UTC025.2 F.FLAVIVIRIDAE V. Dengue. . ZOONOSIS.

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Familia  Flaviviridae  T129  .   MC+E+         CASO CLINICO m549      FAMILIA FLAVIVIRIDAE  (ARBOVIRUS)   RNA MC+ E+  FLAVIVIRUS        pESTIVIRUS, HEPACIVIRUS                                                                                                                 FLAVIVIRUS-T129.  (Dengue, Fiebre amarilla, Encefalitis Japonesa, Encefalitis del Nilo Occidental, Encefalitis de San Luis , Encefalitis Rusa de primavera-verano , Encefalitis de Powassan, M(tabla 60-2)    M550   Estructura  M550,  Caracteristicas propias cuadro 60-1 M550   Replicacion  M550   patogenia M551 ,   respuesta inmune M553,    Epidemiologia M553, cuadro60-3 , M554;  Enfermedades clinicas  M555                                                                                                                                                         Virus de la  Fiebre  amarilla.  Manifestaciones clínicas;    Transmisión y epidemiología,  tabla 60-2 M550,    Patogenia,  Factores de Virulencia, Diagnóstico de laboratorio,     Tratamiento y prevención -T130,  .                                                                                                                                                         Virus del DENGUE-T130, Manifestaciones clínicas;    Transmisión y epidemiología,  Patogenia,  Factores de Virulencia, Diagnóstico de laboratorio,     Tratamiento y prevención                                                                                          V.ENCEFALITIS JAPONESA-T130, y  virus relacionados                                                                              (  V.ENCEFALITIS SAN LUIS,  V NILO OCCIDENTAL-T131, 131   V. ENCEFALITIS DEL VALLE MURRAY-T130,  VHC,  m 592 VHG-  M592,    T132,    M 594        Virus de las hepatitis   C  y G.   Generalidades M 592,   A162,Esrtructura y replicacion  M593,  A162,  Manifestaciones clínicas; M593,  A164,   Transmisión y epidemiología, M593, A163,  Patogenia,  M593,   Factores de Virulencia, Diagnóstico de laboratorio, M592    Tratamiento y prevención  T132  133     M594 .           A165,                                                                                                                     ALUMNOS 32  33  34     35 



 

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Patogénesis Dengue MARZO2 2013




DENGUEepidemiologia microbiologia patogenesis tto



 

 

 

 

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1.The Lancet Infectious Diseases, Volume 9, Issue 11, Pages 678 - 687, November 2009
doi:10.1016/S1473-3099(09)70254-3Cite or Link Using DOI

Progress towards a dengue vaccine

Dr Daniel P Webster FRCPath a Corresponding AuthorEmail Address, Prof Jeremy Farrar FRCP b, Prof Sarah Rowland-Jones FRCP c

Summary

The spread of dengue virus throughout the tropics represents a major, rapidly growing public health problem with an estimated 2·5 billion people at risk of dengue fever and the life-threatening disease, severe dengue. A safe and effective vaccine for dengue is urgently needed. The pathogenesis of severe dengue results from a complex interaction between the virus, the host, and, at least in part, immune-mediated mechanisms. Vaccine development has been slowed by fears that immunisation might predispose individuals to the severe form of dengue infection. A pipeline of candidate vaccines now exists, including live attenuated, inactivated, chimeric, DNA, and viral-vector vaccines, some of which are at the stage of clinical testing. In this Review, we present what is understood about dengue pathogenesis and its implications for vaccine design, the progress that is being made in the development of a vaccine, and the future challenges.
 
 
2.http://www.virologyj.com/content/6/1/211.
Open AccessHighly AccessReview

The relationship of interacting immunological components in dengue pathogenesis

David G Nielsen email

Department of Microbiology and Immunology, Tulane University, (1430 Tulane Avenue) SL-38 (New Orleans) Louisiana (70112-2699) USA

author email corresponding author email

Virology Journal 2009, 6:211doi:10.1186/1743-422X-6-211

The electronic version of this article is the complete one and can be found online at: http://www.virologyj.com/content/6/1/211

Received: 27 October 2009
Accepted: 27 November 2009
Published: 27 November 2009

© 2009 Nielsen; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (
http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The World Health Organization (WHO) estimates that there are over 50 million cases of dengue fever reported annually and approximately 2.5 billion people are at risk. Mild dengue fever presents with headache, fever, rash, myalgia, osteogenic pain, and lethargy. Severe disease can manifest as dengue shock syndrome (DSS) or dengue hemorrhagic fever (DHF). Symptoms of DSS/DHF are leukopenia, low blood volume and pressure encephalitis, cold and sweaty skin, gastrointestinal bleeding, and spontaneous bleeding from gums and nose. Currently, there are no therapeutics available beyond supportive care and untreated complicated dengue fever can have a 50% mortality rate. According to WHO DSS/DHF is the leading cause of childhood mortality in some Asian countries. Dendritic cells are professional antigen presenting cells that are primary targets in a dengue infection. Dengue binds to Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin (DC-SIGN). DC-SIGN has a high affinity for ICAM3 which is expressed in activating T-cells. Previous studies have demonstrated an altered T-cell phenotype expressed in dengue infected patients that could be potentially mediated by dengue-infected DCs.

Dengue is enhanced by three interacting components of the immune system. Dengue begins by infecting dendritic cells which in immature dendritic cells is mediated by DC-SIGN. In mature dendritic cells, antibodies can enhance dengue infection via Fc receptors. Downstream of dendritic cells T-cells become activated and generate the very cytokines implicated in vascular leak and shock in addition to activating effector cells. Both the virus and the antibodies are involved in release of complement and anaphylatoxins which can cause or exacerbate DHF/DSS. These systems are inextricable and strongly associated with dengue pathogenesis.

Dengue Background and Significance

The Dengue Virus is a member of the family Flaviviridae along with other noted viruses Yellow Fever, West Nile, and Japanese Encephalitis. Dengue is a positive stranded RNA arbovirus transmitted by mosquitoes typically Aedes aegypti. Dengue fever has spread from the border lands of Texas to South and Central America, from Africa to the Middle East to Indonesia and Australia. The World Health Organization (WHO) estimates between 50 million and 100 million infections every year all over the world[1]. Dengue fever will often present with fever, rash, headache, and myalgia but can also develop into much more serious cases of Dengue Hemorrhagic Fever and Dengue Shock Syndrome (DHF/DSS). Cases of DHF/DSS are increasing rapidly as the virus increases in geographic range, with approximately 25-37% of symptomatic cases of dengue requiring hospitalization [2]. Case fatality rates for Dengue can be as high as 40-50% in untreated patients [3,4]. The dengue virus has a significant impact on the health of those it infects and represents a burdensome cost to the patient and health infrastructure in places that can ill afford new and varied threats. Patients who acquire the disease the first time (primary infections) are often asymptomatic and will generate immunity to homologous strains of the virus; however, ninety percent of DHF/DSS cases come from a second exposure (secondary infection) to a heterologus strain of dengue[5]. Patients with a secondary heterotypic infection are at least 40-80 times more likely to develop DHF/DSS as patients with a primary infection[6]. The mechanisms by which dengue would cause severe disease are currently being elucidated, but the prevailing literature suggests three interacting components necessary for dengue induced immune enhancement. One component is misregulation of cell mediated immunity. In this context, the cross relationship between B cells and T cells begins with dengue infection of dendritic cells that, in turn, promiscuously activates T cells. T cells during a dengue infection have prolific and cross reactive effector functions in addition to producing copious amounts of cytokines that feature prominently in cases of DHF/DSS. A second component in immune enhancement is Antibody Dependant Enhancement (ADE). Heterologus non-neutralizing antibodies recognize dengue epitopes and enhance infectivity in an Fc dependant manner. Further, antibodies have been implicated in an autoimmune disease which can also exacerbate vascular leak and cytokine production. A third interacting component in immune activation is complement. Many of the key cytokines implicated in the cytokine storm that characterizes DHF/DSS are regulated by Complement proteins and associated anaphylatoxins. These three systems both interact and reinforce each other to create a potentially life threatening situation during a Dengue infection.

Antibodies

Antibody Dependent Enhancement (ADE) has been proposed to be a mechanism by which the immune system may enhance viral pathogenesis[7]. When monkeys were passively immunized concurrently with a viral infection they developed 15 fold higher viral titers than monkeys infected without IgG supplement[8]. However, our understanding of this disease is severely limited by appropriate animal models. Animal models can support viral propagation, but do not exhibit illness unless severely immunocompromised. Epidemiological evidence in Hawaii, Cuba, and Thailand[9] shows populations with previous exposure to the dengue virus are at an increased risk for DHF/DSS. Also infants born to dengue immune mothers were shown to be at an increased risk for DHF/DSS[10]. It's not clear how antibodies enhance viral infection. One hypothesis suggests that non-neutralizing antibodies direct active virions to permissive cells in the immune system[11]. There is no "classical" enhancing antibody since all antibodies will enhance the virus at non-neutralizing concentrations[12]. The Fc receptor (FcR) family is a key component in the ADE pathogenesis model. Fc receptors are found on most phagocytes including dendritic cells and macrophages. The FcR functions as a multisubunit complex that typically binds to IgG and is composed of an α chain for domain recognition, an ITAM (immunoreceptor tyrosine based activation motif), and a γ chain that is responsible for signal transduction. It is thought that IgM does not play a direct role in ADE and instead contributes to disease pathogenesis through activation of complement receptors[13]. IgM antibody enhancement was abrogated when C3R is blocked[14]. A hypothesis suggesting that both IgG and IgM mediate viral enhancement implies that the mechanism for ADE is multivariable. FcR signaling pathways generally leads to activation of the immune cell, though under certain circumstances FcR can lead to immune modulation[15]. The normal interaction of virus with antibody generally leads to neutralization. However, in heterotypic dengue virus infections the antibodies are non-neutralizing and lead to enhancement. Two cell lines expressing either FcγRIA or FcγRIIA have been used to demonstrate that immune complexes can enhance virus infectivity in an FcR mediated fashion. FcγRIA is found exclusively on macrophages and dendritic cells and preferentially binds monomeric IgG, while FcγRIIA is more broadly distributed and preferentially binds immune complexes. When exposed to the immune complexes containing the virus, both cell lines showed enhanced infectivity. However, when the signaling capacity of the Fc Receptor was abrogated, phagocytosis is reduced but enhancement is not affected in FcγRIIA. In the FcγRIA cell line, both the phagocytosis and the immune enhancement are reduced with abrogated cell signaling. The disparity is not yet understood. It does suggest that viral entry and immune enhancement can be mediated by more than a single mechanism. In a different study, three cell types have been used to demonstrate enhancement[16]. U9357 cells which express both FcγRIIA and FcγRI have similar antibody-dependent enhancement capabilities as K562 cells that express just FcγRII. However, the cell type Raji-1 which displays DC-SIGN instead of the Fc receptor showed high viral titers but no antibody enhancement.

Dendritic Cells

The putative receptor and initial target cell for the virus is DC-SIGN (Dendritic Cell-Specific Intercellular adhesion molecule-3 (ICAM3)-Grabbing Non-integrin) (CD209) on dendritic cells [17-19]. Dendritic cells are considered crucial to fighting viral infections because of their ability to acquire and display viral antigens that would otherwise evade the immune system. Dendritic cells affect the dengue virus in two ways. Immature dendritic cells express high levels of DC-SIGN which facilitates initial viral binding and entry. While mature dendritic cells do not posses high levels of DC-SIGN, they do facilitate ADE via FcγIIa and FcγIIb receptors. This effect was most prominent with serum dilutions ranging from 1:640 to 1:2,560 with complete neutralization at 1:10. ADE in dendritic cells can increase viral RNA production by over 100-fold making dendritic cells potent components in dengue pathogenesis[20]. Infected dendritic cells also contribute to vascular leak through the production of matrix metalloproteinases (MMPs). MMP-2, MMP-13, and MMP-9 were all dramatically increased in immature dendritic cells infected with DENV2. As a result cell-cell adhesion in cells co-cultured with infected dendritic cells was reduced, there were changes in cell morphology and actin cytoskeleton, and a decrease in PECAM 1 VE-cadherin expression[21].

DC-SIGN has a high affinity to the ICAM3 molecules expressed on T-cells with a complicated system of cross talk that can lead to a variety of outcomes[22]. To become activated, T-cells go through a time consuming and multiphase process that lasts anywhere from 6-24 hours. Adhesion molecules such as ICAM1 and ICAM3 are critical molecules generated by the T-cell during either phase and can bind to the adhesion molecules of DCs particularly DC-SIGN which is a known target of dengue. These molecules are necessary to form a stable synapse between the DC and T-cell[23]. T-cells, in turn, promote further maturation with the expression of CD40L. Further stimulation by cytokines such as TNFα, IFNγ, IL-6, and others can rapidly promote the maturation and sensitivity of dendritic cells. In contrast, simulation of dendritic cells with IL-10 and other anti-inflammatory cytokines promotes a regulatory phenotype for DCs[24]. Regulatory dendritic cells have been shown to attenuate the immune response and promote tolerance in a way analogous to T-regulatory cells. DCs can also activate B-cells through co-stimulation of CD40, IL-6, and IL-12. The crux of DC interaction is in two places: DC maturation and T-cell synapse. Either point represents a potential target for dengue virus immune evasion. Should DCs fail to mature properly, they will not only fail to stimulate T-cells but they may induce tolerance. The DC-T-cell interaction is highly coordinated and disruption of the DC-T-cell synapse could promote dengue pathogenesis. Dengue-specific memory T-cells undergo simultaneous proliferation and apoptosis during a heterotypic infection. The end result is a less efficient and less specific T-cell response. The mechanism for this is unknown but given the intimacy between DCs and T-cells this represents a potentially productive field of research.

The role of T cells in a dengue infection

There is a clear consensus in the literature about activation of cross-reactive memory T-cells, independent of antibody enhancement, being a pivotal moment in the disease process. As compelling as ADE may be, it can not fully describe a complete picture of dengue pathogenesis such as, intense cytokine storm[25], tissue re-modeling[26], and effector cell activation[27]. The misregulation of T-cells centers around the idea of Original Antigenic Sin, or that a secondary heterotypic dengue infection can stimulate cross-reacting, low affinity T-cells. Activation of effector T-cells and secretion of cytokines define a key development in course of disease associated with dengue virus infection. Four patient studies done in Vietnam[28], India[29], Cuba[30], and Brazil[31] all showed increases in INFγ, TNFα, IL-10, IL-1, IL-6, IL-8, and MCP1 amongst a variety of other cytokines. In vitro studies, IFNγ, IL-6, TNFα, and RANTES upregulation also have been posited as important events in dengue pathogenesis[32]. A review of dengue-associated cytokines listed 15 different cytokines modulated by the disease. In short, these cytokines are consistent with widespread T-cell involvement. In particular IFN and TNFα were strongly associated with disease severity and correlate well with T-cell activation. In addition to increases in cytokine levels cellular markers for T-cell activation, CD69, CD38, and CCR7 have been shown to be increased in dengue infection[33] and IFNγ secretion by dengue specific T-cells has been shown to upregulate the number of Fcγ receptors. These receptors also play a noted role in Antibody dependant enhancement[34].

CD8+ cells have been shown to be important in helping control early viral infection;[35] but, the intense proliferation of CD8+ cells can also be implicated in dengue pathogenesis[36]. In tetramer staining, peripheral T-cells are collected from DHF patients and stained with an MHC tetramer complexed with a dengue-specific peptide. Tetramer positive T-cells can then be isolated and examined. When the tetramer positive cells were stained with Ki67, they show definitive proliferation. The cells are also found to be 'massively' apoptotic as determined by TUNEL staining. The balance of apoptotic cells with proliferative cells may skew T cell responses toward a cross-reactive phenotype. When looking at the specific T-cells involved in secondary infections with DENV1, many of the T-cells show a preference for DENV3 tetramers and infections with DENV2 show preferences in T-cells for DENV1 and 3. Clearly, viruses are able to stimulate a variety of cross-reactive T-cell responses. Memory T-cells have a lower activation threshold than do naïve T-cells[37] and the low affinity non-neutralizing cells are potentially less efficient in clearing the virus[38]. Using a similar approach in a patient currently infected with DENV1 and a previous infection of DENV2, scientists find that 21% of the T-cell population reacted preferentially to DENV2 and 11% were specific for DENV1[39]. Sixty-eight percent of the T-cells in that study were fully cross-reactive between DENV2 and DENV1. When these cells are stimulated with DENV1 derived peptides, 51% of the cells specific for DENV2 responded with either granulation or cytokine release (TNFα/IFNγ) and 75-80% of the cross reactive and DENV1 specific T-cells responded to DENV1 epitopes. The role for the 49% of cells that demonstrate low affinity for DENV1 and do not respond to peptide stimulation is currently unknown, though their proliferation is certainly suggestive. When scientists infect immune competent mice with low dose heterologus dengue viruses they find enhanced CD8+ T-cell responses that were dependent on sequential viral infection as opposed to antibody enhancement. Enhanced cell mediated immunity likely causes target cell lysis through Perforin while bystander cell death is mediated through Fas ligand binding[40].

There is a differential cytokine secretion in response to antigen exposure in CD4+ cells in Dengue infected donors. The highest IFNγ response was seen when cells were exposed homologous antigen. The cross-reaction IFNγ response could potential confer limited protection, however, when cells were exposed to heterologus antigens they produced significantly higher amounts of TNFα in relation to IFNγ[41]. During primary infections in mice, dengue specific CD4+ cells were low; however, in all four viral serotypes of a secondary infection there is a marked increase CD4+ response. Not only did CD4+ cells increase IFNγ production, but they increased CD8+ effector cell activation[42].

Autoimmune disorder

In addition to the antibody enhancement and T-cell disruption, autoimmune disorders are also important to dengue pathogenesis. Anti-NS1 antibody responses in mice have been shown to be cross-reactive in a variety of tissues. When human anti-NS1 antibodies were developed they showed affinity for human fibrinogen, thrombocytes, and endothelial cells[43]. NS1 is a glycoprotein that is secreted by infected cells, heavily present in patient serum supernatants, lacks a membrane spanning motif, but is not, itself, present in the virus. NS1 is known to be a major immune target and high concentrations of anti-NS1 antibodies have been found in severe disease in patient studies[44]. When cells are exposed to NS1 antibodies they undergo intrinsic apoptosis, characterized by DNA fragmentation and phosphatidylserine exposure. Bcl-2 and Bcl-x decreased and P53, Bax, and cytochrome c increased in an iNOS dependent fashion. Apoptosis in response to Anti-NS1 antibody treatment can be blocked with an iNOS inhibitor[45]. The antibody mimicry is intensely inflammatory with anti-NS1 antibodies stimulating the release of IL-6, IL-8, and MCP-1 in an NFκB-dependent manner. Correlated with antibody binding is the upregulation of ICAM1. ICAM1 upregulation can facilitate the adherence of PBMCs to the endothelium. Both NFκB inhibitors and soluble NS1 to block the anti-NS1 antibodies can able to block cytokine release in vitro[46]. Using ELISA flow cytometry, it can be shown that NS1 binds to the surface of uninfected cells. NS1-binding motifs are commonly found in heparan sulfate and chondroitin sulfate E. In mouse experiments, tissues with a preponderance of these proteins are especially susceptible to this interaction and NS1 can be found bound to cells in the lung and liver but not intestine or brain endothelium of mouse tissues[47]. There is a high correlation between NS1 concentration in patient sera and high concentrations of anaphylatoxins which suggests a role for NS1 in complement activation. Further, anaphylatoxins are co-localized to the lungs and plasma in dengue infections. Co-localization experiments with membrane bound NS1 and NS1 specific antibodies showed the formation of complement attack complexes. Fluid phase NS1 can independently activate complement. Supernatants collected from dengue infected cells and mixed with normal sera shows complement activation by NS1 in a dose dependent manner[48]. When Dengue infected supernatants are mixed with purified antibodies from the sera from convalescent patients infected with dengue, complement activation is greatly enhanced. When they added purified NS1 protein to normal or convalescent sera they found synonymous results with NS1 activating complement and complement activation being synergized by anti-dengue antibodies. While NS1 could clearly activate complement in the fluid phase it was unable activate complement when stably expressed on the surface of cells. However, when patient samples were analyzed the found a strong correlation between NS1 concentration and C5b-C9 complex formation.

Complement activated by dengue protein and antibodies

The complement pathway is an ancient defense mechanism designed to serve both in a sentinel capacity and in effector function. There are three pathways to complement activation. The classical pathway begins with the formation of an antibody C1q complex on the surface of a pathogen or pathogen infected cell. This complex, in turn, activates C2 via serine proteases and is itself also a serine protease[49]. The protein C2a combines with newly cleaved protein C4a to generate a C3 convertase, C2aC4b. C3b forms the central protein complex of the complement system either by binding to complement receptors or by complexing with C2aC4b to form C5 convertase, C2aC4bC3b. This complex can bind and stabilize C5a that forms the central effector function of the complement system around which proteins C5-C9 will bind and cooperatively lyse the cell. The mannose binding pathway has a similar cascade as the classical pathway but functions independently of antibody formation. Instead, MASP1 and MASP2 bind to mannose binds to the mannose structures commonly found on pathogens. The Mannan-binding lectin complex is closely homologous to C1q and can activate C2 and C4[50]. In the absence of sialic acid sugars present on normal somatic cells and which are rare on pathogens, C1q begins a lytic cascade. There is a third pathway for complement activation that begins with spontaneous activation of complement proteins. In this pathway the thioester bonds in C3 undergo hydrolysis which allows the binding of Factor B and its subsequent cleavage by plasma protease Factor D. C3b and Factor Bb combine to form a C5 convertase. Runaway complement activation is prevented by binding of Complement Receptor 1 (CR1) and a constitutively active membrane bound Decay Accelerating Factor (DAF, or CD55) which can prevent the complement cascade[51]. In patients with severe dengue, large amounts of C3a have been detected revealing a role for complement in dengue pathogenesis. This finding might be anticipated by the immune complexes that are the putative mechanism for dengue hemorrhage and shock syndromes. C3a finds some measure of importance by being one of several anaphylatoxins produced by complement activation capable of disrupting vasculature. C3a serves to recruit monocytes, macrophages, and dendritic cells, regulates vasodilatation, and increases permeability of small blood vessels and smooth muscle contraction. In macrophages, eosinophiles, and neutrophils anaphylatoxins can induce oxidative burst, basophiles, and mast cells release histamine, and C3a can enhance the effect of other proinflammatory cytokines such as TNFα, IL-6, and SDF-1. While the mechanism for the many reactions precipitated by complement anaphylatoxins has not been fully elucidated, activation of C3aR promotes cytokine expression through AKT phosphorylation as well as MAP kinase activation. C3aR is expressed on key mediators of the immune system like neutrophils, basophiles, eosinophiles, mast cells, monocytes/macrophages, dendritic cells, microglia, as well as, non myeloid cells like astrocytes, epithelial cells, smooth muscles cells, and activated T-cells, but, interestingly, not naïve T-cells. C5aR also activates a number of downstream signaling pathways including PI3K-γ (Phosophoinosital -3 Kinase), PLC (Phospholipase C), PLD (Phospholipase D), Raf and WASP (Wiskott-Aldrich syndrome protein). As a key modulator of the immune system, complement derived proteins clearly have the capacity to affect an extraordinarily large number of cell types and tissues.

Anaphylatoxins

While TNF secretion and immune cell recruitment might be appropriately devastating, the effects of anaphylatoxins (AT) can be equally profound. C3a and C5a regulate vasodilatation, increase permeability of blood vessels, and can trigger degranulation and oxidative burst from neutrophils, eosinophiles, and basophiles. C3a and C5a act on specific receptors to produce local inflammatory responses and when secreted in concentrations high enough to invoke a general systemic response, they cause circulatory collapse similar to an IgE mediated allergic response. ATs modulate the secretion of IL-6, and TNFα from B cells and serve as potent chemoattractants[52]. C5a also works directly on neutrophils and monocytes to increase adhesion molecules, migration, and phagocytosis. Some of the primary sources of C3 are APCs such as dendritic cells and macrophages. Following antigenic stimulation both DCs and T-cells upregulate C3a and C5a receptors, produce C3, alternative complement factors B and D, and downregulate CD55. Reduced CD55 promotes T-cell proliferation and Th1 cytokine expression. In addition to C3 production, APCs cleave C3 leading to autocrine and paracrine C3R signaling. C3R signaling promotes MHC class II expression, IL-12 production and B7 co-stimulatory molecules. Dendritic cells that fail to express C3aR suffer reduced T-cell activation. Anaphylatoxins are well known initiators of inflammation but their role in regulating APC-T cell interactions is becoming increasingly prominent as more information is published. The crux of dengue pathogenesis lies in misregulation of immune processes and complement is sitting, figuratively, at the center of multiple key pathways. Anaphylatoxins become activated by DC antigen uptake and presentation. Cross reactive antibodies activate complement still further. The increase in alternative complement proteins, complement receptors and C protein all facilitate a positive feedback loop that can have dangerous consequences in a dengue infected patient.

Conclusion

Three immune components interact to produce a confluence of symptoms that define DHF/DSS. Dengue virus initially infects immature dendritic cells through the mediation of DC-SIGN. Infected dendritic cells contribute to pathogenesis through production of metalloproteases and cytokines. Downstream of dendritic cells T-cells become activated and generate the very cytokines implicated in vascular leak and shock in addition to activating effector cells. Antibody enhancement is mediated by Fc receptors which are prominently on mature dendritic cells. Viral replication mediated by antibodies is enhanced 100-fold. In addition their effects on dengue replication, antibodies to viral epitopes cross react with cell a protein which has the effect of stimulating CD8 effector cells and production of cytokines and anaphylatoxins. Anaphylatoxins can be generated directly through viral proteins or through formation of an antibody-complement complex. Anaphylatoxins in turn can alter the reactivity of T-cells. Each year 50 million people will acquire dengue fever; 2.5 billion people are at risk. There are few components of the immune that are unaffected by the virus. There are yet questions unanswered and the virus continues to spread unabated. However these immune components are several key elements attractive targets for study that hopefully can advance the field of research.

Competing interests

The author declares that they have no competing interests.

Authors' informations

David Gentry Nielsen was born 27, September 1982 in Reno Nevada. Shortly afterwards he and his family relocated to Brewster Washington. David attended Andrews University where he majored in Biology with a molecular emphasis and minored in Chemistry. He joined the department of Biomedical Sciences in the Tulane School of Medicine in 2005. During the "Hurricane Semester" he accepted a gracious invitation to the University of Washington in order to continue his studies while New Orleans recovered and returned to Tulane in 2006. He completed his Master's degree with this thesis in 2009.

Acknowledgements

I would like to acknowledge Dr. Robert Garry, Dr. Cindy Morris, Dr. Tom Voss, Dr. Deborah Sullivan, and Dr. Wimley for their personal and scientific contributions to this project. Their knowledge and expertise in were critical for its completion.

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    American Journal of Tropical Medicine and Hygiene 2005, 72(4):370-374. PubMed Abstract | Publisher Full Text OpenURL

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 3.http://lib.bioinfo.pl/meid:5176   

Dengue Virus :: immunology

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Institute for Research in Biomedicine, Via Vela 6, 6500 Bellinzona, Switzerland.
If we understand the structural rules governing antibody (Ab)-antigen (Ag) interactions in a given virus, then we have the molecular basis to attempt to design and synthesize new epitopes to be used as vaccines or optimize the antibodies themselves for passive immunization. Comparing the binding of several different antibodies to related Ags should also further our understanding of general principles of recognition. To obtain and compare the three-dimensional structure of a large number of different complexes, however, we need a faster method than traditional experimental techniques. While biocomputational docking is fast, its results might not be accurate. Combining experimental validation with computational prediction may be a solution. As a proof of concept, here we isolated a monoclonal Ab from the blood of a human donor recovered from dengue virus infection, characterized its immunological properties, and identified its epitope on domain III of dengue virus E protein through simple and rapid NMR chemical shift mapping experiments. We then obtained the three-dimensional structure of the Ab/Ag complex by computational docking, using the NMR data to drive and validate the results. In an attempt to represent the multiple conformations available to flexible Ab loops, we docked several different starting models and present the result as an ensemble of models equally agreeing with the experimental data. The Ab was shown to bind a region accessible only in part on the viral surface, explaining why it cannot effectively neutralize the virus.

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[My paper] D J Gubler
Division of Vector-Borne Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado 80522, USA. djg2@cdc.gov
Dengue fever, a very old disease, has reemerged in the past 20 years with an expanded geographic distribution of both the viruses and the mosquito vectors, increased epidemic activity, the development of hyperendemicity (the cocirculation of multiple serotypes), and the emergence of dengue hemorrhagic fever in new geographic regions. In 1998 this mosquito-borne disease is the most important tropical infectious disease after malaria, with an estimated 100 million cases of dengue fever, 500,000 cases of dengue hemorrhagic fever, and 25,000 deaths annually. The reasons for this resurgence and emergence of dengue hemorrhagic fever in the waning years of the 20th century are complex and not fully understood, but demographic, societal, and public health infrastructure changes in the past 30 years have contributed greatly. This paper reviews the changing epidemiology of dengue and dengue hemorrhagic fever by geographic region, the natural history and transmission cycles, clinical diagnosis of both dengue fever and dengue hemorrhagic fever, serologic and virologic laboratory diagnoses, pathogenesis, surveillance, prevention, and control. A major challenge for public health officials in all tropical areas of the world is to develop and implement sustainable prevention and control programs that will reverse the trend of emergent dengue hemorrhagic fever.
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[My paper] A Igarashi
Twenty clones were isolated from cultured Aedes albopictus (Singh) cells in the presence of anti-Chikungunya (CHIK) virus serum. Each clone was tested for its yields of Dengue (DEN) viruses, types 1, 2, 3 and 4, and also CHIK virus. Clone C6 showed the highest yield of each virus tested. Forty-three clones obtained by recloning C6 in the presence of anti-DEN sera showed almost the same virus yields as C6. One of the clones, C6/36, showed mild to extensive cytopathic effects several days after virus infection, in contrast to the original uncloned (SAAR) cells. Fluorescent antibody staining revealed that the amount of virus antigen accumulated in the cytoplasm was almost the same in every cell in the case of clone C6/36, while it was highly heterogeneous for uncloned SAAR cells. Growth curves of the viruses indicated that clone C6/36 gave a significantly higher yield for each virus than uncloned SAAR cells up to 7 days after infection. Virus sensitivity of the C6/36 clone did not change by growing the cells with the medium used for uncloned SAAR cells, nor did the virus sensitivity of uncloned cells increase in medium used for clone C6/36. However, the C6/36 clone became resistant to CHIK virus, but not to DEN or Sindbis viruses, after incubation with the medium used for another A. albopictus cell line (SAAK). The transfer of the specific resistance to CHIK may be mediated by some latent virus related to CHIK.
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Department of Virology, Armed Forces Research Institute, Bangkok, Thailand.
The diagnostic sensitivity and specificity of detection of anti-dengue IgM by antibody capture enzyme-linked immunosorbent assay (ELISA) was investigated in dengue infections in a variety of clinical settings. Sera from uninfected controls were uniformly negative. Serial specimens from experimental and natural infections showed that viremia and fever terminated as anti-dengue IgM became detectable. Anti-dengue IgM appeared in most cases by the 3rd afebrile day of illness and declined to undetectable levels after 30-60 days. Assay sensitivity was 78% in admission sera (924/1,183; 95% CI = 75-81%) and 97% in paired sera (1,030/1,062; 95% CI = 96-98%) thus exceeding or matching the performance of the hemagglutination-inhibition assay. Measurement of the anti-dengue IgM to anti-Japanese encephalitis IgM ratio correctly identified all sera from 112 patients with strictly defined Japanese encephalitis and 98%(307/312; 95% CI = 96-99%) of sera from patients whose dengue infections were confirmed by virus isolation. Dengue infections could be classified as primary or secondary by determining the ratio of units of dengue IgM to IgG antibody. We propose that measurement of dengue and Japanese encephalitis IgM and IgG antibodies upon admission and discharge from hospital care should replace the hemagglutination inhibition assay as the standard dengue serologic technique in regions where these 2 viruses co-circulate.
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Liu Centre for the Study of Global Issues, University of British Columbia, Vancouver, Canada. jerryspiegel@aol.com
This review is an update of dengue and dengue haemorrhagic fever (DHF) based on international and Cuban experience. We describe the virus characteristics and risk factors for dengue and DHF, and compare incidence and the case fatality rates in endemic regions (southeast Asia, western Pacific, and the Americas). The clinical picture and the pathogenesis of the severe disease are explained. We also discuss the viral, individual, and environmental factors that determine severe disease. Much more research is necessary to clarify these mechanisms. Also reviewed are methods for viral isolation and the serological, immunohistochemical, and molecular methods applied in the diagnosis of the disease. We describe the status of vaccine development and emphasise that the only alternative that we have today to control the disease is through control of its vector Aedes aegypti.
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[My paper] S B Halstead
Health Sciences Division, Rockefeller Foundation, New York, New York 10036.
Dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) in children is reliably associated with the presence of dengue antibody--actively or passively acquired--before the onset of illness. Limited observations by electron microscopy and fluorescent antibody testing and the recovery of virus from tissues obtained at autopsy show that dengue viruses are consistently associated with cells of mononuclear phagocyte lineage. In particular, virus is associated with Kupffer cells, pulmonary macrophages, and mononuclear cells in skin and blood. Endothelial cells fail to demonstrate necrosis or inflammatory changes. Since acute vascular permeability, shock, and hemorrhage occur late in illness, a plausible hypothesis is that phlogistic factors, resulting from interactions with elements of the immune response, are released from virus-infected mononuclear phagocytes. Such phenomena as generalized depression of mitotic activity of bone marrow cells, destruction of mature polymorphonuclear leukocytes, complement activation, and abnormal hemostasis may serve as markers of these phlogistic factors. It will be of interest to establish whether other viral hemorrhagic fevers involve the same target cells as in DHF/DSS and are mediated by similar effector mechanisms.
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In January 1980, the municipal area of Rayong, Thailand, and contiguous suburban villages were chosen for a long-term study on dengue epidemiology. From 3,185 children randomly sampled in schools and households, the population prevalence of neutralizing antibody to the four dengue serotypes was estimated. To estimate the incidence of infection with each dengue virus serotype (dengue seroconversions), first grade children were re-bled in January 1981 (cohort study). Children admitted to hospital were studied for dengue virus isolation and antibody responses in paired sera. An epidemic of dengue occurred in 1980. Plaque reduction neutralization tests of 1,009 pre-epidemic sera from children aged less than 1-10 years of age determined that 3.3% were immune to dengue 1, 13.2% to dengue 2, 6.4% to dengue 3, and 5.8% to dengue 4. Examination of pre- and post-epidemic cohort blood samples revealed that the incidence of dengue infection in 251 seronegative children was 39.4%(15.1% dengue 1, 11.1% dengue 2, 2.0% dengue 3, 4.8% dengue 4, and 6.4% two or more dengue viruses). Among the 52,935 residents of the study area, there were 22 cases of virologically and clinically confirmed dengue shock syndrome, in children 15 years or younger. All 22 shock syndrome cases had secondary type antibody responses. Eight of 22 had been included in the random serologic sample prior to onset of shock; five had been immune to dengue 1, two to dengue 3, one to dengue 4, and none to dengue 2. Despite the high rate of dengue 1 infections in 1980, only dengue 2 viruses were recovered from dengue shock syndrome cases, including two dengue 1 immune children with pre-illness serum specimens. Although the pre-epidemic prevalence of antibodies to dengue 1 was the lowest to any type, children with this immunologic background contributed disproportionately to shock cases. In descending order of magnitude, risk factors for dengue shock syndrome in Rayong were secondary infections with dengue 2 which followed primary infections with dengue 1, dengue 3, or dengue 4.
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[My paper] A L Rothman, F A Ennis
Center for Infectious Disease and Vaccine Research, University of Massachusetts Medical School, Worcester, Massachusetts, 01655, USA. alan.rothman@umassmed.edu
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During the fall of 1981, a new method for the routine isolation and identification of dengue viruses in Puerto Rico was implemented utilizing C6/36 cell cultures and serotype specific antidengue monoclonal antibodies. A blind comparison of the monoclonal antibody indirect fluorescent antibody test (IFAT) and the complement fixation (CF) test for identification of 89 newly isolated dengue viruses of all four serotypes from the Caribbean, Asia and Africa showed 100% agreement. Although virus isolation rates were slightly lower than with the mosquito inoculation technique, use of the C6/36 cell culture system was much less time-consuming and allowed the processing of larger numbers of sera. Beginning in November 1981, a new virologic surveillance system was begun in Puerto Rico. Acute sera from persons with suspected dengue were selected for virus isolation attempts on the basis of geographic area of residence on the island, day after onset the blood was taken and clinical signs and symptoms. These sera were processed for virus isolation in C6/36 cell cultures, and virus isolates were identified by the IFAT using the monoclonal antibodies. Using this system, 2,702 sera were tested from November 1981 through August 1982. Dengue virus was isolated from 518, for an isolation rate of 19.2%. Dengue 1 was the predominant virus until December 1981, when dengue 4 became dominant. The changing patterns of dengue 1 and 4 distribution by time and geographic location on Puerto Rico were followed. This system allows the dengue viruses being transmitted in an area to be monitored with a minimal amount of effort and provides the early warning capability necessary to predict epidemic dengue.
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