Serum levels of alpha and gamma interferons in hemorrhagic fever with renal syndrome

Neutrophil depletion suppresses pulmonary vascular hyperpermeability and occurrence of pulmonary edema caused by hantavirus infection in C.B-17 SCID mice

Hantavirus infections are characterized by vascular hyperpermeability and neutrophilia. However, the pathogenesis of this disease is poorly understood. Here, we demonstrate for the first time that pulmonary vascular permeability is increased by Hantaan virus infection and results in the development of pulmonary edema in C.B-17 severe combined immunodeficiency (SCID) mice lacking functional T cells and B cells. Increases in neutrophils in the lung and blood were observed when pulmonary edema began to be observed in the infected SCID mice. The occurrence of pulmonary edema was inhibited by neutrophil depletion. Moreover, the pulmonary vascular permeability was also significantly suppressed by neutrophil depletion in the infected mice. Taken together, the results suggest that neutrophils play an important role in pulmonary vascular hyperpermeability and the occurrence of pulmonary edema after hantavirus infection in SCID mice.

IMPORTANCE

Although hantavirus infections are characterized by the occurrence of pulmonary edema, the pathogenic mechanism remains largely unknown. In this study, we demonstrated for the first time in vivo that hantavirus infection increases pulmonary vascular permeability and results in the development of pulmonary edema in SCID mice. This novel mouse model for human hantavirus infection will be a valuable tool and will contribute to elucidation of the pathogenetic mechanisms. Although the involvement of neutrophils in the pathogenesis of hantavirus infection has largely been ignored, the results of this study using the mouse model suggest that neutrophils are involved in the vascular hyperpermeability and development of pulmonary edema in hantavirus infection. Further study of the mechanisms could lead to the development of specific treatment for hantavirus 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.

Expression of VLA-4 molecule in PBMC from patients with hemorrhagic fever with renal syndrome

OBJECTIVE AND DESIGN

The very late antigen-4 (VLA-4) bound to vascular cell adhesion molecule-1 could provide co-stimulatory signals for the activation of T lymphocytes, and these adhesion molecules play key roles in leukocyte adherence and propagation of inflammatory responses. We examined the levels of VLA-4 in the peripheral blood mononuclear cells (PBMC) of patients with hemorrhagic fever with renal syndrome (HFRS).

MATERIALS AND METHODS

The levels of VLA-4 in PBMC samples collected from 53 patients by immunohistochemical staining were detected.

RESULTS

The expression of VLA-4 in PBMC of HFRS patients at different stages were significantly higher than those in normal controls (P < 0.05), except recovery stage (P > 0.05). The expression of VLA-4 in PBMC of HFRS patients at different types were significantly higher than those in healthy controls (P < 0.05). The levels of VLA-4 in patients with HFRS were positively correlated with serum levels of blood urea nitrogen (BUN) and creatinine (Cr).

CONCLUSIONS

VLA-4 might play an important role in the immunopathological lesions of HFRS. We found that VLA-4 levels were closely correlated to the severity of the HFRS and the degree of kidney damage.

VEGFR2 and Src kinase inhibitors suppress Andes virus-induced endothelial cell permeability

Hantaviruses predominantly infect human endothelial cells and, in the absence of cell lysis, cause two diseases resulting from increased vascular permeability. Andes virus (ANDV) causes a highly lethal acute pulmonary edema termed hantavirus pulmonary syndrome (HPS). ANDV infection enhances the permeability of endothelial cells in response to vascular endothelial growth factor (VEGF) by increasing signaling responses directed by the VEGFR2-Src-VE-cadherin pathway, which directs adherens junction (AJ) disassembly. Here we demonstrate that inhibiting pathway-specific VEGFR2 and Src family kinases (SFKs) blocks ANDV-induced endothelial cell permeability. Small interfering RNA (siRNA) knockdown of Src within ANDV-infected endothelial cells resulted in an ∼70% decrease in endothelial cell permeability compared to that for siRNA controls. This finding suggested that existing FDA-approved small-molecule kinase inhibitors might similarly block ANDV-induced permeability. The VEGFR2 kinase inhibitor pazopanib as well as SFK inhibitors dasatinib, PP1, bosutinib, and Src inhibitor 1 dramatically inhibited ANDV-induced endothelial cell permeability. Consistent with their kinase-inhibitory concentrations, dasatinib, PP1, and pazopanib inhibited ANDV-induced permeability at 1, 10, and 100 nanomolar 50% inhibitory concentrations (IC(50)s), respectively. We further demonstrated that dasatinib and pazopanib blocked VE-cadherin dissociation from the AJs of ANDV-infected endothelial cells by >90%. These findings indicate that VEGFR2 and Src kinases are potential targets for therapeutically reducing ANDV-induced endothelial cell permeability and, as a result, capillary permeability during HPS. Since the functions of VEGFR2 and SFK inhibitors are already well defined and FDA approved for clinical use, these findings rationalize their therapeutic evaluation for efficacy in reducing HPS disease. Endothelial cell barrier functions are disrupted by a number of viruses that cause hemorrhagic, edematous, or neurologic disease, and as a result, our findings suggest that VEGFR2 and SFK inhibitors should be considered for regulating endothelial cell barrier functions altered by additional viral pathogens.

Analysis of the immune response to Hantaan virus nucleocapsid protein C-terminal-specific CD8(+) T cells in patients with hemorrhagic fever with renal syndrome

Hantaan virus (HTNV), the prototype member of the Hantavirus genus in the family Bunyaviridae, causes hemorrhagic fever with renal syndrome (HFRS), which is characterized by capillary leakage, hemorrhage, and renal injury, and is an important public health problem in China. Some kinds of immune cells, particularly CD8(+) T cells, are involved in the pathogenesis of Hantavirus infection. The nucleocapsid protein (NP) of the Hantavirus is the most conserved structural protein and the most abundant viral protein produced during infection. It is one of the important target antigens that induce the CD8(+) T-cell response. In this study, we examined the CD8(+) T-cell response to HTNV NP C-terminal polypeptides. We synthesized 23 overlapping C-terminal polypeptides and detected the antigen-specific CD8(+) T cell response in 15 patients with HFRS. The results demonstrated that there were NP-specific T-cell responses in bulk cultures of peripheral blood mononuclear cells (PBMCs) from 9 of 15 patients. The peptide 51 (aa 301-315: SPSSIWVFAGAPDRC), peptide 60 (aa 355-369: LRKKSSFYQSYLRRT), and peptide 70 (aa 415-429: DVKVKEISNQEPLKL) induced strong CD8(+) T-cell responses. Among them, peptide 70 induced CTL responses in donors 7, 9, and 11, and the strongest responses were seen in donor 11. Depletion of CD8(+) T cells from PBMCs completely abrogated the peptide-specific T-cell response, while depletion of CD4(+) T cells did not diminish the number of IFN-gamma spot-forming cells. These data suggest that infection with HTNV results in CTL responses to immunodominant regions on the NP.

Immunological mechanisms mediating hantavirus persistence in rodent reservoirs

Hantaviruses, similar to several emerging zoonotic viruses, persistently infect their natural reservoir hosts, without causing overt signs of disease. Spillover to incidental human hosts results in morbidity and mortality mediated by excessive proinflammatory and cellular immune responses. The mechanisms mediating the persistence of hantaviruses and the absence of clinical symptoms in rodent reservoirs are only starting to be uncovered. Recent studies indicate that during hantavirus infection, proinflammatory and antiviral responses are reduced and regulatory responses are elevated at sites of increased virus replication in rodents. The recent discovery of structural and non-structural proteins that suppress type I interferon responses in humans suggests that immune responses in rodent hosts could be mediated directly by the virus. Alternatively, several host factors, including sex steroids, glucocorticoids, and genetic factors, are reported to alter host susceptibility and may contribute to persistence of hantaviruses in rodents. Humans and reservoir hosts differ in infection outcomes and in immune responses to hantavirus infection; thus, understanding the mechanisms mediating viral persistence and the absence of disease in rodents may provide insight into the prevention and treatment of disease in humans. Consideration of the coevolutionary mechanisms mediating hantaviral persistence and rodent host survival is providing insight into the mechanisms by which zoonotic viruses have remained in the environment for millions of years and continue to be transmitted to humans.

Emergence and persistence of hantaviruses

Hantaviral diseases have been recognized for hundreds of years but, until 1976, they had not been associated with an infectious agent. When Lee and colleagues isolated what is now known as Hantaan virus, the techniques they introduced allowed further investigations into the etiology of the classical hantavirus disease, hemorrhagic fever with renal syndrome (HFRS), now known to be caused by any of multiple hantaviruses. The discovery of hantavirus pulmonary syndrome (HPS) in the New World, and that it also can be caused by any of multiple hantaviruses (family Bunyaviridae, genus Hantavirus), has opened an entire field of epidemiologic, virologic, molecular, behavioral, and ecologic studies of these viruses. There appears to be a single hantavirus-single rodent host association, such that understanding the idiosyncrasies of each rodent host species and the ecologic variables that affect them are recognized as critical if we are to reduce human risk for infection. This chapter summarizes what is known about hantaviruses with regard to history of these viruses, their taxonomy, recognized geographical distribution, ecologic factors impacting their maintenance and spread of hantaviruses, effect of rodent behavior on hantavirus transmission, influence of host factors on susceptibility to and transmission of hantaviruses, and transmission of hantaviruses from rodents to humans. In addition, we summarize all these complexities and provide suggestions for future research directions.

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.

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.

Establishment of an ELISA system for determining soluble LAIR-1 levels in sera of patients with HFRS and kidney transplant

LAIR-1, the leukocyte-associated Ig-like receptor-1, is a trans-membrane molecule that functions as an inhibitory receptor on natural killer cells, T lymphocytes and monocytes. It has been well known that many trans-membrane receptors can shed from the cell surface and be released into the circulation in soluble form when lymphocytes, endothelials and other immune cells are activated. In many cases, the levels of soluble receptors in the circulation can be used as markers of lymphocyte activation in transplant patients and virus infection patients. To investigate whether LAIR-1 is able to be released into the sera, we developed a sandwich enzyme-linked immunosorbent assay (ELISA) system based on two anti-LAIR-1 monoclonal antibodies (MAb) with different epitope specificities. Using this ELISA, we found that sLAIR-1 existed in the supernatants collected from PMA, PHA or CD3 MAb-stimulated lymphocytes cultures in vitro for the first time. Moreover, we found that LAIR-1 level in serum samples from healthy individuals was 6.2 +/- 3.3 ng/ml, whereas the levels in sera of patients with hemorrhagic fever with renal syndrome (HFRS) and patients 3-7 days after kidney transplant increased to 47.2 +/- 35.9 and 24.4 +/- 16.0 ng/ml, respectively. Furthermore, HFRS patients in oliguric phase showed higher serum sLAIR-1 levels than those in other phases, and transplant patients with rejection showed higher serum sLAIR-1 level than those without rejection. These findings demonstrated that LAIR-1 can be released when lymphocytes are activated, suggesting sLAIR-1 may be used as a predictor for monitoring immune reaction in some virus infections and organ transplants which may be useful in clinical treatment of these diseases.

A new model of Hantaan virus persistence in mice: the balance between HTNV infection and CD8(+) T-cell responses

We established a viral persistence model that involves the adoptive transfer of spleen cells from immunocompetent mice (H-2(d)) into Hantaan virus (HTNV)-infected severe combined immunodeficient (SCID, H-2(d)) mice. The infection is maintained despite the presence of neutralizing antibodies, without apparent signs of disease, and there is a correlation between HTNV persistence and the lack of HTNV-specific CD8(+) T cells. In addition, disseminated HTNV infection before the initiation of immune responses appears to be important for virus persistence. The suppression of HTNV-specific CD8(+) T cells in the present model appears to occur at the periphery. The present study also demonstrates that CD8(+) T cells contribute to the clearance of HTNV. Thus, it seems that HTNV-specific CD8(+) T cells play a key role in HTNV persistence in mice. This model of viral persistence is useful for studies of immune responses and immunocytotherapy against viral infection.

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.

Characterization of HLA-A2.1-restricted epitopes, conserved in both Hantaan and Sin Nombre viruses, in Hantaan virus-infected patients

Nine different CTL epitopes, conserved in both Hantaan virus (HTNV) and Sin Nombre virus (SNV), were selected for study. The binding affinity of each peptide with HLA-A2.1 molecules in vitro was determined and antigen-specific responses from seven donors who had a previous field infection with HTNV were examined. Although the strength or frequency of CTL activity showed different patterns in the seven patients, five of seven patients showed significant activity against at least one or more epitope peptides. In particular, the peptide ILQDMRNTI (HTNV, aa 334-342; SNV, aa 333-341), which elicited CTL activity in five patients, was shown to be specifically HLA-A2.1-restricted in partially cloned CD8+ T cells and also induced activated and effector CD8+ T cell-producing T cytotoxic (Tc) type 1 cytokines, such as IL-2 and IFN-gamma. The results suggest that this epitope would serve as a useful component for the intervention of both HTNV and SNV infection.

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.

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.

Human memory cytotoxic T-lymphocyte (CTL) responses to Hantaan virus infection: identification of virus-specific and cross-reactive CD8(+) CTL epitopes on nucleocapsid protein

Hantaan virus, the prototypic member of the Hantavirus genus, causes hemorrhagic fever with renal syndrome in humans. We examined the human memory T-lymphocyte responses of three donors who had previous laboratory-acquired infections with Hantaan virus. We demonstrated virus-specific responses in bulk cultures of peripheral blood mononuclear cells (PBMC) from all donors. Bulk T-cell responses were directed against either Hantaan virus nucleocapsid (N) or G1 protein, and these responses varied between donors. We established both CD4(+) and CD8(+) N-specific cell lines from two donors and CD4(+) G1-specific cell lines from a third donor. All CD8(+) cytotoxic T-lymphocyte (CTL) lines recognized one of two epitopes on the nucleocapsid protein: one epitope spanning amino acids 12 to 20 and the other spanning amino acids 421 to 429. The CTL lines specific for amino acids 12 to 20 were restricted by HLA B51, and those specific for amino acids 421 to 429 were restricted by HLA A1. The N-specific CTL lines isolated from these two donors included both Hantaan virus-specific CTLs and hantavirus cross-reactive CTLs. Responses to both epitopes are detectable in short-term bulk cultures of PBMC from one donor, and precursor frequency analysis confirms that CTLs specific for these epitopes are present at relatively high precursor frequencies in the peripheral T-cell pool. These data suggest that infection with Hantaan virus results in the generation of CTL to limited epitopes on the nucleocapsid protein and that infection also results in the generation of cross-reactive T-cell responses to distantly related hantaviruses which cause the distinct hantavirus pulmonary syndrome. This is the first demonstration of human T-lymphocyte responses to Hantaan virus.

Pathogenetic and clinical aspects of the renal involvement in hemorrhagic fever with renal syndrome

Hemorrhagic fever with renal syndrome is the most common clinical manifestation of hantavirus infection. The main target organ is the kidney, resulting in an interstitial hemorrhagic nephritis and sometimes acute tubular necrosis. The pathogenesis is still largely unknown, but several recent studies indicate an important role for immune mechanisms including increased expression of cytokines, for example, tumor necrosis factor. Immunohistochemical studies of kidney biopsies have revealed deposits of IgG, IgM, and C3, but deposits were significantly less numerous than in chronic immune complex disease. Since hantaviruses are not cytolytic, a direct detrimental effect of the infecting virus is less likely. The long-term prognosis of hemorrhagic fever with renal syndrome seems to be favorable, but there are reports that previous hantavirus infection is associated with an increased risk of hypertensive renal disease. Prospective longitudinal studies addressing this issue are underway.