

Factors contributing to the disturbance of coagulation and fibrinolysis in dengue virus infection

Hemorrhage is one of the hallmarks of dengue hemorrhagic fever. However, the mechanisms that cause hemorrhage are unclear. In this review we focus on the possible factors that may be involved in the disturbance of coagulation and fibrinolysis during dengue virus (DENV) infection. Factors such as autoantibodies and cytokines induced by DENV infection as well as hemostatic molecules expressed on DENV-infected cells, and DENV viral proteins may all contribute to the defect of hemostasis during DENV infection. It is the combination of these viral and host factors that may tilt the balance of coagulation and fibrinolysis toward bleeding in dengue patients.

Serum proteome changes in dengue virus-infected patients from a dengue-endemic area of India: towards new molecular targets?

The global burden of dengue continues to worsen, specifically in tropical and subtropical countries, and has evolved as a major public health problem. We investigated the changes in serum proteome in dengue fever (DF) patients from a dengue-endemic area of India to obtain mechanistic insights about the disease pathogenesis, the host immune response, and identification of potential serum protein biomarkers of this infectious disease. In this study, serum samples from DF patients, healthy subjects, and patients with falciparum malaria (an infectious disease control) were investigated by 2D-DIGE in combination with MALDI-TOF/TOF MS. The findings were validated with Western blotting. Functional clustering of the identified proteins was performed using PANTHER and DAVID tools. Compared to the healthy controls, we found significant changes in the expression levels of 48 protein spots corresponding to 18 unique proteins (7 downregulated and 11 upregulated) in DF patients (p<0.05). Among these differentially-expressed proteins, 11 candidates exhibited different trends in dengue fever compared to falciparum malaria. Importantly, our results suggest that dengue virus infection leads to alterations in expression levels of multiple serum proteins involved in diverse and vital physiological pathways, including acute phase response signaling, complement cascades, hemostasis, and blood coagulation. For the first time we report here that the serum levels of hemopexin, haptoglobin, serum amyloid P, and kininogen precursor, are altered in DF. This study informs the pathogenesis and host immune response to dengue virus infection, as well as the current search for new diagnostic and molecular drug targets.

Staphylococcus aureus pneumonia and dengue virus co-infection and review of implications of coinfection

Dengue fever is an important public health problem in Jamaica and has various serious manifestations, which if not identified and treated at the appropriate time can lead to dire consequences. Bacterial co-infections have been seen in clinical practice but may be thought of as simply coincidental. This review highlights the importance of bacteria in exacerbating dengue infections and the importance of looking for co-infection in patients with certain clinical manifestations. It also provides the reader with a scientific understanding of the immune pathogenesis of dengue and bacterial co-infections.

Serum profiling of leptospirosis patients to investigate proteomic alterations

Leptospirosis is a zoonotic infectious disease of tropical, subtropical and temperate zones, which is caused by the pathogenic spirochetes of genus Leptospira. Although this zoonosis is generally not considered as fatal, the pathogen can eventually cause severe infection with septic shock, multi-organ failure and lethal pulmonary hemorrhages leading to mortality. In this study, we have performed a proteomic analysis of serum samples from leptospirosis patients (n = 6), febrile controls (falciparum malaria) (n = 8) and healthy subjects (n = 18) to obtain an insight about disease pathogenesis and host immune responses in leptospiral infections. 2DE and 2D-DIGE analysis in combination with MALDI-TOF/TOF MS revealed differential expression of 22 serum proteins in leptospirosis patients compared to the healthy controls. Among the identified differentially expressed proteins, 8 candidates exhibited different trends compared to the febrile controls. Functional analysis suggested the involvement of differentially expressed proteins in vital physiological pathways, including acute phase response, complement and coagulation cascades and hemostasis. This is the first report of analysis of human serum proteome alterations in leptospirosis patients, which revealed several differentially expressed proteins, including α-1-antitrypsin, vitronectin, ceruloplasmin, G-protein signaling regulator, apolipoprotein A-IV, which have not been reported in context of leptospirosis previously. This study will enhance our understanding about leptospirosis pathogenesis and provide a glimpse of host immunological responses. Additionally, a few differentially expressed proteins identified in this study may further be investigated as diagnostic or prognostic serum biomarkers for leptospirosis.

This article is part of a Special Issue entitled: Integrated omics.

Dengue virus-induced autoantibodies bind to plasminogen and enhance its activation

Dengue virus infection can lead to life-threatening dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS) in patients. Abnormal activation of the coagulation and fibrinolysis system is one of the hallmarks associated with DHF/DSS patients. However, the mechanisms that cause pathology in DHF/DSS patients are still unclear. Because conversion of plasminogen (Plg) to plasmin (Plm) is the first step in the activation of fibrinolysis, Abs against Plg found in DHF/DSS patients may be important. Therefore, to investigate the specificity, function, and possible origin of these Abs, we generated several Plg cross-reactive mAbs from DENV-immunized mice. An IgG mAb, 6H11, which recognizes an epitope associated with a dengue envelope protein, demonstrated a high level of cross-reactivity with Plg. The 6H11 Ab was further characterized with regard to its effect on Plg activation. Using Plm-specific chromogenic substrate S-2251, we found that mAb 6H11 demonstrated serine protease activity and could convert Plg directly to Plm. The serine protease activity of mAb 6H11 was further confirmed using serine protease chromogenic substrate S-2288. In addition, we found several Plg cross-reactive mAbs that could enhance urokinase-induced Plg activation. Lastly, mAb 6H11 could induce Plm activity and increase the level of D-dimer (a fibrin degradation product) in both human and mouse platelet-poor plasma. Taken together, these data suggest DENV-induced Plg cross-reactive Abs may enhance Plg conversion to Plm, which would be expected to contribute to hyperfibrinolysis in DHF/DSS patients.

Molecular mimicry between virus and host and its implications for dengue disease pathogenesis

Numerous infectious agents may trigger autoimmunity or even result in autoimmune diseases. Several mechanisms have been proposed for pathogen-triggered autoimmunity including molecular mimicry, cryptic antigens, epitope spreading, bystander activation and polyclonal activation. In the case of dengue virus infection which causes serious public health problems, the mechanisms regarding the pathogenesis of dengue hemorrhagic syndrome are not fully resolved. Our previous studies suggest a mechanism of molecular mimicry in which antibodies directed against dengue virus non-structural protein 1 (NS1) cross-react with human platelets and endothelial cells and cause their damage and dysfunction, which may be related to the clinical features of dengue disease. Several cell surface proteins recognized by patient serum samples and anti-NS1 antibodies have been identified. Based on proteomic studies and sequence analysis, the C-terminal region of dengue virus NS1 shows sequence homology with target proteins. In addition, different regions of dengue virus proteins including core, prM, E and NS1 proteins show sequence homology with different coagulatory molecules. As an example, the amino acid sequence 101-106 of E protein (WGNGCG) shows sequence homology with factors XI, X, IX, VII, II (thrombin), plasminogen and tissue plasminogen activator. Furthermore, single chain variable region against NS1 can interfere with fibrin formation, which leads to prolonged thrombin time. We hypothesize that molecular mimicry between dengue virus proteins and coagulatory molecules may induce cross-reactive autoantibodies that can interfere with coagulation activation. A molecular mimicry pathogenesis for dengue disease which involves cross-reactivity of dengue virus with human endothelial cells, platelets and coagulatory molecules is proposed.

Fibrin formation and lysis studies in dengue virus infection

Dengue virus is a mosquito-borne human viral pathogen that has recently become a major public health concern particularly in tropical and subtropical countries, predominantly in urban and periurban areas. Plasma from five patients infected by the virus was selected since they have in different degrees prolonged thrombin times: +2.1, +3.4, +5.7, +7.1 and +18.5 s, like a transitory acquired dysfibrinogenemia. The serotype could be determined in only two patients, being DEN-1 and DEN-3. The fibrinogen concentration was normal ranging from 2.5 to 3.2 g/l. In general, the fibrin degradation products of the patients were high, reaching values of 6000 ng/ml. The polymerization process was quite similar to that of the control, except in two cases where the final turbidity was almost half the control value. In one of these patients, the fibrinogen was purified and mixed with normal fibrinogen (v: v); the patients' fibrinogen impaired normal fibrin polymerization. Studies of the fibrinolytic process revealed that clots from dengue patients started to lyze before they have reached the maximum turbidity, although this was not reflected in the time needed for complete clot dissolution, which was similar to that of the control for all the patients. Fibrinolysis of clots made by mixing normal and patient purified fibrinogen (2.5: 1) was impaired. Clot images obtained by scanning electron microscopy showed that the patients' fibrin network had some degree of degradation and the fibers were thicker than those of the control (P < 0.05). This preliminary study seems to indicate that the dengue virus infection modifies the balance of coagulation-fibrinolysis toward hyperfibrinolysis and could modify the normal fibrinogen molecule.

Dengue virus-induced hemorrhage in a nonhuman primate model

Lack of a dengue hemorrhagic animal model recapitulating human dengue virus infection has been a significant impediment in advancing our understanding of the early events involved in the pathogenesis of dengue disease. In efforts to address this issue, a group of rhesus macaques were intravenously infected with dengue virus serotype 2 (strain 16 681) at 1 x 10(7) PFU/animal. A classic dengue hemorrhage developed 3 to 5 days after infection in 6 of 6 animals. Blood chemistry appeared to be normal with exception of creatine phosphokinase, which peaked at 7 days after infection. A modest thrombocytopenia and noticeable neutropenia concomitant with slight decrease of hemoglobin and hematocrit were registered. In addition, the concentration of D-dimer was elevated significantly. Viremia peaked at 3 to 5 days after infection followed by an inverse relationship between T and B lymphocytes and a bimodal pattern for platelet-monocytes and platelet-neutrophil aggregates. Dengue virus containing platelets engulfed by monocytes was noted at 8 or 9 days after infection. Thus, rhesus macaques inoculated intravenously with a high dose of dengue virus produced dengue hemorrhage, which may provide a unique platform to define the early events in dengue virus infection and help identify which blood components contribute to the pathogenesis of dengue disease.

Dengue virus regulates the expression of hemostasis-related molecules in human vein endothelial cells

OBJECTIVES

Hemorrhage is considered to be the primary sign of Dengue hemorrhagic fever and Dengue shock syndrome. In the present study we focused on the mechanism in the pro- and anti-coagulation after Dengue virus infection.

METHODS

The effects of Dengue virus on the expression and secretion of tissue factor, tissue factor inhibitor, thrombomodulin, tissue plasminogen activator and plasminogen activator inhibitor type-1 in human umbilical vein endothelial cells were detected in this study.

RESULTS

It was shown that Dengue virus could promote the expression of thrombomodulin in cultured human umbilical vein endothelial cells, thus increasing anticoagulation, and enhancing tissue plasminogen activator activity and therefore increased hemorrhage risk.

CONCLUSIONS

The changes above may play an important role in the development of Dengue hemorrhagic fever and Dengue shock syndrome.

Role of T cells, cytokines and antibody in dengue fever and dengue haemorrhagic fever

Dengue infections are a major cause of morbidity and mortality in the tropical and sub-tropical regions of the world. There is no vaccine for dengue and also there are no anti-viral drugs to treat the infection. Some patients, typically those experiencing a secondary infection with a different dengue serotype, may progress from an acute febrile disease to the more severe forms of disease, dengue haemorrhagic fever and dengue shock syndrome. Here we discuss the significant immunopathological component to severe disease and how T cells, cytokines and cross-reactive antibody combine to contribute to the progression to dengue haemorrhagic fever. These events are thought to lead to vascular leakage, the signature event in dengue haemorrhagic fever, and are addressed in this review by incorporating the concept of heterologous T cell immunity. The need for effective measures against dengue and dengue-related illness is clear. We propose that drugs against dengue virus, or the symptoms of severe dengue disease, are a viable goal.

Elevated levels of plasma VEGF in patients with dengue hemorrhagic fever

Vascular endothelial growth factor (VEGF) can be produced by monocytes and endothelial cells. It plays important role in angiogenesis and vascular permeability. The phenomenon of extensive plasma leakage into various serous cavities of the body is a cardinal symptom of dengue hemorrhagic fever (DHF). This study was performed to investigate the role of VEGF in patients with DHF. Plasma samples collected from the 53 dengue fever (DF) patients (including 14 patients with DHF), and 5 additional subjects with non-dengue febrile illness as controls were tested for VEGF levels using commercial enzyme-linked immunosorbent assay (ELISA) kits. The results showed that median plasma levels of VEGF in the patients with DHF (54.6 pg ml(-1)) were significantly higher than those of DF (14.6 pg ml(-1)) and control group (27.1 pg ml(-1)) (P<0.05). In addition, VEGF levels in DF patients were not significantly different from those of control patients with non-dengue febrile illness (P=0.17). Multiple regression analysis was used to analyze the clinical variables independently associated with VEGF levels. The data showed that D-dimer levels were significantly associated with VEGF levels. In this study, plasma VEGF levels in patients with DHF were significantly higher than values from DF patients. The association between increased plasma VEGF levels and increased plasma D-dimer levels in the patients with dengue illness suggests that activation of the fibrinolytic system may play a role in VEGF production in the patients with DF.