Skip to main content
Download PDF

Regulation of inflammation in Japanese encephalitis

Journal of Neuroinflammation volume 14, Article number: 158 (2017) Cite this article

Abstract

Background

Uncontrolled inflammatory response of the central nervous system is a hallmark of severe Japanese encephalitis (JE). Although inflammation is necessary to mount an efficient immune response against virus infections, exacerbated inflammatory response is often detrimental. In this context, cells of the monocytic lineage appear to be important forces driving JE pathogenesis.

Main body

Brain-infiltrating monocytes, macrophages and microglia play a major role in central nervous system (CNS) inflammation during JE. Moreover, the role of inflammatory monocytes in viral neuroinvasion during JE and mechanisms of cell entry into the CNS remains unclear. The identification of cellular and molecular actors in JE inflammatory responses may help to understand the mechanisms behind excessive inflammation and to develop therapeutics to treat JE patients. This review addresses the current knowledge about mechanisms of virus neuroinvasion, neuroinflammation and therapeutics critical for JE outcome.

Conclusion

Understanding the regulation of inflammation in JE is challenging. Elucidation of the remaining open questions will help to the development of therapeutic approaches avoiding detrimental inflammatory responses in JE.

Background

Japanese encephalitis (JE) is an acute and uncontrolled inflammatory disease of the central nervous system (CNS) in humans, especially affecting children. JE is caused by Japanese encephalitis virus (JEV), a neurotropic single-stranded RNA virus belonging to the Flaviridae family, Flavivirus genus. JEV is transmitted by mosquito vectors in a zoonotic cycle involving wild aquatic bird reservoirs and pigs as amplifying hosts. Humans are dead-end hosts, because low viremia does not allow further viral spread [1]. The incubation period is 5–15 days and common symptoms include fever, headache, vomiting and neurologic symptoms such as paralysis and movement disorders. Seizures can occur in severe cases [1,2,3]. However, less than 1% of JEV infections are symptomatic. JE has an estimated incidence of 70,000 human cases annually, including 5–30% fatal cases and 30–50% of survivors showing permanent neurological sequelae [4, 5]. Therefore, JEV is a leading cause of severe encephalitis in Asia where it is epidemic in northern regions and endemic in southern regions [6]. JEV-infected areas extend from Pakistan to Japan and from Korea to Indonesia [5, 6]. In 1995, Eastern Pacific regions and Northern Australia became infected [7]. During the 2000s, JEV RNA, but no infectious virus, has occasionally been detected in Italy [8, 9]. Recently, JEV RNA was detected in Angola during a yellow fever outbreak in 2016 [10]. Moreover, JEV distribution exists under both tropical/subtropical and temperate climates [11]. Altogether, JEV’s spread to new regions represents an increasing risk [9, 12] and JEV may become a worldwide public health concern.

JEV-induced inflammation contributes to disease severity by inducing neuronal cell death [13, 14], inhibiting the proliferation and differentiation of neural progenitors [15] and disrupting the blood-brain barrier (BBB) [16, 17]. Importantly, JEV-induced inflammation further modulates cytokine/chemokine production [18] as well as the activation and migration of cells [13, 19]. Therefore, production of soluble factors and trafficking of immune cells may lead towards either disease progression or recovery through promotion of protective immune responses.

Although vaccination programs for travellers and inhabitants of regions at risk contribute to prevention of JE [5], unvaccinated individuals remain at risk. Nowadays, no specific cure exists for individuals developing JE [2, 3]. Therefore, the development of an effective and specific curative treatment for JE patients is necessary and requires further investigations.

The present review aims to understand cellular and molecular mechanisms involved in inflammatory responses to JEV infection and to identify key regulators of inflammation in JE. The understanding of these mechanisms may be central for the development of specific curative treatment of JE. Accordingly, the present review presents potential pharmaceutical candidates with promising anti-inflammatory or anti-viral properties.

Tropism and kinetics of viral replication

JEV is detected in various anatomical sites and propagates in various cell types including non-immune and immune cells (Table 1). Individuals are infected by JEV upon the bite of an infected mosquito. The dermis is supposedly the primary site of infection and JEV may propagate in cells of the dermal tissue before reaching lymphoid organs, probably transported by infected migratory immune cells such as Langerhans cells [3, 20, 21]. As a result, JEV has been detected and isolated from the spleen and lymph nodes of infected patients [16, 22,23,24]. During the acute phase of human JE, the virus can be isolated from blood cells [25, 26]. This can be associated with a low and transient viremia [2], and was also described in mouse models [16, 22, 27]. JEV may also replicate in human lymphocytes, albeit at low rate and possibly depending on the virus strain [28, 29]. Monocytes allow viral propagation in vitro by JEV without evidence of cell death [28, 30]. Interestingly, immature but not mature human monocyte-derived dendritic cells (DC) are susceptible to JEV infection in vitro resulting in virus propagation [31, 32]. It would still be necessary to quantify viral RNA over time in mature human DC in order to evaluate virus replication. Also murine DC allows virus replication in vivo and in vitro [33,34,35,36], but not the release of infectious viral particles in vitro [34]. Thus, the identification of the causes for the unproductive JEV infection of murine DC and mature human DC would help to understand key regulators for viral propagation in the latter cell types and others. Moreover, murine plasmacytoid DC (pDC) are permissive to JEV [35]. Human [37] and murine [29, 34,35,36] macrophages support virus propagation in vitro. But, JEV is cytotoxic to macrophages [38].

Table 1 Cellular source of viral propagation with body localization and abilities of neuroinvasion
Full size table

The mechanism behind JEV entry into the CNS is not well understood. Nevertheless in mice, the BBB disrupts only after viral neuroinvasion [16] indicating that neural infection is not necessary a consequence of the breakdown of the BBB, but the other way around. Interestingly, JEV productively infects rodent microvascular brain endothelial cells [39] that may be functionally affected in terms of their role for the BBB [21, 39, 40]. As these form the blood-brain barrier, this may represent a possible way of JEV transmission to brain tissue cells [41], after which the virus could infect pericytes [42] and astrocytes [39, 43]. Also the microglia cells representing CNS-resident macrophages are susceptible to JEV infection in vivo [44]. Murine microglia is also productively infected by JEV for up to 16 weeks in vitro [45]. Although human microglia cells allow JEV replication, infectious virus is transmitted to susceptible cells in a cell-cell dependent manner [46].

After entering into the brain, JEV is found in the nervous tissue and cerebrospinal fluid (CSF) in JE patients [26, 47,48,49] and in the mouse model [16, 23, 24, 49]. In the human brain, JEV antigen is mainly detected in the nuclear grey matter, including the thalamus, the hypothalamus, the hippocampus and the substantia nigra [48,49,50], where most of brain lesions appear [1, 51]. Also in macaques intranasally infected with JEV, viral antigen is detected in the thalamic and brain stem nuclei [44]. Neuronal cells are reported to be the most important target cells of JEV [16, 44, 52], allowing virus propagation [49]. Rodent models indicate that JEV has a particularly high tropism for neuronal precursors and developing neurons, affecting their proliferation and development [15, 52, 53]. Furthermore, JEV infection can cause direct neuronal damage [28, 52], which is further enhanced by JEV-induced inflammation [54, 55]. Actually, some studies suggested a correlation between the fatal outcome and the degree of inflammatory responses, although this remains controversial [3, 44, 49, 50, 56,57,58].

As a potent model for the study of human disease, pigs infected with JEV present a high viral loads in secondary lymphoid tissue. However, these animals have high viremia without association of JEV to blood leukocytes [59]. Also, JEV is consistently found in CNS tissues of animals, even if they did not show clinical symptoms [60]. Unlike human and murine cells, both porcine monocytes-derived DC and macrophages efficiently support virus replication (unpublished observations, A. Summerfield).

Inflammation in JE

Inflammatory cells in JE

Upon JEV infection, various immune cell types increase in number in various compartments of the periphery, including the spleen, lymph nodes and blood. In mice, numbers of macrophages, inflammatory monocytes, granulocytes and pDC increase in lymphoid tissues, such as spleen and lymph nodes [19, 29, 36]. Although not dramatically, natural killer cell population decreased in the spleen of JEV-infected mice [19]. In the blood, leucocytosis characterized by high numbers of monocytes and neutrophils was found in human patients [50, 61]. Similarly, JEV-infected mice show an increase of monocytes and neutrophils in blood [17, 19].

During JE, various peripheral immune cell types infiltrate the CNS (Table 1). In JE, infection of microvascular endothelial cells enhances the expression of adhesion molecules leading to transmigration of leukocytes [39]. In macaques intranasally infected with JEV, evidence of endothelial cells activation is also found [44]. However, DC is critical to maintain the integrity of the BBB by modulating the expression of tight junction and adhesion molecules in mice intraperitoneally infected with JEV [62] and provided adequate signal to differentiate/activate monocytes regulating neuroinflammation and viral propagation into the brain [23]. In the CSF of JE patients, leukocytes count of polymorphonuclear and mononuclear cells increases [15, 63]. In human brains of lethal JE cases, detection of perivascular erythrocytes and peripheral inflammatory mononuclear cells infiltrates indicates major vascular damage [49]. Also, perivascular infiltrates and multifocal lymphohistiocytic meningitis are a hallmark of JEV-infected pigs [59] and macaques [44]. In mice, macrophages/monocytes are the majority of brain-infiltrating inflammatory myeloid cells [19, 24, 49, 64, 65]. In addition, granulocytes and NK cells also infiltrate the brain of JEV-infected mice [19, 65, 66].

In addition to the contribution of peripheral immune cells infiltrating the brain, brain-resident cells interact with JEV upon infection of the brain. Activated microglial cell nodules develop, and the number of reactive astrocytes increases in human [49], macaques [44] and mouse [67]. Such glial nodules and evidences of neuronal degeneration and necrosis were also found [44, 59]. Microglia has been proposed to play a major role in neuronal cell death through release of pro-inflammatory mediators [13].

Inflammatory and anti-viral mediators in JE

Inflammation is a hallmark of JE with various inflammatory chemokines and cytokines having potential anti-viral activity in different body localizations. Inflammatory immune cells described previously, in addition to non-immune cells, can be sources of those mediators in response to JEV (Table 2). Human DC produce the cytokines tumour necrosis factor (TNF)-α, interleukin (IL)-6, type-I interferons (IFN) and the chemokines CCL2, CCL5, CXCL8 (IL-8) and CXCL10 in response to JEV [31, 32]. Upon exposure to JEV, murine DC produce TNF-α IL-6, IL-12, type-I IFN and CCL2 [33,34,35]. However, contrasting results of the various studies may be virus strain-specific since Beijing-1 strain induced TNF-α in murine DC [34, 35] whereas JEV P3 strain did not [33]. Additionally, murine pDC produce type-I IFN in response to JEV [35]. Human [24, 37] and murine [24, 34, 35, 38, 55] macrophages produce TNF-α, IL-6, IFN-α and CCL2 in response to JEV in vitro. Moreover, CXCL-8 has been measured from human macrophages [37] and IL-12, IFN-β and IFN-γ from murine macrophages [34, 35, 38, 55]. Both human [46] and rodent [24, 54, 68] microglia produce CCL2 upon JEV exposure. In addition, human microglia produce CXCL9 and CXCL10 [46]. Rodent microglia also release cytokines such as TNF-α, IL-1β, IL-6 [13, 24, 68, 69] and the chemokine CCL5 [13, 70]. Upon intracranial infection of mice, microglia stain for TNF-α, IL-1β, IL-6 and IL-18 [14, 24] and brain infiltrating monocytes for TNF-α and IL-6 [24]. In JEV-macaques, microglia stains for TNF-α [44]. As part of the BBB, human endothelial cells produce TNF-α and IFN-β in response to JEV [71] and rat endothelial cells produce CCL5 [39]. Rodent pericytes produce IL-6 upon JEV treatment [42]. Astrocytes of rodent origin release the cytokines IL-1β, IL-6, IL-18 and the chemokine CCL5 [13, 14, 43, 70]. Moreover, both JEV-infected human and murine astrocytes are responsible for the production of CXCL10 [72]. Brain sections of JEV-infected macaques reveal staining for TNF-α and IFN-α in astrocytes [44]. Finally, neurons of murine origin release TNF-α, IL-6, IL-12, IFN-α, IFN-γ and CCL2 in response to JEV treatment [73,74,75]. In JEV-infected macaques, neuronal cells are positive for IFN-α staining [44].

Table 2 Cellular source of cytokines and chemokines
Full size table

Chemokines

Chemokine axis plays a crucial role in JE pathogenesis by attracting migrating cells of the lymphatic and blood circulation systems. In JEV-infected mice, the spleen presents upregulated levels of CCL2 and CXCL10 [64, 76]. Alongside, serum of JEV-infected mice has higher levels of CCL2, CCL4 and CXCL10 as compared to uninfected animals [16, 24]. In JE-human patients, plasma and serum contain enhanced levels of CXCL8 and CCL5 [63, 77]. In response to a vaccine containing a live attenuated strain of JEV, serum of immunized human subjects increase levels of IL-8, CCL2, CCL3 and CCL4 [78]. At the CNS level, CSF of JEV-infected mice presents elevated levels of CCL2 [24]. In the CSF of JE-patients, IL-8 and CCL5 are found in elevated levels [63, 77, 79]. Brains of JEV-infected mice have increased levels of CCL2, CCL3, CCL4, CCL5 and CXCL10 [15, 16, 36, 54, 64, 68, 76]. Interestingly, cortex, striatum, thalamus, hippocampus, sub-ventricular zone and midbrain are found to express high levels of CCL2, with highest levels found in the cortex [15, 36, 80]. Moreover, enhanced mRNA levels of CCR1, CCR2, CCR4, CCR5, CXCR2 and CXCR3 have been measured in the brain of JEV-infected mice [19, 67].

The CCL5-CCR5 axis is involved in recovery and may control the level of inflammation during JE. In JE patients, higher levels of CCL5 have been found in CSF of non-survivors than in survivors [77]. Although neutralization of CCL5 does not affect the adhesion of peripheral blood mononuclear cells and neutrophils on a monolayer of human endothelial cells, transmigration of leukocytes across the monolayer is inhibited [39]. In vitro neutralization of CCL5, produced by JEV-infected murine glial cells, inhibits the attraction of murine monocytes/macrophages [18, 70]. However, CCR5-knock-out (KO) mice are more susceptible to lethal JEV infection upon both intravenous [65] and intraperitoneal injection [81] although only intravenous infection leads to higher viral burden in the brain and spinal cord compared to control animals [65]. CCR5-KO mice also present increased numbers of brain infiltrating monocytes and granulocytes, as well as activated microglia and macrophages. Moreover, CCR5-KO mice show higher levels of the mediators IL-1β, IL6, CCL2, CCL3, CCL4 and CCL5 [81].

In the process of brain-invasion by inflammatory cells and potential viral neuroinvasion during JE, the CCL2-CCR2 axis plays a crucial role which further affect brain inflammatory environment. Upon intradermal infection of mice with JEV, CCL2 deficiency increases mortality and morbidity of animals which presented higher viral loads in brain and spinal cord in comparison to control animals [19]. Although neutralization of CCL2 produced by JEV-infected murine glia reduces attraction of murine monocytes/macrophages cell line in vitro [70], monocytes and granulocytes accumulate in the brain of JEV-infected CCL2-deficient mice [19]. Moreover, higher expression levels of the chemokine ligands CCL3, CCL4, CCL5 and CXCL9, as well as the receptors CCR1, CCR2, CCR4 and CCR5 are detected in the brain of the these animals [19]. Interestingly, CCR2 deficiency in mice leads to decreased susceptibility against lethal infection by JEV, but with no difference in viral load in the brain. Moreover, CCR2 deficiency results in a reduced accumulation of monocytes, but not granulocytes in the brain of JEV-infected mice [19]. However, in another mouse model where DC were ablated, CCR2 deficiency increases the speed of accumulation of monocytes into the CNS compared to control animals [23] indicating that the speed of monocytes into the CNS is CCR2-dependent. Finally, JEV-infected CCR2-deficient mice have also reduced expression of CCL3, CCL4, CCL5 and CCR1 in the brain [19].

Cytokines

Cytokines are essential to mount a potent immune response against JEV providing danger signals and anti-viral activity. In JEV-infected mice, increased levels of IL-12 and IFN-γ are found in lymph nodes and spleen [28, 64]. Serum of JEV-infected mice contains TNF-α, IL6, IL-18, as well as IFNs [16, 24, 27, 35, 36, 82]. In JE-human patients, increased levels of TNF-α [83] and IFN-α [84] are measured in blood. At the CNS level, CSF of mice shows elevated levels of TNF-α, IL6 and IL-18 [24] upon JEV infection. In the brain tissue of JEV-infected mice, upregulated levels of TNF-α, IL-1β, IL-6, IL-12, IL-18, IFN-γ and CXCL10 have been reported [14,15,16, 36, 54, 64, 68, 72, 82]. Notably, the cerebral cortex presents the highest level of TNF-α, IL-6 and types I and II IFNs [15, 36, 54, 80]. In JE-patients, an increase of TNF-α, IL-6 and IFN-α is detected in the CSF [77, 79, 83, 84].

In JE, TNF-α has a major impact on the dynamic of inflammation and the outcome of the disease. For instance, high levels of TNF-α in serum and CSF of patient is associated with lethality [83]. Intracranial administration of silencing RNA (siRNA) against the TNF receptor-associated death domain (TRADD) decreases mortality of intravenously JEV-infected mice [85], reduces virus neuroinvasion and neuronal cell death [67]. In vitro neutralization of TNF-α derived from JEV-infected murine microglia cultures also reduces cytotoxicity to neuronal cells [13]. Interestingly, the brain of JEV-infected mice treated with TRADD siRNA has an abrogated expression of adhesion molecules and lower levels of brain-infiltrating neutrophils were found [67]. In vitro neutralization of TNF-α inhibits the production of CCL5 from JEV-infected glia. As a result, the latter supernatants show reduced chemotactic activity towards murine macrophages [18]. Furthermore, TNF-α enhances the production of CCL5 by uninfected murine astrocytes [18] which may enhance the recruitment of leukocytes in JE. Finally, TRADD siRNA treatment of JEV-infected mice reduces the expansion of astrocytes and the activation of microglia. Brain of these mice have reduced levels of the mediators TNF-α, IL-6, IL-12, IFN-γ and CCL2, as well as the receptors CCR1, CCR2 and CXCR3 [67].

Molecular components of JEV recognition

Pattern recognition receptors in the recognition of JEV

JEV has been found to interact with the toll-like receptor 2 (TLR2) in neurons and TLR3 and/or TLR7 in microglial cells [75, 86, 87]. Upon JEV infection, KO of TLR3 in mice enhances lethality and severity of JE, as wells as viral loads in the spinal cord and the brain in comparison to control animals [36]. Actually, knocking-down (KD) of TLR3 with small hairpin RNA increases viral load in murine microglia [87]. Additionally, TLR3-KO mice present stronger permeability of the BBB and increased brain-infiltration of inflammatory monocytes with activation of macrophages/microglia. These animals also show higher levels of systemic IL-6 and IFN-β. In the brain and the spinal cord, higher mRNA levels of IL-6, type-I IFN, CCL2, CCL5 and CXCL10 are detected, whereas CCL3 and CCL4 are only found in the spinal cord [36]. KD of TLR3 in murine microglia reduces the secretion of TNF-α [87]. In contrast to TLR3-KO mice, JEV-infected TLR4-KO mice show reduced severity and lethality of JE and lower viral loads are detected in the brain than in wild-type (WT) animals. Interestingly, TLR4-KO mice do not show any difference in brain-infiltration of inflammatory monocytes and activation of macrophages/microglia. However, these animals secrete high levels of systemic IFN-β [36]. Otherwise, subcutaneous JEV infection of systemic TLR7-KD mice leads to increased mortality in comparison with control animals, whereas specific KD of brain TLR7 does not influence the mortality of the animals. Interestingly, systemic TLR7-KD mice show higher brain viral loads than brain TLR7-KD in mice, indicating the importance of peripheral virus detection in order to control JEV neuroinvasion. Moreover, systemic TRL7-KD mice secrete higher levels of brain IL-6 than brain TLR7-KD in mice. Nevertheless, KD of TLR7 leads to stronger brain-infiltration of monocytes and neutrophils, stronger activation of microglia and higher levels of TNF-α, IL-6 and CCL2, but lower levels of IFN-α in the brain of both models [75]. At the cytoplasmic level, the melanoma differentiation-associated protein 5 (MDA5) and retinoic acid-inducible gene 1 (RIG-I) are important [86]. KD of RIG-I increases viral load in murine microglia [87]. In addition, blockade of RIG-I decreases the release of TNF-α, IL-6 and CCL2 from murine microglia [87] and neurons [73] and of IL-12 from neurons [73]. Overall, TLR3 and RIG-I may rather be protective. Furthermore, TLR7 seems to initiate protective inflammatory signals against JE. In contrast, TLR4 may contribute to pathological JE. JEV has also been reported to interact with the C-type lectin domain family 5 member A (CLEC5A) receptor leading to the phosphorylation of the DNAX activation protein of 12 kDa in human and murine macrophages [24]. In mice infected intraperitoneally with JEV, administration of anti-CLEC5A antibodies via the same route diminishes the susceptibility to lethal JEV infection and reduces JEV neuroinvasion. These animals maintain the integrity of the BBB and reduce brain-infiltration of inflammatory myeloid cells and proliferation of macrophages/microglia. Moreover, lower levels of TNF-α, IL-6, IL-18 and CCL2 are found in serum and CSF [24]. Additionally, KD of NOD-like receptor family pyrin domain containing 3 (NLRP3) by siRNA decreases the production of IL-1β and IL-18 in murine microglia upon JEV treatment. Nevertheless, activation of NLRP3 in JEV-treated microglia is due to secondary signals such as the activity of caspase-1, itself influenced by reactive oxygen species [68]. Thus, CLEC5A and NLRP3, both associated with the inflammasome activation, seem to have major contribution to pathological JE.

Downstream signalling pathways upon JEV recognition

Upon JEV recognition, downstream signalling pathways are induced and may involve adaptor proteins such as myeloid differentiation primary response gene 88 (MyD88) [34, 86]. Upon JEV exposure in vitro, both DC and macrophages from MyD88-KO mice reduce the production of IL-6 and IL-12 in comparison to cells from WT-mice. Moreover, macrophages of MyD88-KO animals also release less TNF-α [34].

Furthermore, kinases such as protein kinase B (Akt) [38], phosphoinositide 3-kinase (PI3K) [32, 38], p38 mitogen-activated protein kinase (p38MAPK) [32, 34, 38, 55, 73, 87] and signal-regulated kinase (ERK) [39, 70, 87,88,89] are found to be involved in signalling pathways upon JEV recognition. Upon inhibition of p38MAPK or PI3K, human DC produces less TNF-α, type-I IFN and CXCL8 [32]. Murine DC diminishes the production of TNF-α, IL-6 and IL-12 after inhibition of p38MAPK [34]. In murine macrophages, inhibition of p38 MAPK reduce the production of TNF-α, IL-6, IL-12, IFN-γ and CCL2, resulting in the loss of cytotoxicity to neuronal cells [55]. In murine microglia, inhibition of p38MAPK or ERK leads to reduced production of TNF-α, IL-6 and CCL2 [87]. Inhibition of ERK also leads to abrogated production of TNF-α and IL-1β by rat microglia [88]. Finally, inhibition of ERK leads to reduced release of CCL5 glial cells [70] and endothelial cells [39] of rodents. In addition, inhibition of ERK leads to reduced expression adhesion molecules in rodent endothelial cells [39].

Finally, transcription factors such as interferon regulated factor 3 (IRF3)/IRF7 [36, 75, 86, 90,91,92], activator protein 1 [87] and nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB) [38, 39, 70, 73, 75, 87] are found to be implicated during JEV infection. In rat microglia, inhibition of NF-κB abrogates the production of TNF-α and IL-1β by rat microglia [88]. In rodent endothelial cells, inhibition of NF-κB reduces the production of CCL5 and adhesion molecules [39].

Importantly, the activity of inflammatory components have also been described to depend on the janus kinase-signal transducer and activator of transcription (JAK-STAT) signalling pathway in JEV infection. This requires the activation of STAT1 [24, 36, 92] and the expression of IFN-dependent and IFN-independent IFN-stimulated genes [36, 37].

MicroRNA upon JEV treatment

MicroRNAs (miRNA) contribute to the regulation of gene expression in various cell types including astrocyte, microglia and neuronal cells upon JEV infection. Replicative JEV modulates cellular miRNA expressions in time- and dose-dependent manners [93,94,95,96]. JEV-influenced miRNAs target elements of pathogen recognition [95, 96] and downstream signalling pathways [93, 94, 97, 98], as well as the JAK-STAT signalling pathway [95, 99,100,101,102].

JEV may modulate the expression of miRNA resulting in inhibition of inflammatory responses. JEV downregulates the expression of miR-432 reducing the production of TNF-α and IL-6 and suppressed JEV replication in human microglia [101]. Moreover, JEV upregulates miR-146a expression reducing the expression of TNF-α and IL-6 in both human and murine microglia [99, 100] and of IL-1β, IFN-α and IFN-β in murine cells [100]. However, miR-146a enhances JEV replication in human microglia [99]. Finally, JEV upregulates miR-301a expression, which inhibits type-I IFN production in human and murine neuronal cells. However, miR-301a promotes JEV replication [102].

Otherwise, the influence of JEV on the expression of miRNA may result in enhanced inflammatory responses as well as increased JE lethality and severity. Such miRNAs represent potential therapeutic targets. In murine microglia cells, JEV upregulates miR-29b expression inducing microglia activation and increased expression of TNF-α, IL-1β, IL-6 and CCL2. Inhibition of miR-29b reduces the expression of inflammatory mediators [98]. In human glioblastoma cells, JEV downregulates the expression of miR-370 enhancing expression IFN-β, inhibited by using a miR-370 mimic. Virus replication rate and JEV-induced cell injury are also inhibited by using miR-370 mimic, but restored by further inhibition of the miR-370 mimic activity [97]. In both human astrocytoma cells and murine microglia cells, JEV upregulates miR-19b-3p [93] and miR-15b [96] increasing the production of TNF-α, IL-1β, IL-6 and CCL5 [93, 96], as well as IL-12, IFN-β and CCL2 [96]. Inhibition of miR-19b-3p or miR-15b suppresses the production of these inflammatory mediators. Importantly, intravenous administration of miR-19b-3p or miR-15b antagonist reduces neuroinflammation and lethality of mice upon intracranial infection with JEV [93, 96]. Finally, JEV upregulates the expression of miR-155 in both human and mouse brain tissue [94]. miR-155 expression enhances the production of TNF-α, IL-6, IFN-β and CCL2 in murine microglia cells [94], but reduces the expression of TNF-α, IL-1β and IFN-β in human microglia cells [103]. miR-155 also suppresses JEV replication in human microglia [103]. Nevertheless, intravenous administration of anti-miR-155 attenuates neuroinflammation, microglial activation and mortality in intravenously JEV-infected mice [94].

Therapeutic candidates to control JE

There is still no specific curative treatment for JE. Nevertheless, anti-inflammatory therapeutic candidates are currently under evaluation. However, such candidates must have specific anti-viral effects against JEV. The following drugs have shown promising effects during the course of a JEV infection.

Arctigenin is a polyphenolic lignan compound found in plants of the Asteraceae family. Upon JEV infection, arctigenin inhibits the activation of kinases such as p38-MAPK, ERK and Akt abrogating microglial activation and production of cytokines such as TNF-α, IL-6, IFN-γ and CCL2 [104]. Arctigenin also reduces JEV-induced neuronal cell death [104]. Importantly, arctigenin reduces brain tissue viral load, induces neuroprotection and protects from JE lethality [104].

Minocycline is a semi-synthetic tetracycline antibiotic. Upon JEV infection, minocycline reduces the phosphorylation of kinases such as PI3K, Akt and p38 MAPK, as well as the transcription factor NF-κB [38]. As a result, minocycline reduces the production of TNF-α, IL-6, IL-12, IFN-γ and CCL2 in the brain [64, 105] and inhibits microglial activation [15, 105]. Interestingly, minocycline also limits the infiltration of innate immune cells into the brain of JEV-infected mice [15, 64]. Finally, minocycline reduces viral replication and the expression of viral antigen in the brain and confers complete protection against JE [64, 105].

2-(2-Methyl-quinoline-4ylamino)-N-(2-chlorophenyl)-acetamide (PP2) is a synthetic anilidoquinoline derivative. In microglia and neuron/glia cultures infected with JEV, PP2 suppresses the activation of NF-κB decreasing the production of TNF-α, IL-1β and CCL5 [89, 106]. PP2 also reduces neurotoxicity of JEV [89, 106, 107]. Although PP2 A does not affect JEV replication, it reduces the phosphorylation of the viral protein NS3 by phospotyrosine resulting in a diminished release of infectious virus particles from neuron/glia cultures [89, 106]. PP2 reduces mature intracellular and brain viral load and confers neuroprotection [107]. Importantly, Mice treated with PP2 show complete protection from lethal JEV infection [107].

Vivo-morpholinos (MOs) are synthetic uncharged anti-sense oligomer analogs of DNA or RNA targeting specific genomic region. MOs targeting JEV genome reduces phosphorylation of the kinases p38 MAPK and ERK as well as the transcription factor NF-κB. Consequently, MOs inhibit the production of TNF-α, IL-6, IFN-γ and CCL2 in the brain and microglial activation [108]. MOs abrogate neurodegeneration, reduce viral load in the brain and protects from JE [108].

In conclusion, therapeutic candidates have anti-inflammatory, antioxidant and JEV-specific anti-viral activities. Importantly, these molecules enter the brain even though administration is in the periphery. Nevertheless, none of these drugs has yet been approved for the treatment of JEV infection in humans.

Conclusions

Systemic and neural inflammation contributes to the anti-viral immune response, but is also responsible for the brain pathology in JE. The balance between anti-viral and brain damaging inflammatory effects is probably the key predictor of the outcome. In that respect, various cells and factors contribute to that balance but may also contribute to dysregulation and pathology. Cells of the monocytic lineage appear to play a central role in inflammatory responses and pathogenesis in JE (Fig. 1). In particular, TNF-α and the axis CCL2-CCR2 has a major impact in neuroinvasion of immune cells including inflammatory monocytes. The activation of TLR3/TLR7 signalling pathways, the activity of CCL2 as well as the intervention of DC inhibits peripheral inflammatory responses to JEV. Furthermore, miR-155b and miR-146a suppress brain inflammation. Finally, therapeutic candidates such as minocycline and PP2 present anti-inflammatory and anti-viral activity upon JEV infection.

Fig. 1
figure 1

Monocytes participate in inflammation and viral propagation and produce TNF-α upon JEV infection. (1) TNF-α is implicated in the activation and differentiation of monocytes as well as (2) the expression of adhesion molecules on endothelial cell surface constituting the BBB which participates in (3) the transmigration of inflammatory monocytes through the BBB. (4) In the brain, inflammatory monocytes, macrophages, microglia and neuronal cells contribute to viral propagation and neuroinflammation. (5) TNF-α and CCL2 lead to microglial activation and astrocytic expansion. (6) Ultimately, neuronal cell death results of direct cytotoxicity of JEV and indirect effects of inflammatory mediators. (in black) Chemokines (CCL2) and pattern recognition receptors (TLR3, TLR7) inhibit cellular and virus neuroinvasion and miRNAs (miR-155b, miR-146a) suppress microglia-derived inflammatory responses during JE. (in red) Promising therapeutic candidates inhibit neuroinflammation in JE

Full size image

Since all therapeutic candidates inhibit microglia activation which are a main producer of inflammatory mediators, future directions of the development of therapeutics should take care of the targeting microglial activation in order to reduce JE neuroinflammation.

Abbreviations

Akt:

Protein kinase B

BBB:

Blood-brain barrier

CLEC5A:

C-type lectin domain family 5 member A

CNS:

Central nervous system

CSF:

Cerebrospinal fluid

DC:

Dendritic cell

ERK:

Signal-regulated kinase

IFN:

Interferon

IL:

Interleukin

JE:

Japanese encephalitis

JEV:

Japanese encephalitis virus

KD:

Knock-down

KO:

Knock-out

MDA5:

Melanoma differentiation-associated protein 5

miRNA:

Micro RNA

MO:

Vivo-morpholinos

NF-κB:

Nuclear factor kappa-light-chain-enhancer of activated B cell

NLRP3:

NOD-like receptor family pyrin domain containing 3

p38MAPK:

p38 mitogen-activated protein kinase

pDC:

plasmacytoid dendritic cell

PP2:

2(2-methyle-quinoline-4ylamino)-N-(2-chlorophenyl)-acetamide

RIG-I:

Retinoic acid-inducible gene 1

siRNA:

Silencing RNA

TLR:

Toll-like receptor

TNF:

Tumour necrosis factor

TRADD:

TNF receptor-associated death domain

WT:

Wild-type

References

  1. Misra UK, Kalita J. Overview: Japanese encephalitis. Prog Neurobiol. 2010;91(2):108–20.

    Article  CAS  PubMed  Google Scholar 

  2. Solomon T. Flavivirus encephalitis. N Engl J Med. 2004;351(4):370–8.

    Article  CAS  PubMed  Google Scholar 

  3. Solomon T, Dung NM, Kneen R, Gainsborough M, Vaughn DW, Khanh VT. Japanese encephalitis. J Neurol Neurosur Ps. 2000;68(4):405–15.

    Article  CAS  Google Scholar 

  4. Centers for Disease C, Prevention. Japanese encephalitis surveillance and immunization--Asia and the Western Pacific, 2012. MMWR Morb Mortal Wkly Rep. 2013;62(33):658–62.

    Google Scholar 

  5. Campbell GL, Hills SL, Fischer M, Jacobson JA, Hoke CH, Hombach JM, Marfin AA, Solomon T, Tsai TF, Tsu VD, et al. Estimated global incidence of Japanese encephalitis: a systematic review. Bull World Health Organ. 2011;89(10):766–74. 774A-774E

    Article  PubMed  PubMed Central  Google Scholar 

  6. Wang H, Liang G. Epidemiology of Japanese encephalitis: past, present, and future prospects. Ther Clin Risk Manag. 2015;11:435–48.

    CAS  PubMed  PubMed Central  Google Scholar 

  7. Hanna JN, Ritchie SA, Phillips DA, Shield J, Bailey MC, Mackenzie JS, Poidinger M, McCall BJ, Mills PJ. An outbreak of Japanese encephalitis in the Torres Strait, Australia, 1995. Med J Aust. 1996;165(5):256–60.

    CAS  PubMed  Google Scholar 

  8. Ravanini P, Huhtamo E, Ilaria V, Crobu MG, Nicosia AM, Servino L, Rivasi F, Allegrini S, Miglio U, Magri A et al. Japanese encephalitis virus RNA detected in Culex pipiens mosquitoes in Italy. Euro Surveill. 2012;17(28):2-5.

  9. Platonov A, Rossi G, Karan L, Mironov K, Busani L, Rezza G. Does the Japanese encephalitis virus (JEV) represent a threat for human health in Europe? Detection of JEV RNA sequences in birds collected in Italy. Euro Surveill. 2012;17(32):21–22.

    Google Scholar 

  10. Simon-Loriere E, Faye O, Prot M, Casademont I, Fall G, Fernandez-Garcia MD, Diagne MM, Kipela JM, Fall IS, Holmes EC, et al. Autochthonous Japanese Encephalitis with Yellow Fever Coinfection in Africa. N Engl J Med. 2017;376(15):1483–5.

    Article  PubMed  Google Scholar 

  11. Jeffries CL, Walker T. The potential use of Wolbachia-based mosquito biocontrol strategies for Japanese encephalitis. PLoS Negl Trop Dis. 2015;9(6):e0003576.

    Article  PubMed  PubMed Central  Google Scholar 

  12. Nett RJ, Campbell GL, Reisen WK. Potential for the emergence of Japanese encephalitis virus in California. Vector Borne Zoonotic Dis. 2009;9(5):511–7.

    Article  CAS  PubMed  Google Scholar 

  13. Chen CJ, Ou YC, Lin SY, Raung SL, Liao SL, Lai CY, Chen SY, Chen JH. Glial activation involvement in neuronal death by Japanese encephalitis virus infection. J Gen Virol. 2010;91(Pt 4):1028–37.

    Article  CAS  PubMed  Google Scholar 

  14. Das S, Mishra MK, Ghosh J, Basu A. Japanese encephalitis virus infection induces IL-18 and IL-1beta in microglia and astrocytes: correlation with in vitro cytokine responsiveness of glial cells and subsequent neuronal death. J Neuroimmunol. 2008;195(1–2):60–72.

    Article  CAS  PubMed  Google Scholar 

  15. Das S, Dutta K, Kumawat KL, Ghoshal A, Adhya D, Basu A. Abrogated inflammatory response promotes neurogenesis in a murine model of Japanese encephalitis. PLoS One. 2011;6(3):e17225.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  16. Li F, Wang Y, Yu L, Cao S, Wang K, Yuan J, Wang C, Wang K, Cui M, Fu ZF. Viral infection of the central nervous system and neuroinflammation precede blood-brain barrier disruption during Japanese encephalitis virus infection. J Virol. 2015;89(10):5602–14.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  17. Mathur A, Khanna N, Chaturvedi UC. Breakdown of blood-brain barrier by virus-induced cytokine during Japanese encephalitis virus infection. Int J Exp Pathol. 1992;73(5):603–11.

    CAS  PubMed  PubMed Central  Google Scholar 

  18. Chen CJ, Ou YC, Chang CY, Pan HC, Liao SL, Raung SL, Chen SY. TNF-alpha and IL-1beta mediate Japanese encephalitis virus-induced RANTES gene expression in astrocytes. Neurochem Int. 2011;58(2):234–42.

    Article  CAS  PubMed  Google Scholar 

  19. Kim JH, Patil AM, Choi JY, Kim SB, Uyangaa E, Hossain FM, Park SY, Lee JH, Kim K, Eo SK. CCL2, but not its receptor, is essential to restrict immune privileged CNS-invasion of Japanese encephalitis virus via regulating accumulation of CD11b+ Ly-6Chigh monocytes. Immunology. 2016;149(2):186–203.

    Article  CAS  PubMed  Google Scholar 

  20. Johnston LJ, Halliday GM, King NJC. Langerhans cells migrate to local lymph nodes following cutaneous infection with an arbovirus. J Investig Dermatol. 2000;114(3):560–8.

    Article  CAS  PubMed  Google Scholar 

  21. Agrawal T, Sharvani V, Nair D, Medigeshi GR. Japanese encephalitis virus disrupts cell-cell junctions and affects the epithelial permeability barrier functions. PLoS One. 2013;8(7):e69465.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  22. Nagata N, Iwata-Yoshikawa N, Hayasaka D, Sato Y, Kojima A, Kariwa H, Takashima I, Takasaki T, Kurane I, Sata T, et al. The pathogenesis of 3 neurotropic flaviviruses in a mouse model depends on the route of neuroinvasion after viremia. J Neuropathol Exp Neurol. 2015;74(3):250–60.

    Article  PubMed  Google Scholar 

  23. Kim JH, Choi JY, Kim SB, Uyangaa E, Patil AM, Han YW, Park SY, Lee JH, Kim K, Eo SK. CD11c(hi) dendritic cells regulate Ly-6C(hi) monocyte differentiation to preserve immune-privileged CNS in lethal neuroinflammation. Sci Rep. 2015;5:17548.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  24. Chen ST, Liu RS, Wu MF, Lin YL, Chen SY, Tan DT, Chou TY, Tsai IS, Li L, Hsieh SL. CLEC5A regulates Japanese encephalitis virus-induced neuroinflammation and lethality. PLoS Pathog. 2012;8(4):e1002655.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  25. Sapkal GN, Wairagkar NS, Ayachit VM, Bondre VP, Gore MM. Detection and isolation of Japanese encephalitis virus from blood clots collected during the acute phase of infection. Am J Trop Med Hyg. 2007;77(6):1139–45.

    CAS  PubMed  Google Scholar 

  26. Swami R, Ratho RK, Mishra B, Singh MP. Usefulness of RT-PCR for the diagnosis of Japanese encephalitis in clinical samples. Scand J Infect Dis. 2008;40(10):815–20.

    Article  CAS  PubMed  Google Scholar 

  27. Rokutanda HK. Relationship between viremia and interferon production of Japanese encephalitis virus. J Immunol. 1969;102(3):662–70.

    CAS  PubMed  Google Scholar 

  28. Yang KD, Yeh WT, Chen RF, Chuon HL, Tsai HP, Yao CW, Shaio MF. A model to study neurotropism and persistency of Japanese encephalitis virus infection in human neuroblastoma cells and leukocytes. J Gen Virol. 2004;85(Pt 3):635–42.

    Article  CAS  PubMed  Google Scholar 

  29. Mathur A, Bharadwaj M, Kulshreshtha R, Rawat S, Jain A, Chaturvedi UC. Immunopathological study of spleen during Japanese encephalitis virus infection in mice. Br J Exp Pathol. 1988;69(3):423–32.

    CAS  PubMed  PubMed Central  Google Scholar 

  30. Hasegawa H, Satake Y, Kobayashi Y. Effect of cytokines on Japanese encephalitis virus production by human monocytes. Microbiol Immunol. 1990;34(5):459–66.

    Article  CAS  PubMed  Google Scholar 

  31. Gupta N, Hegde P, Lecerf M, Nain M, Kaur M, Kalia M, Vrati S, Bayry J, Lacroix-Desmazes S, Kaveri SV. Japanese encephalitis virus expands regulatory T cells by increasing the expression of PD-L1 on dendritic cells. Eur J Immunol. 2014;44(5):1363–74.

    Article  CAS  PubMed  Google Scholar 

  32. Sooryanarain H, Ayachit V, Gore M. Activated CD56(+) lymphocytes (NK+NKT) mediate immunomodulatory and anti-viral effects during Japanese encephalitis virus infection of dendritic cells in-vitro. Virology. 2012;432(2):250–60.

    Article  CAS  PubMed  Google Scholar 

  33. Cao S, Li Y, Ye J, Yang X, Chen L, Liu X, Chen H. Japanese encephalitis Virus wild strain infection suppresses dendritic cells maturation and function, and causes the expansion of regulatory T cells. Virol J. 2011;8:39.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  34. Aleyas AG, George JA, Han YW, Rahman MM, Kim SJ, Han SB, Kim BS, Kim K, Eo SK. Functional modulation of dendritic cells and macrophages by Japanese encephalitis virus through MyD88 adaptor molecule-dependent and -independent pathways. J Immunol. 2009;183(4):2462–74.

    Article  CAS  PubMed  Google Scholar 

  35. Kim SB, Choi JY, Uyangaa E, Patil AM, Hossain FM, Hur J, Park SY, Lee JH, Kim K, Eo SK. Blockage of indoleamine 2,3-dioxygenase regulates Japanese encephalitis via enhancement of type I/II IFN innate and adaptive T-cell responses. J Neuroinflammation. 2016;13(1):79.

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  36. Han YW, Choi JY, Uyangaa E, Kim SB, Kim JH, Kim BS, Kim K, Eo SK. Distinct dictation of Japanese encephalitis virus-induced neuroinflammation and lethality via triggering TLR3 and TLR4 signal pathways. PLoS Pathog. 2014;10(9):e1004319.

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  37. Sooryanarain H, Sapkal GN, Gore MM. Pathogenic and vaccine strains of Japanese encephalitis virus elicit different levels of human macrophage effector functions. Arch Virol. 2012;157(10):1905–18.

    Article  CAS  PubMed  Google Scholar 

  38. Dutta K, Mishra MK, Nazmi A, Kumawat KL, Basu A. Minocycline differentially modulates macrophage mediated peripheral immune response following Japanese encephalitis virus infection. Immunobiology. 2010;215(11):884–93.

    Article  CAS  PubMed  Google Scholar 

  39. Lai CY, Ou YC, Chang CY, Pan HC, Chang CJ, Liao SL, Su HL, Chen CJ. Endothelial Japanese encephalitis virus infection enhances migration and adhesion of leukocytes to brain microvascular endothelia via MEK-dependent expression of ICAM1 and the CINC and RANTES chemokines. J Neurochem. 2012;123(2):250–61.

    Article  CAS  PubMed  Google Scholar 

  40. Al-Obaidi MM, Bahadoran A, Har LS, Mui WS, Rajarajeswaran J, Zandi K, Manikam R, Sekaran SD. Japanese encephalitis virus disrupts blood-brain barrier and modulates apoptosis proteins in THBMEC cells. Virus Res. 2017;233:17–28.

    Article  CAS  PubMed  Google Scholar 

  41. Liu TH, Liang LC, Wang CC, Liu HC, Chen WJ. The blood-brain barrier in the cerebrum is the initial site for the Japanese encephalitis virus entering the central nervous system. J Neurovirol. 2008;14(6):514–21.

    Article  CAS  PubMed  Google Scholar 

  42. Chen CJ, Ou YC, Li JR, Chang CY, Pan HC, Lai CY, Liao SL, Raung SL, Chang CJ. Infection of pericytes in vitro by Japanese encephalitis virus disrupts the integrity of the endothelial barrier. J Virol. 2014;88(2):1150–61.

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  43. Chang CY, Li JR, Chen WY, Ou YC, Lai CY, Hu YH, Wu CC, Chang CJ, Chen CJ. Disruption of in vitro endothelial barrier integrity by Japanese encephalitis virus-Infected astrocytes. Glia. 2015;63(11):1915–32.

    Article  Google Scholar 

  44. Myint KS, Kipar A, Jarman RG, Gibbons RV, Perng GC, Flanagan B, Mongkolsirichaikul D, Van Gessel Y, Solomon T. Neuropathogenesis of Japanese encephalitis in a primate model. PLoS Negl Trop Dis. 2014;8(8):e2980.

    Article  PubMed  PubMed Central  Google Scholar 

  45. Thongtan T, Cheepsunthorn P, Chaiworakul V, Rattanarungsan C, Wikan N, Smith DR. Highly permissive infection of microglial cells by Japanese encephalitis virus: a possible role as a viral reservoir. Microbes Infect. 2010;12(1):37–45.

    Article  CAS  PubMed  Google Scholar 

  46. Lannes N, Neuhaus V, Scolari B, Kharoubi-Hess S, Walch M, Summerfield A, Filgueira L. Interactions of human microglia cells with Japanese encephalitis virus. Virol J. 2017;14(1):8.

    Article  PubMed  PubMed Central  Google Scholar 

  47. Wang L, Fu S, Zhang H, Ye X, Yu D, Deng Z, Yuan J, Zhai Y, Li M, Lv Z, et al. Identification and isolation of Genotype-I Japanese encephalitis virus from encephalitis patients. Virol J. 2010;7:345.

    Article  PubMed  PubMed Central  Google Scholar 

  48. Desai A, Shankar SK, Ravi V, Chandramuki A, Gourie-Devi M. Japanese encephalitis virus antigen in the human brain and its topographic distribution. Acta Neuropathol. 1995;89(4):368–73.

    Article  CAS  PubMed  Google Scholar 

  49. German AC, Myint KS, Mai NT, Pomeroy I, Phu NH, Tzartos J, Winter P, Collett J, Farrar J, Barrett A, et al. A preliminary neuropathological study of Japanese encephalitis in humans and a mouse model. Trans R Soc Trop Med Hyg. 2006;100(12):1135–45.

    Article  PubMed  Google Scholar 

  50. Johnson RT, Burke DS, Elwell M, Leake CJ, Nisalak A, Hoke CH, Lorsomrudee W. Japanese encephalitis: immunocytochemical studies of viral antigen and inflammatory cells in fatal cases. Ann Neurol. 1985;18(5):567–73.

    Article  CAS  PubMed  Google Scholar 

  51. Tiroumourougane SV, Raghava P, Srinivasan S. Japanese viral encephalitis. Postgrad Med J. 2002;78(918):205–15.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  52. Kimura-Kuroda J, Ichikawa M, Ogata A, Nagashima K, Yasui K. Specific tropism of Japanese encephalitis virus for developing neurons in primary rat brain culture. Arch Virol. 1993;130(3–4):477–84.

    Article  CAS  PubMed  Google Scholar 

  53. Das S, Basu A. Japanese encephalitis virus infects neural progenitor cells and decreases their proliferation. J Neurochem. 2008;106(4):1624–36.

    CAS  PubMed  Google Scholar 

  54. Ghoshal A, Das S, Ghosh S, Mishra MK, Sharma V, Koli P, Sen E, Basu A. Proinflammatory mediators released by activated microglia induces neuronal death in Japanese encephalitis. Glia. 2007;55(5):483–96.

    Article  PubMed  Google Scholar 

  55. Nazmi A, Dutta K, Das S, Basu A. Japanese encephalitis virus-infected macrophages induce neuronal death. J NeuroImmune Pharmacol. 2011;6(3):420–33.

    Article  PubMed  Google Scholar 

  56. Tiwari S, Singh RK, Tiwari R, Dhole TN. Japanese encephalitis: a review of the Indian perspective. Braz J Infect Dis. 2012;16(6):564–73.

    Article  PubMed  Google Scholar 

  57. Miyake M. The Pathology of Japanese Encephalitis. A Review. Bull World Health Organ. 1964;30:153–60.

    CAS  PubMed  PubMed Central  Google Scholar 

  58. Zimmerman MD, Scott RM, Vaughn DW, Rajbhandari S, Nisalak A, Shrestha MP. Short report: an outbreak of Japanese encephalitis in Kathmandu, Nepal. Am J Trop Med Hyg. 1997;57(3):283–4.

    Article  CAS  PubMed  Google Scholar 

  59. Ricklin ME, Garcia-Nicolas O, Brechbuhl D, Python S, Zumkehr B, Posthaus H, Oevermann A, Summerfield A. Japanese encephalitis virus tropism in experimentally infected pigs. Vet Res. 2016;47(1):34.

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  60. Ricklin ME, Garcia-Nicolas O, Brechbuhl D, Python S, Zumkehr B, Nougairede A, Charrel RN, Posthaus H, Oevermann A, Summerfield A. Vector-free transmission and persistence of Japanese encephalitis virus in pigs. Nat Commun. 2016;7:10832.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  61. Chaturvedi UC, Mathur A, Tandon P, Natu SM, Rajvanshi S, Tandon HO. Variable effect on peripheral blood leucocytes during JE virus infection of man. Clin Exp Immunol. 1979;38(3):492–8.

    CAS  PubMed  PubMed Central  Google Scholar 

  62. Kim JH, Hossain FM, Patil AM, Choi JY, Kim SB, Uyangaa E, Park SY, Lee JH, Kim B, Kim K, et al. Ablation of CD11c(hi) dendritic cells exacerbates Japanese encephalitis by regulating blood-brain barrier permeability and altering tight junction/adhesion molecules. Comp Immunol Microbiol Infect Dis. 2016;48:22–32.

    Article  PubMed  Google Scholar 

  63. Singh A, Kulshreshtha R, Mathur A. Secretion of the chemokine interleukin-8 during Japanese encephalitis virus infection. J Med Microbiol. 2000;49(7):607–12.

    Article  CAS  PubMed  Google Scholar 

  64. Dutta K, Kumawat KL, Nazmi A, Mishra MK, Basu A. Minocycline differentially modulates viral infection and persistence in an experimental model of Japanese encephalitis. J NeuroImmune Pharmacol. 2010;5(4):553–65.

    Article  PubMed  Google Scholar 

  65. Larena M, Regner M, Lobigs M. The chemokine receptor CCR5, a therapeutic target for HIV/AIDS antagonists, is critical for recovery in a mouse model of Japanese encephalitis. PLoS One. 2012;7(9):e44834.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  66. Larena M, Regner M, Lobigs M. Cytolytic effector pathways and IFN-gamma help protect against Japanese encephalitis. Eur J Immunol. 2013;43(7):1789–98.

    Article  CAS  PubMed  Google Scholar 

  67. Swarup V, Ghosh J, Das S, Basu A. Tumor necrosis factor receptor-associated death domain mediated neuronal death contributes to the glial activation and subsequent neuroinflammation in Japanese encephalitis. Neurochem Int. 2008;52(7):1310–21.

    Article  CAS  PubMed  Google Scholar 

  68. Kaushik DK, Gupta M, Kumawat KL, Basu A. NLRP3 inflammasome: key mediator of neuroinflammation in murine Japanese encephalitis. PLoS One. 2012;7(2):e32270.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  69. Chen CJ, Ou YC, Chang CY, Pan HC, Liao SL, Chen SY, Raung SL, Lai CY. Glutamate released by Japanese encephalitis virus-infected microglia involves TNF-alpha signaling and contributes to neuronal death. Glia. 2012;60(3):487–501.

    Article  PubMed  Google Scholar 

  70. Chen CJ, Chen JH, Chen SY, Liao SL, Raung SL. Upregulation of RANTES gene expression in neuroglia by Japanese encephalitis virus infection. J Virol. 2004;78(22):12107–19.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  71. Shwetank, Date OS, Kim KS, Manjunath R. Infection of human endothelial cells by Japanese encephalitis virus: increased expression and release of soluble HLA-E. PLoS One. 2013;8(11):e79197.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  72. Bhowmick S, Duseja R, Das S, Appaiahgiri MB, Vrati S, Basu A. Induction of IP-10 (CXCL10) in astrocytes following Japanese encephalitis. Neurosci Lett. 2007;414(1):45–50.

    Article  CAS  PubMed  Google Scholar 

  73. Nazmi A, Dutta K, Basu A. RIG-I mediates innate immune response in mouse neurons following Japanese encephalitis virus infection. PLoS One. 2011;6(6):e21761.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  74. Das S, Ghosh D, Basu A. Japanese encephalitis virus induce immuno-competency in neural stem/progenitor cells. PLoS One. 2009;4(12):e8134.

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  75. Nazmi A, Mukherjee S, Kundu K, Dutta K, Mahadevan A, Shankar SK, Basu A. TLR7 is a key regulator of innate immunity against Japanese encephalitis virus infection. Neurobiol Dis. 2014;69:235–47.

    Article  CAS  PubMed  Google Scholar 

  76. Yang Y, Ye J, Yang X, Jiang R, Chen H, Cao S. Japanese encephalitis virus infection induces changes of mRNA profile of mouse spleen and brain. Virol J. 2011;8:80.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  77. Winter PM, Dung NM, Loan HT, Kneen R, Wills B, Thu le T, House D, White NJ, Farrar JJ, Hart CA, et al. Proinflammatory cytokines and chemokines in humans with Japanese encephalitis. J Infect Dis. 2004;190(9):1618–26.

    Article  CAS  PubMed  Google Scholar 

  78. Zhang JS, Zhao QM, Zuo SQ, Jia N, Guo XF. Cytokine and chemokine responses to Japanese encephalitis live attenuated vaccine in a human population. Int J Infect Dis. 2012;16(4):e285–8.

    Article  CAS  PubMed  Google Scholar 

  79. Kalita J, Srivastava R, Mishra MK, Basu A, Misra UK. Cytokines and chemokines in viral encephalitis: a clinicoradiological correlation. Neurosci Lett. 2010;473(1):48–51.

    Article  CAS  PubMed  Google Scholar 

  80. Srivastava R, Kalita J, Khan MY, Misra UK. Status of proinflammatory and anti-inflammatory cytokines in different brain regions of a rat model of Japanese encephalitis. Inflamm Res. 2012;61(4):381–9.

    Article  CAS  PubMed  Google Scholar 

  81. Kim JH, Patil AM, Choi JY, Kim SB, Uyangaa E, Hossain FM, Park SY, Lee JH, Eo SK. CCR5 ameliorates Japanese encephalitis via dictating the equilibrium of regulatory CD4(+)Foxp3(+) T and IL-17(+)CD4(+) Th17 cells. J Neuroinflammation. 2016;13(1):223.

    Article  PubMed  PubMed Central  Google Scholar 

  82. Saxena V, Mathur A, Krishnani N, Dhole TN. An insufficient anti-inflammatory cytokine response in mouse brain is associated with increased tissue pathology and viral load during Japanese encephalitis virus infection. Arch Virol. 2008;153(2):283–92.

    Article  CAS  PubMed  Google Scholar 

  83. Ravi V, Parida S, Desai A, Chandramuki A, Gourie-Devi M, Grau GE. Correlation of tumor necrosis factor levels in the serum and cerebrospinal fluid with clinical outcome in Japanese encephalitis patients. J Med Virol. 1997;51(2):132–6.

    Article  CAS  PubMed  Google Scholar 

  84. Burke DS, Morill JC. Levels of interferon in the plasma and cerebrospinal fluid of patients with acute Japanese encephalitis. J Infect Dis. 1987;155(4):797–9.

    Article  CAS  PubMed  Google Scholar 

  85. Swarup V, Das S, Ghosh S, Basu A. Tumor necrosis factor receptor-1-induced neuronal death by TRADD contributes to the pathogenesis of Japanese encephalitis. J Neurochem. 2007;103(2):771–83.

    Article  CAS  PubMed  Google Scholar 

  86. Fadnis PR, Ravi V, Desai A, Turtle L, Solomon T. Innate immune mechanisms in Japanese encephalitis virus infection: effect on transcription of pattern recognition receptors in mouse neuronal cells and brain tissue. Viral Immunol. 2013;26(6):366–77.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  87. Jiang R, Ye J, Zhu B, Song Y, Chen H, Cao S. Roles of TLR3 and RIG-I in mediating the inflammatory response in mouse microglia following Japanese encephalitis virus infection. J Immunol Res. 2014;2014:787023.

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  88. Chen CJ, Ou YC, Chang CY, Pan HC, Lin SY, Liao SL, Raung SL, Chen SY, Chang CJ. Src signaling involvement in Japanese encephalitis virus-induced cytokine production in microglia. Neurochem Int. 2011;58(8):924–33.

    Article  CAS  PubMed  Google Scholar 

  89. Raung SL, Chen SY, Liao SL, Chen JH, Chen CJ. Japanese encephalitis virus infection stimulates Src tyrosine kinase in neuron/glia. Neurosci Lett. 2007;419(3):263–8.

    Article  CAS  PubMed  Google Scholar 

  90. Jin R, Zhu W, Cao S, Chen R, Jin H, Liu Y, Wang S, Wang W, Xiao G. Japanese encephalitis virus activates autophagy as a viral immune evasion strategy. PLoS One. 2013;8(1):e52909.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  91. Manocha GD, Mishra R, Sharma N, Kumawat KL, Basu A, Singh SK. Regulatory role of TRIM21 in the type-I interferon pathway in Japanese encephalitis virus-infected human microglial cells. J Neuroinflammation. 2014;11:24.

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  92. Adhya D, Dutta K, Kundu K, Basu A. Histone deacetylase inhibition by Japanese encephalitis virus in monocyte/macrophages: a novel viral immune evasion strategy. Immunobiology. 2013;218(10):1235–47.

    Article  CAS  PubMed  Google Scholar 

  93. Ashraf U, Zhu B, Ye J, Wan S, Nie Y, Chen Z, Cui M, Wang C, Duan X, Zhang H, et al. MicroRNA-19b-3p Modulates Japanese Encephalitis Virus-Mediated Inflammation via Targeting RNF11. J Virol. 2016;90(9):4780–95.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  94. Thounaojam MC, Kundu K, Kaushik DK, Swaroop S, Mahadevan A, Shankar SK, Basu A. MicroRNA 155 regulates Japanese encephalitis virus-induced inflammatory response by targeting Src homology 2-containing inositol phosphatase 1. J Virol. 2014;88(9):4798–810.

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  95. Kumari B, Jain P, Das S, Ghosal S, Hazra B, Trivedi AC, Basu A, Chakrabarti J, Vrati S, Banerjee A. Dynamic changes in global microRNAome and transcriptome reveal complex miRNA-mRNA regulated host response to Japanese Encephalitis Virus in microglial cells. Sci Rep. 2016;6:20263.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  96. Zhu B, Ye J, Nie Y, Ashraf U, Zohaib A, Duan X, Fu ZF, Song Y, Chen H, Cao S. MicroRNA-15b Modulates Japanese Encephalitis Virus-Mediated Inflammation via Targeting RNF125. J Immunol. 2015;195(5):2251–62.

    Article  CAS  PubMed  Google Scholar 

  97. Li W, Cheng P, Nie S, Cui W. miR-370 mimic inhibits replication of Japanese encephalitis virus in glioblastoma cells. Neuropsychiatr Dis Treat. 2016;12:2411–7.

    Article  PubMed  PubMed Central  Google Scholar 

  98. Thounaojam MC, Kaushik DK, Kundu K, Basu A. MicroRNA-29b modulates Japanese encephalitis virus-induced microglia activation by targeting tumor necrosis factor alpha-induced protein 3. J Neurochem. 2014;129(1):143–54.

    Article  CAS  PubMed  Google Scholar 

  99. Sharma N, Verma R, Kumawat KL, Basu A, Singh SK. miR-146a suppresses cellular immune response during Japanese encephalitis virus JaOArS982 strain infection in human microglial cells. J Neuroinflammation. 2015;12:30.

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  100. Deng M, Du G, Zhao J, Du X. miR-146a negatively regulates the induction of proinflammatory cytokines in response to Japanese encephalitis virus infection in microglial cells. Arch Virol. 2017;162(6):1495–1505.

    Article  CAS  PubMed  Google Scholar 

  101. Sharma N, Kumawat KL, Rastogi M, Basu A, Singh SK. Japanese encephalitis virus exploits the microRNA-432 to regulate the expression of Suppressor of Cytokine Signaling (SOCS) 5. Sci Rep. 2016;6:27685.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  102. Hazra B, Kumawat KL, Basu A. The host microRNA miR-301a blocks the IRF1-mediated neuronal innate immune response to Japanese encephalitis virus infection. Sci Signal. 2017;10(466):eaaf5185.

    Article  PubMed  Google Scholar 

  103. Pareek S, Roy S, Kumari B, Jain P, Banerjee A, Vrati S. MiR-155 induction in microglial cells suppresses Japanese encephalitis virus replication and negatively modulates innate immune responses. J Neuroinflammation. 2014;11:97.

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  104. Swarup V, Ghosh J, Mishra MK, Basu A. Novel strategy for treatment of Japanese encephalitis using arctigenin, a plant lignan. J Antimicrob Chemother. 2008;61(3):679–88.

    Article  CAS  PubMed  Google Scholar 

  105. Mishra MK, Basu A. Minocycline neuroprotects, reduces microglial activation, inhibits caspase 3 induction, and viral replication following Japanese encephalitis. J Neurochem. 2008;105(5):1582–95.

    Article  CAS  PubMed  Google Scholar 

  106. Raung SL, Chen SY, Liao SL, Chen JH, Chen CJ. Tyrosine kinase inhibitors attenuate Japanese encephalitis virus-induced neurotoxicity. Biochem Biophys Res Commun. 2005;327(2):399–406.

    Article  CAS  PubMed  Google Scholar 

  107. Ghosh J, Swarup V, Saxena A, Das S, Hazra A, Paira P, Banerjee S, Mondal NB, Basu A. Therapeutic effect of a novel anilidoquinoline derivative, 2-(2-methyl-quinoline-4ylamino)-N-(2-chlorophenyl)-acetamide, in Japanese encephalitis: correlation with in vitro neuroprotection. Int J Antimicrob Agents. 2008;32(4):349–54.

    Article  CAS  PubMed  Google Scholar 

  108. Nazmi A, Dutta K, Basu A. Antiviral and neuroprotective role of octaguanidinium dendrimer-conjugated morpholino oligomers in Japanese encephalitis. PLoS Negl Trop Dis. 2010;4(11):e892.

    Article  PubMed  PubMed Central  CAS  Google Scholar 

Download references

Acknowledgements

Not applicable.

Funding

The present work was supported by Fonds de recherche of the University of Fribourg (to NL) and the Stiftung Forschung 3R (to LF).

Availability of data and materials

Not applicable.

Author information

Authors and Affiliations

  1. Unit of Anatomy, Department of Medicine, University of Fribourg, Route Albert-Gockel 1, Fribourg, Switzerland

    Nils Lannes & Luis Filgueira

  2. Institute of Virology and Immunology, Sensemattstrasse 293, Mittelhäusern, Switzerland

    Artur Summerfield

  3. Department of Infectious Diseases and Pathobiology, Vetsuisse Faculty, University of Bern, Langassstrasse 122, Bern, Switzerland

    Artur Summerfield

Authors
  1. Nils Lannes
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Artur Summerfield
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Luis Filgueira
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

NL, AS and LF wrote and revised the manuscript. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Nils Lannes.

Ethics declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Lannes, N., Summerfield, A. & Filgueira, L. Regulation of inflammation in Japanese encephalitis. J Neuroinflammation 14, 158 (2017). https://doi.org/10.1186/s12974-017-0931-5

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1186/s12974-017-0931-5

Keywords

  • Infiltrated Brain
  • Inflammatory Monocytes
  • Neuroinvasion
  • NOD-like Receptor Family Pyrin Domain Containing 3 (NLRP3)
  • C-type Lectin Domain Family 7 Member A (CLEC5A)

Journal of Neuroinflammation

ISSN: 1742-2094