Cellular immune response to Hantaan virus nucleocapsid protein in the acute phase of hemorrhagic fever with renal syndrome: correlation with disease severity

Neurological manifestations of Flaviviridae, Togaviridae, and Peribunyaviridae as vector-borne viruses

Vector-borne viruses pose a significant health problem worldwide, as they are transmitted to humans through the bite of infected arthropods such as mosquitoes and ticks. In recent years, emerging and re-emerging vector-borne diseases have gained attention as they can cause a wide spectrum of neurological manifestations. The neurological manifestations of vector-borne viruses encompass a board spectrum of clinical manifestations, ranging from mild and self-limiting symptoms to severe and life-threatening conditions. Common neurological complications include viral encephalitis, acute flaccid paralysis, aseptic meningitis, and various neuromuscular disorders. The specific viruses responsible for these neurological sequelae vary by geographic region and include Orthoflavivirus nilense, Zika virus, dengue virus, chikungunya virus, Japanese encephalitis virus, and tick-borne encephalitis virus. This review focuses on the pathogenesis of these neurologic complications and highlights the mechanisms by which vector-borne viruses invade the central nervous system and trigger neuroinflammatory responses. Diagnostic challenges and strategies for early detection of neurological manifestations are discussed, emphasising the importance of clinical suspicion and advanced laboratory testing.

HLA-E-restricted Hantaan virus-specific CD8+ T cell responses enhance the control of infection in hemorrhagic fever with renal syndrome

Infection with the Hantaan virus (HTNV) may result in severe hemorrhagic fever with renal syndrome (HFRS). The functions of HLA-E-restricted CD8+ T lymphocytes in virus control and vaccine development have recently received increased attention. The purpose of this research is to discover HLA-E-restricted CD8+ T cell epitopes on HTNV as well as the features of these epitope-specific CD8+ T cells in HFRS patients. To anticipate HLA-E-restricted HTNV epitopes, the NetMHCpan servers were utilized. The K562/HLA-E cell binding test and the enzyme-linked immunospot assay were used to confirm epitope binding to HLA-E. The number and features of HLA-E-restricted epitope-specific CD8+ T lymphocytes in HFRS patients were investigated using tetramer staining, intracellular cytokine labeling, proliferation, and cytotoxicity assays. Six HTNV-derived HLA-E-restricted CD8+ T cell epitopes were found in this study. In mild/moderate HFRS patients, the frequency of HLA-E-restricted epitope-specific CD8+ T cells was greater than in severe/critical patients. CD38+HLA-DR+ HLA-E-restricted CD8+ T cells were identified. Meanwhile, CD45RA+CCR7- effector memory-re-expressing CD45RA T cells with early and intermediate maturation and differentiation characteristics predominated. Notably, CD8+ T cells from milder HFRS patients produced more interferon-γ, interleukin-2, and granzyme B, had a stronger proliferative potential, and were inversely linked with the amount of plasma HTNV virus load. Furthermore, HLA-E-restricted epitope-specific CD8+ T cells demonstrated improved cytotoxic activity in vitro during the acute stage of HFRS. Taken together, the findings demonstrate the protective effects of HLA-E-restricted CD8+ T cells during HTNV infection, suggesting that HLA-E-targeted vaccines against HTNV might be developed for HLA-diverse populations.

Hemorrhagic Fever with Renal Syndrome in Asia: History, Pathogenesis, Diagnosis, Treatment, and Prevention

Hemorrhagic Fever with Renal Syndrome (HFRS) is the most frequently diagnosed zoonosis in Asia. This zoonotic infection is the result of exposure to the virus-contaminated aerosols. Orthohantavirus infection may cause Hemorrhagic Fever with Renal Syndrome (HRFS), a disease that is characterized by acute kidney injury and increased vascular permeability. Several species of orthohantaviruses were identified as causing infection, where Hantaan, Puumala, and Seoul viruses are most common. Orthohantaviruses are endemic to several Asian countries, such as China, South Korea, and Japan. Along with those countries, HFRS tops the list of zoonotic infections in the Far Eastern Federal District of Russia. Recently, orthohantavirus circulation was demonstrated in small mammals in Thailand and India, where orthohantavirus was not believed to be endemic. In this review, we summarized the current data on orthohantaviruses in Asia. We gave the synopsis of the history and diversity of orthohantaviruses in Asia. We also described the clinical presentation and current understanding of the pathogenesis of orthohantavirus infection. Additionally, conventional and novel approaches for preventing and treating orthohantavirus infection are discussed.

Increased blood CD226- inflammatory monocytes with low antigen presenting potential correlate positively with severity of hemorrhagic fever with renal syndrome

BACKGROUND

Hantaan virus (HTNV) infection can cause severe hemorrhagic fever with renal syndrome (HFRS). Inflammatory monocytes (iMOs) are involved in early antiviral responses. Previous studies have found that blood iMOs numbers increase in the acute phase of HFRS. Here, we further identified the phenotypic characteristics of iMOs in HFRS and explored whether phenotypic changes in iMOs were associated with HFRS severity.

MATERIALS AND METHODS

Blood samples from 85 HFRS patients were used for phenotypic analysis of iMOs by flow cytometry. Plasma HTNV load was determined using RT-PCR. THP-1 cells overexpressing CD226 were used to investigate the effects of CD226 on HLA-DR/DP/DQ and CD80 expression. A mouse model was used to test macrophage phenotype following HTNV infection.

RESULTS

The proportion of CD226- iMOs in the acute phase of HFRS was 66.83 (35.05-81.72) %, which was significantly higher than that in the convalescent phase (5.32 (1.36-13.52) %) and normal controls (7.39 (1.15-18.11) %) (p < 0.0001). In the acute phase, the proportion of CD226- iMOs increased more in patients with more severe HFRS and correlated positively with HTNV load and negatively with platelet count. Notably, CD226- iMOs expressed lower levels of HLA-DR/DP/DQ and CD80 than CD226+ iMOs, and overexpression CD226 could enhance the expression of HLA-DR/DP/DQ and CD80. In a mouse model, HTNV also induced the expansion of CD226- macrophages, with decreased expression of I-A/I-E and CD80.

CONCLUSIONS

CD226- iMOs increased during HTNV infection and the decrease in CD226 hampered the expression of HLA-DR/DP/DQ and CD80, which may promote the immune escape of HTNV and exacerbate clinical symptoms.

IL-15 induced bystander activation of CD8+ T cells may mediate endothelium injury through NKG2D in Hantaan virus infection

Introduction

Hantaan virus (HTNV) can cause endothelium injury in hemorrhagic fever with renal syndrome (HFRS) patients. Bystander activation of CD8+ T cells by virus infection has been shown that was involved in host injury, but it is unclear during HTNV infection. This project aimed to study the effect of bystander-activated CD8+ T cell responses in HTNV infection.

Methods

The in vitro infection model was established to imitate the injury of endothelium in HFRS patients. Flow cytometry was performed to detect the expression of markers of tetramer+ CD8+ T cells and human umbilical vein endothelial cells (HUVECs). The levels of interleukin-15 (IL-15) in serum and supermanant were detected using ELISA kit. The expression of MICA of HUVECs was respectively determined by flow cytometry and western blot. The cytotoxicity of CD8+ T cells was assessed through the cytotoxicity assay and antibody blocking assay.

Results

EBV or CMV-specific CD8+ T cells were bystander activated after HTNV infection in HFRS patients. HTNV-infected HUVECs in vitro could produce high levels of IL-15, which was positively correlated with disease severity and the expression of NKG2D on bystander-activated CD8+ T cells. Moreover, the elevated IL-15 could induce activation of CD122 (IL-15Rβ)+NKG2D+ EBV/CMV-specific CD8+ T cells. The expression of IL-15Rα and ligand for NKG2D were upregulated on HTNV-infected HUVECs. Bystander-activated CD8+ T cells could exert cytotoxicity effects against HTNV-infected HUVECs, which could be enhanced by IL-15 stimulation and blocked by NKG2D antibody.

Discussion

IL-15 induced bystander activation of CD8+ T cells through NKG2D, which may mediate endothelium injury during HTNV infection in HFRS patients.

The Immune Correlates of Orthohantavirus Vaccine

Zoonotic transmission of orthohantaviruses from rodent reservoirs to humans has been the cause of severe fatalities. Human infections are reported worldwide, but vaccines have been approved only in China and Korea. Orthohantavirus vaccine development has been pursued with no sense of urgency due to the relative paucity of cases in countries outside China and Korea. However, the orthohantaviruses continuously evolve in hosts and thus the current vaccine may not work as well against some variants. Therefore, a more effective vaccine should be prepared against the orthohantaviruses. In this review, we discuss the issues caused by the orthohantavirus vaccine. Given the pros and cons of the orthohantavirus vaccine, we suggest strategies for the development of better vaccines in terms of pandemic preparedness.

MAIT cell activation is associated with disease severity markers in acute hantavirus infection

Hantaviruses are zoonotic RNA viruses that cause severe acute disease in humans. Infected individuals have strong inflammatory responses that likely cause immunopathology. Here, we studied the response of mucosal-associated invariant T (MAIT) cells in peripheral blood of individuals with hemorrhagic fever with renal syndrome (HFRS) caused by Puumala orthohantavirus, a hantavirus endemic in Europe. We show that MAIT cell levels decrease in the blood during HFRS and that residual MAIT cells are highly activated. This activation correlates with HFRS severity markers. In vitro activation of MAIT cells by hantavirus-exposed antigen-presenting cells is dependent on type I interferons (IFNs) and independent of interleukin-18 (IL-18). These findings highlight the role of type I IFNs in virus-driven MAIT cell activation and suggest a potential role of MAIT cells in the disease pathogenesis of viral infections.

MAIT cells are activated in individuals with hemorrhagic fever with renal syndrome (HFRS)

MAIT cell activation correlates with HFRS severity markers during hantavirus infection

MAIT cell blood levels decline during acute HFRS

Hantavirus-mediated MAIT cell activation is type I IFN dependent

Comparison of Lymphocyte Populations in Patients With Dobrava or Puumala orthohantavirus Infection

Hemorrhagic fever with renal syndrome (HFRS), caused by Dobrava (DOBV) and Puumala (PUUV) orthohantaviruses, is an endemic disease in Slovenia. DOBV is mainly responsible for a more severe disease, whereas PUUV usually causes a milder form. Therefore, the aim of our study was to determine whether any differences in lymphocyte population in patients infected with these two viruses exist. Mononuclear cells from peripheral blood (PBMCs) were isolated from DOBV or PUUV infected patients and different lymphocyte subpopulations were analyzed with flow cytometry. Decreased concentrations of lymphocyte subpopulation were observed in DOBV and in PUUV infected patients compared with a healthy control, which was especially evident in DOBV infected patients. The lower values of T cells are likely due to the extravasation of the activated cells from the circulation to the infected tissue. Higher percentage of NK cells were detected in DOBV infected patients in comparison to PUUV infected patients, which could be associated with a more severe HFRS caused by DOBV. PUUV infected patients had a significantly higher concentration of activated T cell subsets, expressing markers CD25, CD69, and HLA-DR in comparison to DOBV infected patients. Higher activation of T cell subsets in PUUV infected patients could be a contributor to a milder HFRS. Further studies are necessary to elucidate the relation between the protective and the harmful role of activated lymphocytes subsets in HFRS pathogenesis.

Differential CD4 T Regulatory Cell Phenotype Induced by Andes Hantavirus Glycoprotein

Hantavirus cardiopulmonary syndrome (HCPS) caused by Andes orthohantavirus (ANDV) in South America is a public health threat due to the significant rate of mortality and the lack of a specific treatment. Interestingly, the virus does not produce cytopathic effect, thereby the strong antiviral immune response is suspected to contribute to pathogenesis, hence is important to understand the balance between protective and harmfully immunity. CD4⁺ T regulatory cells (Treg) are essential to control an exacerbated immune response. In human ANDV infection, little is known about CD4⁺ Treg cells, which may be involved in control immunopathology associated to the infection. In this report, we characterize the phenotype of memory CD4⁺ Tregs in a HCPS survivor's cohort. Based on the expression of CXCR3, CCR4, and CCR6, we identified different Th-like Treg populations in ANDV survival's PBMCs. In addition, the effect of ANDV-glycoprotein virus like particles (VLP) was determined. We demonstrated that memory CD4⁺ Treg from HCPS present a specific phenotype, showing higher frequency of PD-1 compared to healthy donors (HD). In addition, it was observed a decrease in the frequency of Th1-like memory CD4⁺ Treg in HCPS, important to highlight that this signature could be preserved even years after resolution of infection. Moreover, to gain insight in the mechanism involved, we evaluated whether ANDV-glycoprotein (GP) VLP could modulate CD4⁺ Treg. Interestingly, ANDV-GP VLP induced a decrease in the frequency of CXCR3 (Th1-like) and an increase in CCR4 (Th2-like) memory CD4⁺ Treg in both HD and HCPS PBMCs, indicating that ANDV-GP could specifically act over CXCR3 and CCR4 in CD4⁺ Treg. This report contributes to the study of human CD4⁺ Treg cells in ANDV infection.

Innate and adaptive immune responses against human Puumala virus infection: immunopathogenesis and suggestions for novel treatment strategies for severe hantavirus-associated syndromes

Two related hyperinflammatory syndromes are distinguished following infection of humans with hantaviruses: haemorrhagic fever with renal syndrome (HFRS) seen in Eurasia and hantavirus pulmonary syndrome (HPS) seen in the Americas. Fatality rates are high, up to 10% for HFRS and around 35%-40% for HPS. Puumala virus (PUUV) is the most common HFRS-causing hantavirus in Europe. Here, we describe recent insights into the generation of innate and adaptive cell-mediated immune responses following clinical infection with PUUV. First described are studies demonstrating a marked redistribution of peripheral blood mononuclear phagocytes (MNP) to the airways, a process that may underlie local immune activation at the site of primary infection. We then describe observations of an excessive natural killer (NK) cell activation and the persistence of highly elevated numbers of NK cells in peripheral blood following PUUV infection. A similar vigorous CD8 Tcell response is also described, though Tcell responses decline with viraemia. Like MNPs, many NK cells and CD8 T cells also localize to the lung upon acute PUUV infection. Following this, findings demonstrating the ability of hantaviruses, including PUUV, to cause apoptosis resistance in infected target cells, are described. These observations, and associated inflammatory cytokine responses, may provide new insights into HFRS and HPS disease pathogenesis. Based on similarities between inflammatory responses in severe hantavirus infections and other hyperinflammatory disease syndromes, we speculate whether some therapeutic interventions that have been successful in the latter conditions may also be applicable in severe hantavirus infections.

T-Cell Response to Viral Hemorrhagic Fevers

Viral hemorrhagic fevers (VHF) are a group of clinically similar diseases that can be caused by enveloped RNA viruses primarily from the families Arenaviridae, Filoviridae, Hantaviridae, and Flaviviridae. Clinically, this group of diseases has in common fever, fatigue, dizziness, muscle aches, and other associated symptoms that can progress to vascular leakage, bleeding and multi-organ failure. Most of these viruses are zoonotic causing asymptomatic infections in the primary host, but in human beings, the infection can be lethal. Clinical and experimental evidence suggest that the T-cell response is needed for protection against VHF, but can also cause damage to the host, and play an important role in disease pathogenesis. Here, we present a review of the T-cell immune responses to VHF and insights into the possible ways to improve counter-measures for these viral agents.

Novel Identified HLA-A*0201-Restricted Hantaan Virus Glycoprotein Cytotoxic T-Cell Epitopes Could Effectively Induce Protective Responses in HLA-A2.1/Kb Transgenic Mice May Associate with the Severity of Hemorrhagic Fever with Renal Syndrome

Hantaan virus (HTNV) infections can cause severe hemorrhagic fever with renal syndrome (HFRS) in humans, which is associated with high fatality rates. Cytotoxic T cell (CTL) responses contribute to virus elimination; however, to date, HLA class I allele-restricted HTNV glycoprotein (GP) epitopes recognized by CTLs have not been reported, limiting our understanding of CTL responses against HTNV infection in humans. In this study, 34 HTNV GP nine-mer epitopes that may bind to HLA-A*0201 molecules were predicted using the BIMAS and SYFPEITHI database. Seven of the epitopes were demonstrated to bind to HLA-A*0201 molecules with high affinity via the T2 cell binding assay and were successfully used to synthesize peptide/HLA-A*0201 tetramers. The results of tetramer staining showed that the frequencies of each epitope-specific CTL were higher in patients with milder HFRS, which indicated that the epitopes may induce protective CTL responses after HTNV infection. IFN-γ-enzyme-linked immunospot analysis further confirmed the immunoreactivity of epitopes by eliciting epitope-specific IFN-γ-producing CTL responses. In an HTNV challenge trial, significant inhibition of HTNV replication characterized by lower levels of antigens and RNA loads was observed in major target organs (liver, spleen, and kidneys) of HLA-A2.1/K^b transgenic mice pre-vaccinated with nonapeptides VV9 (aa8–aa16, VMASLVWPV), SL9 (aa996–aa1004, SLTECPTFL) and LL9 (aa358–aa366, LIWTGMIDL). Importantly, LL9 exhibited the best ability to induce protective CTL responses and showed a prominent effect on the kidneys, potentially preventing kidney injury after HTNV infection. Taken together, our results highlight that HTNV GP-derived HLA-A*0201-restricted epitopes could elicit protective CTL responses against the virus, and that epitope LL9 functions as an immunodominant protective epitope that may advance the design of safe and effective CTL-based HTNV peptide vaccines for humans.

Serum Cytokine Profiles Differentiating Hemorrhagic Fever with Renal Syndrome and Hantavirus Pulmonary Syndrome

Hantavirus infection is an acute zoonosis that clinically manifests in two primary forms, hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). HFRS is endemic in Europe and Russia, where the mild form of the disease is prevalent in the Tatarstan region. HPS is endemic in Argentina, as well as other countries of North and South American. HFRS and HPS are usually acquired via the upper respiratory tract by inhalation of virus-contaminated aerosol. Although the pathogenesis of HFRS and HPS remains largely unknown, postmortem tissue studies have identified endothelial cells as the primary target of infection. Importantly, cell damage due to virus replication, or subsequent tissue repair, has not been documented. Since no single factor has been identified that explains the complexity of HFRS or HPS pathogenesis, it has been suggested that a cytokine storm may play a crucial role in the manifestation of both diseases. In order to identify potential serological markers that distinguish HFRS and HPS, serum samples collected during early and late phases of the disease were analyzed for 48 analytes using multiplex magnetic bead-based assays. Overall, serum cytokine profiles associated with HPS revealed a more pro-inflammatory milieu as compared to HFRS. Furthermore, HPS was strictly characterized by the upregulation of cytokine levels, in contrast to HFRS where cases were distinguished by a dichotomy in serum cytokine levels. The severe form of hantavirus zoonosis, HPS, was characterized by the upregulation of a higher number of cytokines than HFRS (40 vs 21). In general, our analysis indicates that, although HPS and HFRS share many characteristic features, there are distinct cytokine profiles for these diseases. These profiles suggest a strong activation of an innate immune and inflammatory responses are associated with HPS, relative to HFRS, as well as a robust activation of Th1-type immune responses. Finally, the results of our analysis suggest that serum cytokines profiles of HPS and HFRS cases are consistent with the presence of extracellular matrix degradation, increased mononuclear leukocyte proliferation, and transendothelial migration.

Cytokine response to Hantaan virus infection in patients with hemorrhagic fever with renal syndrome

Hantaan virus (HTNV) infection of the human body causes a severe acute infectious disease known as hemorrhagic fever renal syndrome (HFRS). The aim of this study was to correlate patient cytokine profiles to HFRS severity. In this study, we discuss the clinical significance of evaluating HFRS treatment outcomes using cytokine information. The levels of 18 cytokines were quantitatively determined in three groups: 34 HTNV IgM+ cases, 63 HTNV IgM- negative cases, and 78 healthy volunteers. The level of 14 serum cytokines were higher in the patient group than that in the healthy control group. In the 34 HTNV IgM+ patient sera, a set of 27 cytokines was further assessed. The cytokines of TNF-β, IL-1ra, and IL-6 were detected at higher level in the IgM+ group than that in the IgM- group. The deterioration of HFRS was accompanied with multiple cytokines increased, such as IL-1ra, IL-12p70, IL-10, IP-10, IL-17, IL-2, and IL-6. Our data indicate that serum cytokine levels are associated with the progression of HFRS.

Structure and Function of HLA-A*02-Restricted Hantaan Virus Cytotoxic T-Cell Epitope That Mediates Effective Protective Responses in HLA-A2.1/K(b) Transgenic Mice

Hantavirus infections cause severe emerging diseases in humans and are associated with high mortality rates; therefore, they have become a global public health concern. Our previous study showed that the CD8(+) T-cell epitope aa129-aa137 (FVVPILLKA, FA9) of the Hantaan virus (HTNV) nucleoprotein (NP), restricted by human leukocyte antigen (HLA)-A*02, induced specific CD8(+) T-cell responses that controlled HTNV infection in humans. However, the in vivo immunogenicity of peptide FA9 and the effect of FA9-specific CD8(+) T-cell immunity remain unclear. Here, based on a detailed structural analysis of the peptide FA9/HLA-A*0201 complex and functional investigations using HLA-A2.1/K(b) transgenic (Tg) mice, we found that the overall structure of the peptide FA9/HLA-A*0201 complex displayed a typical MHC class I fold with Val2 and Ala9 as primary anchor residues and Val3 and Leu7 as secondary anchor residues that allow peptide FA9 to bind tightly with an HLA-A*0201 molecule. Residues in the middle portion of peptide FA9 extruding out of the binding groove may be the sites that allow for recognition by T-cell receptors. Immunization with peptide FA9 in HLA-A2.1/K(b) Tg mice induced FA9-specific cytotoxic T-cell responses characterized by the induction of high expression levels of interferon-γ, tumor necrosis factor-α, granzyme B, and CD107a. In an HTNV challenge trial, significant reductions in the levels of both the antigens and the HTNV RNA loads were observed in the liver, spleen, and kidneys of Tg mice pre-vaccinated with peptide FA9. Thus, our findings highlight the ability of HTNV epitope-specific CD8(+) T-cell immunity to control HTNV and support the possibility that the HTNV-NP FA9 peptide, naturally processed in vivo in an HLA-A*02-restriction manner, may be a good candidate for the development HTNV peptide vaccines.

CD8low CD100- T Cells Identify a Novel CD8 T Cell Subset Associated with Viral Control during Human Hantaan Virus Infection

Hantaan virus (HTNV) infection can cause a severe lethal hemorrhagic fever with renal syndrome (HFRS) in humans. CD8(+) T cells play a critical role in combating HTNV infections. However, the contributions of different CD8(+) T cell subsets to the immune response against viral infection are poorly understood. Here, we identified a novel subset of CD8(+) T cells characterized by the CD8(low) CD100(-) phenotype in HFRS patients. The CD8(low) CD100(-) subset accounted for a median of 14.3% of the total CD8(+) T cells in early phase of HFRS, and this percentage subsequently declined in the late phase of infection, whereas this subset was absent in healthy controls. Furthermore, the CD8(low) CD100(-) cells were associated with high activation and expressed high levels of cytolytic effector molecules and exhibited a distinct expression profile of effector CD8(+) T cells (CCR7(+/-) CD45RA(-) CD127(high) CD27(int) CD28(low) CD62L(-)). When stimulated with specific HTNV nucleocapsid protein-derived peptide pools, most responding CD8(+) cells (gamma interferon [IFN-γ] positive and/or tumor necrosis factor alpha [TNF-α] positive) were CD8(low) CD100(-) cells. The frequency of CD8(low) CD100(-) cells among HTNV-specific CD8(+) T cells was higher in milder cases than in more severe cases. Importantly, the proportion of the CD8(low) CD100(-) subset among CD8(+) T cells in early phase of HFRS was negatively correlated with the HTNV viral load, suggesting that CD8(low) CD100(-) cells may be associated with viral clearance. The contraction of the CD8(low) CD100(-) subset in late phase of infection may be related to the consistently high expression levels of PD-1. These results may provide new insights into our understanding of CD8(+) T cell-mediated protective immunity as well as immune homeostasis after HTNV infection in humans.

IMPORTANCE

CD8(+) T cells play important roles in the antiviral immune response. We found that the proportion of CD8(low) CD100(-) cells among CD8(+) T cells from HFRS patients was negatively correlated with the HTNV viral load, and the frequency of CD8(low) CD100(-) cells among virus-specific CD8(+) T cells was higher in milder HFRS cases than in more severe cases. These results imply a beneficial role for the CD8(low) CD100(-) cell subset in viral control during human HTNV infection.

Elevated Plasma Soluble CD14 Levels Correlate with the Monocyte Response Status During Hantaan Virus Infection in Humans

Hantaan virus (HTNV) infection can cause severe hemorrhagic fever with renal syndrome (HFRS) in humans. CD14, a pattern recognition receptor recognizing lipopolysaccharide, is highly expressed on monocytes and can be shed as soluble CD14 (sCD14) upon monocyte activation. To understand the role of sCD14 in HFRS, the sCD14 plasma concentrations from 45 HFRS patients were quantified, and the relationships between the plasma sCD14 level and the monocyte response status and clinical parameters were analyzed. The plasma sCD14 levels were significantly higher in the HFRS patients and they correlated with monocyte expansion and activation, which were characterized by increased blood monocyte counts, the proportion of CD14(++)CD16(+) intermediate monocytes, as well as elevated plasma tumor necrosis factor-α (TNF-α) and soluble CD163 (sCD163) levels. Additionally, the high plasma sCD14 levels positively correlated with white blood cell counts and blood urea nitrogen levels and negatively correlated with platelet counts in the HFRS patients. Taken together, our data indicate that elevated plasma sCD14 levels are associated with the monocyte response status during HTNV infection in humans.

Kinetics and Immunodominance of Virus-Specific T Cell Responses During Hantaan Virus Infection

Immunodominant T cell responses are important for protection against virus challenge. However, studies screening for the immunodominant T cell responses and following their kinetics in acute Hantaan virus (HTNV) infection are very limited. Herein, the HTNV nucleocapsid protein-specific T cell responses were longitudinally screened in 15 patients with acute HTNV infection, eight of whom had a particularly severe hemorrhagic fever with renal syndrome (HFRS). An extremely impaired IFN-γ-producing T cell response was observed in patients with severe HFRS at the early stage of infection, especially to the immunodominant epitopes detected in the mild to moderate group, namely peptides N127-141, N139-153, N241-255, and N355-369. The initially insufficient T cell response to the immunodominant epitopes may play a role in influencing the severity of HTNV infection. These findings provide information that may aid the design of future vaccines against hantaviruses.

Hantaan virus infection induces both Th1 and ThGranzyme B+ cell immune responses that associated with viral control and clinical outcome in humans

Hantaviruses infection causing severe emerging diseases with high mortality rates in humans has become public health concern globally. The potential roles of CD4(+)T cells in viral control have been extensively studied. However, the contribution of CD4(+)T cells to the host response against Hantaan virus (HTNV) infection remains unclear. Here, based on the T-cell epitopes mapped on HTNV glycoprotein, we studied the effects and characteristics of CD4(+)T-cell responses in determining the outcome of hemorrhagic fever with renal syndrome. A total of 79 novel 15-mer T-cell epitopes on the HTNV glycoprotein were identified, among which 20 peptides were dominant target epitopes. Importantly, we showed the presence of both effective Th1 responses with polyfunctional cytokine secretion and ThGranzyme B(+) cell responses with cytotoxic mediators production against HTNV infection. The HTNV glycoprotein-specific CD4(+)T-cell responses inversely correlated with the plasma HTNV RNA load in patients. Individuals with milder disease outcomes showed broader epitopes targeted and stronger CD4(+)T-cell responses against HTNV glycoproteins compared with more severe patients. The CD4(+)T cells characterized by broader antigenic repertoire, stronger polyfunctional responses, better expansion capacity and highly differentiated effector memory phenotype(CD27-CD28-CCR7-CD45RA-CD127(hi)) would elicit greater defense against HTNV infection and lead to much milder outcome of the disease. The host defense mediated by CD4(+)T cells may through the inducing antiviral condition of the host cells and cytotoxic effect of ThGranzyme B+ cells. Thus, these findings highlight the efforts of CD4(+)T-cell immunity to HTNV control and provide crucial information to better understand the immune defense against HTNV infection.

Soluble Scavenger Receptor CD163 Is Associated with Severe Acute Kidney Injury in Patients with Hantaan Virus Infection

CD163, a hemoglobin scavenger receptor for haptoglobin-hemoglobin complexes, is expressed by monocytes/macrophages and is often shed as soluble CD163 (sCD163) in response to inflammatory stimuli. This scavenger receptor is reported to dampen the inflammatory response, and high plasma levels of sCD163, which are thought to reflect the total level of CD163 expression, may predict the severity of disease. To understand the role of sCD163 in the pathogenesis of hemorrhagic fever with renal syndrome (HFRS) better, the concentrations of sCD163 in plasma from 66 patients were quantified, and the relationships between sCD163 level and disease course, severity, and clinical parameters were analyzed. The level of plasma sCD163 in HFRS patients was elevated from fever onset and during the course of the disease, and it peaked in the oliguria stage at 874.5 (549.9-1138.0) ng/mL compared with controls at 192.8 (54.9-282.1) ng/mL. The correlations between plasma sCD163 and renal dysfunction suggest that sCD163 may play an important role in the development of acute renal failure in patients infected with Hantaan virus.

IL-33/ST2 correlates with severity of haemorrhagic fever with renal syndrome and regulates the inflammatory response in Hantaan virus-infected endothelial cells

BACKGROUND

Hantaan virus (HTNV) causes a severe lethal haemorrhagic fever with renal syndrome (HFRS) in humans. Despite a limited understanding of the pathogenesis of HFRS, the importance of the abundant production of pro-inflammatory cytokines has been widely recognized. Interleukin 33 (IL-33) has been demonstrated to play an important role in physiological and pathological immune responses. After binding to its receptor ST2L, IL-33 stimulates the Th2-type immune response and promotes cytokine production. Depending on the disease model, IL-33 either protects against infection or exacerbates inflammatory disease, but it is unknown how the IL-33/ST2 axis regulates the immune response during HTNV infection.

METHODOLOGY/PRINCIPAL FINDINGS

Blood samples were collected from 23 hospitalized patients and 28 healthy controls. The levels of IL-33 and soluble ST2 (sST2) in plasma were quantified by ELISA, and the relationship between IL-33, sST2 and the disease severity was analyzed. The role of IL-33/sST2 axis in the production of pro-inflammatory cytokines was studied on HTNV-infected endothelial cells. The results showed that the plasma IL-33 and sST2 were significantly higher in patients than in healthy controls. Spearman analysis showed that elevated IL-33 and sST2 levels were positively correlated with white blood cell count and viral load, while negatively correlated with platelet count. Furthermore, we found that IL-33 enhanced the production of pro-inflammatory cytokines in HTNV-infected endothelial cells through NF-κB pathway and that this process was inhibited by the recombinant sST2.

CONCLUSION/SIGNIFICANCE

Our results indicate that the IL-33 acts as an initiator of the "cytokine storm" during HTNV infection, while sST2 can inhibit this process. Our findings could provide a promising immunotherapeutic target for the disease control.

The fundamental role of endothelial cells in hantavirus pathogenesis

Hantavirus, a genus of rodent- and insectivore-borne viruses in the family Bunyaviridae, is a group of emerging zoonotic pathogens. Hantaviruses cause hemorrhagic fever with renal syndrome and hantavirus cardiopulmonary syndrome in man, often with severe consequences. Vascular leakage is evident in severe hantavirus infections, and increased permeability contributes to the pathogenesis. This review summarizes the current knowledge on hantavirus interactions with hematopoietic and endothelial cells, and their effects on the increased vascular permeability.

Increased plasma cell-free DNA level during HTNV infection: correlation with disease severity and virus load

Cell-free DNA (cf-DNA) in blood represents a promising DNA damage response triggered by virus infection or trauma, tumor, etc. Hantavirus primarily causes two diseases: haemorrhagic fever with renal syndrome (HFRS) and Hantavirus cardiopulmonary syndrome (HCPS), depending on different Hantavirus species. The aim of this study was to evaluate plasma cf-DNA levels in acute phase of HFRS, and to correlate plasma cf-DNA with disease severity and plasma Hanttan virus (HTNV) load. We observed the appearance of cf-DNA in 166 plasma samples from 76 HFRS patients: the plasma cf-DNA levels peaked at the hypotensive stage of HFRS, and then decreased gradually. Until the diuretic stage, there was no significant difference in plasma cf-DNA level between patients and the healthy control. Exclusively in the febrile/hypotensive stage, the plasma cf-DNA levels of severe/critical patients were higher than those of the mild/moderate group. Moreover, the plasma cf-DNA value in the early stage of HFRS was correlated with HTNV load and disease severity. In most of the patients, plasma cf-DNA displayed a low-molecular weight appearance, corresponding to the size of apoptotic DNA. In conclusion, the plasma cf-DNA levels were dynamically elevated during HFRS, and correlated with disease severity, which suggests that plasma cf-DNA may be a potential biomarker for the pathogenesis and prognosis of HFRS.

Upregulation of IFN-γ and IL-12 is associated with a milder form of hantavirus hemorrhagic fever with renal syndrome

Hantavirus hemorrhagic fever with renal syndrome (HFRS) is a zoonotic disease characterized by acute onset, fever, malaise, and back pain. As the disease progresses, hemorrhagic disturbances and kidney dysfunctions predominate. The examination of tissue collected postmortem supports the premise that virus replication is not responsible for this pathology; therefore, it is widely believed that virus-induced immune responses lead to the clinical manifestations associated with HFRS. The overproduction of inflammatory cytokines is commonly reported in subjects with HFRS and has given rise to the hypothesis that a so-called "cytokine storm" may play a pivotal role in the pathogenesis of this disease. Currently, supportive care remains the only effective treatment for HFRS. Our data show that serum levels of interferon (IFN)-γ, interleukin (IL)-10, CCL2, and IL-12 are upregulated in HFRS cases when compared to healthy controls and the level of upregulation is dependent on the phase and severity of the disease. Furthermore, we observed an association between the mild form of the disease and elevated serum levels of IFN-γ and IL-12. Collectively, these observations suggest that the administration of exogenous IFN-γ and IL-12 may provide antiviral benefits for the treatment of HFRS and, thus, warrants further investigations.

Hantaan virus infection induces CXCL10 expression through TLR3, RIG-I, and MDA-5 pathways correlated with the disease severity

Hantaan virus (HTNV) is a major agent causing hemorrhagic fever with renal syndrome (HFRS). Although the pathogenesis of HFRS is unclear, some reports have suggested that the abundant production of proinflammatory cytokines and uncontrolled inflammatory responses may contribute to the development of HFRS. CXCL10 is one of these cytokines and is found to be involved in the pathogenesis of many virus infectious diseases. However, the role of CXCL10 in the pathogenesis of HFRS and the molecular regulation mechanism of CXCL10 in HTNV infection remain unknown. In this study, we report that CXCL10 expresses highly in the HFRS patients' sera and the elevated CXCL10 is positively correlated with the severity of HFRS. We find that HTNV, a single-strand RNA virus, can act as a double-strand RNA to activate the TLR3, RIG-I, and MDA-5 signaling pathways. Through the downstream transcription factors of these pathways, NF-κB and IRF7, which bind directly to the CXCL10's promoter, the expression of CXCL10 is increased. Our results may help to better understand the role of CXCL10 in the development of HFRS and may provide some novel insights into the immune response of HTNV infection.

The adaptive immune response does not influence hantavirus disease or persistence in the Syrian hamster

Pathogenic New World hantaviruses cause severe disease in humans characterized by a vascular leak syndrome, leading to pulmonary oedema and respiratory distress with case fatality rates approaching 40%. Hantaviruses infect microvascular endothelial cells without conspicuous cytopathic effects, indicating that destruction of the endothelium is not a mechanism of disease. In humans, high levels of inflammatory cytokines are present in the lungs of patients that succumb to infection. This, along with other observations, suggests that disease has an immunopathogenic component. Currently the only animal model available to study hantavirus disease is the Syrian hamster, where infection with Andes virus (ANDV), the primary agent of disease in South America, results in disease that closely mimics that seen in humans. Conversely, inoculation of hamsters with a passaged Sin Nombre virus (SNV), the virus responsible for most cases of disease in North America, results in persistent infection with high levels of viral replication. We found that ANDV elicited a stronger innate immune response, whereas SNV elicited a more robust adaptive response in the lung. Additionally, ANDV infection resulted in significant changes in the blood lymphocyte populations. To determine whether the adaptive immune response influences infection outcome, we depleted hamsters of CD4(+) and CD8(+) T cells before infection with hantaviruses. Depletion resulted in inhibition of virus-specific antibody responses, although the pathogenesis and replication of these viruses were unaltered. These data show that neither hantavirus replication, nor pathogenesis caused by these viruses, is influenced by the adaptive immune response in the Syrian hamster.

A recombinant pseudotyped lentivirus expressing the envelope glycoprotein of hantaan virus induced protective immunity in mice

Background

Hantaviruses cause acute hemorrhagic fever with renal syndrome (HFRS). Currently, several types of inactivated HFRS vaccines are widely used, however the limited ability of these immunogen to elicit neutralizing antibodies restricts vaccine efficacy. Development of an effective vaccine to overcome this weakness is must.

Methods

In the present study, a recombinant pseudotyped lentivirus bearing the hantaan virus (HTNV) envelope glycoproteins (GP), rLV-M, was constructed. C57BL/6 mice were immunized with the rLV-M and a series of immunological assays were conducted to determine the immunogenicity of the recombinant pseudotyped lentivirus. The humoral and cell-mediated immune responses induced by rLV-M were compared with those of the inactivated HFRS vaccine.

Results

Indirect immunofluorescence assay (IFA) showed the rLV-M expressed target proteins in HEK-293cells. In mice, the rLV-M efficiently induced GP-specific humoral responses and protection against HTNV infection. Furthermore, the rLV-M induced higher neutralizing antibody titers than the inactivated HFRS vaccine control.

Conclusions

The results indicated the potential of using a pseudotyped lentivirus as a delivery vector for a hantavirus vaccine immunogen.

Levels of HTNV-specific CD8+ T lymphocytes in PBMC from the patients with hemorrhagic fever with renal syndrome

The pathogenesis of hemorrhagic fever with renal syndrome (HFRS) has not been fully clarified. Cell-mediated immunity appears to play a crucial role in the immune pathogenesis of HFRS. To explore the relationship between Hantaan (HTNV)-specific CD8(+) T lymphocytes and the immune pathogenesis of HFRS, the levels of interferon γ (IFN-γ) secreted by HTNV-specific CD8(+) T lymphocytes were detected by flow cytometry in peripheral blood mononuclear cells. Levels of HTNV-specific CD8(+) T lymphocytes in patients with HFRS were associated with different phases of HFRS. In fever phase, it was significantly elevated. The levels of HTNV-specific CD8(+) T lymphocytes in PBMC of patients with HFRS were negatively correlated with the levels of blood urea nitrogen and creatinine in plasma. The results show that the HTNV-specific CD8(+) T lymphocyte levels correlate with disease phases. Therefore, dynamic observation of these levels in patients with HFRS can help to judge the status of HFRS disease and to clarify the immune pathogenesis of HFRS.

HLA-A2 and B35 restricted hantaan virus nucleoprotein CD8+ T-cell epitope-specific immune response correlates with milder disease in hemorrhagic fever with renal syndrome

BACKGROUND

Hantaan virus (HTNV) infection in humans is a serious public health concern in Asia. A potent T cell activation peptide vaccine from HTNV structure protein represents a promising immunotherapy for disease control. However, the T cell epitopes of the HTNV restricted by the HLA alleles and the role of epitope-specific T cell response after HTNV infection remain largely unexplored.

METHODOLOGY/PRINCIPAL FINDINGS

Five well-conserved novel CD8(+) T-cell epitopes of the HTNV nucleoprotein restricted by the most popular HLA alleles in Chinese Han population were defined with interferon-γ enzyme-linked immunospot assay in 37 patients infected with HTNV during hospitalization. Two epitopes aa129-aa137 and aa131-aa139 restricted by HLA-A2 and B35, respectively, were selected to evaluate the epitope-specific CD8(+) T-cell response. HLA-peptide pentamer complex staining showed that the frequency of single epitope-specific CD8(+) T cell could be detected in patients (95% confidence interval for aa129-aa137: 0.080%-0.208%; for aa131-aa139: 0.030%-0.094%). The frequency of epitope-specific pentamer(+) CD8(+) T-cell response was much higher in mild/moderate patients than in severe/critical ones at the acute stage of the disease. Moreover, the frequency of epitope-specific CD8(+) T cells at acute stage was inversely associated with the peak level of serum creatinine and was positively associated with the nadir platelet counts during the hospitalization. The intracellular cytokine staining and the proliferation assay showed that the effective epitope-specific CD8(+) T cells were characterized with the production of interferon-γ, expression of CD69 and the strong capacity of proliferation.

CONCLUSION/SIGNIFICANCE

The novel HLA class I restricted HTNV nucleoprotein epitopes-specific CD8(+) T-cell responses would be closely related with the progression and the severity of the disease, which could provide the first step toward effective peptide vaccine development against HTNV infection in humans.

Thrombocytopenia as a predictor of severe acute kidney injury in patients with Hantaan virus infections

Background

Hematological abnormalities often occur several days before kidney injury in patients with hemorrhagic fever with renal syndrome (HFRS). We aimed to investigate the prevalence and prognostic value of the early hematological markers in patients with HFRS caused by Hantaan virus (HTNV) infection.

Methods

In a retrospective cohort study, we analyzed the case records of 112 patients with acute HTNV infection and evaluated the hematological markers for early prediction and risk stratification of HFRS patients with acute kidney injury (AKI).

Results

Of 112 patients analyzed, 66 (59%) developed severe AKI, defined as either receipt of acute dialysis or increased serum creatinine ≥354 µmol/L. The prognostic accuracy of hematological markers, as quantified by the area under the receiver-operating-characteristic curve (AUC), was highest with the nadir platelet count (AUC, 0.89; 95% CI, 0.83–0.95), as compared with the admission platelet count (AUC, 0.84; 95% CI, 0.77–0.92), and the admission and peak leukocyte counts. The nadir platelet count correlated moderately with the levels of peak blood urea nitrogen (r = –0.616) and serum creatinine (r = –0.589), the length of hospital stay (r = –0.599), and the number of dialysis sessions that each patient received during hospital stay (r = –0.625). By multivariate analysis, decreased nadir platelet count remained independently associated with the development of severe AKI (odds ratio, 27.57; 95% CI, 6.96–109.16; P<0.0001).

Conclusions

Thrombocytopenia, rather than leukocytosis, is independently associated with subsequent severe AKI among patients with acute HTNV infection.

Elevated serum concentrations of inflammatory cytokines and chemokines in patients with haemorrhagic fever with renal syndrome

OBJECTIVE

Prospective case-control study, undertaken to investigate serum cytokine and chemokine concentrations during all clinical phases and in different clinical types of haemorrhagic fever with renal syndrome (HFRS).

METHODS

Serum was collected at various disease phases from patients with HFRS (n = 35) and healthy control subjects (n = 10). Tumour necrosis factor (TNF)-α, interleukin (IL)-6, IL-4, interferon (IFN)-γ, IL-8, interferon inducible protein-10 (IP-10) and chemokine (C-C motif) ligand 5 (also known as 'regulated upon activation, normal T-cell expressed and secreted' [RANTES]) were quantified using commercial enzyme-linked immunosorbent assay kits.

RESULTS

Serum concentrations of TNF-α, IL-6, IFN-γ, IL-8, IP-10 and RANTES (but not IL-4) were significantly higher in patients compared with controls. Highest concentrations were generally found during the febrile, hypotensive and oliguric disease phases, as well as in clinically severe and critical cases.

CONCLUSION

Serum concentrations of proinflammatory cytokines and chemokines increased in line with disease severity in HFRS patients.

Sustained high level of serum VEGF at convalescent stage contributes to the renal recovery after HTNV infection in patients with hemorrhagic fever with renal syndrome

To investigate the role of vascular endothelial growth factor (VEGF) in the increased permeability of vascular endothelial cells after Hantaan virus (HTNV) infection in humans, the concentration of VEGF in serum from HTNV infected patients was quantified with sandwich ELISA. Generally, the level of serum VEGF in patients was elevated to 607.0 (542.2-671.9) pg/mL, which was dramatically higher compared with healthy controls (P < 0.001). There was a rapid increase of the serum VEGF level in all patients from the fever onset to oliguric stage, at which the serum creatinine reached the peak level of the disease, indicating that VEGF may be involved in the pathogenesis of renal hyper-permeability. Moreover, the serum VEGF level at convalescent stage was positively correlated with the degree of the disease severity. The sustained high level of serum VEGF at convalescence was observed in critical HFRS patients, suggesting that VEGF would probably contribute to the renal recovery after the virus clearance. Taken together, our results suggested that the VEGF would be involved in the pathogenesis of renal dysfunction at the oliguric stage after HTNV infection, but may function as a recovery factor during the convalescence to help the body self-repair of the renal injury.

The genetic polymorphisms of HLA are strongly correlated with the disease severity after Hantaan virus infection in the Chinese Han population

The polymorphism of human leukocyte antigen (HLA), which is a genetic factor that influences the progression of hemorrhagic fever with renal syndrome (HFRS) after Hantaan virus (HTNV) infection, was incompletely understood. In this case-control study, 76 HFRS patients and 370 healthy controls of the Chinese Han population were typed for the HLA-A, -B, and -DRB1 loci. The general variation at the HLA-DRB1 locus was associated with the onset of HFRS (P < 0.05). The increasing frequencies of HLA-DRB1∗09 and HLA-B*46-DRB1*09 in HFRS patients were observed as reproducing a previous study. Moreover, the HLA-B*51-DRB1*09 was susceptible to HFRS (P = 0.037; OR = 3.62; 95% CI: 1.00-13.18). The increasing frequencies of HLA-B*46, HLA-B*46-DRB1*09, and HLA-B*51-DRB1*09 were observed almost in severe/critical HFRS patients. The mean level of maximum serum creatinine was higher in HLA-B∗46-DRB1*09 (P = 0.011), HLA-B*51-DRB1*09 (P = 0.041), or HLA-B*46 (P = 0.011) positive patients than that in the negative patients. These findings suggest that the allele HLA-B*46 and haplotypes HLA-B*46-DRB1*09 and HLA-B*51-DRB1*09 in patients could contribute to a more severe degree of HFRS and more serious kidney injury, which improve our understanding of the HLA polymorphism for a different outcome of HTNV infection.

Hantaan virus RNA load in patients having hemorrhagic fever with renal syndrome: correlation with disease severity

To investigate the role of viral load in the pathogenesis of hemorrhagic fever with renal syndrome, the Hantaan virus RNA load in plasma from 101 patients was quantified, and the relationships between viral load and disease course, severity, and level of specific humoral immunity were analyzed. The viral load, detectable in 79 patients, ranged from 3.43 to 7.33 log10 copies/mL of plasma. In the early stage of disease, patients in severe/critical group were found to have higher viral loads than those in the mild/moderate group (5.90 vs 5.03 log10 copies/mL; P = .001), suggesting an association between Hantaan virus load and disease severity.

Identification of three novel CTL epitopes within nucleocapsid protein of Hantaan virus

Hantaan virus (HTNV) is a member of the Hantavirus genus that causes human hemorrhagic fever with renal syndrome (HFRS) in humans. The CTL response seems to play a key role in control of viral infection, but only a few HTNV epitopes recognized by the CTLs have been reported. Herein, we screened a panel of overlapping peptides covering the HTNV nucleocapsid protein by ELISPOT assays for those that can elicit IFN-γ production in vitro. Three novel CD8(+) CTL epitopes, N197-205 (RYRTAVCGL), N245-253 (KLLPDTAAV), and N258-266 (GPATNRDYL), were defined on the nucleocapsid protein and were found to be restricted by various HLA alleles including A11, A24, and B7. The epitopes were highly conserved among the reported HTNV strains and other hantanviruses, including Dobrava-Belgrade virus and Seoul virus, supporting their potential use in vaccine designs.

Modification of the adenoviral transfer vector enhances expression of the Hantavirus fusion protein GnS0.7 and induces a strong immune response in C57BL/6 mice

Hantavirus glycoproteins (Gn and Gc) are significant components of vaccines for haemorrhagic fever with renal syndrome (HFRS); however, they are not effective due to weak immunogenicity and low levels of production in expression systems. To circumvent this problem, a 0.7-kb fragment of the S segment was fused to Gn, and a hybrid CAG promoter/enhancer in conjunction with (or without) the WPRE (Woodchuck hepatitis virus post-transcriptional regulatory element) was used to improve the expression of fusion protein GnS0.7 in the adenoviral expression system. The expression level of the fusion protein as well as the response of mice immunized with recombinant adenoviruses containing GnS0.7 was investigated. In addition, a series of immunological assays were conducted to determine the immunogenicity of the recombinant adenoviruses. The results showed that the recombinant adenovirus with the CAG promoter/enhancer (rAd-GnS0.7-pCAG) expressed approximately 2.1-fold more GnS0.7 than the unmodified recombinant adenovirus containing GnS0.7 (rAd-GnS0.7-pShuttle). This enhanced expression level was also higher than for other modified recombinant adenoviruses studied. Animal experiments showed that rAd-GnS0.7-pCAG induced a stronger Hantaan virus (HTNV)-specific humoral and cellular immune response in mice, with the cellular immune response to the GnS0.7 being stronger than the HFRS vaccine control. These results demonstrate that the CAG promoter/enhancer improved significantly the expression of the chimeric gene GnS0.7 in the adenovirus expression system. These findings may have significant implications for the development of genetically engineered vaccines for HFRS.

Longitudinal analysis of the human T cell response during acute hantavirus infection

Longitudinal studies of T cell immune responses during viral infections in humans are essential for our understanding of how effector T cell responses develop, clear infection, and provide long-lasting immunity. Here, following an outbreak of a Puumala hantavirus infection in the human population, we longitudinally analyzed the primary CD8 T cell response in infected individuals from the first onset of clinical symptoms until viral clearance. A vigorous CD8 T cell response was observed early following the onset of clinical symptoms, determined by the presence of high numbers of Ki67(+)CD38(+)HLA-DR(+) effector CD8 T cells. This response encompassed up to 50% of total blood CD8 T cells, and it subsequently contracted in parallel with a decrease in viral load. Expression levels of perforin and granzyme B were high throughout the initial T cell response and likewise normalized following viral clearance. When monitoring regulatory components, no induction of regulatory CD4 or CD8 T cells was observed in the patients during the infection. However, CD8 as well as CD4 T cells exhibited a distinct expression profile of inhibitory PD-1 and CTLA-4 molecules. The present results provide insight into the development of the T cell response in humans, from the very onset of clinical symptoms following a viral infection to resolution of the disease.

T cells and pathogenesis of hantavirus cardiopulmonary syndrome and hemorrhagic fever with renal syndrome

We previously hypothesized that increased capillary permeability observed in both hantavirus cardiopulmonary syndrome (HCPS) and hemorrhagic fever with renal syndrome (HFRS) may be caused by hantavirus-specific cytotoxic T cells attacking endothelial cells presenting viral antigens on their surface based on clinical observations and in vitro experiments. In HCPS, hantavirus-specific T cell responses positively correlated with disease severity. In HFRS, in one report, contrary to HCPS, T cell responses negatively correlated with disease severity, but in another report the number of regulatory T cells, which are thought to suppress T cell responses, negatively correlated with disease severity. In rat experiments, in which hantavirus causes persistent infection, depletion of regulatory T cells helped infected rats clear virus without inducing immunopathology. These seemingly contradictory findings may suggest delicate balance in T cell responses between protection and immunopathogenesis. Both too strong and too weak T cell responses may lead to severe disease. It is important to clarify the role of T cells in these diseases for better treatment (whether to suppress T cell functions) and protection (vaccine design) which may need to take into account viral factors and the influence of HLA on T cell responses.

Human pathogenic hantaviruses and prevention of infection

Hantaviruses are emerging viruses which are hosted by small mammals. When transmitted to humans, they can cause two clinical syndromes, hemorrhagic fever with renal syndrome or hantavirus cardiopulmonary syndrome. The review compiles the current list of hantaviruses which are thought to be pathogenic in humans on the basis of molecular or at least serological evidence. Whereas induction of a neutralizing humoral immune response is considered to be protective against infection, the dual role of cellular immunity (protection versus immunopathogenicity) is discussed. For active immunisation, inactivated virus vaccines are licensed in certain Asian countries. Moreover, several classical and molecular vaccine approaches are in pre-clinical stages of development. The development of hantavirus vaccines is hampered by the lack of adequate animal models of hantavirus-associated disease. In addition to active immunization strategies, the review summarizes other ways of infection prevention, as passive immunization, chemoprophylaxis, and exposition prophylaxis.

Serum levels of inflammatory and regulatory cytokines in patients with hemorrhagic fever with renal syndrome

Background

Hantaviruses are the causative agents of two zoonotic diseases: hemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS). The pathogenesis of HFRS is poorly understood. However, it has been suggested that immune mechanisms, including cytokines, might have an important role in HFRS pathogenesis. Thus, the aim of our study was to investigate cytokine profiles in serum samples of HFRS patients from Slovenia and explore a possible correlation between cytokine levels and disease severity.

Methods

Acute-phase serum samples from 52 patients, diagnosed with DOBV infection, and 61 patients, diagnosed with PUUV infection, were included in this study. Patients were divided into two groups - severe or mild - based on disease severity. Levels of IL-10, IL-12, INF-γ and TNF-α were measured in the serum samples with commercial ELISA tests.

Results

Increased levels of IL-10, INF-γ, and TNF-α were found in almost all the serum samples tested. On average, higher concentrations were detected in patients infected with DOBV than PUUV. Furthermore, significantly higher levels of IL-10 (P = 0.001) and TNF-α (P = 0.003) were found in patients with a more severe clinical course of disease. The same association between IL-10 (P < 0.001) and TNF-α (P = 0.021), and the severity of the disease was observed also when only patients infected with DOBV were considered. No differences in cytokine concentrations according to disease severity were observed in patients infected with PUUV. Concentrations of serum IL-12 in HFRS patients were in the normal range, however, higher levels were detected in patients infected with PUUV than in patients infected with DOBV.

Conclusions

We suggest that imbalance in production of proinflammatory and regulatory cytokines might be in part responsible for a more severe course of HFRS.

Cystatin C, a novel urinary biomarker for sensitive detection of acute kidney injury during haemorrhagic fever with renal syndrome

To explore the value of cystatin C for evaluating acute kidney injury (AKI) in haemorrhagic fever with renal syndrome (HFRS), the concentrations of cystatin C in serum and urine samples from HFRS patients were determined. The serum and urinary cystatin C concentrations significantly increased in HFRS patients compared with normal controls (p < 0.001). In the acute phase of HFRS, urinary cystatin C increased to higher levels than serum creatinine, especially in severe or critical cases in the oliguric stage. Furthermore, higher levels of urinary cystatin C in the acute phase positively correlated with increased severity of the subsequent kidney injury. In conclusion, urinary cystatin C is a more sensitive clinical marker for AKI in HFRS, which may enable us to initiate treatment measures as early as possible.

Switch to high-level virus replication and HLA class I upregulation in differentiating megakaryocytic cells after infection with pathogenic hantavirus

Hantaan virus (HTNV), the prototype member of the Hantavirus genus in the family Bunyaviridae, causes hemorrhagic fever with renal syndrome (HFRS) in humans. Hemorrhage is due to endothelial barrier damage and a sharp decrease in platelet counts. The mechanisms underlying HTNV-associated acute thrombocytopenia have not been elucidated so far. Platelets are produced by mature megakaryocytes that develop during megakaryopoiesis. In this study, we show that HTNV targets megakaryocytic cells whereas rather non-pathogenic hantaviruses did not infect this cell type. After induction of differentiation megakaryocytic cells switched from low-level to high-level HTNV production without reduction in cell survival or alteration in differentiation. However, increased HTNV replication resulted in strong upregulation of HLA class I molecules although HTNV escaped type I interferon (IFN)-associated innate responses. Taken together, HTNV efficiently replicates in differentiating megakaryocytic cells resulting in upregulation of HLA class I molecules, the target structures for cytotoxic T cells (CTLs).

Highly differentiated, resting gn-specific memory CD8+ T cells persist years after infection by andes hantavirus

In man, infection with South American Andes virus (ANDV) causes hantavirus cardiopulmonary syndrome (HCPS). HCPS due to ANDV is endemic in Southern Chile and much of Argentina and increasing numbers of cases are reported all over South America. A case-fatality rate of about 36% together with the absence of successful antiviral therapies urge the development of a vaccine. Although T-cell responses were shown to be critically involved in immunity to hantaviruses in mouse models, no data are available on the magnitude, specificity and longevity of ANDV-specific memory T-cell responses in patients. Using sets of overlapping peptides in IFN-γ ELISPOT assays, we herein show in 78 Chilean convalescent patients that Gn-derived epitopes were immunodominant as compared to those from the N- and Gc-proteins. Furthermore, while the relative contribution of the N-specific response significantly declined over time, Gn-specific responses remained readily detectable ex vivo up to 13 years after the acute infection. Tetramer analysis further showed that up to 16.8% of all circulating CD3⁺CD8⁺ T cells were specific for the single HLA-B*3501-restricted epitope Gn_465–473 years after the acute infection. Remarkably, Gn_465–473–specific cells readily secreted IFN-γ, granzyme B and TNF-α but not IL-2 upon stimulation and showed a ‘revertant’ CD45RA⁺CD27⁻CD28⁻CCR7⁻CD127⁻ effector memory phenotype, thereby resembling a phenotype seen in other latent virus infections. Most intriguingly, titers of neutralizing antibodies increased over time in 10/17 individuals months to years after the acute infection and independently of whether they were residents of endemic areas or not. Thus, our data suggest intrinsic, latent antigenic stimulation of Gn-specific T-cells. However, it remains a major task for future studies to proof this hypothesis by determination of viral antigen in convalescent patients. Furthermore, it remains to be seen whether Gn-specific T cells are critical for viral control and protective immunity. If so, Gn-derived immunodominant epitopes could be of high value for future ANDV vaccines.

In man, hantavirus cardiopulmonary syndrome (HCPS) caused by Andes Virus (ANDV) is endemic in the Southern cone of Chile and Argentina but cases of HCPS are being increasingly reported all over South America since 1995. HCPS is characterized by fulminant pulmonary edema which progresses to shock and death in about 36% of patients with HCPS. Nevertheless, to date, neither antiviral treatments nor vaccines inducing neutralizing antibodies (NAb) have proven effective against HCPS-causing hantaviruses. We set out for the first study on human cellular immunity towards ANDV in 78 convalescent survivors of ANDV infection. We found that Gn-specific responses were predominant as compared to N- and Gc-specific responses, even up to 13 years after the infection. Surprisingly, most of the Gn-specific responses were restricted to two neighboring epitopes within the Gn carboxyterminus. Interestingly, among HLA-B*3501⁺ patients, Gn_465−473-specific CD8⁺ T-cells showed highly differentiated but resting phenotype and functions. It remains to be seen in future studies whether the immunodominace of Gn-specific T-cells is crucial for protective immunity. Most intriguingly, titers of neutralizing antibodies increased in 10/17 individuals months to years after the acute infection and independently of whether they were residents of endemic areas or not. Thus, our data suggest viral persistence or latency in part of ANDV-convalescent patients. However, it remains a major task for future studies to proof the concept of latent/persistent human ANDV infection by the determination of viral antigen in convalescent patients.