Antiviral activity of porphyrins and porphyrin-like compounds against tick-borne encephalitis virus: Blockage of the viral entry/fusion machinery by photosensitization-mediated destruction of the viral envelope

Tick-borne encephalitis virus (TBEV), the causative agent of tick-borne encephalitis (TBE), is a medically important flavivirus endemic to the European-Asian continent. Although more than 12,000 clinical cases are reported annually worldwide, there is no anti-TBEV therapy available to treat patients with TBE. Porphyrins are macrocyclic molecules consisting of a planar tetrapyrrolic ring that can coordinate a metal cation. In this study, we investigated the cytotoxicity and anti-TBEV activity of a large series of alkyl- or (het)aryl-substituted porphyrins, metalloporphyrins, and chlorins and characterized their molecular interactions with the viral envelope in detail. Our structure-activity relationship study showed that the tetrapyrrole ring is an essential structural element for anti-TBEV activity, but that the presence of different structurally distinct side chains with different lengths, charges, and rigidity or metal cation coordination can significantly alter the antiviral potency of porphyrin scaffolds. Porphyrins were demonstrated to interact with the TBEV lipid membrane and envelope protein E, disrupt the TBEV envelope and inhibit the TBEV entry/fusion machinery. The crucial mechanism of the anti-TBEV activity of porphyrins is based on photosensitization and the formation of highly reactive singlet oxygen. In addition to blocking viral entry and fusion, porphyrins were also observed to interact with RNA oligonucleotides derived from TBEV genomic RNA, indicating that these compounds could target multiple viral/cellular structures. Furthermore, immunization of mice with porphyrin-inactivated TBEV resulted in the formation of TBEV-neutralizing antibodies and protected the mice from TBEV infection. Porphyrins can thus be used to inactivate TBEV while retaining the immunogenic properties of the virus and could be useful for producing new inactivated TBEV vaccines.

Functional characterization and immunogenicity of a novel vaccine candidate against tick-borne encephalitis virus based on Leishmania-derived virus-like particles

Tick-borne encephalitis virus (TBEV) is a major cause of neurological infections in many regions of central, eastern and northern Europe and northern Asia. In approximately 15% of cases, TBEV infections lead to the development of severe encephalitis or meningitis. The main route of TBEV transmission is tick bites; however, ingestion of dairy products from infected animals (goats, cattle and sheep) is also a frequent cause of the disease. Therefore, vaccination of livestock in virus endemic regions could also contribute to the decrease in TBEV infection among humans. Although few vaccines against TBEV based on inactivated viruses are available for humans, due to high costs, vaccination is not mandatory in most of the affected countries. Moreover, there is still no vaccine for veterinary use. Here, we present a characterization and immunogenicity study of a new potential TBEV vaccine based on virus-like particles (VLPs) produced in Leishmania tarentolae cells. VLPs, which mimic native viral particles but do not contain genetic material, show good immunogenic potential. For the first time, we showed that the protozoan L. tarentolae expression system can be successfully used for the production of TBEV virus-like particles with highly efficient production. We confirmed that TBEV recombinant structural proteins (prM/M and E) from VLPs are highly recognized by neutralizing antibodies in in vitro analyses. Therefore, VLPs in combination with AddaVax adjuvant were used in immunization studies in a mouse model. VLPs proved to be highly immunogenic and induced the production of high levels of neutralizing antibodies. In a challenge experiment, immunization with VLPs provided full protection from lethal TBE in mice. Thus, we suggest that Leishmania-derived VLPs may be a good candidate for a safe alternative human vaccine with high efficiency of production. Moreover, this potential vaccine candidate may constitute a low-cost candidate for veterinary use.

Detection of Leptospira species in bat cadavers, Czech and Slovak Republics

Kidney samples from 300 bat cadavers from the Czech and Slovak Republics were tested for Leptospira DNA using PCR and sequencing of three genes (lipL32, flab, and 16S ribosomal RNA). Overall detection rate was 4.7% and two bat species (Myotis myotis and Nyctalus noctula) were PCR-positive for at least one gene. Detected Leptospira sequences were similar to L. interrogans and L. borgpetersenii, and included a potentially novel species related to L. weilii.

Guanine quadruplexes in the RNA genome of the tick-borne encephalitis virus: their role as a new antiviral target and in virus biology

We have identified seven putative guanine quadruplexes (G4) in the RNA genome of tick-borne encephalitis virus (TBEV), a flavivirus causing thousands of human infections and numerous deaths every year. The formation of G4s was confirmed by biophysical methods on synthetic oligonucleotides derived from the predicted TBEV sequences. TBEV-5, located at the NS4b/NS5 boundary and conserved among all known flaviviruses, was tested along with its mutated variants for interactions with a panel of known G4 ligands, for the ability to affect RNA synthesis by the flaviviral RNA-dependent RNA polymerase (RdRp) and for effects on TBEV replication fitness in cells. G4-stabilizing TBEV-5 mutations strongly inhibited RdRp RNA synthesis and exhibited substantially reduced replication fitness, different plaque morphology and increased sensitivity to G4-binding ligands in cell-based systems. In contrast, strongly destabilizing TBEV-5 G4 mutations caused rapid reversion to the wild-type genotype. Our results suggest that there is a threshold of stability for G4 sequences in the TBEV genome, with any deviation resulting in either dramatic changes in viral phenotype or a rapid return to this optimal level of G4 stability. The data indicate that G4s are critical elements for efficient TBEV replication and are suitable targets to tackle TBEV infection.

Tick-Borne Encephalitis in an 8.5-Month-Old Boy Suspected of Febrile Seizures

Tick-borne encephalitis (TBE) is a serious viral neuroinfection affecting humans in large areas of Europe and Asia. TBE can occur at any age, but only a few reports of TBE in infants younger than 1 year have been published. Here, we report a case of severe TBE in an 8.5-month-old boy presenting with seizures at the beginning of the neurological phase.

Broad and potent neutralizing human antibodies to tick-borne flaviviruses protect mice from disease

Tick-borne encephalitis virus (TBEV) is an emerging human pathogen that causes potentially fatal disease with no specific treatment. Mouse monoclonal antibodies are protective against TBEV, but little is known about the human antibody response to infection. Here, we report on the human neutralizing antibody response to TBEV in a cohort of infected and vaccinated individuals. Expanded clones of memory B cells expressed closely related anti-envelope domain III (EDIII) antibodies in both groups of volunteers. However, the most potent neutralizing antibodies, with IC50s below 1 ng/ml, were found only in individuals who recovered from natural infection. These antibodies also neutralized other tick-borne flaviviruses, including Langat, louping ill, Omsk hemorrhagic fever, Kyasanur forest disease, and Powassan viruses. Structural analysis revealed a conserved epitope near the lateral ridge of EDIII adjoining the EDI-EDIII hinge region. Prophylactic or early therapeutic antibody administration was effective at low doses in mice that were lethally infected with TBEV.

Molecular communication between the monogenea and fish immune system

Monogeneans parasitise mainly the outer structures of fish, such as the gills, fins, and skin, that is, tissues covered with a mucous layer. While attached by sclerotised structures to host's surface, monogeneans feed on its blood or epidermal cells and mucus. Besides being a rich source of nutrients, these tissues also contain humoral immune factors and immune cells, which are ready to launch defence mechanisms against the tegument or gastrointestinal tract of these invaders. The exploitation of hosts' resources by the Monogenea must, therefore, be accompanied by suppressive and immunomodulatory mechanisms which protect the parasites against attacks by host immune system. Elimination of hosts' cytotoxic molecules and evasion of host immune response is often mediated by proteins secreted by the parasites. The aim of this review is to summarise existing knowledge on fish immune responses against monogeneans. Results gleaned from experimental infections illustrate the various interactions between parasites and the innate and adaptive immune system of the fish. The involvement of monogenean molecules (mainly inhibitors of peptidases) in molecular communication with host immune system is discussed.

2020 taxonomic update for phylum Negarnaviricota (Riboviria: Orthornavirae), including the large orders Bunyavirales and Mononegavirales

In March 2020, following the annual International Committee on Taxonomy of Viruses (ICTV) ratification vote on newly proposed taxa, the phylum Negarnaviricota was amended and emended. At the genus rank, 20 new genera were added, two were deleted, one was moved, and three were renamed. At the species rank, 160 species were added, four were deleted, ten were moved and renamed, and 30 species were renamed. This article presents the updated taxonomy of Negarnaviricota as now accepted by the ICTV.

Effect of cysteine peptidase inhibitor of Eudiplozoon nipponicum (Monogenea) on cytokine expression of macrophages in vitro

The gills of the common carp, whose mucosal surface belongs to the key defence mechanisms of piscine immunity, can be infested with both the larval and adult stage of Eudiplozoon nipponicum (Monogenea). Although on their own, monogeneans do not considerably compromise their hosts' health status, fish with epithelial barriers damaged in parasite feeding and attachment sites are at an increased risk of bacterial challenge with possible harmful consequences. Several studies suggest that helminth parasites of teleost fish evade and manipulate host immune system via their excretory-secretory products, but our knowledge of these processes in the monogeneans is limited. Cysteine peptidase inhibitors (CPI), which are found in the secretions of numerous parasites, often induce immunosuppression by subverting Th1 mechanisms and drawing the immune system towards a Th2/Treg response. We employed the qPCR to test the effect of recently characterised CPI of E. nipponicum (rEnStef) on the mRNA expression of pro-inflammatory cytokine TNF-α and anti-inflammatory cytokine IL-10 produced by porcine macrophages in vitro. After an initial preincubation with rEnStef, we stimulated the macrophages using LPS. By inducing a Th1 pro-inflammatory response, we imitated the immune reaction during a bacterial challenge in tissue damaged by the feeding and attachment of E. nipponicum. We observed a significant dose-dependent downregulation of the expression of TNF-α and IL-10 cytokines. The observed suppression of TNF-alpha expression by rEnStef could result in decreased pathogen control, which might in turn lead to increased rates of secondary bacterial infections in fish infected by E. nipponicum.

A novel locus on mouse chromosome 7 that influences survival after infection with tick-borne encephalitis virus

Background

Tick-borne encephalitis (TBE) is the main tick-borne viral infection in Eurasia. Its manifestations range from inapparent infections and fevers with complete recovery to debilitating or fatal encephalitis. The basis of this heterogeneity is largely unknown, but part of this variation is likely due to host genetic. We have previously found that BALB/c mice exhibit intermediate susceptibility to the infection of TBE virus (TBEV), STS mice are highly resistant, whereas the recombinant congenic strain CcS-11, carrying 12.5% of the STS genome on the background of the BALB/c genome is even more susceptible than BALB/c. Importantly, mouse orthologs of human TBE controlling genes Oas1b, Cd209, Tlr3, Ccr5, Ifnl3 and Il10, are in CcS-11 localized on segments derived from the strain BALB/c, so they are identical in BALB/c and CcS-11. As they cannot be responsible for the phenotypic difference of the two strains, we searched for the responsible STS-derived gene-locus. Of course the STS-derived genes in CcS-11 may operate through regulating or epigenetically modifying these non-polymorphic genes of BALB/c origin.

Methods

To determine the location of the STS genes responsible for susceptibility of CcS-11, we analyzed survival of TBEV-infected F₂ hybrids between BALB/c and CcS-11. CcS-11 carries STS-derived segments on eight chromosomes. These were genotyped in the F₂ hybrid mice and their linkage with survival was tested by binary trait interval mapping. We have sequenced genomes of BALB/c and STS using next generation sequencing and performed bioinformatics analysis of the chromosomal segment exhibiting linkage with TBEV survival.

Results

Linkage analysis revealed a novel suggestive survival-controlling locus on chromosome 7 linked to marker D7Nds5 (44.2 Mb). Analysis of this locus for polymorphisms between BALB/c and STS that change RNA stability and genes’ functions led to detection of 9 potential candidate genes: Cd33, Klk1b22, Siglece, Klk1b16, Fut2, Grwd1, Abcc6, Otog, and Mkrn3. One of them, Cd33, carried a nonsense mutation in the STS strain.

Conclusions

The robust genetic system of recombinant congenic strains of mice enabled detection of a novel suggestive locus on chromosome 7. This locus contains 9 candidate genes, which will be focus of future studies not only in mice but also in humans.

Combination therapy of rabies-infected mice with inhibitors of pro-inflammatory host response, antiviral compounds and human rabies immunoglobulin

Recent studies demonstrated that inhibitors of pro-inflammatory molecular cascades triggered by rabies infection in the central nervous system (CNS) can enhance survival in mouse model and that certain antiviral compounds interfere with rabies virus replication in vitro. In this study different combinations of therapeutics were tested to evaluate their effect on survival in rabies-infected mice, as well as on viral load in the CNS. C57Bl/6 mice were infected with Silver-haired bat rabies virus (SHBRV)-18 at virus dose approaching LD₅₀ and LD₁₀₀. In one experimental group daily treatments were initiated 4 h before-, in other groups 48 or 96 h after challenge. In the first experiment therapeutic combination contained inhibitors of tumour necrosis factor-α (infliximab), caspase-1 (Ac-YVAD-cmk), and a multikinase inhibitor (sorafenib). In the treated groups there was a notable but not significant increase of survival compared to the virus infected, non-treated mice. The addition of human rabies immunoglobulins (HRIG) to the combination in the second experiment almost completely prevented mortality in the pre-exposure treatment group along with a significant reduction of viral titres in the CNS. Post-exposure treatments also greatly improved survival rates. As part of the combination with immunomodulatory compounds, HRIG had a higher impact on survival than alone. In the third experiment the combination was further supplemented with type-I interferons, ribavirin and favipiravir (T-705). As a blood-brain barrier opener, mannitol was also administered. This treatment was unable to prevent lethal consequences of SHBRV-18 infection; furthermore, it caused toxicity in treated mice, presumably due to interaction among the components. In all experiments, viral loads in the CNS were similar in mice that succumbed to rabies regardless of treatment. According to the findings, inhibitors of detrimental host response to rabies combined with antibodies can be considered among the possible therapeutic and post-exposure options in human rabies cases.

Salivary Tick Cystatin OmC2 Targets Lysosomal Cathepsins S and C in Human Dendritic Cells

To ensure successful feeding tick saliva contains a number of inhibitory proteins that interfere with the host immune response and help to create a permissive environment for pathogen transmission. Among the potential targets of the salivary cystatins are two host cysteine proteases, cathepsin S, which is essential for antigen- and invariant chain-processing, and cathepsin C (dipeptidyl peptidase 1, DPP1), which plays a critical role in processing and activation of the granule serine proteases. Here, the effect of salivary cystatin OmC2 from Ornithodoros moubata was studied using differentiated MUTZ-3 cells as a model of immature dendritic cells of the host skin. Following internalization, cystatin OmC2 was initially found to inhibit the activity of several cysteine cathepsins, as indicated by the decreased rates of degradation of fluorogenic peptide substrates. To identify targets, affinity chromatography was used to isolate His-tagged cystatin OmC2 together with the bound proteins from MUTZ-3 cells. Cathepsins S and C were identified in these complexes by mass spectrometry and confirmed by immunoblotting. Furthermore, reduced increase in the surface expression of MHC II and CD86, which are associated with the maturation of dendritic cells, was observed. In contrast, human inhibitor cystatin C, which is normally expressed and secreted by dendritic cells, did not affect the expression of CD86. It is proposed that internalization of salivary cystatin OmC2 by the host dendritic cells targets cathepsins S and C, thereby affecting their maturation.

Concurrent infection with porcine reproductive and respiratory syndrome virus and Haemophilus parasuis in two types of porcine macrophages: apoptosis, production of ROS and formation of multinucleated giant cells

Porcine reproductive and respiratory syndrome (PRRS) is one of the most significant and economically important infectious diseases affecting swine worldwide and can predispose pigs to secondary bacterial infections caused by, e.g. Haemophilus parasuis. The aim of the presented study was to compare susceptibility of two different types of macrophages which could be in contact with both pathogens during infection with PRRS virus (PRRSV) and in co-infection with H. parasuis. Alveolar macrophages (PAMs) as resident cells provide one of the first lines of defence against microbes invading lung tissue. On the other hand, monocyte derived macrophages (MDMs) represent inflammatory cells accumulating at the site of inflammation. While PAMs were relatively resistant to cytopathogenic effect caused by PRRSV, MDMs were much more sensitive to PRRSV infection. MDMs infected with PRRSV increased expression of pro-apoptotic Bad, Bax and p53 mRNA. Increased mortality of MDMs may be also related to a higher intensity of ROS production after infection with PRRSV. In addition, MDMs (but not PAMs) infected with H. parasuis alone formed multinucleated giant cells (MGC); these cells were not observed in MDMs infected with both pathogens. Higher sensitivity of MDMs to PRRSV infection, which is associated with limited MDMs survival and restriction of MGC formation, could contribute to the development of multifactorial respiratory disease of swine.

Novel hantavirus identified in European bat species Nyctalus noctula

Hantaviruses are emerging RNA viruses that cause human diseases predominantly in Asia, Europe, and the Americas. Besides rodents, insectivores and bats serve as hantavirus reservoirs. We report the detection and genome characterization of a novel bat-borne hantavirus isolated from insectivorous common noctule bat. The newfound virus was tentatively named as Brno virus.

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Novel tentative Hantavirus species (Brno virus; BRNV) was identified in European bat species Nyctalus noctula

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BRNV represents the first identified bat-borne hantavirus in Europe

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Nearly complete sequence of all genomic segments of BRNV was determined

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BRNV phylogenetically groups with other novel hantaviruses from bats

Detection of Diverse Novel Bat Astrovirus Sequences in the Czech Republic

Astroviruses are a major cause of gastroenteritis in humans and animals. Recently, novel groups of astroviruses were identified in apparently healthy insectivorous bats. We report the detection of diverse novel astrovirus sequences in nine different European bat species: Eptesicus serotinus, Hypsugo savii, Myotis emarginatus, M. mystacinus, Nyctalus noctula, Pipistrellus nathusii or P. pygmaeus, P. pipistrellus, Vespertilio murinus, and Rhinolophus hipposideros. In six bat species, astrovirus sequences were detected for the first time. One astrovirus strain detected in R. hipposideros clustered phylogenetically with Chinese astrovirus strains originating from bats of the families Rhinolophidae and Hipposideridae. All other Czech astrovirus sequences from vesper bats formed, together with one Hungarian sequence, a separate monophyletic lineage within the bat astrovirus group. These findings provide new insights into the molecular epidemiology, ecology, and prevalence of astroviruses in European bat populations.

Analysis of serum levels of cytokines, chemokines, growth factors, and monoamine neurotransmitters in patients with tick-borne encephalitis: identification of novel inflammatory markers with implications for pathogenesis

Tick-borne encephalitis (TBE) is a leading human neuroinfection in Europe and northeastern Asia. However, the pathophysiology of TBE is not understood completely. This study sought to determine the specific serum mediators that are associated with acute TBE. The levels of 30 cytokines, chemokines, and growth factors were measured in serum samples from 87 patients with clinically and serologically confirmed acute TBE and from 32 control subjects using the Cytokine Human Magnetic 30-Plex Panel for the Luminex platform. Serum levels of the monoamine neurotransmitters serotonin, dopamine, and noradrenaline were measured via enzyme-linked immunosorbent assay. TBE virus infection elicited increased levels of the pro-inflammatory cytokines interleukin (IL)-6, IL-8, and IL-12. TBE patients had higher IL-12:IL-4 and IL-12:IL-10 ratios than control patients, reflecting the global pro-inflammatory cytokine balance. Serum levels of the monoamine neurotransmitters serotonin, dopamine, and noradrenaline were significantly lower in TBE patients than in the control group. Most interestingly, increased levels of hepatocyte growth factor and vascular endothelial growth factor were observed in TBE patients; these proteins may be novel and mechanistically important inflammatory biomarkers of TBE.

Infection and injury of human astrocytes by tick-borne encephalitis virus

Tick-borne encephalitis (TBE), a disease caused by tick-borne encephalitis virus (TBEV), represents the most important flaviviral neural infection in Europe and north-eastern Asia. In the central nervous system (CNS), neurons are the primary target for TBEV infection; however, infection of non-neuronal CNS cells, such as astrocytes, is not well understood. In this study, we investigated the interaction between TBEV and primary human astrocytes. We report for the first time, to the best of our knowledge, that primary human astrocytes are sensitive to TBEV infection, although the infection did not affect their viability. The infection induced a marked increase in the expression of glial fibrillary acidic protein, a marker of astrocyte activation. In addition, expression of matrix metalloproteinase 9 and several key pro-inflammatory cytokines/chemokines (e.g. tumour necrosis factor α, interferon α, interleukin (IL)-1β, IL-6, IL-8, interferon γ-induced protein 10, macrophage inflammatory protein, but not monocyte chemotactic protein 1) was upregulated. Moreover, we present a detailed description of morphological changes in TBEV-infected cells, as investigated using three-dimensional electron tomography. Several novel ultrastructural changes were observed, including the formation of unique tubule-like structures of 17.9 ±0.15 nm diameter with associated viral particles and/or virus-induced vesicles and located in the rough endoplasmic reticulum of the TBEV-infected cells. This is the first demonstration that TBEV infection activates primary human astrocytes. The infected astrocytes might be a potential source of pro-inflammatory cytokines in the TBEV-infected brain, and might contribute to the TBEV-induced neurotoxicity and blood-brain barrier breakdown that occurs during TBE. The neuropathological significance of our observations is also discussed.

Seroprevalence of Borrelia burgdorferi sensu lato and tick-borne encephalitis virus in zoo animal species in the Czech Republic

This study was conducted to evaluate the prevalence of antibodies against Borrelia bugdorferi (Bb) s.l. and tick-borne encephalitis virus (TBEV) in zoo animals in the Czech Republic. We collected 133 serum samples from 69 animal species from 5 zoos located in different parts of the country. The samples were obtained from even-toed ungulates (n=78; 42 species), odd-toed ungulates (n=32; 11 species), carnivores (n=13; 9 species), primates (n=2, 2 species), birds (n=3; 2 species), and reptiles (n=5; 3 species). A high antibody prevalence (60%) was observed for Bb s.l. On the other hand, only two animals had TBEV-specific antibodies: a markhor (Capra falconeri) and a reindeer (Rangifer tarandus), both from the same zoo, located in an area endemic for TBEV. Both of these animals were also positive for Bb s.l. antibodies. Our results indicate that a high number of animal species in the Czech zoos were exposed to Bb s.l. and that TBEV infection occurred at least in one of the investigated zoos. Considering the pathogenic potential of these two tick-borne pathogens, clinical and serological monitoring should be continued, and therapeutic and preventive measures should be taken when necessary.

The use of anchored agonists of phagocytic receptors for cancer immunotherapy: B16-F10 murine melanoma model

The application of the phagocytic receptor agonists in cancer immunotherapy was studied. Agonists (laminarin, molecules with terminal mannose, N-Formyl-methioninyl-leucyl-phenylalanine) were firmly anchored to the tumor cell surface. When particular agonists of phagocytic receptors were used together with LPS (Toll-like receptor agonist), high synergy causing tumour shrinkage and a temporary or permanent disappearance was observed. Methods of anchoring phagocytic receptor agonists (charge interactions, anchoring based on hydrophobic chains, covalent bonds) and various regimes of phagocytic agonist/LPS mixture applications were tested to achieve maximum therapeutic effect. Combinations of mannan/LPS and f-MLF/LPS (hydrophobic anchors) in appropriate (pulse) regimes resulted in an 80% and 60% recovery for mice, respectively. We propose that substantial synergy between agonists of phagocytic and Toll-like receptors (TLR) is based on two events. The TLR ligand induces early and massive inflammatory infiltration of tumors. The effect of this cell infiltrate is directed towards tumor cells, bearing agonists of phagocytic receptors on their surface. The result of these processes was effective killing of tumor cells. This novel approach represents exploitation of innate immunity mechanisms for treating cancer.

Mice with different susceptibility to tick-borne encephalitis virus infection show selective neutralizing antibody response and inflammatory reaction in the central nervous system

Background

The clinical course of tick-borne encephalitis (TBE), a disease caused by TBE virus, ranges from asymptomatic or mild influenza-like infection to severe debilitating encephalitis or encephalomyelitis. Despite the medical importance of this disease, some crucial steps in the development of encephalitis remain poorly understood. In particular, the basis of the disease severity is largely unknown.

Methods

TBE virus growth, neutralizing antibody response, key cytokine and chemokine mRNA production and changes in mRNA levels of cell surface markers of immunocompetent cells in brain were measured in mice with different susceptibilities to TBE virus infection.

Results

An animal model of TBE based on BALB/c-c-STS/A (CcS/Dem) recombinant congenic mouse strains showing different severities of the infection in relation to the host genetic background was developed. After subcutaneous inoculation of TBE virus, BALB/c mice showed medium susceptibility to the infection, STS mice were resistant, and CcS-11 mice were highly susceptible. The resistant STS mice showed lower and delayed viremia, lower virus production in the brain and low cytokine/chemokine mRNA production, but had a strong neutralizing antibody response. The most sensitive strain (CcS-11) failed in production of neutralizing antibodies, but exhibited strong cytokine/chemokine mRNA production in the brain. After intracerebral inoculation, all mouse strains were sensitive to the infection and had similar virus production in the brain, but STS mice survived significantly longer than CcS-11 mice. These two strains also differed in the expression of key cytokines/chemokines, particularly interferon gamma-induced protein 10 (IP-10/CXCL10) and monocyte chemotactic protein-1 (MCP-1/CCL2) in the brain.

Conclusions

Our data indicate that the genetic control is an important factor influencing the clinical course of TBE. High neutralizing antibody response might be crucial for preventing host fatality, but high expression of various cytokines/chemokines during TBE can mediate immunopathology and be associated with more severe course of the infection and increased fatality.

Activated CD8+ T cells contribute to clearance of gastric Cryptosporidium muris infections

The role of CD4+ and CD8+ T lymphocytes in the development of a protective immune response against Cryptosporidium muris infection was studied by the reconstitution of severe combined immunodeficient (SCID) mice with well-defined populations of either naive or immune CD8+ or CD4+ T lymphocytes. Adoptive transfer of both naive and immune CD4+ T lymphocyte subpopulations protects SCID mice against cryptosporidiosis. Moreover, a significant biological impact of activated CD8+ T cells against gastric cryptosporidiosis was observed. The significant difference in the course and intensity of the infection in reconstituted SCID mice was found to be dependent on the protective function of both the CD4+ and CD8+ T-cell populations transferred. While SCID mice reconstituted with either immune or naive CD4+ or immune CD8+ T-cell subpopulations resolved the infection within 29, 37 and 51 days post-infection, respectively, those reconstituted with naive CD8+ T cells suffered from chronic infection similar to control SCID mice. Reconstitution with CD4+ T cells resulted in suppression of oocyst excretion and shortening of patent period in comparison with SCID mice reconstituted with CD8+ T cells. Thus, although CD4+ T cells are considered important in protective immunity, our results are the first to demonstrate the involvement of activated CD8+ T lymphocytes in the protection of mice against gastric cryptosporidiosis.

Breakdown of the blood-brain barrier during tick-borne encephalitis in mice is not dependent on CD8+ T-cells

Tick-borne encephalitis (TBE) virus causes severe encephalitis with serious sequelae in humans. The disease is characterized by fever and debilitating encephalitis that can progress to chronic illness or fatal infection. In this study, changes in permeability of the blood-brain barrier (BBB) in two susceptible animal models (BALB/c, and C57Bl/6 mice) infected with TBE virus were investigated at various days after infection by measuring fluorescence in brain homogenates after intraperitoneal injection of sodium fluorescein, a compound that is normally excluded from the central nervous system. We demonstrate here that TBE virus infection, in addition to causing fatal encephalitis in mice, induces considerable breakdown of the BBB. The permeability of the BBB increased at later stages of TBE infection when high virus load was present in the brain (i.e., BBB breakdown was not necessary for TBE virus entry into the brain), and at the onset of the first severe clinical symptoms of the disease, which included neurological signs associated with sharp declines in body weight and temperature. The increased BBB permeability was in association with dramatic upregulation of proinflammatory cytokine/chemokine mRNA expression in the brain. Breakdown of the BBB was also observed in mice deficient in CD8⁺ T-cells, indicating that these cells are not necessary for the increase in BBB permeability that occurs during TBE. These novel findings are highly relevant to the development of future therapies designed to control this important human infectious disease.

Anti-tumour necrosis factor-? activity in Ixodes ricinus saliva

Tumour necrosis factor-alpha (TNF-alpha) is one of the most prominent inflammatory mediators playing a central role in starting off the inflammatory reactions of the innate immune system. We identified a TNF-alpha-inhibitory activity in the saliva and salivary gland extract (SGE) from partially fed Ixodes ricinus ticks. Using mouse and human TNF-alpha specific ELISA, we showed that tick saliva or SGE markedly reduced the level of detectable cytokine. Both saliva and SGE inhibited the cytotoxic effect of TNF-alpha in a bioassay. Elimination of the TNF-alpha-inhibitory activity in SGE by trypsin digestion demonstrated that the anti-TNF-alpha factor is a protein. Fast protein liquid chromatography fractionation of SGE showed one peak of TNF-alpha-inhibitory activity corresponding to a protein with estimated molecular mass 23 kDa. The likely mechanism of the inhibitory effect is a direct binding of the cytokine. The TNF-alpha-inhibitory molecule seems to play an important role in the anti-inflammatory effect of tick saliva at the tick feeding site, providing a gateway to the host for tick-borne pathogens.

Antibodies enhance the protective effect of CD4+ T lymphocytes in SCID mice perorally infected with Encephalitozoon cuniculi

The role of antibodies in the immune response to microsporidiosis was studied using a novel anti-exospore monoclonal antibody (MAb) P5/H1, which recognizes surface antigens of Encephalitozoon cuniculi. The effect of the MAb on microsporidial infection in vivo was to prolong the survival of previously CD4+ reconstituted, perorally infected and intraperitoneally MAb-treated SCID mice. The MAb decreased the numbers of E. cuniculi spores in peritoneal smears obtained post mortem. These results suggest a possible role for antibodies in protection against perorally acquired E. cuniculi infection.

Co-inoculation of Borrelia afzelii with tick salivary gland extract influences distribution of immunocompetent cells in the skin and lymph nodes of mice

The impact of Ixodes ricinus salivary gland extract (SGE) on inflammatory changes in the skin and draining lymph nodes of mice, elicited by the infection with the important human pathogen, B. afzelii, was determined using flow cytometry. SGE injected together with spirochetes reduced the numbers of leukocytes and gammadelta-T lymphocytes in infected epidermis at early time-points post infection. In draining lymph nodes, the anti-inflammatory effect of SGE was manifested by the decrease of total cell count compared with that in mice treated with inactivated SGE. Changes in subpopulations of immunocompetent cells apparently reflected the effect of SGE on the proliferation of spirochetes in the host. The significance of tick saliva anti-inflammatory effect for saliva activated transmission of B. afzelii is shown.

Etiprednol dicloacetate, a new soft glucocorticoid drug candidate. Development of chemistry

During development of chemistry of the soft drug candidate etiprednol dicloacetate (BNP-166) 1) optimization studies on the three-step chemical synthesis resulted in a process that could be scaled-up to the kg level, 2) the impurity profile was determined, 3) synthetic routes were developed for the preparation of the radiolabeled target compound, and 4) a series of hydroxylated metabolites was prepared.

Experimental infection of immunocompetent and immunodeficient mice with Encephalitozoon cuniculi

An experimental infection with the microsporidian Encephalitozoon cuniculi Levaditi, Nicolau et Schoen, 1923 was studied using a model of immunocompetent BALB/c mice and immunodeficient SCID mice. The course of infection after intraperitoneal inoculation of E. cuniculi spores was evaluated using the presence of spores in peritoneal macrophages as a criterion. First significant decrease in the proportion of infected cells was recorded on day 9 post infection (p.i.) in BALB/c mice. From day 14 p.i. no spores were observed in macrophages from BALB/c mice, while the number of infected macrophages from SCID mice increased until the death of the mice. The natural killer (NK) cell activity of mouse splenocytes was compared with the production of interferon gamma (IFN-gamma) by these cells. While in BALB/c mice NK activity peaked on days 9 and 14 p.i., in SCID mice the marked increase of NK activity was recorded close before death of mice, on day 21 p.i. in correlation with the production of IFN-gamma. Production of specific antibodies was demonstrated from day 9 p.i. in sera from BALB/c mice. It is concluded that intraperitoneal infection of SCID mice with spores of E. cuniculi results in the marked increase in the number of peritoneal exudate cells and in the percentage of infected cells close before death of mice. Neither high activity of NK cells nor increased production of IFN-gamma are sufficient for the recovery of SCID mice from an E. cuniculi infection.

[Encephalitozoon cuniculi and Encephalitozoon intestinalis--causes of opportunistic infections]

Microsporidia (phylum Microsporidia) are intracellular parasites that infect a wide range of protozoa, invertebrates and vertebrate hosts. Over a 1000 species have been classified into approximately 100 genera. Historically, microsporidial infections in silkworms, honey bees, and salmonid fish have been responsible for significant economic losses. More recently, microsporidiosis has been recognized as an important opportunistic infection in immunologically compromised patients. In this review there is information on the immunobiology of microsporidia Encephalitozoon cuniculi and Encephalitozoon intestinalis which were identified as the most common causative agents of microsporidiosis in mammals. Most of what is known about the immunology of microsporidiosis is based on experiments with the microsporidian Encephalitozoon cuniculi.

CD8+ T lymphocytes protect SCID mice against Encephalitozoon cuniculi infection

Microsporidia are obligate intracellular parasites that cause opportunistic infections in immunocompromised patients. The role of two main T cell subsets in anti-microsporidial immunity has been studied using an Encephalitozoon cuniculi-severe combined immunodeficient (SCID) mouse model. Whereas SCID mice reconstituted with CD4+ T lymphocyte-depleted naive BALB/c splenocytes resolved the infection, adoptive transfer of CD8+ T cell-depleted splenocytes failed to protect the animals against a lethal E. cuniculi infection. Splenocytes from E. cuniculi-immune mice specifically killed syngeneic infected macrophages in a short-term 51Cr-release assay. These results suggest the crucial role of cytotoxic T lymphocytes in the protection against E. cuniculi infection.