High levels of cytokine-producing cells in the lung tissues of patients with fatal hantavirus pulmonary syndrome

Andes Hantavirus as possible cause of disease in travellers to South America

BACKGROUND

Hantaviruses in Europe and Asia cause haemorrhagic fever with renal syndrome and epidemic nephritis (mortality rate <1-15%). New strains of Hantaviruses cause Hantavirus pulmonary syndrome (HPS) from Canada to South America. Andes virus mortality rate is about 30% in Chile.

METHOD

Clinical charts of 54 patients were reviewed.

RESULTS

Inhalation of aerosolized urine, faeces or saliva of rodents is the principal cause of infection. The incubation period is between 8 and 43 days. The main prodromal symptoms are: myalgias, fever, fatigue, gastrointestinal disorders, dyspnoea, petechiae and coughing. After the 4th day pulmonary oedema, hypotension and renal failure appear. Haemorrhagic disorders may occur. The first laboratory tests presenting alterations are: haemoconcentration, leukocytosis, low platelet count <150 micro/L, and presence of immunoblasts. The treatment is supportive: mechanical ventilation, vasopressor drugs, haemofiltration or haemodialysis, and extracorporeal membrane oxygenation. There is no specific treatment for HPS. Preventive measures must be empathised.

CONCLUSION

The principal risk factors for tourists are: accommodation in abandoned or closed up facilities; failure to use indicated pathways when walking in forests; camping outside recommended areas; drinking water from natural sources and fishing in risk areas. The risk of infection for foreign tourists in Chile is low.

Drotrecogin alpha (activated) in two patients with the hantavirus cardiopulmonary syndrome

Hantavirus cardiopulmonary syndrome (HCPS) is associated with rapid cardiopulmonary collapse from endothelial injury, resulting in massive capillary leak, shock and severe hypoxemic respiratory failure. To date, treatment remains supportive and includes mechanical ventilation, vasopressors and extracorporeal membrane oxygenation, with mortality approaching 50%. Two HCPS survivors initially given drotrecogin alpha (activated) (DAA) for presumed bacterial septic shock are described. Vasoactive medications were required for a maximum of 52 h, whereas creatinine levels and platelet counts normalized within seven to nine days. Given the similar presentations of HCPS and bacterial septic shock, empirical DAA therapy will likely be initiated before a definitive diagnosis of HCPS is made. Further observations of DAA in HCPS seem warranted.

Levels of soluble vascular cell adhesion molecule-1 and soluble intercellular adhesion molecule-2 in plasma of patients with hemorrhagic fever with renal syndrome, and significance of the changes in level

Hemorrhagic fever with renal syndrome (HFRS) is an acute viral disease characterized by endothelial dysfunction. Vascular cell adhesion molecule (VCAM)-1 and intercellular adhesion molecule (ICAM)-2 provide costimulatory signals for the activation of T lymphocytes; these adhesion molecules play key roles in leukocyte adherence and propagation of inflammatory responses. They may be involved in the immunologic response that leads to vascular endothelial cell (VEC) and kidney damage of HFRS patients, and increased levels of soluble (s)VCAM-1 and sICAM-2 in plasma may indicate the severity of HFRS. We examined the presence of sVCAM-1 and sICAM-2 in 52 plasma samples collected from 52 patients. We tested these plasma samples for sVCAM-1 and sICAM-2 by double-antibody sandwich ELISA. We found variable, but persistently elevated, levels of sVCAM-1 and sICAM-2 throughout the various phases and types of the disease, which suggested sVCAM-1 may play an important role in the immunopathological lesions of HFRS and is closely correlated to the severity of HFRS and the degree of kidney damage. sICAM-2 may be associated with the hyperfunctioning of the cellular immune response.

Viral hemorrhagic fevers

A taxonomically diverse set of single-stranded ribonucleic acid(ssRNA) viruses from four diverse viral families Arenaviridae,Bunyaviridae, Filoviridae, and Flaviviridae cause an acute systemic febrile syndrome called viral hemorrhagic fever (VHF). The syndrome produces combinations of prostration, malaise, increased vascular permeability, and coagulation maladies. In severe illness,VHF may include generalized bleeding but the bleeding does not typically constitute a life-threatening loss of blood volume. To a certain extent, it is a sign of damage to the vascular endothelium and is an indicator of disease severity in specific target organs. Although the viruses that cause hemorrhagic fever (HF) can productively replicate in endothelial cells, much of the disease pathology including impairment to the vascular system is thought to result primarily from the release of a variety of mediators from virus-infected cells, such as monocytes and macrophages that subsequently alter vascular function and trigger the coagulation disorders that epitomize these infections. While significant progress has been made over the last several years in dissecting out the molecular biology and pathogenesis of the HF viruses, there are currently no vaccines or drugs licensed available for most of the VHFs.

Increased permeability of human endothelial cell line EA.hy926 induced by hantavirus-specific cytotoxic T lymphocytes

Hantavirus infection causes two human diseases, hemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome. The typical feature of these diseases is increased permeability in microvascular beds in the kidneys and the lungs, respectively. The mechanism of capillary leakage, however, is not understood. Some evidence suggests that hantavirus disease pathogenesis is immunologically mediated by cytotoxic T lymphocytes and other immune cells in target organs producing inflammatory cytokines. In this study we examined the roles of virus-specific cytotoxic T lymphocytes in increased permeability of human endothelial cells infected with hantavirus. We used a human CD8(+) hantavirus-specific cytotoxic T lymphocyte line, 1A-E2, specific for the HLA-A24-restricted epitope in Sin Nombre and Puumala virus G2 protein, and the human endothelial cell line, EA.hy926 that expresses HLA-A24 molecule. The cytotoxic T lymphocyte line recognized and lysed target cells infected with Sin Nombre virus, and in transwell permeability assays increased permeability of EA.hy926 cell monolayer infected with Sin Nombre virus or recombinant adenovirus expressing the Sin Nombre virus G2 protein. These results suggest that cytotoxic T lymphocyte activity contribute to capillary leakage observed in patients with hantavirus pulmonary syndrome or hemorrhagic fever with renal syndrome.

Profiling helper T cell subset gene expression in deer mice

Background

Deer mice (Peromyscus maniculatus) are the most common mammals in North America and are reservoirs for several zoonotic agents, including Sin Nombre virus (SNV), the principal etiologic agent of hantavirus cardiopulmonary syndrome (HCPS) in North America. Unlike human HCPS patients, SNV-infected deer mice show no overt pathological symptoms, despite the presence of virus in the lungs. A neutralizing IgG antibody response occurs, but the virus establishes a persistent infection. Limitations of detailed analysis of deer mouse immune responses to SNV are the lack of reagents and methods for evaluating such responses.

Results

We developed real-time PCR-based detection assays for several immune-related transcription factor and cytokine genes from deer mice that permit the profiling of CD4⁺ helper T cells, including markers of Th1 cells (T-bet, STAT4, IFNγ, TNF, LT), Th2 cells (GATA-3, STAT6, IL-4, IL-5) and regulatory T cells (Fox-p3, IL-10, TGFβ1). These assays compare the expression of in vitro antigen-stimulated and unstimulated T cells from individual deer mice.

Conclusion

We developed molecular methods for profiling immune gene expression in deer mice, including a multiplexed real-time PCR assay for assessing expression of several cytokine and transcription factor genes. These assays should be useful for characterizing the immune responses of experimentally- and naturally-infected deer mice.

Bioregulators as prototypic nontraditional threat agents

Bioregulators are naturally occurring organic compounds that regulate a multitude of biologic processes. Under natural circumstances, bioregulators are synthesized in minute quantities in a variety of living organisms and are essential for physiologic homeostasis. In the wrong hands, these compounds have the capability to be used as nontraditional threat agents that are covered by the prohibitions of the Chemical Weapons Convention and the Biological and Toxin Weapons Convention. Unlike traditional biowarfare/bioterrorism agents that have a latency period of hours to days,the onset of action of bioregulators may occur within minutes after host exposure. Concerns regarding the potential misuse of bioregulators for nefarious purposes relate to the ability of these nontraditional agents to induce profound physiologic effects.

Corticosteroids combined with continuous veno-venous hemodiafiltration for treatment of hantavirus pulmonary syndrome caused by Puumala virus infection

Reported here are two cases of hantavirus pulmonary syndrome caused by Puumala virus infection, which rapidly resolved after initiation of corticosteroid treatment combined with continuous veno-venous hemodiafiltration. These cases emphasize the role of the inflammatory response in the pathogenesis of hantavirus pulmonary syndrome.

Hantavirus cardiopulmonary syndrome: immune response and pathogenesis

Hantaviruses are emerging viruses in the Americas that cause cardiopulmonary syndrome with high lethality. The intense cellular immune response to hantavirus alters normal endothelial cell barrier functions and seems to be harmful to the host. On the other hand, the humoral immune response seems to be essential for recovery from infection.

Induction of innate immune response genes by Sin Nombre hantavirus does not require viral replication

Maladaptive immune responses are considered to be important factors in the pathogenesis of the two diseases caused by hantaviruses, hemorrhagic fever with renal syndrome and hantavirus cardiopulmonary syndrome (HCPS). While the intensity of adaptive antiviral T-cell responses seems to correlate with the severity of HCPS, there is increasing evidence that innate antiviral responses by endothelial cells, the native targets for hantavirus infection in vivo, are induced within hours of exposure to infectious hantaviruses. To investigate early events in the innate response to Sin Nombre virus (SNV), the principal etiologic agent of HCPS in North America, we treated human endothelial cells with live virus, or virus subjected to inactivation by UV irradiation at minimal doses required to inhibit replication, and assayed host expression of interferon-stimulated genes (ISG) by microarray and reverse transcription-PCR. We show herein that a variety of ISG are induced between 4 and 24 h after exposure to both live and killed virus. The levels of such induction at early time points (before 24 h) were generally higher in cells treated with SNV particles that had been killed by exposure to UV irradiation. Additionally, SNV exposed to increasing doses of UV irradiation induced ISG better than live virus despite increased disruption of viral RNA integrity. However, SNV replication was required for continued ISG overexpression by 3 days posttreatment. These results suggest that hantavirus particles may themselves be capable of early induction of ISG and that ongoing production of viral particles during infection could contribute to the pathogenic process.

Increased levels of tumor necrosis factor-alpha and decreased levels of interleukin-12 p 70 in tracheal aspirates, within 2 hrs after birth, are associated with mortality among ventilated preterm infants

OBJECTIVE

To determine the association of antibacterial interleukin (IL)-12 p 70 levels as well as the pathogen-induced proinflammatory cytokine response in tracheal aspirate (TA) to respiratory failure and mortality among ventilated preterm infants.

DESIGN

A prospective observational clinical cohort study with measurements of cytokine levels and microbial cultures of TA from ventilated preterm neonates. Interleukin (IL)-1 beta, IL-8, IL-6, IL-10, IL-12 p 70, and tumor necrosis factor (TNF)-alpha were measured in TA within 2 hrs of birth, and comorbidity characteristics were recorded prospectively. The association between cytokine levels in TA and neonatal mortality was determined, with correction for comorbidity factors by means of multivariate stepwise logistic regression.

SETTING

A single tertiary neonatal intensive care unit at the University Hospital of Antwerp, Belgium.

PATIENTS

One hundred forty-one neonates born before a gestational age of 31 wks and who required ventilation were enrolled in the study; 31 (22%) died and 37 (26%) had airway colonization.

MEASUREMENTS AND MAIN RESULTS

The airway colonization rate was significantly greater among deceased neonates (45% vs. 21%; chi-square, 7.4; p=.007). Neonates who died had a significantly lower IL-12 p 70 cytokine level (6 pg/mL vs. 11 pg/mL; p<.05) in their TA. Neonates with a low IL-12 p 70 cytokine level had more pronounced respiratory failure (significantly higher oxygenation index, higher degree of radiologic respiratory distress syndrome, higher critical index for babies score, and more surfactant use). Multivariate analysis revealed that, after correction for severity of disease by critical index for babies score, the degree of intraventricular hemorrhage (odds ratio, 5.0 [95% confidence interval, 2.6-9.7]), low IL-12 p 70 levels (odds ratio, 4.9 [95% confidence interval, 2.1-11.7]), and high TNF-alpha levels in TA (odds ratio, 3.5 [95% confidence interval, 1.6-7.5]) were significantly associated with neonatal mortality.

CONCLUSIONS

Pathogen-induced excessive production of the proinflammatory cytokine TNF-alpha and lack of antibacterial IL-12 p 70 response in the TA are associated with increased neonatal mortality among ventilated preterm infants.

Differential expression of immunoregulatory genes in male and female Norway rats following infection with Seoul virus

Males of many species are more susceptible than females to infections caused by parasites, bacteria, fungi, and viruses. Following inoculation with Seoul virus, male rats have more virus present in target organs and shed virus longer than females. The goal of this study was to test the hypothesis that variation in the expression of genes associated with immune function mediates sex differences in hantavirus infection. Using DNA microarrays, we examined changes in gene expression in lung tissue during the early (when animals are viremic and shedding virus; Day 15 post-inoculation (p.i.)) and late (animals have low levels of infectious virus, but high antibody titers; Day 40 p.i.) phases of infection in adult male and female rats. After normalizing the gene expression levels from infected animals to the gene expression levels from same-sex uninfected controls, our data revealed that 1,813 genes were differentially expressed between the sexes during infection. The expression of key transcriptional factors (e.g., eIF-2 alpha, NF-kappa B, IRF-1, NF-IL-6, and STAT6) and genes that encode for proinflammatory (e.g., TNF alpha R, IL-1R, and IL-1RAcP), antiviral (e.g., IFN gamma R and Mx proteins), T cell (e.g., CD3 and TCR), and Ig superfamily (e.g., IgM, IgG, and MHC class I and II) proteins was higher in females than males. Conversely, males had higher expression of heat shock protein genes (e.g., hsp70) suggesting that cellular stress is elevated in males. These data provide candidate genes and cellular pathways that may underlie sex differences in responses to Seoul virus and possibly other hemorrhagic fever viruses.

Tula hantavirus infection of Vero E6 cells induces apoptosis involving caspase 8 activation

Hantaviruses are known to cause two severe human diseases: haemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome. The mechanisms of pathogenesis of these two diseases are progressively becoming understood. Recently, two hantaviruses, Hantaan and Prospect Hill were reported to cause programmed cell death of Vero E6 cells. This study shows that Tula hantavirus (TULV) infection efficiently triggers an apoptotic programme in infected Vero E6 cells, and that the replication of TULV is required for the activation of caspase 3 and the cleavage of poly (ADP-ribose) polymerase, two molecular hallmarks of apoptosis. The enforced treatment of infected Vero E6 cells with tumour necrosis factor alpha (TNF-alpha), but not interferon alpha (IFN-alpha), advanced the time course of apoptosis. Furthermore, caspase 8 was activated on day 4 post-infection, the same day when caspase 3 was activated. TNF receptor 1 was induced during a late stage of TULV infection. These data suggest that, unlike during influenza A virus infection, TNF-alpha, but not type I IFN-alpha/beta, may contribute significantly to apoptosis in a synergistic manner with TULV propagation. Interestingly, pretreatment with a broad-spectrum caspase inhibitor, z-VAD-fmk, efficiently inhibited apoptosis of TULV-infected Vero E6 cells. Taken together, these results suggest that TULV replication initiates a typical apoptotic programme involving caspase 8 activation.

Emerging viral infections

"Emerging infections" have been defined as infections that have newly appeared, that have appeared previously but are expanding in incidence and geographic range, or that threaten to increase in the near future. This article focuses on nine emerging viral infectious agents. These viruses illustrate how such agents emerge: by encroaching on previously unvisited habitats (eg, hantaviruses), by air travel (eg, SARS), and by accidental importation (eg, monkeypox). Additionally, the example of SARS demonstrates not only how quickly emerging viral infections can spread but also how quickly they can be identified and contained with motivated cooperation.

Hantaviruses: Immunology, Treatment, and Prevention

Hantaviruses are rodent-borne bunyaviruses that are associated with two main clinical diseases in humans: hemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome. It has been suggested that host-related immune mechanisms rather than direct viral cytopathology may be responsible for the principal abnormality (vascular dysfunction) in these syndromes. This review summarizes the current knowledge on hantaviral host immune responses, immune abnormalities, laboratory diagnosis, and antiviral therapy as well as the current approaches in vaccine development.

Generation of competent bone marrow-derived antigen presenting cells from the deer mouse (Peromyscus maniculatus)

Background

Human infections with Sin Nombre virus (SNV) and related New World hantaviruses often lead to hantavirus cardiopulmonary syndrome (HCPS), a sometimes fatal illness. Lungs of patients who die from HCPS exhibit cytokine-producing mononuclear infiltrates and pronounced pulmonary inflammation. Deer mice (Peromyscus maniculatus) are the principal natural hosts of SNV, in which the virus establishes life-long persistence without conspicuous pathology. Little is known about the mechanisms SNV employs to evade the immune response of deer mice, and experimental examination of this question has been difficult because of a lack of methodologies for examining such responses during infection. One such deficiency is our inability to characterize T cell responses because susceptible syngeneic deer mice are not available.

Results

To solve this problem, we have developed an in vitro method of expanding and generating competent antigen presenting cells (APC) from deer mouse bone marrow using commercially-available house mouse (Mus musculus) granulocyte-macrophage colony stimulating factor. These cells are capable of processing and presenting soluble protein to antigen-specific autologous helper T cells in vitro. Inclusion of antigen-specific deer mouse antibody augments T cell stimulation, presumably through Fc receptor-mediated endocytosis.

Conclusions

The use of these APC has allowed us to dramatically expand deer mouse helper T cells in culture and should permit extensive characterization of T cell epitopes. Considering the evolutionary divergence between deer mice and house mice, it is probable that this method will be useful to other investigators using unconventional models of rodent-borne diseases.

Andes virus M genome segment is not sufficient to confer the virulence associated with Andes virus in Syrian hamsters

Sin Nombre virus (SNV) and Andes virus (ANDV), members of the genus Hantavirus, in the family Bunyaviridae, are causative agents of hantavirus pulmonary syndrome (HPS) in North and South America, respectively. Although ANDV causes a lethal HPS-like disease in hamsters, SNV, and all other HPS-associated hantaviruses that have been tested, cause asymptomatic infections of laboratory animals, including hamsters. In an effort to understand the pathogenicity of ANDV in the hamster model, we generated ANDV/SNV reassortant viruses. Plaque isolation of viruses from cell cultures infected with both parental viruses yielded only one type of stable reassortant virus: large (L) and small (S) segments of SNV and M segment of ANDV. This virus, designated SAS reassortant virus, had in vitro growth and plaque morphology characteristics similar to those of ANDV. When injected into hamsters, the SAS reassortant virus was highly infectious and elicited high-titer, ANDV-specific neutralizing antibodies; however, the virus did not cause HPS and was not lethal. These data indicate that the ANDV M genome segment is not sufficient to confer the lethal HPS phenotype associated with ANDV.

Urinary excretion of interleukin-6 correlates with proteinuria in acute Puumala hantavirus-induced nephritis

BACKGROUND

Nephropathia epidemica (NE) is a mild type of hemorrhagic fever with renal syndrome caused by Puumala Hantavirus. Cytokines are thought to have an important role in the pathogenesis of NE. The aim of this study is to evaluate whether cytokines contribute to renal involvement in NE.

METHODS

Overnight urinary excretion of interleukin-1beta (IL-1beta), IL-1 receptor antagonist (IL-1Ra), IL-6, tumor necrosis factor-alpha (TNF-alpha), albumin, immunoglobulin G (IgG), and alpha1-microglobulin and quantitative 24-hour urinary protein excretion were measured for 3 consecutive days from 70 hospitalized patients with acute NE (49 men, 21 women; age, 15 to 70 years; median age, 39 years). Plasma levels of the respective cytokines also were measured. Urinary collections were repeated after 1 year. The control group for blood samples included 400 healthy blood donors.

RESULTS

Maximum median urinary IL-6 excretion in the acute phase of NE was increased compared with values detected after 1 year (49.5 versus 0.7 pg/min; P < 0.001). Correspondingly, maximum median plasma IL-6 concentration in patients was increased compared with controls (14.6 versus 1.2 pg/mL; P < 0.001). Urinary IL-6 excretion correlated with urinary albumin, IgG, and protein excretion (r = 0.79; P < 0.001; r = 0.76; P < 0.001; and r = 0.65; P < 0.001, respectively), but not plasma IL-6 levels (r = 0.18; P = 0.148).

CONCLUSION

Plasma IL-6 concentrations and urinary IL-6 excretion were markedly increased in patients with acute NE, but there was no correlation between plasma and urinary IL-6 levels. The high urinary IL-6 levels might reflect local production of this proinflammatory cytokine in the kidneys during acute infection.

Regulation of Cellular Gene Expression in Endothelial Cells by Sin Nombre and Prospect Hill Viruses

Mechanisms of hantavirus-induced vascular leakage remain unknown. This study was initiated to determine whether hantavirus-induced changes in endothelial cell gene expression may provide insight into disease mechanisms. Additionally, by using pathogenic Sin Nombre virus (SNV) and non-pathogenic Prospect Hill virus (PHV), we wanted to identify cellular responses that are likely to differentiate pathogenic from nonpathogenic hantaviruses. Using the Affymetrix DNA Array, we found that PHV and SNV did not significantly differ in the number of activated genes (18 versus 14 genes) in infected endothelial cells at 4 h PI. However, a smaller group of genes (36) were up-regulated by PHV compared to SNV (175) at 12 h PI. Only two genes were down-regulated in SNV-infected cells. Expression of the functionally diverse group of genes was altered at an early stage of infection (4 and 12 h PI). The genes affected include putative anti-viral factors, transcription factors, growth factors, chemokines, receptors, structural proteins, metabolism, and kinases. Although many genes were activated in cells infected with SNV and PHV, overall cellular transcriptional responses were more altered by pathogenic SNV compared to non-pathogenic PHV.

Role of Specific CD8+ T Cells in the Severity of a Fulminant Zoonotic Viral Hemorrhagic Fever, Hantavirus Pulmonary Syndrome

We report on the role of specific CD8(+) T cells in the pathogenesis of a highly lethal human viral disease, hantavirus pulmonary syndrome (HPS). HPS is a zoonotic disease caused by transmission of Sin Nombre virus (SNV) from chronically infected deer mice. In humans, this fulminant infection is characterized by lung capillary leakage, respiratory failure, and cardiogenic shock. Individuals with HLA-B*3501 have an increased risk of developing severe HPS, suggesting that CD8(+) T cell responses to SNV contribute to pathogenesis. We identified three CD8(+) T cell epitopes in SNV presented by HLA-B*3501 and quantitated circulating SNV-specific CD8(+) T cells in 11 acute HPS patients using HLA/peptide tetramers. We found significantly higher frequencies of SNV-specific T cells in patients with severe HPS requiring mechanical ventilation (up to 44.2% of CD8(+) T cells) than in moderately ill HPS patients hospitalized but not requiring mechanical ventilation (up to 9.8% of CD8(+) T cells). These results imply that virus-specific CD8(+) T cells contribute to HPS disease outcome. Intense CD8(+) T cell responses to SNV may be induced by the encounter of the unnatural human host to this zoonotic virus without coevolution. This may also be the immunopathologic basis of other life-threatening human virus infections.

Immune responses to Puumala virus infection and the pathogenesis of nephropathia epidemica

Puumala virus, causative agent of a mild form of hemorrhagic fever with renal syndrome, also known as nephropathia epidemica, induces long-lasting humoral and cellular immunity in patients. The virus itself is not cytopathic, and the immune responses to the virus may be involved in teh pathogenesis of the disease.

Cloning and characterization of deer mouse (Peromyscus maniculatus) cytokine and chemokine cDNAs

Background

Sin Nombre virus (SNV) establishes a persistent infection in the deer mouse, Peromyscus maniculatus. A strong antibody response occurs in response to SNV infection, but the role of the innate immune response is unclear. To address this issue, we have initiated an effort to identify and characterize deer mouse cytokine and chemokine genes. Such cytokines and chemokines are involved in various aspects of immunity, including the transition from innate to adaptive responses, type I and type II responses, recruitment of leukocytes to sites of infection, and production of mature cells from bone marrow progenitors.

Results

We established a colony of SNV antibody-negative deer mice and cloned 11 cytokine and chemokine partial cDNA sequences using directed PCR. Most of the deer mouse sequences were highly conserved with orthologous sequences from other rodent species and functional domains were identified in each putative polypeptide.

Conclusions

The availability of these sequences will allow the examination of the role of these cytokines in deer mouse responses to infection with Sin Nombre virus.

Síndrome pulmonar e cardiovascular por hantavírus

A síndrome pulmonar e cardiovascular por hantavírus é uma doença de conhecimento relativamente recente e freqüentemente fatal, apresentando-se como síndrome do desconforto respiratório agudo. No Brasil, desde o primeiro surto, relatado em novembro/dezembro de 1993, em Juquitiba, 226 casos já foram registrados pela Fundação Nacional da Saúde. A doença afeta indivíduos previamente hígidos, apresentando-se com pródromo febril e sintomas semelhantes aos de um resfriado comum, podendo rapidamente evoluir para edema pulmonar, insuficiência respiratória aguda e choque. A hemoconcentração e a plaquetopenia são comuns da síndrome pulmonar e cardiovascular por hantavírus, e o quadro radiológico típico é de um infiltrado intersticial bilateral difuso, que progride rapidamente para consolidações alveolares, paralelamente à piora do quadro clínico. A mortalidade inicial era em torno de 75% e declinou para aproximadamente 35%, nos últimos anos. Os pacientes que sobrevivem geralmente recuperam-se completamente, cerca de uma semana após o estabelecimento do quadro respiratório. O agente causal, não reconhecido até há pouco, foi identificado como um hantavírus, cujo reservatório natural são animais roedores da família Muridae, subfamília Sigmodontinae. O tratamento específico antiviral ainda não é bem estabelecido, estando em estudo a eficácia de ribavirina. Cuidados de terapia intensiva como ventilação mecânica e monitoramento hemodinâmico invasivo são necessários nas formas mais graves da doença. Essas medidas, se instituídas precocemente, podem melhorar o prognóstico e a sobrevida dos pacientes com síndrome pulmonar e cardiovascular por hantavírus.

[Significant factors in the pathogenesis of hemorrhagic fevers]

<zakljucak> Patogeneza sindroma virusnih hemoragijskih groznica je slozena Virusi i njihovi antigeni, nadjeni u celijama vise organa, dovode do ostecenja celija i tkiva. Pored toga, vise cinilaca domacina je aktivno ukljuceno u nastanak bolesti. Medju njima su posebno znacajne endotelne celije za koje se smatra da zapocinju, a mononuklearne celije da direktnim delovanjem ili preko medijatora (citokina) dovrsavaju proces patogeneze. Kao posledica ove interakcije nastaje disfunkcija endotelnih celija u odrzavanju barijere izmedju vaskularnog i intersticijalnog prostora. Bolje poznavanje patogenetskih cinilaca sindroma virusnih hemoragijskih groznica moze doprineti poboljsanju lecenja obolelih.

Hantavirus immunology

Two clinical syndromes are associated with hantavirus infection in humans: hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). Autopsy findings typically reveal a common feature of increased permeability in microvascular beds, suggesting vascular endothelium is a prime target for virus infection. Endothelial cells are susceptible to hantavirus infection; however, virus does not cause cytopathic effects, to explain increased endothelium permeability. Therefore, immune mechanisms were suggested to play a crucial role in hantavirus pathogenesis. In this review, we summarize data on hantavirus-induced immune disturbances and discuss their implication in capillary leakage caused by hantavirus infection.

Hantavirus pulmonary syndrome-associated hantaviruses contain conserved and functional ITAM signaling elements

Hantaviruses infect human endothelial and immune cells, causing two human diseases, hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). We have identified key signaling elements termed immunoreceptor tyrosine-based activation motifs (ITAMs) within the G1 cytoplasmic tail of all HPS-causing hantaviruses. ITAMs direct receptor signaling within immune and endothelial cells and the presence of ITAMs in all HPS-causing hantaviruses provides a means for altering normal cellular responses which maintain vascular integrity. The NY-1 G1 ITAM was shown to coprecipitate a complex of phosphoproteins from cells, and the G1 ITAM is a substrate for the Src family kinase Fyn. The hantavirus ITAM coprecipitated Lyn, Syk, and ZAP-70 kinases from T or B cells, while mutagenesis of the ITAM abolished these interactions. In addition, G1 ITAM tyrosines directed intracellular interactions with Syk by mammalian two-hybrid analysis. These findings demonstrate that G1 ITAMs bind key cellular kinases that regulate immune and endothelial cell functions. There is currently no means for establishing the role of the G1 ITAM in hantavirus pathogenesis. However, the conservation of G1 ITAMs in all HPS-causing hantaviruses and the role of these signaling elements in immune and endothelial cells suggest that functional G1 ITAMs are likely to dysregulate normal immune and endothelial cell responses and contribute to hantavirus pathogenesis.

Long-lived memory T lymphocyte responses after hantavirus infection

Puumala virus (PUUV) is a hantavirus that causes hemorrhagic fever with renal syndrome (HFRS), which is an important public health problem in large parts of Europe. We examined the memory cytolytic T lymphocyte (CTL) responses in 13 Finnish individuals who had HFRS between 1984 and 1995. In seven of these donors, we detected virus-specific CTL responses against the PUUV nucleocapsid (N) protein after in vitro stimulation with PUUV. Six novel CD8(+) CTL epitopes were defined on the N protein and were found to be restricted by various HLA alleles including A2, A28, B7, and B8. This is the first demonstration of PUUV-specific CTL responses in humans, and the first identification of CTL epitopes on PUUV. In addition, this study provides one of the few characterizations of a human antiviral memory T cell response, without the complicating issues of virus persistence or reinfection. Interferon (IFN)-gamma ELISPOT analysis showed that memory CTL specific for these epitopes were present at high frequency in PUUV-immune individuals many years after acute infection in the absence of detectable viral RNA. The frequencies of PUUV-specific CTL were comparable to or exceeded those found in other viral systems including influenza, EBV and HIV, in which CTL responses may be boosted by periodic reinfection or virus persistence.

Elevated generation of reactive oxygen/nitrogen species in hantavirus cardiopulmonary syndrome

Hantavirus cardiopulmonary syndrome (HCPS) is a life-threatening respiratory disease characterized by profound pulmonary edema and myocardial depression. Most cases of HCPS in North America are caused by Sin Nombre virus (SNV), which is carried asymptomatically by deer mice (Peromyscus maniculatus). The underlying pathophysiology of HCPS is poorly understood. We hypothesized that pathogenic SNV infection results in increased generation of reactive oxygen/nitrogen species (RONS), which contribute to the morbidity and mortality of HCPS. Human disease following infection with SNV or Andes virus was associated with increased nitrotyrosine (NT) adduct formation in the lungs, heart, and plasma and increased expression of inducible nitric oxide synthase (iNOS) in the lungs compared to the results obtained for normal human volunteers. In contrast, NT formation was not increased in the lungs or cardiac tissue from SNV-infected deer mice, even at the time of peak viral antigen expression. In a murine (Mus musculus) model of HCPS (infection of NZB/BLNJ mice with lymphocytic choriomeningitis virus clone 13), HCPS-like disease was associated with elevated expression of iNOS in the lungs and NT formation in plasma, cardiac tissue, and the lungs. In this model, intraperitoneal injection of 1400W, a specific iNOS inhibitor, every 12 h during infection significantly improved survival without affecting intrapulmonary fluid accumulation or viral replication, suggesting that cardiac damage may instead be the cause of mortality. These data indicate that elevated production of RONS is a feature of pathogenic New World hantavirus infection and that pharmacologic blockade of iNOS activity may be of therapeutic benefit in HCPS cases, possibly by ameliorating the myocardial suppressant effects of RONS.

Hantavirus pulmonary syndrome: the new American hemorrhagic fever

The recognition of hantavirus pulmonary syndrome (HPS) after the investigation of a cluster of unexplained respiratory deaths in the southwestern United States during the spring of 1993 showcased our ability to recognize new and emerging diseases, given the correct juxtaposition of a new clinical entity with circumscribed epidemiologic features that are analyzed with novel diagnostic methods. In less than a decade, HPS has become established as a pan-American zoonosis due to numerous viruses maintained by sigmodontine rodents with rodent- and virus-specific epidemiologic profiles. The classical features of the syndrome-acute febrile illness associated with prominent cardiorespiratory compromise after direct contact or inhalation of aerosolized rodent excreta-has been extended to include clinical variants, including disease with frank hemorrhage, that have confirmed that this syndrome is a viral hemorrhagic fever. Efforts are under way to refine prevention strategies, to understand the pathogenesis of the shock, and to identify therapeutic modalities.

Cytokine gene expression and protein production in peripheral blood mononuclear cells of children with acute dengue virus infections

Plasma leakage in dengue hemorrhagic fever (DHF) is associated with elevated plasma levels of cytokines. To define further the contribution of immune activation to DHF and the source of cytokines, we analyzed the production of cytokines in peripheral blood mononuclear cells (PBMC) obtained from children with dengue, using RT-PCR and immunostaining. Tumor necrosis factor-alpha (TNF-alpha) and TNF-beta expression was detected in all samples by PCR and in < 50% of samples by immunostaining. Interferon-gamma (IFN-gamma) expression was detected in < 50% of samples by either method. Interleukin-2 (IL-2) and IL-4 expression was detected in a few samples by immunostaining but was not detectable by PCR. We found greater expression of TNF-alpha and IL-4 in DHF than in dengue fever or other (non-dengue) febrile illnesses. These results support the model of immunopathogenesis of DHF. However, low levels of cytokine expression in PBMC suggest that cellular activation in tissues may contribute to high serum cytokine levels in DHF.

Role of the endothelium in viral hemorrhagic fevers

OBJECTIVE

To describe endothelial participation in the pathogenesis of viral hemorrhagic fevers and certain other acute infectious diseases.

DATA EXTRACTION AND SYNTHESIS

Survey of published literature on viral hemorrhagic fevers interpreted in light of observations in patients and research on those diseases.

CONCLUSIONS

Endothelial involvement is an extremely important factor in the clinical syndrome termed viral hemorrhagic fever. Endothelial dysfunction is important in the genesis of bleeding, which is not universal and is commonly seen only in the presence of thrombocytopenia or severe platelet dysfunction. The pathogenesis of endothelial dysfunction varies in the different diseases. In some situations, direct endothelial infection is important in increased vascular permeability, changes in the procoagulant vs. anticoagulant balance, or cytokine production. In all the viral hemorrhagic fevers studied to date, cytokine induction is an important factor and also acts on the endothelium. Poor myocardial contractility is a very important issue in viral hemorrhagic fever and is not caused by direct viral infection of the heart; it is increasingly being recognized that these patients present with low cardiac output and high peripheral resistance and that they respond poorly to fluid infusion. The clinical findings in viral hemorrhagic fever differ from those in the sepsis syndrome and should be studied and interpreted separately; this approach will sharpen therapeutic approaches and could shed light on the problems of sepsis in general.

Sequence and expression analysis of deer mouse interferon-gamma, interleukin-10, tumor necrosis factor, and lymphotoxin-alpha

Deer mice (Peromyscus maniculatus) are the principal host species of Sin Nombre (SN) virus, the primary etiologic agent of hantavirus cardiopulmonary syndrome in North America. The disease is a cytokine-mediated immunopathology characterized by pulmonary mononuclear infiltrates without discernible viral pathology. Infected deer mice remain life-long carriers and virus is found in many organs, including the lungs, but without pathology. It is unclear how deer mice respond to SN virus because no tools exist to examine the immune response in infected animals. As an initial step in examining host responses to SN virus, we have cloned partial cDNAs of deer mouse interferon-gamma (IFN-gamma), interleukin-10 (IL-10), tumor necrosis factor (TNF) and lymphotoxin-alpha (LTalpha). IL-10, TNF and LTalpha sequences are highly conserved compared to orthologs of other mammalian species, while IFN-gamma is substantially less conserved. Phylogenetic analyses indicate that the amino acid sequences of IFN-gamma and TNF may be useful in resolving relationships at the subfamily level within the rodent family Muridae. While all four sets of analyses were able to reconstruct clade Rodentia, they were not able to resolve the relationships among the mammalian orders represented in this study. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis of concanavalin A-stimulated splenocytes determined that maximal IFN-gamma and TNF expression occurred rapidly while IL-10 and LTalpha expression was maximal at 24 h.

Radiographic findings in 20 patients with Hantavirus pulmonary syndrome correlated with clinical outcome

OBJECTIVE

Hantavirus is a rare rodent-borne pathogen responsible for the Hantavirus pulmonary syndrome. The objective of this study was to review the clinical and radiographic findings of patients presenting with Hantavirus pulmonary syndrome in northern Alberta, Canada.

MATERIALS AND METHODS

We retrospectively reviewed the cases of 20 patients who presented with Hantavirus pulmonary syndrome from 1989 to 1999.

RESULTS

Two patterns of presentation were identified. One group (13/20 patients) presented with fulminant clinical and radiographic findings and required intensive care support. Six (46%) of the 13 died within a few days of presentation. Some presented in respiratory failure with bilateral parenchymal infiltrates or a rapid progression from mild bilateral interstitial changes to bilateral interstitial and alveolar infiltrates with pleural effusions. The radiographic findings paralleled these clinical symptoms. The second group (7/20) consisted of patients whose clinical course was more limited, as were their corresponding radiographic findings. These patients had a limited hospital stay, and only minimal changes were identified on radiographs. None of the second group of patients died.

CONCLUSION

Clearly, in our study, the patients with Hantavirus pulmonary syndrome presented as two groups: those with the fulminant form of the illness and those with the limited type. Of the patients we studied, the group with the fulminant form presented with severe clinical symptoms and radiographic signs of pulmonary disease and had a 46% mortality rate. The group with the limited form presented with mild clinical symptoms and minimal radiographic changes and had no mortalities.

Hantavirus infection induces the expression of RANTES and IP-10 without causing increased permeability in human lung microvascular endothelial cells

Sin Nombre virus (SNV) and Hantaan virus (HTN) infect endothelial cells and are associated with different patterns of increased vascular permeability during human disease. It is thought that such patterns of increased vascular permeability are a consequence of endothelial activation and subsequent dysfunction mediated by differential immune responses to hantavirus infection. In this study, the ability of hantavirus to directly induce activation of human lung microvascular endothelial cells (HMVEC-Ls) was examined. No virus-specific modulation in the constitutive or cytokine-induced expression of cellular adhesion molecules (CD40, CD54, CD61, CD62E, CD62P, CD106, and major histocompatibility complex classes I and II) or in cytokines and chemokines (eotaxin, tumor necrosis factor alpha, interleukin 1beta [IL-1beta], IL-6, IL-8, MCP-1, MIP-1alpha, and MIP-1beta) was detected at either the protein or message level in hantavirus-infected HMVEC-Ls. Furthermore, no virus-specific enhancement of paracellular or transcellular permeability or changes in the organization and distribution of endothelial intercellular junctional proteins was observed. However, infection with either HTN or SNV resulted in detectable levels of the chemokines RANTES and IP-10 (the 10-kDa interferon-inducible protein) in HMVEC-Ls within 72 h and was associated with nuclear translocation of interferon regulatory factor 3 (IRF-3) and IRF-7. Gamma interferon (IFN-gamma)-induced expression of RANTES and IP-10 could also be detected in uninfected HMVEC-Ls and was associated with nuclear translocation of IRF-1 and IRF-3. Treatment of hantavirus-infected HMVEC-Ls with IFN-gamma for 24 h resulted in a synergistic enhancement in the expression of both RANTES and IP-10 and was associated with nuclear translocation of IRF-1, IRF-3, IRF-7, and NF-kappaB p65. These results reveal a possible mechanism by which hantavirus infection and a TH1 immune response can cooperate to synergistically enhance chemokine expression by HMVEC-Ls and trigger immune-mediated increases in vascular permeability.

Cellular receptors and hantavirus pathogenesis

Hantaviruses cause two potentially lethal diseases, HPS and HFRS, and both diseases result in defects in vascular permeability and platelet function. Human beta 3 integrins confer cellular susceptibility to HPS- and HFRS-causing hantaviruses, a fact directly linking platelets, endothelial cells, and hantavirus diseases to the use of [figure: see text] cellular receptors that maintain capillary integrity and regulate platelet function. The role of vitronectin, PAI-1, uPAR, and complement cascades in hantavirus pathogenesis are unstudied but may contribute to specific disease syndromes effected by hantaviruses. The divergence of hantavirus surface glycoproteins and common beta 3-integrin usage provides further insight into the interaction of hantaviruses with cells. G1 and G2 glycoprotein variation is likely to contribute to additional interactions that determine pathogenic responses to individual viruses. beta 3-integrin usage also suggests that common elements exist on G1 or the more highly conserved G2 surface glycoprotein, which mediate viral attachment to integrins. Although there is currently no data defining the virion attachment protein, the development of antibodies that recognize the hantavirus attachment protein and block integrin interactions is of interest since it is likely to provide an additional point for therapeutic intervention and vaccine development. There are a plethora of effects that could be elicited by hantavirus regulation of cellular beta 3 integrins and their ligands that are consistent with hantavirus diseases. Since beta 3 integrins are critical adhesive receptors on platelets and endothelial cells and regulate both vascular permeability and platelet activation and adhesion, the use of these receptors by hantaviruses is likely to be fundamental to hantavirus pathogenesis. The lack of an animal model for hantavirus pathogenesis has prevented a systematic analysis of immune and cellular responses to hantavirus infections, and it impedes our ability to study protective or therapeutic approaches to hantavirus diseases. However, recent findings suggest that human beta 3 integrins within transgenic mice may provide animal models of hantavirus pathogenesis and have the potential to radically alter the ability to investigate hantavirus disease.

Hantavirus pulmonary syndrome: at the crossroads

The initial identification in 1993 of hantavirus pulmonary syndrome as a novel, highly fatal respiratory illness among American Indians in the southwestern USA in 1993 opened the window to the recognition of a well-established pan-American zoonosis with a myriad of causative viruses and rodent vectors, although all are New World hantaviruses among New World sigmodontine rodents. The clinical spectrum of symptoms has also been expanded to include asymptomatic infection through to fulminant hemorrhagic fever. Although the use of ribavirin, an antiviral drug, was disappointing in an early, open-labeled trial, early detection and supportive care is much better refined. However, much work remains in probing the pathogenesis of this syndrome to help define and explore therapeutic options and the mechanism of person-to-person transmission with Andes virus, one of the viruses that cause hantavirus pulmonary syndrome. Current remote sensing efforts and longitudinal ecologic investigations need to be expanded in order to focus prevention efforts better.

T-helper and humoral responses to Puumala hantavirus nucleocapsid protein: identification of T-helper epitopes in a mouse model

Puumala hantavirus (PUUV) is a rodent-borne agent causing nephropathia epidemica in humans, a milder form of haemorrhagic fever with renal syndrome occurring in Fennoscandia, central Europe and western Russia. In this study we characterized the immunogenicity of an E. coli-expressed nucleocapsid (N) protein of PUUV (strain Kazan-E6) in inbred mice (BALB/c, CBA and C57/BL6). The recombinant N (rN) protein raised PUUV-specific antibodies in all three tested murine haplotypes, and all IgG subclasses were detected. Epitope mapping using peptides spanning the N protein revealed that the B-cell recognition sites were mainly located at the amino-terminal part of the protein. Proliferative T-helper (Th) lymphocyte responses were detected in all haplotypes after a single immunization with rN. Several Th-recognition sites, spanning amino acids 6-27, 96-117, 211-232 and 256-277, were identified using overlapping peptides. Peptides representing the identified sites could also prime Th-lymphocytes to proliferate in response to recall with rN protein, thereby confirming the authenticity of the identified sites. The rN-primed Th-lymphocytes produced predominantly interleukin (IL)-2 and gamma interferon, together with lower levels of IL-4 and IL-6, indicating a mixed Th1/Th2 response.

Hantavirus Pulmonary Syndrome in the United States

Since the first outbreak of hantavirus pulmonary syndrome (HPS) in 1993, understanding of the vast distribution and potential impact of hantaviruses has grown. At least 277 cases of HPS have been documented in the United States. The full clinical spectrum has yet to be elucidated, and one outbreak suggested the possibility of person-to-person transmission. New research has identified the b-3 integrins as cellular receptors for hantaviruses and has determined the pivotal role of the immune system in pathogenesis. Rapid diagnosis has been facilitated by a new immunoblot assay to detect Sin Nombre virus infection. Treatment remains primarily supportive; however, a placebo- controlled trial of ribavirin is ongoing. Extracorporeal membrane oxygenation may be a potential therapy in severe cases; inhaled nitric oxide needs further study. Vaccines developed against hantaviruses associated with hemorrhagic fever and renal syndrome might be effective against HPS-associated strains.

Effects of tumor necrosis factor alpha on sin nombre virus infection in vitro

Previous data indicate that immune mechanisms may be involved in developing capillary leakage during Sin Nombre virus (SNV) infection. Therefore, we investigated production of tumor necrosis factor alpha (TNF-alpha) by human alveolar macrophages and human umbilical vein endothelial cells (HUVEC) after infection with SNV. In addition, we examined the effect of TNF-alpha on HUVEC monolayer leakage. Our results reveal that although TNF-alpha decreases accumulation of viral nucleoproteins, TNF-alpha levels do not change in SNV-infected cells. In addition, supernatants from SNV-infected human alveolar macrophages did not cause a significant increase in endothelial monolayer permeability.

Experimental infection model for Sin Nombre hantavirus in the deer mouse (Peromyscus maniculatus)

The relationship between hantaviruses and their reservoir hosts is not well understood. We successfully passaged a mouse-adapted strain of Sin Nombre virus from deer mice (Peromyscus maniculatus) by i.m. inoculation of 4- to 6-wk-old deer mouse pups. After inoculation with 5 ID(50), antibodies to the nucleocapsid (N) antigen first became detectable at 14 d whereas neutralizing antibodies were detectable by 7 d. Viral N antigen first began to appear in heart, lung, liver, spleen, and/or kidney by 7 d, whereas viral RNA was present in those tissues as well as in thymus, salivary gland, intestine, white fat, and brown fat. By 14 d nearly all tissues examined displayed both viral RNA and N antigen. We noted no consistent histopathologic changes associated with infection, even when RNA load was high. Viral RNA titers peaked on 21 d in most tissues, then began to decline by 28 d. Infection persisted for at least 90 d. The RNA titers were highest in heart, lung, and brown fat. Deer mice can be experimentally infected with Sin Nombre virus, which now allows provocative examination of the virus-host relationship. The prominent involvement of heart, lung, and brown fat suggests that these sites may be important tissues for early virus replication or for maintenance of the virus in nature.

Hemorrhagic fever virus-induced changes in hemostasis and vascular biology

Viral hemorrhagic fever (VHF) denotes a virus-induced acute febrile, hemorrhagic disease reported from wide areas of the world. Hemorrhagic fever (HF) viruses are encapsulated, single-stranded RNA viruses that are associated with insect or rodent vectors whose interaction with humans defines the mode of disease transmission. There are 14 HF viruses, which belong to four viral families: Arenaviridae, Bunyaviridae, Filoviridae and Flaviviridae. This review presents, in order, the following aspects of VHF: (1) epidemiology, (2) anomalies of platelets and coagulation factors, (3) vasculopathy, (4) animal models of VHFs, (5) pathogenic mechanisms, and (6) treatment and future studies. HF viruses produce the manifestations of VHFs either by direct effects on cellular functions or by activation of immune and inflammatory pathways. In Lassa fever, Rift Valley fever and Crimean-Congo HF, the main feature of fatal illness appears to be impaired/delayed cellular immunity, which leads to unchecked viremia. However, in HF with renal syndrome and dengue HF, the immune response plays an active role in disease pathogenesis. The interplay of hemostasis, immune response, and inflammation is very complex. Molecular biologic techniques and the use of animal models have helped to unravel some of these interactions.

Hantavirus pulmonary syndrome in Brazil: clinical aspects of three new cases

Hantavirus pulmonary syndrome (HPS) has been recognized recently in Brazil, where 28 cases have been reported as of September 1999. We report here the clinical and laboratory findings of three cases whose diagnoses were confirmed serologically. All the patients were adults who presented a febrile illness with respiratory symptoms that progressed to respiratory failure that required artificial ventilation in two of them. Laboratory findings were most of the time consistent with those reported in the United States in patients infected with the Sin Nombre virus, and included elevated hematocrit and thrombocytopenia; presence of atypical lymphocytes was observed in one patient. The chest radiological findings observed in all the patients were bilateral, diffuse, reticulonodular infiltrates. Two patients died. Histopathological examination of the lungs of these patients revealed interstitial and alveolar edema, alveolar hemorrhage, and mild interstitial pneumonia characterized by infiltrate of immunoblasts and mononuclear cells. In the epidemiologic investigation of one of the cases, serologic (ELISA) tests were positive in 3 (25%) out of 12 individuals who shared the same environmental exposure. HPS should be included in the differential diagnosis of interstitial pneumonia progressing to acute respiratory failure.