Acute Rift Valley fever virus infection induces inflammatory cytokines and cell death in ex vivo rat brain slice culture.

Rift Valley fever virus (RVFV) is an emerging arboviral disease with pandemic potential. While infection is often self-limiting, a subset of individuals may develop late-onset encephalitis, accounting for up to 20 % of severe cases. Importantly, individuals displaying neurologic disease have up to a 53 % case fatality rate, yet the neuropathogenesis of RVFV infection remains understudied. In this study, we evaluated whether ex vivo postnatal rat brain slice cultures (BSCs) could be used to evaluate RVFV infection in the central nervous system. BSCs mounted an inflammatory response after slicing, which resolved over time, and they were viable in culture for at least 12 days. Infection of rat BSCs with pathogenic RVFV strain ZH501 induced tissue damage and apoptosis over 48 h. Viral replication in BSCs reached up to 1×107 p.f.u. equivalents/ml, depending on inoculation dose. Confocal immunofluorescent microscopy of cleared slices confirmed direct infection of neurons as well as activation of microglia and astrocytes. Further, RVFV-infected rat BSCs produced antiviral cytokines and chemokines, including MCP-1 and GRO/KC. This study demonstrates that rat BSCs support replication of RVFV for ex vivo studies of neuropathogenesis. This allows for continued and complementary investigation into RVFV infection in an ex vivo postnatal brain slice culture format.

Understanding the link between neurotropic viruses, BBB permeability, and MS pathogenesis.

Neurotropic viruses can infiltrate the CNS by crossing the blood-brain barrier (BBB) through various mechanisms including paracellular, transcellular, and "Trojan horse" mechanisms during leukocyte diapedesis. These viruses belong to several families, including retroviruses; human immunodeficiency virus type 1 (HIV-1), flaviviruses; Japanese encephalitis (JEV); and herpesviruses; herpes simplex virus type 1 (HSV-1), Epstein-Barr virus (EBV), and mouse adenovirus 1 (MAV-1). For entering the brain, viral proteins act upon the tight junctions (TJs) between the brain microvascular endothelial cells (BMECs). For instance, HIV-1 proteins, such as glycoprotein 120, Nef, Vpr, and Tat, disrupt the BBB and generate a neurotoxic effect. Recombinant-Tat triggers amendments in the BBB by decreasing expression of the TJ proteins such as claudin-1, claudin-5, and zona occludens-1 (ZO-1). Thus, the breaching of BBB has been reported in myriad of neurological diseases including multiple sclerosis (MS). Neurotropic viruses also exhibit molecular mimicry with several myelin sheath proteins, i.e., antibodies against EBV nuclear antigen 1 (EBNA1) aa411-426 cross-react with MBP and EBNA1 aa385-420 was found to be associated with MS risk haplotype HLA-DRB1*150. Notably, myelin protein epitopes (PLP139-151, MOG35-55, and MBP87-99) are being used to generate model systems for MS such as experimental autoimmune encephalomyelitis (EAE) to understand the disease mechanism and therapeutics. Viruses like Theiler's murine encephalomyelitis virus (TMEV) are also commonly used to generate EAE. Altogether, this review provide insights into the viruses' association with BBB leakiness and MS along with possible mechanistic details which could potentially use for therapeutics.

RVG Peptide-Functionalized Favipiravir Nanoparticle Delivery System Facilitates Antiviral Therapy of Neurotropic Virus Infection in a Mouse Model.

Neurotropic viruses severely damage the central nervous system (CNS) and human health. Common neurotropic viruses include rabies virus (RABV), Zika virus, and poliovirus. When treating neurotropic virus infection, obstruction of the blood-brain barrier (BBB) reduces the efficiency of drug delivery to the CNS. An efficient intracerebral delivery system can significantly increase intracerebral delivery efficiency and facilitate antiviral therapy. In this study, a rabies virus glycopeptide (RVG) functionalized mesoporous silica nanoparticle (MSN) packaging favipiravir (T-705) was developed to generate T-705@MSN-RVG. It was further evaluated for drug delivery and antiviral treatment in a VSV-infected mouse model. The RVG, a polypeptide consisting of 29 amino acids, was conjugated on the nanoparticle to enhance CNS delivery. The T-705@MSN-RVG caused a significant decrease in virus titers and virus proliferation without inducing substantial cell damage in vitro. By releasing T-705, the nanoparticle promoted viral inhibition in the brain during infection. At 21 days post-infection (dpi), a significantly enhanced survival ratio (77%) was observed in the group inoculated with nanoparticle compared with the non-treated group (23%). The viral RNA levels were also decreased in the therapy group at 4 and 6 dpi compared with that of the control group. The T-705@MSN-RVG could be considered a promising system for CNS delivery for treating neurotropic virus infection.

Severe acute respiratory syndrome coronavirus 2 infection reaches the human nervous system: How?

Without protective and/or therapeutic agents the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection known as coronavirus disease 2019 is quickly spreading worldwide. It has surprising transmissibility potential, since it could infect all ages, gender, and human sectors. It attacks respiratory, gastrointestinal, urinary, hepatic, and endovascular systems and can reach the peripheral nervous system (PNS) and central nervous system (CNS) through known and unknown mechanisms. The reports on the neurological manifestations and complications of the SARS-CoV-2 infection are increasing exponentially. Herein, we enumerate seven candidate routes, which the mature or immature SARS-CoV-2 components could use to reach the CNS and PNS, utilizing the within-body cross talk between organs. The majority of SARS-CoV-2-infected patients suffer from some neurological manifestations (e.g., confusion, anosmia, and ageusia). It seems that although the mature virus did not reach the CNS or PNS of the majority of patients, its unassembled components and/or the accompanying immune-mediated responses may be responsible for the observed neurological symptoms. The viral particles and/or its components have been specifically documented in endothelial cells of lung, kidney, skin, and CNS. This means that the blood-endothelial barrier may be considered as the main route for SARS-CoV-2 entry into the nervous system, with the barrier disruption being more logical than barrier permeability, as evidenced by postmortem analyses.

Cerebral organoids and their potential for studies of brain diseases in domestic animals.

The brain is a complex organ and any model for studying it in its normal and pathological aspects becomes a tool of choice for neuroscientists. The mastering and dissemination of protocols allowing brain organoids development have paved the way for a whole range of new studies in the field of brain development, modeling of neurodegenerative or neurodevelopmental diseases, understanding tumors as well as infectious diseases that affect the brain. While studies are so far limited to the use of human cerebral organoids, there is a growing interest in having similar models in other species. This review presents what is currently developed in this field, with a particular focus on the potential of cerebral organoids for studying neuro-infectious diseases in human and domestic animals.

CARD9 Deficiency Increases Hippocampal Injury Following Acute Neurotropic Picornavirus Infection but Does Not Affect Pathogen Elimination.

Neurotropic viruses target the brain and contribute to neurologic diseases. Caspase recruitment domain containing family member 9 (CARD9) controls protective immunity in a variety of infectious disorders. To investigate the effect of CARD9 in neurotropic virus infection, CARD9-/- and corresponding C57BL/6 wild-type control mice were infected with Theiler's murine encephalomyelitis virus (TMEV). Brain tissue was analyzed by histology, immunohistochemistry and molecular analyses, and spleens by flow cytometry. To determine the impact of CARD9 deficiency on T cell responses in vitro, antigen presentation assays were utilized. Genetic ablation of CARD9 enhanced early pro-inflammatory cytokine responses and accelerated infiltration of T and B cells in the brain, together with a transient increase in TMEV-infected cells in the hippocampus. CARD9-/- mice showed an increased loss of neuronal nuclear protein+ mature neurons and doublecortin+ neuronal precursor cells and an increase in ß-amyloid precursor protein+ damaged axons in the hippocampus. No effect of CARD9 deficiency was found on the initiation of CD8+ T cell responses by flow cytometry and co-culture experiments using virus-exposed dendritic cells or microglia-enriched glial cell mixtures, respectively. The present study indicates that CARD9 is dispensable for the initiation of early antiviral responses and TMEV elimination but may contribute to the modulation of neuroinflammation, thereby reducing hippocampal injury following neurotropic virus infection.

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.

Porcine Hemagglutinating Encephalomyelitis Virus Activation of the Integrin α5ß1-FAK-Cofilin Pathway Causes Cytoskeletal Rearrangement To Promote Its Invasion of N2a Cells.

Porcine hemagglutinating encephalomyelitis virus (PHEV) is a highly neurotropic virus that causes diffuse neuronal infection with neurological damage and high mortality. Virus-induced cytoskeletal dynamics are thought to be closely related to this type of nerve damage. Currently, the regulation pattern of the actin cytoskeleton and its molecular mechanism remain unclear when PHEV enters the host cells. Here, we demonstrate that entry of PHEV into N2a cells induces a biphasic remodeling of the actin cytoskeleton and a dynamic change in cofilin activity. Viral entry is affected by the disruption of actin kinetics or alteration of cofilin activity. PHEV binds to integrin α5ß1 and then initiates the integrin α5ß1-FAK signaling pathway, leading to virus-induced early cofilin phosphorylation and F-actin polymerization. Additionally, Ras-related C3 botulinum toxin substrate 1 (Rac1), cell division cycle 42 (Cdc42), and downstream regulatory gene p21-activated protein kinases (PAKs) are recruited as downstream mediators of PHEV-induced dynamic changes of the cofilin activity pathway. In conclusion, we demonstrate that PHEV utilizes the integrin α5ß1-FAK-Rac1/Cdc42-PAK-LIMK-cofilin pathway to cause an actin cytoskeletal rearrangement to promote its own invasion, providing theoretical support for the development of PHEV pathogenic mechanisms and new antiviral targets.IMPORTANCE PHEV, a member of the Coronaviridae family, is a typical neurotropic virus that primarily affects the nervous system of piglets to produce typical neurological symptoms. However, the mechanism of nerve damage caused by the virus has not been fully elucidated. Actin is an important component of the cytoskeleton of eukaryotic cells and serves as the first obstacle to the entry of pathogens into host cells. Additionally, the morphological structure and function of nerve cells depend on the dynamic regulation of the actin skeleton. Therefore, exploring the mechanism of neuronal injury induced by PHEV from the perspective of the actin cytoskeleton not only helps elucidate the pathogenesis of PHEV but also provides a theoretical basis for the search for new antiviral targets. This is the first report to define a mechanistic link between alterations in signaling from cytoskeleton pathways and the mechanism of PHEV invading nerve cells.

Microglia control the spread of neurotropic virus infection via P2Y12 signalling and recruit monocytes through P2Y12-independent mechanisms.

Neurotropic herpesviruses can establish lifelong infection in humans and contribute to severe diseases including encephalitis and neurodegeneration. However, the mechanisms through which the brain's immune system recognizes and controls viral infections propagating across synaptically linked neuronal circuits have remained unclear. Using a well-established model of alphaherpesvirus infection that reaches the brain exclusively via retrograde transsynaptic spread from the periphery, and in vivo two-photon imaging combined with high resolution microscopy, we show that microglia are recruited to and isolate infected neurons within hours. Selective elimination of microglia results in a marked increase in the spread of infection and egress of viral particles into the brain parenchyma, which are associated with diverse neurological symptoms. Microglia recruitment and clearance of infected cells require cell-autonomous P2Y12 signalling in microglia, triggered by nucleotides released from affected neurons. In turn, we identify microglia as key contributors to monocyte recruitment into the inflamed brain, which process is largely independent of P2Y12. P2Y12-positive microglia are also recruited to infected neurons in the human brain during viral encephalitis and both microglial responses and leukocyte numbers correlate with the severity of infection. Thus, our data identify a key role for microglial P2Y12 in defence against neurotropic viruses, whilst P2Y12-independent actions of microglia may contribute to neuroinflammation by facilitating monocyte recruitment to the sites of infection.

The spectrum of aseptic central nervous system infections in southern Germany - demographic, clinical and laboratory findings.

BACKGROUND AND PURPOSE: Aseptic infections of the central nervous system (CNS) are frequently observed in Germany. However, no study has systematically addressed the spectrum of aseptic CNS infections in Germany. METHODS: Data on 191 adult patients diagnosed from January 2007 to December 2014 with aseptic meningitis or encephalitis/meningoencephalitis at our hospital were collected by chart review and analyzed for demographic, clinical and laboratory findings. Patients were stratified according to the causative virus and findings were compared between groups. RESULTS: In our cohort, meningitis was caused in 36% by enterovirus (EV), 15% by herpes simplex virus (HSV), 12% by varicella zoster virus (VZV) and 5% by tick borne encephalitis (TBE). Encephalitis/meningoencephalitis was caused in 13% by HSV, 13% by VZV, and three out of 11 tested patients were positive for TBE. The highest incidence of EV infections was between 25 and 35 years and of HSV infections between 30 and 60 years. VZV infections had a bimodal distribution peaking below 30 and above 70 years. VZV and EV infections were more frequently observed during summer, whereas HSV infections showed no seasonal preference. Inflammatory changes in cerebrospinal fluid (CSF) were highest in HSV and lowest in EV infections. CONCLUSIONS: Polymerase chain reaction tests for HSV, VZV and EV in CSF and TBE serology determined the causative virus in over 60% of tested patients. The age of affected patients, seasonal distribution, disease course and inflammatory changes in CSF differ between groups of patients affected by the most common viral infections.

Serological evidence of increased susceptibility to varicella-zoster virus reactivation or reinfection in natalizumab-treated patients with multiple sclerosis.

BACKGROUND: Serious adverse drug reactions of disease-modifying drugs in multiple sclerosis (MS) therapy may include enhanced susceptibility to reactivation of neurotropic herpes viruses like varicella-zoster virus (VZV) and the John Cunningham (JC) polyomavirus. OBJECTIVE: Because symptomatic reactivation of these viruses are rare events, we determined the incidence of rises in anti-VZV IgG antibody levels as a potential marker for enhanced susceptibility to subclinical and symptomatic reactivation of neurotropic viruses. METHODS: Anti-VZV IgG levels were measured in paired serum samples taken 6-8 months apart from natalizumab-treated MS patients, healthy blood donors and human immunodeficiency virus (HIV) infected patients. RESULTS: The incidence of significant rises in anti-VZV IgG levels in natalizumab-treated MS patients was 4.26 per 100 person-years, which was significantly higher than in healthy blood donors. Retrospective evaluation of the available medical records of patients with rises of anti-VZV IgG levels did not reveal herpes zoster (i.e. shingles) manifestations. CONCLUSIONS: The increased incidence of significant rises of anti-VZV IgG levels in natalizumab-treated MS patients might indicate an association of natalizumab treatment of MS with an elevated risk of a subclinical VZV reactivation and/or reinfection events. Whether this is predictive of an increased risk of herpes zoster or even symptomatic reactivation of other neurotropic viruses remains to be determined in larger prospective studies.

Organotypic culture of human brain explants as a preclinical model for AI-driven antiviral studies.

Viral neuroinfections represent a major health burden for which the development of antivirals is needed. Antiviral compounds that target the consequences of a brain infection (symptomatic treatment) rather than the cause (direct-acting antivirals) constitute a promising mitigation strategy that requires to be investigated in relevant models. However, physiological surrogates mimicking an adult human cortex are lacking, limiting our understanding of the mechanisms associated with viro-induced neurological disorders. Here, we optimized the Organotypic culture of Post-mortem Adult human cortical Brain explants (OPAB) as a preclinical platform for Artificial Intelligence (AI)-driven antiviral studies. OPAB shows robust viability over weeks, well-preserved 3D cytoarchitecture, viral permissiveness, and spontaneous local field potential (LFP). Using LFP as a surrogate for neurohealth, we developed a machine learning framework to predict with high confidence the infection status of OPAB. As a proof-of-concept, we showed that antiviral-treated OPAB could partially restore LFP-based electrical activity of infected OPAB in a donor-dependent manner. Together, we propose OPAB as a physiologically relevant and versatile model to study neuroinfections and beyond, providing a platform for preclinical drug discovery.

Engagement of AKT and ERK signaling pathways facilitates infection of human neuronal cells with West Nile virus.

West Nile virus (WNV) is an important neurotropic virus that accounts for the emergence of human arboviral encephalitis and meningitis. The interaction of WNV with signaling pathways plays a key role in controlling WNV infection. We have investigated the roles of the AKT and ERK pathways in supporting WNV propagation and modulating the inflammatory response following WNV infection. WNV established a productive infection in neuronal cell lines originated from human and mouse. Expression of IL-11 and TNF-α was markedly up-regulated in the infected human neuronal cells, indicating elicitation of inflammation response upon WNV infection. WNV incubation rapidly activated signaling cascades of AKT (AKT-S6-4E-BP1) and ERK (MEK-ERK-p90RSK) pathways. Treatment with AKT inhibitor MK-2206 or MEK inhibitor U0126 abrogated WNV-induced AKT or ERK activation. Strong activation of AKT and ERK signaling pathways could be detectable at 24 h after WNV infection, while such activation was abolished at 48 h post infection. U0126 treatment or knockdown of ERK expression significantly increased WNV RNA levels and viral titers and efficiently decreased IL-11 production induced by WNV, suggesting the involvement of ERK pathway in WNV propagation and IL-11 induction. MK-2206 treatment enhanced WNV RNA replication accompanied with a moderate decrease in IL-11 production. These results demonstrate that engagement of AKT and ERK signaling pathways facilitates viral infection and may be implicated in WNV pathogenesis.

Post-Viral Longitudinally Extensive Transverse Myelitis: A Case Report.

Longitudinally extensive transverse myelitis is a rare neurological manifestation caused by dengue infection. Here, we describe the uncommon presentation of a 24-year-old male with fever and maculopapular rash followed by flaccid quadriparesis with acute urinary retention. Magnetic resonance imaging of the whole spine with contrast revealed a long-segment ill-defined hyperintense signal noted in the cord. The patient was managed conservatively with intravenous steroids and later intravenous immunoglobulins. The patient is on regular follow-up and doing well. Currently, the patient is on tablet prednisolone with a tapering dose.

3D Spheroid and Organoid Models to Study Neuroinfection of RNA Viruses.

Three-dimensional culture models of the brain enable the study of neuroinfection in the context of a complex interconnected cell matrix. Depending on the differentiation status of the neural cells, two models exist: 3D spheroids also called neurospheres and cerebral organoids. Here, we describe the preparation of 3D spheroids and cerebral organoids and give an outlook on their usage to study Rift Valley fever virus and other neurotropic viruses.

Neurotropic virus infection and neurodegenerative diseases: Potential roles of autophagy pathway.

Neurodegenerative diseases (NDs) constitute a group of disorders characterized by the progressive deterioration of nervous system functionality. Currently, the precise etiological factors responsible for NDs remain incompletely elucidated, although it is probable that a combination of aging, genetic predisposition, and environmental stressors participate in this process. Accumulating evidence indicates that viral infections, especially neurotropic viruses, can contribute to the onset and progression of NDs. In this review, emerging evidence supporting the association between viral infection and NDs is summarized, and how the autophagy pathway mediated by viral infection can cause pathological aggregation of cellular proteins associated with various NDs is discussed. Furthermore, autophagy-related genes (ARGs) involved in Herpes simplex virus (HSV-1) infection and NDs are analyzed, and whether these genes could link HSV-1 infection to NDs is discussed. Elucidating the mechanisms underlying NDs is critical for developing targeted therapeutic approaches that prevent the onset and slow the progression of NDs.

Cell Intrinsic Determinants of Alpha Herpesvirus Latency and Pathogenesis in the Nervous System.

Alpha herpesvirus infections (α-HVs) are widespread, affecting more than 70% of the adult human population. Typically, the infections start in the mucosal epithelia, from which the viral particles invade the axons of the peripheral nervous system. In the nuclei of the peripheral ganglia, α-HVs establish a lifelong latency and eventually undergo multiple reactivation cycles. Upon reactivation, viral progeny can move into the nerves, back out toward the periphery where they entered the organism, or they can move toward the central nervous system (CNS). This latency-reactivation cycle is remarkably well controlled by the intricate actions of the intrinsic and innate immune responses of the host, and finely counteracted by the viral proteins in an effort to co-exist in the population. If this yin-yang- or Nash-equilibrium-like balance state is broken due to immune suppression or genetic mutations in the host response factors particularly in the CNS, or the presence of other pathogenic stimuli, α-HV reactivations might lead to life-threatening pathologies. In this review, we will summarize the molecular virus-host interactions starting from mucosal epithelia infections leading to the establishment of latency in the PNS and to possible CNS invasion by α-HVs, highlighting the pathologies associated with uncontrolled virus replication in the NS.

Polyomavirus Wakes Up and Chooses Neurovirulence.

JC polyomavirus (JCPyV) is a human-specific polyomavirus that establishes a silent lifelong infection in multiple peripheral organs, predominantly those of the urinary tract, of immunocompetent individuals. In immunocompromised settings, however, JCPyV can infiltrate the central nervous system (CNS), where it causes several encephalopathies of high morbidity and mortality. JCPyV-induced progressive multifocal leukoencephalopathy (PML), a devastating demyelinating brain disease, was an AIDS-defining illness before antiretroviral therapy that has "reemerged" as a complication of immunomodulating and chemotherapeutic agents. No effective anti-polyomavirus therapeutics are currently available. How depressed immune status sets the stage for JCPyV resurgence in the urinary tract, how the virus evades pre-existing antiviral antibodies to become viremic, and where/how it enters the CNS are incompletely understood. Addressing these questions requires a tractable animal model of JCPyV CNS infection. Although no animal model can replicate all aspects of any human disease, mouse polyomavirus (MuPyV) in mice and JCPyV in humans share key features of peripheral and CNS infection and antiviral immunity. In this review, we discuss the evidence suggesting how JCPyV migrates from the periphery to the CNS, innate and adaptive immune responses to polyomavirus infection, and how the MuPyV-mouse model provides insights into the pathogenesis of JCPyV CNS disease.

The brain-specific upregulation of CARD11 in response to avian brain-neurotropic virus infection serves as a potential biomarker.

Avian neurotropic viruses are critical problems in poultry industry causing severe central nervous system (CNS) damage with neuroinvasive and neurovirulence properties. Biomarker of neurotropic viral intracranial invasion is of great application value for the diagnosis, but that of avian neurotropic viruses remains elusive. Previously, we found that chicken caspase recruitment domain family, member 11 (CARD11) was only upregulated in virulent Newcastle disease virus-infected chickens and in chicken primary neuronal cells. In this study, CARD11 was systemically expressed in chickens and pigeons detected by absolute qPCR and immunohistochemical (IHC) assay. After virus challenging, only avian neurotropic viruses (avian encephalomyelitis virus [AEV] and pigeon paramyxovirus type 1 [PPMV-1]) except Marek's disease virus (MDV) can invade brain and cause pathological changes. The relative mRNA expression of CARD11 was brain-upregulated in AEV- or PPMV-1-infected animals, rather than MDV and non-neurotropic viruses (fowl adenovirus serotype 4 [FAdV-4] and infectious bronchitis virus [IBV]). Similarly, the protein expression of CARD11 was only upregulated in the cerebra and cerebella infected by avian brain-neurotropic virus using IHC assay. And there were no correlations between the change level of CARD11 and viral load. Our preliminary data suggested that avian CARD11 may be a potential brain biomarker for avian brain-neurotropic virus invasion.