Hemorrhagic fever with renal syndrome is a serious public health problem in China.
The purpose of this study was to investigate the induction of inducible nitric oxide synthase (iNOS) mRNA in the brain tissue of rats and mice under the following experimental conditions: in rats infected with borna disease virus and rabies virus, in mice infected with herpes simplex virus, and in rats after the induction of experimental allergic encephalitis. The results showed that iNOS mRNA, normally nondetectable in the brain, was present in animals after viral infection or after induction of experimental allergic encephalitis. The induction of iNOS mRNA coincided with the severity of clinical signs and in some cases with the presence of inflammatory cells in the brain. The results indicate that nitric oxide produced by cells induced by iNOS may be the toxic factor accounting for cell damage and this may open the door to approaches to the study of the pathogenesis of neurological diseases.The mechanisms involved in the development of central nervous system (CNS) lesions are readily understood only in those pathological conditions in which there is evidence that a virus destroys its target cell as a direct cytopathic consequence of viral replication (e.g., polio virus or other neurotrophic viruses; refs. 1 and 2). However, the effector mechanisms involved in tissue damage associated with a far wider variety of viral infections of the CNS, involving such viruses as the measles and rubella viruses as well as human immunodeficiency virus 1, are unclear. Likewise, the mediators responsible for the CNS damage associated with chronic neurologic diseases such as multiple sclerosis remain the subject of speculation. Interestingly, morphologic analyses have revealed that lesions in affected brain tissues are frequently surrounded by infiltrating inflammatory cell populations. Although the precise role that these cells play in CNS pathology is the subject of ongoing investigation, previous studies have focused on the ability of leukocyte populations to generate proinflammatory cytokines (e.g., interleukin 1, tumor necrosis factor, etc.), neurotoxins (e.g., quinolinic acid), or reactive oxygen intermediates (3). Recently, increased attention has focused on the possibility that reactive nitrogen intermediates (NOI) generated by a family of cytochrome P-450 reductase-like enzymes, the nitric oxide synthases (NOS), directly damage host tissues in a diverse array of pathogenic states (4).To date, at least three NOS genes have been cloned and characterized, and these have been provisionally categorized on the basis of their sensitivity to regulation by Ca2+ transients (4). In this schema, NOS forms that bind calmodulin in a reversible Ca2+-dependent manner are termed the constitutive forms of NOS, and those forms of the enzyme that bind calmodulin tightly at resting [Ca2+] are termed inducible NOSs (iNOSs). After the addition of rapid-acting agonists, the constitutive NOS system generates only low levels of the NOI, nitric oxide (NO), whereas the iNOS system begins to generate NO several hours after exposure to cyto...
Nitric oxide (NO) has been implicated as a pathogenic mediator in a variety of central nervous system (CNS) We have reported (1) that Borna disease virus, rabies virus, and herpes simplex virus induce the increased expression of inducible nitric oxide synthase (iNOS) mRNA in the brains of intrathecally infected mice and rats. We and others (2) also found that the induction of experimental allergic encephalomyelitis resulted in a similar increase in iNOS mRNA expression, suggesting that a similar phenomenon may occur in the brains of patients with multiple sclerosis (MS). We investigated this hypothesis by detecting iNOS mRNA in extracts of brains from patients who died with MS and from extracts of brain tissues from patients who died from nonneurological diseases. We have also colocalized the iNOS expressing cells by using immunocytochemical techniques combined with reverse transcriptase (RT) driven-in situ PCR and demonstrated the presence of iNOS protein by the same double labeling procedures. Finally, as a surrogate marker for nitric oxide (NO) presence, we have immunocytochemically localized nitroty-The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.rosine adducts in histological sections of brain from MS patients. MATERIALS AND METHODSSources and Selection of Specimens. The samples used in these studies were collected from patients with an antemortem diagnosis of MS based on clinical presentation and reconfirmed by histopathology after death. All MS samples were found to contain pathognomonic MS plaques; control brains were examined and found to be pathologically unremarkable. In most cases, autopsy samples were of frontal lobes, which provided mixed white and gray matter.In two of the MS cases, special efforts were made to preserve the tissue morphology. Small portions of the brain specimens were frozen in liquid nitrogen immediately after sectioning and then stored at -70°C. This procedure preserved the architecture of the brain significantly better than direct freezing of fresh brain specimens at -80°C, which results in ice crystal formation in the tissue and distorts its architecture.Cell Culture and Cytokine Activation. A549 human pulmonary epithelial cells were purchased from the American Type Culture Collection. Cells were grown in Ham's F-12 medium supplemented with 10% (vol/vol) fetal calf serum, penicillin (50 units/ml), streptomycin (50 ,ug/ml), and 5 ,tM L-glutamine. Cells were seeded into 6-well tissue culture clusters (Falcon) for Northern blot analysis or seeded into 8-well Lab-Tek culture slides (Nunc) for RT-in situ PCR. For those cultures stimulated for the expression of iNOS, interleukin 1(3 (IL-1,B at 100 units/ml), tumor necrosis factor a (TNF-a at 10 ng/ml), and interferon y (IFN-,y at 500 units/ml) were added for 8 h.For use in Northern blot analysis, the cells were scraped from the culture substrate, washed three ti...
Japanese encephalitis is an acute zoonotic, mosquito-borne disease caused by Japanese encephalitis virus (JEV). Japanese encephalitis is characterized by extensive inflammation in the central nervous system (CNS) and disruption of the blood-brain barrier (BBB). However, the pathogenic mechanisms contributing to the BBB disruption are not known. Here, using a mouse model of intravenous JEV infection, we show that virus titers increased exponentially in the brain from 2 to 5 days postinfection. This was accompanied by an early, dramatic increase in the level of inflammatory cytokines and chemokines in the brain. Enhancement of BBB permeability, however, was not observed until day 4, suggesting that viral entry and the onset of inflammation in the CNS occurred prior to BBB damage. In vitro studies revealed that direct infection with JEV could not induce changes in the permeability of brain microvascular endothelial cell monolayers. However, brain extracts derived from symptomatic JEV-infected mice, but not from mock-infected mice, induced significant permeability of the endothelial monolayer. Consistent with a role for inflammatory mediators in BBB disruption, the administration of gamma interferon-neutralizing antibody ameliorated the enhancement of BBB permeability in JEV-infected mice. Taken together, our data suggest that JEV enters the CNS, propagates in neurons, and induces the production of inflammatory cytokines and chemokines, which result in the disruption of the BBB. IMPORTANCEJapanese encephalitis (JE) is the leading cause of viral encephalitis in Asia, resulting in 70,000 cases each year, in which approximately 20 to 30% of cases are fatal, and a high proportion of patients survive with serious neurological and psychiatric sequelae. Pathologically, JEV infection causes an acute encephalopathy accompanied by BBB dysfunction; however, the mechanism is not clear. Thus, understanding the mechanisms of BBB disruption in JEV infection is important. Our data demonstrate that JEV gains entry into the CNS prior to BBB disruption. Furthermore, it is not JEV infection per se, but the inflammatory cytokines/ chemokines induced by JEV infection that inhibit the expression of TJ proteins and ultimately result in the enhancement of BBB permeability. Neutralization of gamma interferon (IFN-␥) ameliorated the enhancement of BBB permeability in JEV-infected mice, suggesting that IFN-␥ could be a potential therapeutic target. This study would lead to identification of potential therapeutic avenues for the treatment of JEV infection. J apanese encephalitis (JE) is an acute zoonotic, mosquito-borne infectious disease caused by JE virus (JEV) infection. JEV is a single-stranded, positive-sense RNA virus, belonging to the genus Flavivirus of the family Flaviviridae (1, 2). JEV is a neurotropic virus and infection causes an acute encephalopathy. JE commonly affects children in the South Pacific regions of Asia (3, 4). Of nearly 70,000 cases of JE reported each year, ca. 20 to 30% of cases are fatal, and a high proport...
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