Evaluation of CXCL10, CXCL11, CXCL12 and CXCL13 chemokines in serum and cerebrospinal fluid in patients with tick borne encephalitis (TBE)

The Role of Chitinase 3-Like-1 (YKL-40) and Proinflammatory Biomarkers in the Pathogenesis of Pediatric Tick-Borne Encephalitis in a Polish Cohort

Background

Chitinase 3-like-1 (CHI3L1), also known as YKL-40, is a potential biomarker for neuroinflammatory conditions. It is upregulated in Alzheimer's disease, multiple sclerosis, and traumatic brain injury. However, its involvement in pediatric tick-borne encephalitis (TBE) has not been addressed yet. This study aimed to evaluate CHI3L1 and its relationship with other inflammatory cytokines, blood-brain barrier (BBB) integrity, immune response, and disease severity in pediatric patients with TBE.

Patients and Methods

A total of 22 pediatric TBE patients hospitalized in Bialystok, Poland were included in this study. Participants were categorized as having meningoencephalitis (n=6) or meningitis (n=16). The integrity of the brain-blood barrier (BBB) was assessed using the albumin quotient (albQ). Biomarker indices were calculated to account for variations in BBB permeability. The concentrations of CHI3L1, CCL2, chemerin, CXCL2, IFN-γ, IL-1-β, IL-4, IL-6, IL-13, and TNF-α in both serum and CSF, were measured using the Luminex Multiplex Assay od admission and two weeks later when symptoms resolved.

Results

CSF and serum concentrations of CHI3L1 did not differ between the encephalitis and meningitis cases. After adjusting for BBB permeability, the CHI3L1 index was 2.4-fold lower in patients with encephalitis than in those with meningitis (P=0.008). There was a post-treatment reduction of CHI3L1, IL-6, and TNF-α CSF concentrations. We also found and improvement in BBB permeability in younger children but in older albQ remained abnormal. Correlation analysis revealed associations between CHI3L1 levels and pro-inflammatory markers, notably chemerin, IL-6, and TNF-α, across both clinical groups.

Conclusion

Our findings suggest that CHI3L1 CSF levels reflect the inflammatory activity in pediatric TBE and may help to differentiate between meningoencephalitis and meningitis. The observed interactions between CHI3L1 and other cytokines underscore its potential involvement in inflammatory response to the virus. The prolonged disruption in BBB integrity in older children might reflect age-dependent differences in the severity of TBE. These insights advance our understanding of TBE pathogenesis in children and support further investigation of CHI3L1 as a biomarker for TBE diagnosis and management.

Robust CXCL10/IP-10 and CCL5/RANTES Production Induced by Tick-Borne Encephalitis Virus in Human Brain Pericytes Despite Weak Infection

Tick-borne encephalitis virus (TBEV) targets the central nervous system (CNS), leading to potentially severe neurological complications. The neurovascular unit plays a fundamental role in the CNS and in the neuroinvasion of TBEV. However, the role of human brain pericytes, a key component of the neurovascular unit, during TBEV infection has not yet been elucidated. In this study, TBEV infection of the primary human brain perivascular pericytes was investigated with highly virulent Hypr strain and mildly virulent Neudoerfl strain. We used Luminex assay to measure cytokines/chemokines and growth factors. Both viral strains showed comparable replication kinetics, peaking at 3 days post infection (dpi). Intracellular viral RNA copies peaked at 6 dpi for Hypr and 3 dpi for Neudoerfl cultures. According to immunofluorescence staining, only small proportion of pericytes were infected (3% for Hypr and 2% for Neudoerfl), and no cytopathic effect was observed in the infected cells. In cell culture supernatants, IL-6 production was detected at 3 dpi, together with slight increases in IL-15 and IL-4, but IP-10, RANTES and MCP-1 were the main chemokines released after TBEV infection. These chemokines play key roles in both immune defense and immunopathology during TBE. This study suggests that pericytes are an important source of these signaling molecules during TBEV infection in the brain.

Molecular Mechanisms Associated with Neurodegeneration of Neurotropic Viral Infection

Viral infections of the central nervous system (CNS) cause variable outcomes from acute to severe neurological sequelae with increased morbidity and mortality. Viral neuroinvasion directly or indirectly induces encephalitis via dysregulation of the immune response and contributes to the alteration of neuronal function and the degeneration of neuronal cells. This review provides an overview of the cellular and molecular mechanisms of virus-induced neurodegeneration. Neurotropic viral infections influence many aspects of neuronal dysfunction, including promoting chronic inflammation, inducing cellular oxidative stress, impairing mitophagy, encountering mitochondrial dynamics, enhancing metabolic rewiring, altering neurotransmitter systems, and inducing misfolded and aggregated pathological proteins associated with neurodegenerative diseases. These pathogenetic mechanisms create a multidimensional injury of the brain that leads to specific neuronal and brain dysfunction. The understanding of the molecular mechanisms underlying the neurophathogenesis associated with neurodegeneration of viral infection may emphasize the strategies for prevention, protection, and treatment of virus infection of the CNS.

Proinflammatory Chemokine Levels in Cerebrospinal Fluid of Patients with Neuroinvasive Flavivirus Infections

Tick-borne encephalitis virus (TBEV) and West Nile virus (WNV) are the most important neuroinvasive arboviruses detected in Europe. In this study, we analyzed cerebrospinal fluid (CSF) concentrations of 12 proinflammatory chemokines (CCL2, CCL3, CCL4, CCL11, CCL17, CCL20, CXCL1, CXCL5, CXCL8, CXCL9, CXCL10, and CXCL11) in 77 patients with neuroinvasive diseases (NIDs). Flavivirus infection was confirmed in 62 patients (TBEV and WNV in 31 patients each), while in 15 patients the etiology of NID was not determined (NDE). Similar patterns of high-level expression of chemokines regulating monocyte/macrophage responses (CCL2), neutrophil recruitment (CXCL1 and CXCL8), and interferon-inducible chemoattractants for leukocytes (CXCL10 and CXCL11) have been observed in WNV and TBEV groups. None of the tested chemokines significantly differed between patients with TBEV or WNV. Concentrations of CCL17, CCL20, CXCL5, CXCL10, and CXCL11 were significantly lower in both WNV and TBEV groups compared to NID NDE patients. The logistic regression model showed that CSF concentrations of CXCL11, CXCL5, and CXCL10 could potentially be used for the classification of patients into the WNV or TBEV group versus groups with other NIDs. This study identified, for the first time, similar patterns of CSF chemokine expression in WNV and TBEV infections, suggesting common immunopathogenic mechanisms in neuroinvasive flavivirus infections that should be further evaluated.

CXCL13 in Cerebrospinal Fluid: Clinical Value in a Large Cross-Sectional Study

C-X-C-motif chemokine ligand 13 (CXCL13) in cerebrospinal fluid (CSF) is increasingly used in clinical routines, although its diagnostic specificity and divergent cut-off values have been defined so far mainly for neuroborreliosis. Our aim was to evaluate the value of CSF-CXCL13 as a diagnostic and treatment response marker and its role as an activity marker in a larger disease spectrum, including neuroborreliosis and other neuroinflammatory and malignant CNS-disorders. Patients who received a diagnostic lumbar puncture (LP) (n = 1234) between July 2009 and January 2023 were included in our retrospective cross-sectional study. The diagnostic performance of CSF-CXCL13 for acute neuroborreliosis was highest at a cut-off of 428.92 pg/mL (sensitivity: 92.1%; specificity: 96.5%). In addition, CXCL13 levels in CSF were significantly elevated in multiple sclerosis with clinical (p = 0.001) and radiographic disease activity (p < 0.001). The clinical utility of CSF-CXCL13 appears to be multifaceted. CSF-CXCL13 is significantly elevated in patients with neuroborreliosis and shows a rapid and sharp decline with antibiotic therapy, but it is not specific for this disease and is also highly elevated in less common subacute neuroinfectious diseases, such as neurosyphilis and cryptococcal meningitis or in primary/secondary B-cell lymphoma.

Tick-Borne Encephalitis (TBE): From Tick to Pathology

Tick-borne encephalitis (TBE) is a viral arthropod infection, endemic to large parts of Europe and Asia, and is characterised by neurological involvement, which can range from mild to severe, and in 33-60% of cases, it leads to a post-encephalitis syndrome and long-term morbidity. While TBE virus, now identified as Orthoflavivirus encephalitidis, was originally isolated in 1937, the pathogenesis of TBE is not fully appreciated with the mode of transmission (blood, tick, alimentary), viral strain, host immune response, and age, likely helping to shape the disease phenotype that we explore in this review. Importantly, the incidence of TBE is increasing, and due to global warming, its epidemiology is evolving, with new foci of transmission reported across Europe and in the UK. As such, a better understanding of the symptomatology, diagnostics, treatment, and prevention of TBE is required to inform healthcare professionals going forward, which this review addresses in detail. To this end, the need for robust national surveillance data and randomised control trial data regarding the use of various antivirals (e.g., Galidesivir and 7-deaza-2'-CMA), monoclonal antibodies, and glucocorticoids is required to improve the management and outcomes of TBE.

Development of a novel virus-like particle-based vaccine for preventing tick-borne encephalitis virus infection

Tick-borne encephalitis virus (TBEV) is an important tick-borne pathogen that poses as a serious public health concern. The coverage and immunogenicity of the currently available vaccines against TBEV are relatively low; therefore, it is crucial to develop novel and effective vaccines against TBEV. The present study describes a novel strategy for the assembly of virus-like particles (VLPs) by co-expressing the structural (core/prM/E) and non-structural (NS2B/NS3Pro) proteins of TBEV. The efficacy of the VLPs was subsequently evaluated in C57BL/6 mice, and the resultant IgG serum could neutralize both Far-Eastern and European subtypes of TBEV. These findings indicated that the VLP-based vaccine elicited the production of cross-subtype reactive antibodies. The VLPs provided protection to mice lacking the type I interferon receptor (IFNAR-/-) against lethal TBEV challenge, with undetectable viral load in brain and intestinal tissues. Furthermore, the group that received the VLP vaccine did not exhibit significant pathological changes and the inflammatory factors were significantly suppressed compared to the control group. Immunization with the VLP vaccine induced the production of multiple-cytokine-producing antiviral CD4+ T cells in vivo, including TNF-α+, IL-2+, and IFN-γ+ T cells. Altogether, the findings suggest that noninfectious VLPs can serve as a potentially safe and effective vaccine candidate against diverse subtypes of TBEV.

Cerebrospinal fluid CXCL13 in non-borrelial central nervous system infections: contribution of CXCL13 to the differential diagnosis

BACKGROUND

The chemokine CXCL13 in cerebrospinal fluid (CSF) is used as a diagnostic marker of Lyme neuroborreliosis (LNB). However, the elevated levels in other non-borrelial CNS infections and the lack of a clearly defined cut-off value are limitations of the test.

METHODS

In our prospective study, we evaluated CSF CXCL13 levels in patients with LNB (47 patients), tick-borne encephalitis (TBE; 46 patients), enteroviral CNS infections (EV; 45 patients), herpetic CNS infections (HV; 23 patients), neurosyphilis (NS; 11 patients) and controls (46 patients). The correlation of CXCL13 with CSF mononuclears was determined in all groups.

RESULTS

Median CXCL13 was significantly higher in LNB group; however, the cut-off value of 162 pg/mL was also exceeded in 22% of TBE patients, 2% EV patients, 44% HV patients and in 55% patients with NS. Sensitivity and specificity were 0.83 and 0.78, respectively, with a Youden index of 0.62. CXCL13 was significantly correlated with CSF mononuclears (p = .0024), but the type of infectious agent had a greater influence on CXCL13 levels.

CONCLUSIONS

Increased CXCL13 levels are useful for LNB diagnostics, but other non-purulent CNS infections causes should be considered if intrathecal synthesis of borrelia specific antibodies is not confirmed or clinical manifestations are atypical.

Comparison of laboratory and immune characteristics of the initial and second phase of tick-borne encephalitis

Tick-borne encephalitis (TBE) usually has a biphasic course which begins with unspecific febrile illness, followed by central nervous system involvement. Because TBE is not yet suspected during the initial phase, knowledge of early TBE pathogenesis is incomplete. Herein we evaluated laboratory and immune findings in the initial and second (meningoencephalitic) phase of TBE in 88 well-defined adult patients. Comparison of nine laboratory blood parameters in both phases of TBE revealed that laboratory abnormalities, consisting of low leukocyte and platelet counts and increased liver enzymes levels, were predominately associated with the initial phase of TBE and resolved thereafter. Assessment of 29 immune mediators in serum during the initial phase, and in serum and cerebrospinal fluid (CSF) during the second phase of TBE revealed highly distinct clustering patterns among the three groups. In the initial phase of TBE, the primary finding in serum was a rather heterogeneous immune response involving innate (CXCL11), B cell (CXCL13, BAFF), and T cell mediators (IL-27 and IL-4). During the second phase of TBE, growth factors associated with angiogenesis (GRO-α and VEGF-A) were the predominant characteristic in serum, whereas innate and Th1 mediators were the defining feature of immune responses in CSF. These findings imply that distinct immune processes play a role in the pathophysiology of different phases of TBE and in different compartments.

Tick-borne encephalitis affects sleep–wake behavior and locomotion in infant rats

Background/Aims

Tick-borne encephalitis (TBE) is a disease affecting the central nervous system. Over the last decade, the incidence of TBE has steadily increased in Europe and Asia despite the availably of effective vaccines. Up to 50% of patients after TBE suffer from post-encephalitic syndrome that may develop into long-lasting morbidity. Altered sleep–wake functions have been reported by patients after TBE. The mechanisms causing these disorders in TBE are largely unknown to date. As a first step toward a better understanding of the pathology of TBEV-inducing sleep dysfunctions, we assessed parameters of sleep structure in an established infant rat model of TBE.

Methods

13-day old Wistar rats were infected with 1 × 10⁶ FFU Langat virus (LGTV). On day 4, 9, and 21 post infection, Rotarod (balance and motor coordination) and open field tests (general locomotor activity) were performed and brains from representative animals were collected in each subgroup. On day 28 the animals were implanted with a telemetric EEG/EMG system. Sleep recording was continuously performed for 24 consecutive hours starting at day 38 post infection and visually scored for Wake, NREM, and REM in 4 s epochs.

Results

As a novelty of this study, infected animals showed a significant larger percentage of time spend awake during the dark phase and less NREM and REM compared to the control animals (p < 0.01 for all comparisons). Furthermore, it was seen, that during the dark phase the wake bout length in infected animals was prolonged (p = 0.043) and the fragmentation index decreased (p = 0.0085) in comparison to the control animals. LGTV-infected animals additionally showed a reduced rotarod performance ability at day 4 (p = 0.0011) and day 9 (p = 0.0055) and day 21 (p = 0.0037). A lower locomotor activity was also seen at day 4 (p = 0.0196) and day 9 (p = 0.0473).

Conclusion

Our data show that experimental TBE in infant rats affects sleep–wake behavior, leads to decreased spontaneous locomotor activity, and impaired moto-coordinative function.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00859-7.

Quantification of Antiviral Cytokines in Serum, Cerebrospinal Fluid and Urine of Patients with Tick-Borne Encephalitis in Croatia

BACKGROUND

Tick-borne encephalitis virus (TBEV) is one of the most significant arboviruses affecting the human central nervous system (CNS) in Europe. Data on cytokine response in TBEV infection are limited.

METHODS

We analyzed the cytokine response in serum, cerebrospinal fluid (CSF) and urine samples of patients with TBE. The control group consisted of patients with 'febrile headache' who had normal CSF cytology. The panel included 12 cytokines: TNF-α, IL-6, Th1 (IL-2, IFN-γ), Th2 (IL-4, IL-5, IL-13), Th9 (IL-9), Th17 (IL-17A, IL-17F), Th22 (IL-22) cytokines and IL-10.

RESULTS

TBE patients were more likely to have increased levels of IL-6 and IFN-γ in CSF compared to controls (85.7% vs. 58.8% and 85.7% vs. 47.1%, respectively). However, concentrations of IL-6 (the most abundant cytokine in the CSF of both groups), IL-10 and IL-9 were lower in TBEV patients compared with controls, but the difference was statistically significant for IL-9 only (p = 0.001). By analyzing the cytokine levels in different clinical samples, all measured cytokines were detected in the serum, with the highest concentrations found for IFN-γ, TNF-α, IL-10, IL-17F and IL-22. Higher concentrations of cytokines in the CSF compared with serum were observed for IL-5, IL-6 and IL-22. All cytokines except IL-13 were detectable in urine but in a small proportion of patients, except for IL-22, which was detectable in 95.8% of patients.

CONCLUSIONS

Cytokine composition in different clinical samples of TBE patients reveals a different network of early innate immune response cytokines, Th1, Th2, Th9, Th22, Th17 and anti-inflammatory cytokines.

Cytokines and chemokines profile in encephalitis patients: A meta-analysis

BACKGROUND

Encephalitis is caused by autoimmune or infectious agents marked by brain inflammation. Investigations have reported altered concentrations of the cytokines in encephalitis. This study was conducted to determine the relationship between encephalitis and alterations of cytokine levels in cerebrospinal fluid (CSF) and serum.

METHODS

We found possibly suitable studies by searching PubMed, Embase, Scopus, and Web of Science, systematically from inception to August 2021. 23 articles were included in the meta-analysis. To investigate sources of heterogeneity, subgroup analysis and sensitivity analysis were conducted. The protocol of the study has been registered in PROSPERO with a registration ID of CRD42021289298.

RESULTS

A total of 23 met our eligibility criteria to be included in the meta-analysis. A total of 12 cytokines were included in the meta-analysis of CSF concentration. Moreover, 5 cytokines were also included in the serum/plasma concentration meta-analysis. According to the analyses, patients with encephalitis had higher CSF amounts of IL-6, IL-8, IL-10, CXCL10, and TNF-α than healthy controls. The alteration in the concentration of IL-2, IL-4, IL-17, CCL2, CXCL9, CXCL13, and IFN-γ was not significant. In addition, the serum/plasma levels of the TNF-α were increased in encephalitis patients, but serum/plasma concentration of the IL-6, IL-10, CXCL10, and CXCL13 remained unchanged.

CONCLUSIONS

This meta-analysis provides evidence for higher CSF concentrations of IL-6, IL-8, IL-10, CXCL10, and TNF-α in encephalitis patients compared to controls. The diagnostic and prognostic value of these cytokines and chemokines should be investigated in future studies.

Serum and cerebrospinal fluid phosphorylated neurofilament heavy subunit as a marker of neuroaxonal damage in tick-borne encephalitis

Extensive axonal and neuronal loss is the main cause of severe manifestations and poor outcomes in tick-borne encephalitis (TBE). Phosphorylated neurofilament heavy subunit (pNF-H) is an essential component of axons, and its detection in cerebrospinal fluid (CSF) or serum can indicate the degree of neuroaxonal damage. We examined the use of pNF-H as a biomarker of neuroaxonal injury in TBE. In 89 patients with acute TBE, we measured CSF levels of pNF-H and 3 other markers of brain injury (glial fibrillary acidic protein, S100B and ubiquitin C-terminal hydrolase L1) and compared the results to those for patients with meningitis of other aetiology and controls. Serum pNF-H levels were measured in 80 patients and compared with findings for 90 healthy blood donors. TBE patients had significantly (P<0.001) higher CSF pNF-H levels than controls as early as hospital admission. Serum pNF-H concentrations were significantly higher in samples from TBE patients collected at hospital discharge (P<0.0001) than in controls. TBE patients with the highest peak values of serum pNF-H, exceeding 10 000 pg ml^-1, had a very severe disease course, with coma or tetraplegia. Patients requiring intensive care had significantly higher serum pNF-H levels than other TBE patients (P<0.01). Elevated serum pNF-H values were also observed in patients with incomplete recovery (P<0.05). Peak serum pNF-H levels correlated positively with the duration of hospitalization (P=0.005). Measurement of pNF-H levels in TBE patients might be useful for assessing disease severity and determining prognosis.

Powassan Viruses Spread Cell to Cell during Direct Isolation from Ixodes Ticks and Persistently Infect Human Brain Endothelial Cells and Pericytes

Powassan viruses (POWVs) are neurovirulent tick-borne flaviviruses emerging in the northeastern United States, with a 2% prevalence in Long Island (LI) deer ticks (Ixodes scapularis). POWVs are transmitted within as little as 15 min of a tick bite and enter the central nervous system (CNS) to cause encephalitis (10% of cases are fatal) and long-term neuronal damage. POWV-LI9 and POWV-LI41 present in LI Ixodes ticks were isolated by directly inoculating VeroE6 cells with tick homogenates and detecting POWV-infected cells by immunoperoxidase staining. Inoculated POWV-LI9 and LI41 were exclusively present in infected cell foci, indicative of cell to cell spread, despite growth in liquid culture without an overlay. Cloning and sequencing establish POWV-LI9 as a phylogenetically distinct lineage II POWV strain circulating in LI deer ticks. Primary human brain microvascular endothelial cells (hBMECs) and pericytes form a neurovascular complex that restricts entry into the CNS. We found that POWV-LI9 and -LI41 and lineage I POWV-LB productively infect hBMECs and pericytes and that POWVs were basolaterally transmitted from hBMECs to lower-chamber pericytes without permeabilizing polarized hBMECs. Synchronous POWV-LI9 infection of hBMECs and pericytes induced proinflammatory chemokines, interferon-β (IFN-β) and proteins of the IFN-stimulated gene family (ISGs), with delayed IFN-β secretion by infected pericytes. IFN inhibited POWV infection, but despite IFN secretion, a subset of POWV-infected hBMECs and pericytes remained persistently infected. These findings suggest a potential mechanism for POWVs (LI9/LI41 and LB) to infect hBMECs, spread basolaterally to pericytes, and enter the CNS. hBMEC and pericyte responses to POWV infection suggest a role for immunopathology in POWV neurovirulence and potential therapeutic targets for preventing POWV spread to neuronal compartments. IMPORTANCE We isolated POWVs from LI deer ticks (I. scapularis) directly in VeroE6 cells, and sequencing revealed POWV-LI9 as a distinct lineage II POWV strain. Remarkably, inoculation of VeroE6 cells with POWV-containing tick homogenates resulted in infected cell foci in liquid culture, consistent with cell-to-cell spread. POWV-LI9 and -LI41 and lineage I POWV-LB strains infected hBMECs and pericytes that comprise neurovascular complexes. POWVs were nonlytically transmitted basolaterally from infected hBMECs to lower-chamber pericytes, suggesting a mechanism for POWV transmission across the blood-brain barrier (BBB). POWV-LI9 elicited inflammatory responses from infected hBMEC and pericytes that may contribute to immune cell recruitment and neuropathogenesis. This study reveals a potential mechanism for POWVs to enter the CNS by infecting hBMECs and spreading basolaterally to abluminal pericytes. Our findings reveal that POWV-LI9 persists in cells that form a neurovascular complex spanning the BBB and suggest potential therapeutic targets for preventing POWV spread to neuronal compartments.

Epidemiological characteristics and cerebrospinal fluid cytokine profiles of enterovirus encephalitis in children in Hangzhou, China

Enteroviruses (EVs) are common causes of viral encephalitis in children. To better understand the epidemiological and pathological characteristics of EV encephalitis, we enrolled suspected encephalitis patients younger than 15 years old in Hangzhou, China, from October 2016 to September 2019 for cerebrospinal fluid (CSF) collection and analyses. A total of 7735 CSF samples were collected, among which 330 (4.27%) were positive for the EV genome. The positivity rate was significantly higher in boys than girls (χ²  =  5.68, p =  0.02). The monthly case numbers peaked from June to August (80.30%). Among the different age groups, the 0-2 months age group showed the highest number of cases (28.48% of all cases). The 6-7 years (10.82%) and 9-10 years (9.29%) age groups showed the highest EV-positivity rates among suspected encephalitis cases. Sixty-two EV-positive and 53 control CSF samples were collected for Bio-Plex Pro human cytokine assays that simultaneously tested 48 cytokines. Principle component analyses showed significant separation between EV-positive and control samples, but insignificant separation between children and newborns. The levels of 28 cytokines and chemokines were significantly elevated in the EV-positive group including many proinflammatory and a few anti-inflammatory cytokines, as well as chemokines belonging to the CC and CXC subfamilies. Only one cytokine, stem cell growth factor-β, showed a decrease in the EV-positive group. Thus, this study revealed age, sex, and seasonal preferences for EV encephalitis incidences in children and identified many cytokines dysregulated during EV encephalitis.

Selected Biomarkers of Tick-Borne Encephalitis: A Review

Tick-borne encephalitis (TBE) is an acute disease caused by the tick-borne encephalitis virus. Due to the viral nature of the condition, there is no effective causal treatment for full-blown disease. Current and nonspecific TBE treatments only relieve symptoms. Unfortunately, the first phase of TBE is characterized by flu-like symptoms, making diagnosis difficult during this period. The second phase is referred to as the neurological phase as it involves structures in the central nervous system-most commonly the meninges and, in more severe cases, the brain and the spinal cord. Therefore, it is important that early markers of TBE that will guide clinical decision-making and the choice of treatment are established. In this review, we performed an extensive search of literature reports relevant to biomarkers associated with TBE using the MEDLINE/PubMed database. We observed that apart from routinely determined specific immunoglobulins, free light chains may also be useful in the evaluation of intrathecal synthesis in the central nervous system (CNS) during TBEV infection. Moreover, selected metalloproteinases, chemokines, or cytokines appear to play an important role in the pathogenesis of TBE as a consequence of inflammatory reactions and recruitment of white blood cells into the CNS. Furthermore, we reported promising findings on tau protein or Toll-like receptors. It was also observed that some people may be predisposed to TBE. Therefore, to understand the role of selected tick-borne encephalitis biomarkers, we categorized these factors and discussed their potential application in the diagnosis, prognosis, monitoring, or management of TBE.

Upregulated Intrathecal Expression of VEGF-A and Long Lasting Global Upregulation of Proinflammatory Immune Mediators in Vaccine Breakthrough Tick-Borne Encephalitis

Although anti-TBE vaccines are highly effective, vaccine breakthrough (VBT) cases have been reported. With increasing evidence for immune system involvement in TBE pathogenesis, we characterized the immune mediators reflecting innate and adaptive T and B cell responses in neurological and convalescent phase in VBT TBE patients. At the beginning of the neurological phase, VBT patients have significantly higher serum levels of several innate and adaptive inflammatory cytokines compared to healthy donors, reflecting a global inflammatory state. The majority of cytokines, particularly those associated with innate and Th1 responses, are highly concentrated in CSF and positively correlate with intrathecal immune cell counts, demonstrating the localization of Th1 and proinflammatory responses in CNS, the site of disease in TBE. Interestingly, compared to unvaccinated TBE patients, VBT TBE patients have significantly higher CSF levels of VEGF-A and IFN-β and higher systemic levels of neutrophil chemoattractants IL-8/CXCL8 and GROα/CXCL1 on admission. Moreover, serum levels of IL-8/CXCL8 and GROα/CXCL1 remain elevated for two months after the onset of neurological symptoms, indicating a prolonged systemic immune activation in VBT patients. These findings provide the first insights into the type of immune responses and their dynamics during TBE in VBT patients. An observed systemic upregulation of neutrophil derived inflammation in acute and convalescent phase of TBE together with highly expressed VEGF-A could contribute to BBB disruption that facilitates the entry of immune cells and supports the intrathecal localization of Th1 responses observed in VBT patients.

Comparison of Clinical, Laboratory and Immune Characteristics of the Monophasic and Biphasic Course of Tick-Borne Encephalitis

The biphasic course of tick-borne encephalitis (TBE) is well described, but information on the monophasic course is limited. We assessed and compared the clinical presentation, laboratory findings, and immune responses in 705 adult TBE patients: 283 with monophasic and 422 with biphasic course. Patients with the monophasic course were significantly (p ≤ 0.002) older (57 vs. 50 years), more often vaccinated against TBE (7.4% vs. 0.9%), more often had comorbidities (52% vs. 37%), and were more often treated in the intensive care unit (12.4% vs. 5.2%). Multivariate logistic regression found strong association between the monophasic TBE course and previous TBE vaccination (OR = 18.45), presence of underlying illness (OR = 1.85), duration of neurologic involvement before cerebrospinal fluid (CSF) examination (OR = 1.39), and patients’ age (OR = 1.02). Furthermore, patients with monophasic TBE had higher CSF levels of immune mediators associated with innate and adaptive (Th1 and B-cell) immune responses, and they had more pronounced disruption of the blood–brain barrier. However, the long-term outcome 2–7 years after TBE was comparable. In summary, the monophasic course is a frequent and distinct presentation of TBE that is associated with more difficult disease course and higher levels of inflammatory mediators in CSF than the biphasic course; however, the long-term outcome is similar.

CXCR7, CXCR4, and Their Ligand Expression Profile in Traumatic Brain Injury

OBJECTIVE

Traumatic brain injury (TBI) is a health problem worldwide, and therapeutic strategies to enhance brain tissue repair to lessen neurologic sequels are imperative. We aimed to analyze the impact of the inflammatory process in TBI through CXCR4 and CXCR7 chemokine receptors and their ligands' CXCL11 and CXCL12 expression profile in search for potential new druggable targets.

METHODS

Twelve pericontusional tissues from severe TBI patients submitted to surgical treatment, and 20 control brain tissues from normal autopsy were analyzed for expression profile by real-time quantitative-polymerase chain reaction. CXCR7 and CXCR4 protein expressions were analyzed by immunohistochemistry. The findings were correlated with the clinical evolution.

RESULTS

Increased gene expression of both receptors and their ligands was observed in TBI compared with controls, presenting high sensitivity and specificity to differentiate TBI from normal control (area under the curve ranging from 0.85 to 0.98, P < 0.001). In particular, CXCR7 expression highly correlated with CXCR4 and both ligands' expressions in TBI. Higher immunoreactions for CXCR7 and CXCR4 were identified in neurons and endothelial cells of TBI samples compared with controls. The patients presenting upregulated chemokine expression levels showed a trend toward favorable clinical evolution at up to 6 months of follow-up.

CONCLUSIONS

The neuroprotective trend of CXCR4, CXCR7, CXCL11, and CXCL12 in TBI observed in this initial analysis warrants further studies with more patients, analyzing the involved signaling pathways for the development of new therapeutic strategies for TBI.

Effector CD8 T Cell-Dependent Zika Virus Control in the CNS: A Matter of Time and Numbers

Zika virus (ZIKV), a mosquito-borne flavivirus, came into the spotlight in 2016 when it was found to be associated with an increased rate of microcephalic newborns in Brazil. The virus has further been recognized to cause neurologic complications in children and adults in the form of myelitis, encephalitis, acute disseminated encephalomyelitis (ADEM) and Guillain Barre Syndrome in a fraction of infected individuals. With the ultimate goal of identifying correlates of protection to guide the design of an effective vaccine, the study of the immune response to ZIKV infection has become the focus of research worldwide. Both innate and adaptive immune responses seem to be essential for controlling the infection. Induction of sufficient levels of neutralizing antibodies has been strongly correlated with protection against reinfection in various models, while the role of CD8 T cells as antiviral effectors in the CNS has been controversial. In an attempt to improve our understanding regarding the role of ZIKV-induced CD8 T cells in protective immunity inside the CNS, we have expanded on previous studies in intracranially infected mice. In a recent study, we have demonstrated that, peripheral ZIKV infection in adult C57BL/6 mice induces a robust CD8 T cell response that peaks within a week. In the present study, we used B cell deficient as well as wild-type mice to show that there is a race between CXCR3-dependent recruitment of the effector CD8 T cells and local ZIKV replication, and that CD8 T cells are capable of local viral control if they arrive in the brain early after viral invasion, in appropriate numbers and differentiation state. Our data highlight the benefits of considering this subset when designing vaccines against Zika virus.

The potential for CXCL13 in CSF as a differential diagnostic tool in central nervous system infection

Introduction: Central nervous system (CNS) infections can be life-threatening and are often associated with disabling sequelae. One important factor in most CNS infections is a timely pathogen-specific treatment. The diagnostic methods available, however, do not always reach a satisfying sensitivity and specificity. In these cases, there is need for additional diagnostic biomarkers. Chemokines represent potential candidates as biomarkers, since they are an important pillar of the host immune response. The aim of this review is to discuss the diagnostic potential of cerebrospinal fluid (CSF) CXCL13 in patients with CNS infections. Areas covered: Data were obtained from a literature search in PubMed up to October 2019. This review focusses on articles on the potential of CXCL13 as a diagnostic tool. The majority of identified studies aimed to characterize its role in two diseases, namely Lyme neuroborreliosis and neurosyphilis. Expert opinion: CSF CXCL13 has a significant potential as a diagnostic and monitoring add-on marker in Lyme neuroborreliosis. Differences in study design, control groups and clinical parameters between studies, however, affect sensitivity, specificity and cutoff values, underlining the need of further studies to address these issues and pave the way for a generalized clinical practice.

Pathological modeling of TBEV infection reveals differential innate immune responses in human neurons and astrocytes that correlate with their susceptibility to infection

BACKGROUND

Tick-borne encephalitis virus (TBEV) is a member of the Flaviviridae family, Flavivirus genus, which includes several important human pathogens. It is responsible for neurological symptoms that may cause permanent disability or death, and, from a medical point of view, is the major arbovirus in Central/Northern Europe and North-Eastern Asia. TBEV tropism is critical for neuropathogenesis, yet little is known about the molecular mechanisms that govern the susceptibility of human brain cells to the virus. In this study, we sought to establish and characterize a new in vitro model of TBEV infection in the human brain and to decipher cell type-specific innate immunity and its relation to TBEV tropism and neuropathogenesis.

METHOD

Human neuronal/glial cells were differentiated from neural progenitor cells and infected with the TBEV-Hypr strain. Kinetics of infection, cellular tropism, and cellular responses, including innate immune responses, were characterized by measuring viral genome and viral titer, performing immunofluorescence, enumerating the different cellular types, and determining their rate of infection and by performing PCR array and qRT-PCR. The specific response of neurons and astrocytes was analyzed using the same approaches after enrichment of the neuronal/glial cultures for each cellular subtype.

RESULTS

We showed that infection of human neuronal/glial cells mimicked three major hallmarks of TBEV infection in the human brain, namely, preferential neuronal tropism, neuronal death, and astrogliosis. We further showed that these cells conserved their capacity to mount an antiviral response against TBEV. TBEV-infected neuronal/glial cells, therefore, represented a highly relevant pathological model. By enriching the cultures for either neurons or astrocytes, we further demonstrated qualitative and quantitative differential innate immune responses in the two cell types that correlated with their particular susceptibility to TBEV.

CONCLUSION

Our results thus reveal that cell type-specific innate immunity is likely to contribute to shaping TBEV tropism for human brain cells. They describe a new in vitro model for in-depth study of TBEV-induced neuropathogenesis and improve our understanding of the mechanisms by which neurotropic viruses target and damage human brain cells.

Chemokine CXCL13 in serum, CSF and blood-CSF barrier function: evidence of compartment restriction

Background and purpose

Elevation of the chemokine CXCL13 in CSF frequently occurs during active and acute CNS inflammatory processes and presumably is associated with B cell-related immune activation. Elevation levels, however, vary a lot and “leaking” of CXCL13 from blood across dysfunctional brain barriers is a possible source. The aim was to clarify the relation between CXCL13 concentrations in CSF, CXCL13 concentrations in serum and blood–CSF barrier (BCSFB) function for a correct interpretation of the intrathecal origin of CXCL13.

Methods

We retrospectively analyzed CXCL13 of banked CSF/serum samples (n = 69) selected from patient records and categorized the CSF CXCL13 elevations as CXCL13 negative (< 30 pg/ml), low (30–100 pg/ml), medium (101–250 pg/ml), or high (> 250 pg/ml). CXCL13 concentrations in CSF and serum and the corresponding CSF/serum CXCL13 quotients (Qcxcl13) were compared to CSF/serum albumin quotients (QAlb) as a measure for BCSFB function. The CXCL13 negative category included two subgroups with normal and dysfunctional BCSFB.

Results

Serum CXCL13 concentrations were similar across categories with median levels around 100 pg/ml but differed between individuals (29 to > 505 pg/ml). Despite clear evidence in serum, CXCL13 was detectable only at trace amounts (medians 3.5 and 7.5 pg/ml) in CSF of the two CXCL13 negative subgroups irrespective of a normal or pathological QAlb. Moreover, we found no association between CSF and serum CXCL13 levels or between QAlb and CSF CXCL13 levels in any of the CSF CXCL13-delineated categories. CXCL13 apparently does not “leak” from blood into CSF. This implies an intrathecal origin also for low CSF CXCL13 levels and a caveat for analyzing the Qcxcl13, because higher serum than CSF concentrations arithmetically depress the Qcxcl13 resulting in misleadingly low CSF/serum quotients.

Conclusion

We demonstrated that CXCL13 does not cross from blood into CSF, not even during severe BCSFB dysfunction. CSF CXCL13 elevations therefore most likely always are CNS-derived, which highlights their relevance as indicator of inflammatory CNS processes. We recommend data should not be corrected for BCSFB permeability (QAlb) and not to calculate CSF/serum quotients for CXCL13 as these may introduce error.

Evaluation of cerebrospinal fluid CXCL13 concentrations and lymphocyte subsets in tick-borne encephalitis

OBJECTIVES

Recent studies suggest that the clinical presentation of tick-borne encephalitis (TBE) is determined by the host immune responses to the tick-borne encephalitis virus (TBEV). The aim of the study was to characterize immune responses in TBE to give a better insight into the immunopathogenesis of this disease.

METHODS

Anti-TBEV antibody levels, cerebrospinal fluid (CSF) and blood lymphoid populations, and concentrations of CXCL13 (a potent B-cell and T-cell chemoattractant), were analyzed in 35 patients with TBE (20 adults and 15 children).

RESULTS

When compared with the blood, the CSF lymphoid population was significantly enriched in CD4+ T-cells and relatively depleted in natural killer (NK) cells and B lymphocytes. In comparison with TBE meningitis, patients suffering from TBE meningoencephalitis (n = 11, 31%) had a 3.5-fold higher median CSF CXCL13 concentration, 1.8-fold higher CSF/serum ratio of anti-TBEV IgG antibodies, and 1.8-fold higher median CSF cell count. CSF CXCL13 levels did not change significantly in children with TBE meningitis receiving supportive treatment, but decreased in children with TBE meningoencephalitis who received intravenous steroids.

CONCLUSIONS

CD4+ cells are abundant in the CSF of patients with TBE. CXCL13 may be involved in the neuropathology of TBE by attracting different subsets of lymphocytes to the CSF.

Neutrophil Extracellular Traps (NETs) in the Cerebrospinal Fluid Samples from Children and Adults with Central Nervous System Infections

Neutrophils operate as part of the innate defence in the skin and may eliminate the Borrelia spirochaete via phagocytosis, oxidative bursts, and hydrolytic enzymes. However, their importance in Lyme neuroborreliosis (LNB) is unclear. Neutrophil extracellular trap (NET) formation, which is associated with the production of reactive oxygen species, involves the extrusion of the neutrophil DNA to form traps that incapacitate bacteria and immobilise viruses. Meanwhile, NET formation has recently been studied in pneumococcal meningitis, the role of NETs in other central nervous system (CNS) infections has previously not been studied. Here, cerebrospinal fluid (CSF) samples from clinically well-characterised children (N = 111) and adults (N = 64) with LNB and other CNS infections were analysed for NETs (DNA/myeloperoxidase complexes) and elastase activity. NETs were detected more frequently in the children than the adults (p = 0.01). NET presence was associated with higher CSF levels of CXCL1 (p < 0.001), CXCL6 (p = 0.007), CXCL8 (p = 0.003), CXCL10 (p < 0.001), MMP-9 (p = 0.002), TNF (p = 0.02), IL-6 (p < 0.001), and IL-17A (p = 0.03). NETs were associated with fever (p = 0.002) and correlated with polynuclear pleocytosis (r_s = 0.53, p < 0.0001). We show that neutrophil activation and active NET formation occur in the CSF samples of children and adults with CNS infections, mainly caused by Borrelia and neurotropic viruses. The role of NETs in the early phase of viral/bacterial CNS infections warrants further investigation.

Changes in cytokine and chemokine profiles in mouse serum and brain, and in human neural cells, upon tick-borne encephalitis virus infection

Background

Tick-borne encephalitis (TBE) is a severe neuropathological disorder caused by tick-borne encephalitis virus (TBEV). Brain TBEV infection is characterized by extensive pathological neuroinflammation. The mechanism by which TBEV causes CNS destruction remains unclear, but growing evidence suggests that it involves both direct neuronal damage by the virus infection and indirect damage caused by the immune response. Here, we aimed to examine the TBEV-infection-induced innate immune response in mice and in human neural cells. We also compared cytokine/chemokine communication between naïve and infected neuronal cells and astrocytes.

Methods

We used a multiplexed Luminex system to measure multiple cytokines/chemokines and growth factors in mouse serum samples and brain tissue, and in human neuroblastoma cells (SK-N-SH) and primary cortical astrocytes (HBCA), which were infected with the highly pathogenic TBEV strain Hypr. We also investigated changes in cytokine/chemokine production in naïve HBCA cells treated with virus-free supernatants from TBEV-infected SK-N-SH cells and in naïve SK-N-SH cells treated with virus-free supernatants from TBEV-infected HBCA cells. Additionally, a plaque assay was performed to assess how cytokine/chemokine treatment influenced viral growth following TBEV infection.

Results

TBEV-infected mice exhibited time-dependent increases in serum and brain tissue concentrations of multiple cytokines/chemokines (mainly CXCL10/IP-10, and also CXCL1, G-CSF, IL-6, and others). TBEV-infected SK-N-SH cells exhibited increased production of IL-8 and RANTES and downregulated MCP-1 and HGF. TBEV infection of HBCA cells activated production of a broad spectrum of pro-inflammatory cytokines, chemokines, and growth factors (mainly IL-6, IL-8, CXCL10, RANTES, and G-CSF) and downregulated the expression of VEGF. Treatment of SK-N-SH with supernatants from infected HBCA induced expression of a variety of chemokines and pro-inflammatory cytokines, reduced SK-N-SH mortality after TBEV infection, and decreased virus growth in these cells. Treatment of HBCA with supernatants from infected SK-N-SH had little effect on cytokine/chemokine/growth factor expression but reduced TBEV growth in these cells after infection.

Conclusions

Our results indicated that both neurons and astrocytes are potential sources of pro-inflammatory cytokines in TBEV-infected brain tissue. Infected/activated astrocytes produce cytokines/chemokines that stimulate the innate neuronal immune response, limiting virus replication, and increasing survival of infected neurons.

Inflammatory Immune Responses in Patients with Tick-Borne Encephalitis: Dynamics and Association with the Outcome of the Disease

Information on the association of inflammatory immune responses and disease outcome after tick-borne encephalitis (TBE) is limited. In the present study, we assessed the levels of 24 cytokines/chemokines associated with innate and adaptive immune responses in matched serum and cerebrospinal fluid (CSF) samples of 81 patients at first visit, and in serum at follow-up time points. Serum levels of several cytokines/chemokines obtained during the meningoencephalitic phase of TBE differed compared to the levels at a follow-up visit 2 months later; several significant differences were also found in cytokine/chemokine levels in serum at 2 months compared to the last time point, 2–7 years after acute illness. Cytokines/chemokines levels in CSF or serum obtained at the time of acute illness or serum levels obtained 2 months after the onset of TBE did not have predictive value for an unfavorable outcome 2–7 years later. In contrast, serum levels of mediators associated with Th17 responses were lower in patients with unfavorable outcome whereas those associated with other adaptive or innate immune responses were higher at the last visit in those with an unfavorable outcome. These findings provide new insights into the immunopathogenesis of TBE and implicate inflammatory immune responses with post-encephalitic syndrome years after the initial infection.

Utility of chemokines CCL2, CXCL8, 10 and 13 and interleukin 6 in the pediatric cohort for the recognition of neuroinflammation and in the context of traditional cerebrospinal fluid neuroinflammatory biomarkers

BACKGROUND

The recognition of active inflammation in the central nervous system (CNS) in the absence of infectious agents is challenging. The present study aimed to determine the diagnostic relevance of five selected chemo/cytokines in the recognition of CNS inflammation and in the context of traditional cerebrospinal fluid (CSF) biomarkers (white blood cell [WBC] counts, oligoclonal bands, protein levels, CSF/serum albumin ratios) and clinical diagnoses.

METHODS

C-C and C-X-C motif ligands (CCL2, CXCL8, 10 and 13) and interleukin (IL) 6 levels in the CSF and serum from 37 control and 87 symptomatic children with ten different (mostly noninfectious) inflammatory CNS disorders (16 of which had follow-up samples after recovery) were determined using Luminex multiple bead technology and software. Nonparametric tests were used; p < 0.05 was considered statistically significant. Receiver operating characteristic curves were constructed to analyze controls and 1) all symptomatic samples or 2) symptomatic samples without CSF pleocytosis.

RESULTS

Compared with the control CSF samples, levels of all investigated chemo/cytokines were increased in symptomatic CSF samples, and only IL-6 remained elevated in recovery samples (p ≤ 0.001). CSF CXCL-13 levels (> 10.9 pg/mL) were the best individual discriminatory criterion to differentiate neuroinflammation (specificity/sensitivity: 97/72% and 97/61% for samples without pleocytosis), followed by CSF WBC counts (specificity/sensitivity: 97/62%). The clinical utility of the remaining CSF chemo/cytokine levels was determined in descending order of sensitivities corresponding to thresholds that ensured 97% specificity for neuroinflammation in samples without pleocytosis (pg/mL; sensitivity %): IL-6 (3.8; 34), CXCL8 (32; 26), CXCL10 (317; 24) and CCL2 (387; 10). Different diagnosis-related patterns of CSF chemo/cytokines were observed.

CONCLUSIONS

The increased CSF level of CXCL13 was the marker with the greatest predictive utility for the general recognition of neuroinflammation among all of the individually investigated biomarkers. The potential clinical utility of chemo/cytokines in the differential diagnosis of neuroinflammatory diseases was identified.

Exome-wide search and functional annotation of genes associated in patients with severe tick-borne encephalitis in a Russian population

Background

Tick-borne encephalitis (TBE) is a viral infectious disease caused by tick-borne encephalitis virus (TBEV). TBEV infection is responsible for a variety of clinical manifestations ranging from mild fever to severe neurological illness. Genetic factors involved in the host response to TBEV that may potentially play a role in the severity of the disease are still poorly understood. In this study, using whole-exome sequencing, we aimed to identify genetic variants and genes associated with severe forms of TBE as well as biological pathways through which the identified variants may influence the severity of the disease.

Results

Whole-exome sequencing data analysis was performed on 22 Russian patients with severe forms of TBE and 17 Russian individuals from the control group. We identified 2407 candidate genes harboring rare, potentially pathogenic variants in exomes of patients with TBE and not containing any rare, potentially pathogenic variants in exomes of individuals from the control group. According to DAVID tool, this set of 2407 genes was enriched with genes involved in extracellular matrix proteoglycans pathway and genes encoding proteins located at the cell periphery. A total of 154 genes/proteins from these functional groups have been shown to be involved in protein-protein interactions (PPIs) with the known candidate genes/proteins extracted from TBEVHostDB database. By ranking these genes according to the number of rare harmful minor alleles, we identified two genes (MSR1 and LMO7), harboring five minor alleles, and three genes (FLNA, PALLD, PKD1) harboring four minor alleles.

When considering genes harboring genetic variants associated with severe forms of TBE at the suggestive P-value < 0.01, 46 genes containing harmful variants were identified. Out of these 46 genes, eight (MAP4, WDFY4, ACTRT2, KLHL25, MAP2K3, MBD1, OR10J1, and OR2T34) were additionally found among genes containing rare pathogenic variants identified in patients with TBE; and five genes (WDFY4,ALK, MAP4, BNIPL, EPPK1) were found to encode proteins that are involved in PPIs with proteins encoded by genes from TBEVHostDB. Three genes out of five (MAP4, EPPK1, ALK) were found to encode proteins located at cell periphery.

Conclusions

Whole-exome sequencing followed by systems biology approach enabled to identify eight candidate genes (MAP4, WDFY4, ACTRT2, KLHL25, MAP2K3, MBD1, OR10J1, and OR2T34) that can potentially determine predisposition to severe forms of TBE. Analyses of the genetic risk factors for severe forms of TBE revealed a significant enrichment with genes controlling extracellular matrix proteoglycans pathway as well as genes encoding components of cell periphery.

Electronic supplementary material

The online version of this article (10.1186/s12920-019-0503-x) contains supplementary material, which is available to authorized users.

Inflammatory Immune Responses in the Pathogenesis of Tick-Borne Encephalitis

Clinical manifestations of tick-borne encephalitis (TBE) are thought to result from the host immune responses to infection, but knowledge of such responses is incomplete. We performed a detailed clinical evaluation and characterization of innate and adaptive inflammatory immune responses in matched serum and cerebrospinal fluid (CSF) samples from 81 adult patients with TBE. Immune responses were then correlated with laboratory and clinical findings. The inflammatory immune responses were generally site-specific. Cytokines and chemokines associated with innate and Th1 adaptive immune responses were significantly higher in CSF, while mediators associated with Th17 and B-cell responses were generally higher in serum. Furthermore, mediators associated with innate and Th1 adaptive immune responses were positively associated with disease severity, whereas Th17 and B cell immune responses were not. During the meningoencephalitic phase of TBE, innate and Th1 adaptive inflammatory mediators were highly concentrated in CSF, the site of the disease. The consequence of this robust immune response was more severe acute illness. In contrast, inflammatory mediators associated with B cell and particularly Th17 responses were concentrated in serum. These findings provide new insights into the immunopathogenesis of TBE and implicate innate and Th1 adaptive responses in severity and clinical presentation of acute illness.

Cocaine-induced release of CXCL10 from pericytes regulates monocyte transmigration into the CNS

Cocaine is known to facilitate the transmigration of inflammatory leukocytes into the brain, an important mechanism underlying neuroinflammation. Pericytes are well-recognized as important constituents of the blood-brain barrier (BBB), playing a key role in maintaining barrier integrity. In the present study, we demonstrate for the first time that exposure of human brain vascular pericytes to cocaine results in enhanced secretion of CXCL10, leading, in turn, to increased monocyte transmigration across the BBB both in vitro and in vivo. This process involved translocation of σ-1 receptor (σ-1R) and interaction of σ-1R with c-Src kinase, leading to activation of the Src-PDGFR-β-NF-κB pathway. These findings imply a novel role for pericytes as a source of CXCL10 in the pericyte-monocyte cross talk in cocaine-mediated neuroinflammation, underpinning their role as active components of the innate immune responses.

Cerebrospinal fluid CXLC13 indicates disease course in neuroinfection: an observational study

BACKGROUND

The chemokine CXCL13 is an intensively investigated biomarker in Lyme neuroborreliosis (LNB). Its role in other neuroinfections is increasingly recognized but less clear.

OBJECTIVE

To determine the significance of CXCL13 in established central nervous system (CNS) infections other than LNB by matching cerebrospinal fluid (CSF) CXCL13 elevations with severity of the disease course.

METHODS

We investigated 26 patients with bacterial (n = 10) and viral (n = 16; tick-borne encephalitis, n = 6; varicella zoster infection, n = 10) neuroinfections of whom CSF CXCL13 levels were available twice, from lumbar punctures (LP) performed at admission and follow-up. As outcome classification, we dichotomized disease courses into "uncomplicated" (meningitis, monoradiculitis) and "complicated" (signs of CNS parenchymal involvement such as encephalitis, myelitis, abscesses, or vasculitis). CXCL13 elevations above 250 pg/ml were classified as highly elevated.

RESULTS

Eight of 26 patients (31%) with both bacterial (n = 4) and viral (n = 4) neuroinfections had a complicated disease course. All of them but only 3/18 patients (17%) with an uncomplicated disease course had CSF CXCL13 elevations > 250 pg/ml at the follow-up LP (p < 0.001). At admission, 4/8 patients (50%) with a complicated disease course and 3/18 patients (17%) with an uncomplicated disease course showed CXCL13 elevations > 250 pg/ml. All four patients with a complicated disease course but only one with an uncomplicated disease course had sustained CXCL13 elevations at follow-up. Patient groups did not differ with regard to age, time since symptom onset, LP intervals, type of infections, and anti-pathogen treatments.

CONCLUSION

Our study revealed pronounced CXCL13 elevations in CSF of patients with severe disease courses of bacterial and viral neuroinfections. This observation indicates a role of CXCL13 in the CNS immune defense and points at an additional diagnostic value as biomarker for unresolved immune processes leading to or associated with complications.

Neuronal transcriptomic responses to Japanese encephalitis virus infection with a special focus on chemokine CXCL11 and pattern recognition receptors RIG-1 and MDA5

Japanese encephalitis virus (JEV) causes central nervous system neuronal injury and inflammation. A clear understanding of neuronal responses to JEV infection remains elusive. Using the Affymetrix array to investigate the transcriptome of infected SK-N-MC cells, 1316 and 2737 dysregulated genes (≥ 2/-2 fold change, P < 0.05) were found at 48 hours post-infection (hpi) and 60 hpi, respectively. The genes were mainly involved in anti-microbial responses, cell signalling, cellular function and maintenance, and cell death and survival. Among the most highly upregulated genes (≥ 10 folds, P < 0.05) were chemokines CCL5, CXCL11, IL8 and CXCL10. The upregulation and expression of CXCL11 were confirmed by qRT-PCR and immunofluorescence. Pathogen recognition receptors retinoic acid-inducible gene-1 (RIG-1) and melanoma differentiation-associated protein 5 (MDA5) were also upregulated. Our results strongly suggest that neuronal cells play a significant role in immunity against JEV. CXCL11, RIG-1 and MDA5 and other cytokines may be important in neuropathogenesis.

Tick-Borne Encephalitis Virus Nonstructural Protein NS5 Induces RANTES Expression Dependent on the RNA-Dependent RNA Polymerase Activity

Tick-borne encephalitis virus (TBEV) is one of the flaviviruses that targets the CNS and causes encephalitis in humans. The mechanism of TBEV that causes CNS destruction remains unclear. It has been reported that RANTES-mediated migration of human blood monocytes and T lymphocytes is specifically induced in the brain of mice infected with TBEV, which causes ensuing neuroinflammation and may contribute to brain destruction. However, the viral components responsible for RANTES induction and the underlying mechanisms remain to be fully addressed. In this study, we demonstrate that the NS5, but not other viral proteins of TBEV, induces RANTES production in human glioblastoma cell lines and primary astrocytes. TBEV NS5 appears to activate the IFN regulatory factor 3 (IRF-3) signaling pathway in a manner dependent on RIG-I/MDA5, which leads to the nuclear translocation of IRF-3 to bind with RANTES promoter. Further studies reveal that the activity of RNA-dependent RNA polymerase (RdRP) but not the RNA cap methyltransferase is critical for TBEV NS5-induced RANTES expression, and this is likely due to RdRP-mediated synthesis of dsRNA. Additional data indicate that the residues at K359, D361, and D664 of TBEV NS5 are critical for RdRP activity and RANTES induction. Of note, NS5s from other flaviviruses, including Japanese encephalitis virus, West Nile virus, Zika virus, and dengue virus, can also induce RANTES expression, suggesting the significance of NS5-induced RANTES expression in flavivirus pathogenesis. Our findings provide a foundation for further understanding how flaviviruses cause neuroinflammation and a potential viral target for intervention.

The intrathecal expression and pathogenetic role of Th17 cytokines and CXCR2-binding chemokines in tick-borne encephalitis

BACKGROUND

Tick-borne encephalitis (TBE) is a clinically variable but potentially severe Flavivirus infection, with the outcome strongly dependent on secondary immunopathology. Neutrophils are present in cerebrospinal fluid (CSF) of TBE patients, but their pathogenetic role remains unknown. In animal models, neutrophils contributed both to the Flavivirus entry into central nervous system (CNS) and to the control of the encephalitis, which we attempted to evaluate in human TBE.

METHODS

We analyzed records of 240 patients with TBE presenting as meningitis (n = 110), meningoencephalitis (n = 114) or meningoencephalomyelitis (n = 16) assessing CSF neutrophil count on admission and at follow-up 2 weeks later, and their associations with other laboratory and clinical parameters. We measured serum and CSF concentrations of Th17-type cytokines (interleukin-17A, IL-17F, IL-22) and chemokines attracting neutrophils (IL-8, CXCL1, CXCL2) in patients with TBE (n = 36 for IL-8, n = 15 for other), with non-TBE aseptic meningitis (n = 6) and in non-meningitis controls (n = 7), using commercial ELISA assays. The results were analyzed with non-parametric tests with p < 0.05 considered as significant.

RESULTS

On admission, neutrophils were universally present in CSF constituting 25% (median) of total pleocytosis, but on follow-up, they were absent in most of patients (58%) and scarce (< 10%) in 36%. CSF neutrophil count did not correlate with lymphocyte count and blood-brain barrier integrity, did not differ between meningitis and meningoencephalitis, but was higher in meningoencephalomyelitis patients. Prolonged presence of neutrophils in follow-up CSF was associated with encephalitis and neurologic sequelae. All the studied cytokines were expressed intrathecally, with IL-8 having the highest CSF concentration index. Additionally, IL-17A concentration was significantly increased in serum. IL-17F and CXCL1 CSF concentrations correlated with neutrophil count and CXCL1 concentration was higher in patients with encephalitis.

CONCLUSIONS

The neutrophil CNS infiltrate does not correlate directly with TBE severity, but is associated with clinical features like myelitis, possibly being involved in its pathogenesis. Th17 cytokine response is present in TBE, especially intrathecally, and contributes to the CNS neutrophilic inflammation. IL-8 and CXCL1 may be chemokines directly responsible for the neutrophil migration.

Intrathecal expression of IL-5 and humoral response in patients with tick-borne encephalitis

AIM

The aim of the study was to assess the role of an early specific humoral response in human infection with a tick-borne encephalitis virus (TBEV) and the role of IL-5 as its potential mediator and marker.

MATERIALS AND METHODS

The retrospective study involved a cohort of 199 patients diagnosed with TBE, in whom anti-TBEV IgM and IgG antibody titers were analyzed on admission and compared with clinical presentation and basic laboratory parameters. The prospective study included 50 TBE patients in whom IL-5 serum and CSF concentration was measured with ELISA on admission in the TBE neurologic phase and in selected patients before discharge, at follow-up or in samples obtained before the neurologic phase onset.

RESULTS

The serum anti-TBEV IgM correlated with good clinical outcome and the CSF anti-TBEV IgM with more pronounced CSF inflammation on admission, but also with its more complete resolution on follow-up. The serum anti-TBEV IgG correlated with milder presentation and better outcome. Concentration of IL-5 was increased in CSF but not in the serum of TBE patients. IL-5 concentration index on admission favored its intrathecal synthesis. IL-5 did not correlate significantly with clinical presentation and specific IgM and IgG titers.

CONCLUSIONS

Specific anti-TBEV IgM systemic and intrathecal response and IgG systemic response are protective, together favoring milder presentation, better outcome and resolution of central nervous system (CNS) inflammation. IL-5 is expressed intrathecally in TBE, but its pathogenetic role remains unclear.

CXCL9 concentrations in cerebrospinal fluid and serum of patients with tick-borne encephalitis

INTRODUCTION

The aim of our current study was to evaluate cerebrospinal fluid (CSF) and serum CXCL9 concentrations and diagnostic usefulness of this molecule in tick-borne encephalitis (TBE). The study included TBE patients in the acute phase (TBE I) and after 2 weeks of follow-up (TBE II). The control group consisted of patients investigated for suspected central nervous system (CNS) infection, but with normal CSF findings.

MATERIAL AND METHODS

Concentrations of CXCL9 were measured using enzyme-linked immunosorbent assay (ELISA).

RESULTS

Cerebrospinal fluid and serum concentrations of CXCL9 in patients with TBE were significantly higher than in controls (p < 0.001). This alteration was also observed in the case of the CXCL9 index (I_CXCL9; CSF CXCL9 concentration divided by serum CXCL9 concentration) (p < 0.001); moreover, I_CXCL9 significantly decreased after 2 weeks (p < 0.001). This is the first study to evaluate the CSF and serum levels of CXCL9 in subjects with TBE.

CONCLUSIONS

CXCL9 is a ligand for CXCR3, which was found on all Th1 memory lymphocytes present in the peripheral blood; therefore the elevated concentrations of CXCL9 in TBE patients as compared to the controls might indicate that this chemokine perhaps takes part in the trafficking of Th₁ cells into the CNS. The results presented here support the hypothesis that CXCL9 may play a role in TBE. However, further studies are required to determine whether this protein might be used as a potential tool for the diagnosis and monitoring of inflammation in TBE.

Chemokines CXCL10, CXCL11, and CXCL13 in acute disseminated encephalomyelitis, non-polio enterovirus aseptic meningitis, and neuroborreliosis: CXCL10 as initial discriminator in diagnostic algorithm?

We investigated potential diagnostic usefulness of serum and cerebrospinal fluid (CSF) concentrations of chemokines CXCL10, CXCL11, and CXCL13 in pediatric patients with acute disseminated encephalomyelitis (ADEM) (n = 23), non-polio enterovirus aseptic meningitis (NPEV AM) (n = 20), and neuroborreliosis (NB) (n = 21) and children with acute infectious diseases with neurological symptoms but with excluded neuroinfection/neuroinflammation (controls, n = 20). CSF levels of CXCL10 and CXCL11 were higher in patients with NPEV AM than those in other children, and CXCL10 levels showed a high discriminative potential (area under the receiver operating characteristic curve, ROC, 0.982) with high specificity and sensitivity (both 95%). CSF levels of CXCL13 were higher in NB patients than those in other children; however, discriminative potential (area under ROC curve 0.814) and diagnostic properties were moderate (sensitivity 67%, specificity 97%). Data suggest usefulness of chemokine quantification as a diagnostic aid in children with suspected ADEM, NPEV AM, or NB.

A database of human genes and a gene network involved in response to tick-borne encephalitis virus infection

BACKGROUND

Tick-borne encephalitis is caused by the neurotropic, positive-sense RNA virus, tick-borne encephalitis virus (TBEV). TBEV infection can lead to a variety of clinical manifestations ranging from slight fever to severe neurological illness. Very little is known about genetic factors predisposing to severe forms of disease caused by TBEV. The aims of the study were to compile a catalog of human genes involved in response to TBEV infection and to rank genes from the catalog based on the number of neighbors in the network of pairwise interactions involving these genes and TBEV RNA or proteins.

RESULTS

Based on manual review and curation of scientific publications a catalog comprising 140 human genes involved in response to TBEV infection was developed. To provide access to data on all genes, the TBEVhostDB web resource ( http://icg.nsc.ru/TBEVHostDB/ ) was created. We reconstructed a network formed by pairwise interactions between TBEV virion itself, viral RNA and viral proteins and 140 genes/proteins from TBEVHostDB. Genes were ranked according to the number of interactions in the network. Two genes/proteins (CCR5 and IFNAR1) that had maximal number of interactions were revealed. It was found that the subnetworks formed by CCR5 and IFNAR1 and their neighbors were a fragments of two key pathways functioning during the course of tick-borne encephalitis: (1) the attenuation of interferon-I signaling pathway by the TBEV NS5 protein that targeted peptidase D; (2) proinflammation and tissue damage pathway triggered by chemokine receptor CCR5 interacting with CD4, CCL3, CCL4, CCL2. Among nine genes associated with severe forms of TBEV infection, three genes/proteins (CCR5, IL10, ARID1B) were found to have protein-protein interactions within the network, and two genes/proteins (IFNL3 and the IL10, that was just mentioned) were up- or down-regulated in response to TBEV infection. Based on this finding, potential mechanisms for participation of CCR5, IL10, ARID1B, and IFNL3 in the host response to TBEV infection were suggested.

CONCLUSIONS

A database comprising 140 human genes involved in response to TBEV infection was compiled and the TBEVHostDB web resource, providing access to all genes was created. This is the first effort of integrating and unifying data on genetic factors that may predispose to severe forms of diseases caused by TBEV. The TBEVHostDB could potentially be used for assessment of risk factors for severe forms of tick-borne encephalitis and for the design of personalized pharmacological strategies for the treatment of TBEV infection.

Significance of CCL2, CCL5 and CCR2 polymorphisms for adverse prognosis of Japanese encephalitis from an endemic population of India

Japanese encephalitis (JE) is a major contributor for viral encephalitis in Asia. Vaccination programme has limited success for largely populated JE endemic countries like India and disease exposure is unavoidable. Involvement of chemokines and its co-receptors for adverse prognosis of JE have been documented both in vitro and in vivo. Identification of the genetic predisposing factor for JE infection in humans is crucial but not yet established. Therefore, we investigated the association of single nucleotide polymorphisms (SNPs) in chemokines (CCL2 and CCL5) and its co-receptors (CCR2 and CCR5) with their protein level for JE. The study enrolled 87 symptomatic JE cases (mild: severe = 24:63) and 94 asymptomatic controls. Our study demonstrated that CCL2 (rs1024611G), CCL5 (rs2280788G) and CCR2 (rs1799864A) significantly associated with JE (Odds ratio = 1.63, 2.95 and 2.62, respectively and P = 0.045, P = 0.05 and P = 0.0006, respectively). The study revealed that rs1024611G allele was associated with elevated level of CCL2. CCL5 elevation associated with JE mortality having a Cox proportional hazard of 1.004 (P = 0.033). In conclusion, SNPs of chemokine viz. CCL2 (rs1024611G) and its receptor CCR2 (rs1799864A) significantly associated with JE which may serve as possible genetic predisposing factor and CCL5 protein level may act as marker for disease survival.

Biomarkers in Cerebrospinal Fluid of Children With Tick-borne Encephalitis: Association With Long-term Outcome

BACKGROUND

Tick-borne encephalitis (TBE) is a major cause of meningoencephalitis in children in endemic areas, and long-term residual problems are not uncommon. Currently, no predictive markers in the acute phase are available that identify children at risk of incomplete recovery. We measured cytokines, chemokines and markers of neuronal damage in cerebrospinal fluid (CSF) in children with TBE and central nervous system (CNS) involvement.

METHODS

CSF from 37 children with TBE with CNS involvement was analyzed. Concentrations of 16 cytokines, chemokines and 5 markers of neuronal damage were assessed in CSF, using a multiplex assay, and correlated with clinical findings in the acute phase (n = 37), and with long-term outcome (n=22).

RESULTS

Significantly higher levels of CSF interferon (IFN)-γ, interleukin (IL)-4, IL-6 and IL-8 were detected in the acute phase from children who later developed sequelae. Although most of the studied markers of neuronal damage displayed no significant differences between children with sequelae and those with good outcome, neuron-specific enolase correlated inversely. The grade of CSF pleocytosis correlated positively with the levels of IFN-γ, IL-4 and IL-6; however, pleocytosis alone did not predict sequelae. Increasing age correlated positively with IL-4, IL-6 and IL-8 values.

CONCLUSIONS

The mechanism underlying the CNS pathology causing sequelae in TBE appears related to the grade of inflammation in CNS, rather than to direct neuronal destruction. High concentration of IFN-γ, IL-4, IL-6 and IL-8 in CSF might indicate a risk for incomplete recovery in childhood TBE.

Tick-borne encephalitis virus induces chemokine RANTES expression via activation of IRF-3 pathway

Background

Tick-borne encephalitis virus (TBEV) is one of the most important flaviviruses that targets the central nervous system (CNS) and causes encephalitides in humans. Although neuroinflammatory mechanisms may contribute to brain tissue destruction, the induction pathways and potential roles of specific chemokines in TBEV-mediated neurological disease are poorly understood.

Methods

BALB/c mice were intracerebrally injected with TBEV, followed by evaluation of chemokine and cytokine profiles using protein array analysis. The virus-infected mice were treated with the CC chemokine antagonist Met-RANTES or anti-RANTES mAb to determine the role of RANTES in affecting TBEV-induced neurological disease. The underlying signaling mechanisms were delineated using RANTES promoter luciferase reporter assay, siRNA-mediated knockdown, and pharmacological inhibitors in human brain-derived cell culture models.

Results

In a mouse model, pathological features including marked inflammatory cell infiltrates were observed in brain sections, which correlated with a robust up-regulation of RANTES within the brain but not in peripheral tissues and sera. Antagonizing RANTES within CNS extended the survival of mice and reduced accumulation of infiltrating cells in the brain after TBEV infection. Through in vitro studies, we show that virus infection up-regulated RANTES production at both mRNA and protein levels in human brain-derived cell lines and primary progenitor-derived astrocytes. Furthermore, IRF-3 pathway appeared to be essential for TBEV-induced RANTES production. Site mutation of an IRF-3-binding motif abrogated the RANTES promoter activity in virus-infected brain cells. Moreover, IRF-3 was activated upon TBEV infection as evidenced by phosphorylation of TBK1 and IRF-3, while blockade of IRF-3 activation drastically reduced virus-induced RANTES expression.

Conclusions

Our findings together provide insights into the molecular mechanism underlying RANTES production induced by TBEV, highlighting its potential importance in the process of neuroinflammatory responses to TBEV infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0665-9) contains supplementary material, which is available to authorized users.

CXCL13 chemokine as a promising biomarker to diagnose neurosyphilis in HIV-negative patients

BACKGROUND

Chemokine ligand 13 (CXCL13) is believed to play a role in the recruitment of B cells in the central nervous system during neuroinflammation. Neurosyphilis is a group of clinical syndromes of the central nervous system caused by Treponema pallidum (T. pallidum) infection. The relationship between CXCL13 and neurosyphilis still needs further study. In our study, CSF and serum CXCL13 concentrations were detected among 40 neurosyphilis patients, 31 syphilis/non-neurosyphilis patients, 26 non-syphilis/other central nervous system diseases patients. Serum CXCL13 concentrations were detected in 49 healthy persons. All enrolled persons were HIV-negative. Receiver operating characteristic (ROC) analysis was performed to determine the threshold value that could distinguish neurosyphilis from syphilis.

RESULTS

We found that the CSF CXCL13 concentrations and CXCL13 quotient (QCXCL13) were significantly increased in neurosyphilis patients compared to syphilis/non-neurosyphilis (χ(2) = 21.802, P < 0.001) and non-syphilis patients (χ(2) = 7.677, P = 0.002). ROC curve analyses revealed that CSF CXCL13 concentrations and QCXCL13 could serve as valuable biomarkers for differentiating neurosyphilis from non-neurosyphilis/syphilis.

CONCLUSIONS

The CSF CXCL13 and QCXCL13 could serve as valuable biomarkers for differentiating neurosyphilis from non-neurosyphilis/syphilis in HIV-negative patients.

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.

Increased concentration of interferon lambda-3, interferon beta and interleukin-10 in the cerebrospinal fluid of patients with tick-borne encephalitis

Tick-borne encephalitis (TBE) has a wide clinical spectrum, from asymptomatic to severe encephalitis, and host-dependent factors determining the outcome remain elusive. We have measured concentrations of pro-inflammatory/Th1 interferon-γ (IFNγ), immunomodulatory/Th2 interleukin-10 (IL-10), anti-viral type I (IFNβ) and type III (IFNλ3) interferons in cerebrospinal fluid (csf) and serum of 18 TBE patients, simultaneously genotyped for polymorphisms associated with the expression of genes IFNL3 (coding IFNλ3), IL10, CD209 and CCR5. IL-10, IFNβ and IFNλ3 were up-regulated in csf, with IFNλ3 level higher in patients with the milder clinical presentation (meningitis) than in meningoencephalitis. There was an increased serum IFNβ and a tendency for increased serum IL-10 in meningitis patients. Genotype in rs12979860 locus upstream of IFNL3 was associated with IFNλ3 expression and in rs287886 (CD209) - IL-10 expression. IL-10, IFNβ and IFNλ3 are expressed and play a protective role in TBE and their expression in TBE patients is associated with genetic polymorphisms.

Chemokine receptors as important regulators of pathogenesis during arboviral encephalitis

The central nervous system (CNS) is a highly complex network comprising long-lived neurons and glial cells. Accordingly, numerous mechanisms have evolved to tightly regulate the initiation of inflammatory responses within the brain. Under neuroinflammatory conditions, as in the case of viral encephalitides, the infiltration of leukocytes is often required for efficient viral clearance and recovery. The orchestration of leukocyte migration into the inflamed CNS is largely coordinated by a large family of chemotactic cytokines and their receptors. In this review, we will summarize our current understanding of how chemokines promote protection or pathogenesis during arbovirus induced encephalitis, focusing on neurotropic flaviviruses and alphaviruses. Furthermore, we will highlight the latest developments in chemokine and chemokine receptor based drugs that could have potential as therapeutics and have been shown to play a pivotal role in shaping the outcome of disease.

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.

Temporal expression profile of CXC chemokines in serum of patients with spinal cord injury

Chemokines, a subclass of cytokine superfamily have both pro-inflammatory and migratory role and serve as chemoattractant of immune cells during the inflammatory responses ensuing spinal cord injury (SCI). The chemokines, especially CXCL-1, CXCL-9, CXCL-10 and CXCL-12 contribute significant part in the inflammatory secondary damage of SCI. Inhibiting chemokine's activity and thereby the secondary damage cascades has been suggested as a chemokine-targeted therapeutic approach to SCI. To optimize the inhibition of secondary injury through targeted chemokine therapy, accurate knowledge about the temporal profile of these cytokines following SCI is required. Hence, the present study was planned to determine the serum levels of CXCL-1, CXCL-9, CXCL-10 and CXCL-12 at 3-6h, 7 and 28days and 3m after SCI in male and female SCI patients (n=78) and compare with age- and sex-matched patients with non-spinal cord injuries (NSCI, n=70) and healthy volunteers (n=100). ANOVA with Tukey post hoc analysis was used to determine the differences between the groups. The data from the present study show that the serum level of CXCL-1, CXCL-9 and CXCL-10 peaked on day 7 post-SCI and then declined to the control level. In contrast, significantly elevated level of CXCL-12 persisted for 28 days post SCI. In addition, post-SCI expression of CXCL-12 was found to be sex-dependent. Male SCI patients expressed significantly higher CXCL-12 when compared to control and SCI female. We did not observe any change in chemokines level of NSCI. Further, the age of the patients did not influence chemokines expression after SCI. These observations along with SCI-induced CSF-chemokine level should contribute to the identification of selective and temporal chemokine targeted therapy after SCI.

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.