The pathogenesis of spinal cord involvement in the encephalomyelitis of mice caused by neuroadapted Sindbis virus infection

Weanling mice develop an acute encephalomyelitis with high mortality after intracerebral inoculation of neuroadapted Sindbis virus. The mice develop kyphoscoliosis and hindlimb paralysis. Immunohistochemical and in situ hybridization studies have demonstrated virus in the gray matter of the brain and spinal cord. Ventral horn cells are prominently infected, providing an anatomical basis for the clinical poliomyelitis. A novel route of spread of inoculated virus within the central nervous system has been found. The virus enters the ventricular system, and then travels caudally in the central canal of the spinal cord where ependymal cells are infected. The virus subsequently spreads into the gray matter. The distribution of virus in the spinal cord is likely dependent both on variations in the susceptibility of neural cells and on this route of entry and subsequent spread.     

Autoimmune pathogenesis in dengue virus infection

The pathogenic mechanisms of dengue hemorrhagic fever and dengue shock syndrome (DHF/DSS) caused by dengue virus (DV) infection remain unresolved. Patients with DHF/DSS are characterized by several manifestations, including severe thrombocytopenia, vascular leakage, and hepatomegaly. In addition to the effect of virus load and virus variation, abnormal immune responses of the host after DV infection may also account for the progression of DHF/DSS. Actually, viral autoimmunity is involved in the pathogenesis of numerous viral infections, such as human immunodeficiency virus, human hepatitis C virus, human cytomegalovirus, herpes simplex virus, Epstein- Barr virus, and DV. In this review, we discuss the implications of autoimmunity in dengue pathogenesis. Antibodies directed against DV nonstructural protein 1 (NS1) showed cross-reactivity with human platelets and endothelial cells, which lead to platelet and endothelial cell damage and inflammatory activation. Based on these findings, we hypothesize that anti-DV NS1 is involved in the pathogenesis of DF and DHF/DSS, and this may provide important information in dengue vaccine development.     

Experimental herpetic infection of the CNS with predominant involvement of the spinal cord

Clinical, morphological, and virological characteristics of a model of herpes infection of the CNS with predominant involvement of the spinal cord, an acute ascending myelitis with primary demyelinization, are presented. The development of spinal cord lesions after HSV inoculation into the spleen was observed in different species of laboratory animals: mice, hamsters, guinea pigs, and rabbits; some animals (30%-70%) developed generalized infection with the involvement of the brain. The frequency of the spinal cord involvement was found to depend on the age of the animal and the dose of the virus-containing inoculum. Differences in the clinical and morphological manifestations of herpes infection were due to different mechanisms of herpes simplex virus spread in the body: either centripetally on the axons of the visceral nerves innervating the spleen into the thoracal cord, or hematogenic disseminations with virus penetration across the hematoencephalic barrier. The total duration of the disease was 3-12 days depending on the animal species.     

Role of antibodies in controlling dengue virus infection

The incidence and disease burden of arthropod-borne flavivirus infections have dramatically increased during the last decades due to major societal and economic changes, including massive urbanization, lack of vector control, travel, and international trade. Specifically, in the case of dengue virus (DENV), the geographical spread of all four serotypes throughout the subtropical regions of the world has led to larger and more severe outbreaks. Many studies have established that recovery from infection by one DENV serotype provides immunity against that serotype, whereas reinfection with another serotype may result in severe disease. Pre-existing antibodies thus play a critical role in controlling viral infection. Both neutralization and enhancement of DENV infection by antibodies are thought to be related to the natural route of viral entry into cells. In this review, we will describe the current knowlegde on the mechanisms involved in flavivirus cell entry and discuss how antibodies may influence the course of infection towards neutralization or enhancement of viral disease.     

A detrimental role for invariant natural killer T cells in the pathogenesis of experimental dengue virus infection

Dengue virus (DENV), a member of the mosquito-borne flaviviruses, is a serious public health problem in many tropical countries. We assessed the in vivo physiologic contribution of invariant natural killer T (iNKT) cells, a population of nonconventional lipid-reactive αβ T lymphocytes, to the host response during experimental DENV infection. We used a mouse-adapted DENV serotype 2 strain that causes a disease that resembles severe dengue in humans. On DENV challenge, splenic and hepatic iNKT cells became activated insofar as CD69 and Fas ligand up-regulation and interferon-γ production. C57BL/6 mice deficient in iNKT cells (Jα18(-/-)) were more resistant to lethal infection than were wild-type animals, and the phenotype was reversed by adoptive transfer of iNKT cells to Jα18(-/-) animals. The absence of iNKT cells in Jα18(-/-) mice was associated with decreased systemic and local inflammatory responses, less liver injury, diminished vascular leak syndrome, and reduced activation of natural killer cells and neutrophils. iNKT cell functions were not necessary for control of primary DENV infection, after either natural endogenous activation or exogenous activation with the canonical iNKT cell agonist α-galactosylceramide. Together, these data reveal a novel and critical role for iNKT cells in the pathogenesis of severe experimental dengue disease.     

Pathogenesis of vascular leak in dengue virus infection

Endothelial dysfunction leading to vascular leak is the hallmark of severe dengue. Vascular leak typically becomes clinically evident 3–6 days after the onset of illness, which is known as the critical phase. This critical phase follows the period of peak viraemia, and lasts for 24–48 hr and usually shows rapid and complete reversal, suggesting that it is likely to occur as a result of inflammatory mediators, rather than infection of the endothelium. Cytokines such as tumour necrosis factor‐α, which are known to be elevated in the critical phase of dengue, are likely to be contributing factors. Dengue NS1, a soluble viral protein, has also been shown to disrupt the endothelial glycocalyx and thus contribute to vascular leak, although there appears to be a discordance between the timing of NS1 antigenaemia and occurrence of vascular leak. In addition, many inflammatory lipid mediators are elevated in acute dengue viral infection such as platelet activating factor (PAF) and leukotrienes. Furthermore, many other inflammatory mediators such as vascular endothelial growth factor and angiopoietin‐2 have been shown to be elevated in patients with dengue haemorrhagic fever, exerting their action in part by inducing the activity of phospholipases, which have diverse inflammatory effects including generation of PAF. Platelets have also been shown to significantly contribute to endothelial dysfunction by production of interleukin‐1β through activation of the NLRP3 inflammasome and also by inducing production of inflammatory cytokines by monocytes. Drugs that block down‐stream immunological mediator pathways such as PAF may also be beneficial in the treatment of severe disease.     

Effect of immunosuppression on dengue virus infection in mice

Mean survival time following intracerebral inoculation of dengue virus was reduced and the titre of the virus in the brain of immunosuppressed mice was markedly increased. A single dose of cyclophosphamide given 24 h after dengue virus i.c. or i.p. substantially reduced the number of antibody forming cells in the spleen. Three doses of dengue virus, each followed by cyclophosphamide 24 h later, produced specific hyporesponsiveness to the dengue virus but not to a heterologous virus (Coxsackie B4), with a reduction in antibody forming cells in the spleen of such animals against dengue virus but not against Coxsackie B4 virus. Adoptive immunity by antiserum was abolished along with increased titres of the virus in the brain of immunosuppressed mice but the protection could be restored by a second dose of antiserum. Pre-treatment of mice with immune or normal spleen cells i.v. or reconstitution of immunosuppressed mice by such cells had no effect. Thus, humoral antibodies play a crucially important role in host defence mechanism in recovery of mice from primary dengue virus infection.     

Experimental Zika virus infection induces spinal cord injury and encephalitis in newborn Swiss mice

A widespread epidemic of Zika virus (ZIKV) infection was reported in 2015 in South and Central America, with neurological symptons including meningoencephalitis and Guillain-Barré syndrome in adults, besides an apparent increased incidence of microcephaly in infants born to infected mothers. It is becoming a necessity to have a trustworthy animal model to better understand ZIKV infection. In this study we used newborn white Swiss mice as a model to investigate the ZIKV strain recently isolated in Brazil. ZIKV was inoculated via intracerebral and subcutaneous routes and analysed through gross histopathology and immunohistochemistry. Here we demonstrated first that the intracerebral group (ICG) displayed severe cerebral lesions, with neuronal death, presence of apoptotic bodies, white matter degeneration and neutrophil perivascular cuffing. In the subcutaneous group (SCG), we observed moderate cerebral lesions, morphologically similar to that found in ICG and additional myelopathy, with architectural loss, marked by neuronal death and apoptotic bodies. Interestingly, we found an intense astrogliosis in brain of both groups, with increased immunoexpression of GFAP (glial fibrillary acidic protein) and presence of hypertrophic astrocytes. The spinal cord of subcutaneous group (SCG) exhibited reduction of astrocytes, but those positive for GFAP were hypertrophic and presented prolonged cellular processes. Finally significant lesions in the central nervous system (CNS) were present in newborn mice inoculated by both routes, but SCG method led to an important neurological manifestations (including myelopathy), during a longer period of time and appears for us to be a better model for ZIKV infection.     

Antibody-dependent enhancement of dengue virus infection in vitro by undiluted sera from monkeys infected with heterotypic dengue virus

Two monkeys (Macaca fascicularis) each were infected with dengue virus type 1 (DENV-1) and type 2 (DENV-2). High levels of neutralizing antibody to homotypic serotype were detected from day 10 to week 58 after infection. Levels of cross-reactive neutralizing antibody to other serotypes were at lower levels or undetectable. Serum samples collected from day 10 to week 58 enhanced infection by homotypic and heterotypic serotypes of DENV when diluted, demonstrating antibody-dependent enhancement (ADE). The ADE activities to heterotypic and homotypic dengue virus infections peaked at dilutions of 1:10–1:100 and 1:100–1:1,000, respectively. Serum samples collected enhanced heterotypic dengue virus infection without any dilution. The results indicate that sera from infected monkeys have an ability to enhance heterotypic dengue virus infection in vitro without dilution, although some of these sera also possess neutralizing activity.     

Acute transverse myelitis following dengue virus infection.

The spinal cord is infrequently affected following dengue virus infection. We report a case of transverse myelitis that developed 2 weeks after acute dengue infection and review the literature to elucidate the pathogenesis of spinal cord involvement in dengue infection. We postulate that temporal factors may play a role in the different clinical manifestations, i.e. that acute parainfectious dengue infection presents with flaccid paralysis, whereas late-stage (postinfectious) dengue infection, presents with spastic weakness. Further studies need to be performed to elucidate the mechanisms of spinal neurological damage in dengue.     

重组登革病毒E蛋白结构域Ⅲ抑制登革病毒感染的初步研究

目的 了解原核表达的登革病毒(dengue virus, DV)的E蛋白结构域Ⅲ直接抑制登革病毒感染及其抗体的中和作用.方法 在大肠埃希菌中表达1~4型登革病毒E蛋白结构域Ⅲ(EⅢ).重组蛋白纯化后,进行阻断DV-2感染BHK~21细胞试验.用重组蛋白制备免疫血清,检测抗体中和作用.结果 在大肠埃希菌中成功表达了1-4型登革病毒E蛋白结构域埃希菌,4型重组E蛋白结构域Ⅲ均能够阻断2型DV感染,4型重组蛋白的免疫血清均能中和2型DV,但中和抗体效价不同.结论 原核表达的登革病毒结构域Ⅲ可以直接抑制病毒感染,所产生的抗体具有中和作用.直接抑制和中和抗体均对同型病毒作用较强.     

The pathogenesis of respiratory syncytial virus infection in cotton rats.

The cotton rat is susceptible to respiratory synctial virus infection in both the upper and lower portions of the respiratory tract. Virus replicates to high titer in the nose and lungs and to relatively low titer in the trachea. Immunofluorescence studies demonstrated viral antigen in the nasal epithelium and the bronchial and bronchiolar epithelium but not in the trachea or the alveolar cells of the lungs. Histopathologic changes included a desquamative, exudative rhinitis of moderate severity and a mild proliferative bronchiolitis. Serum neutralizing antibody developed in all animals by the ninth day after infection, reaching extremely high titer in several instances. Unlike the previously described response of experimentally infected infant ferrets, cotton rats are uniformly susceptible to pulmonary infection throughout life, thereby offering a model for long-term pulmonary studies heretofore not available.     

Dengue virus infection: predictors for severe dengue

Dengue virus (DENV) infection is a mosquito born disease that is endemic in all WHO regions, except European region, and may present a broad range of severity. It may appear as an asymptomatic condition, dengue fever (DF), or life threatening forms, such as dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS), or the currently defined severe dengue. Currently there are means to diagnose DENV infection, but there is no accurate means to early predict the progress into severe manifestations. Therefore, this article addresses the factors that might be used to predict the progress into severe dengue. Predictors for severe dengue are the previously established warning signs, and coexisting conditions, as is recommended by the WHO, in addition to Caucasian race, and people with AB blood group. In the future, viral load assessment, viral serotype testing, NS1, cytokine, elastase, hyaluronan, soluble thrombomodulin, and NO level, and circulating endothelial cell detection test are promising to be studied and developed as early predictors of severe dengue.     

The pathogenesis of respiratory syncytial virus infection in infant ferrets.

The infant ferret is susceptible to respiratory syncytial virus infection in both the upper and lower respiratory tracts. In the nose, viral replication is restricted to the surface respiratory epithelium in the nasal passages and turbinates. In the lungs, viral replication is of a lower order of magnitude and is localized in the alveolar cells. The pattern of viral replication in nasal tissues is independent of the age of the animal at infection, whereas the pattern in lung tissues shows a striking age dependence, with viral replication progressively decreasing as a function of age. Thes age dependence appears to be due to an intrinsic age-related mechanism yet to be defined. We feel that the infant ferret is an acceptable model for the study of respiratory syncytial virus disease and that the study of age dependence observed in ferrets may allow elucidation of the mechanisms involved in the age dependence seen in humans.