Virally expressed interleukin-10 ameliorates acute encephalomyelitis and chronic demyelination in coronavirus-infected mice

Neurotropic murine coronavirus mediated demyelination: Factors dampening pathogenesis

Virus infections and autoimmune responses are implicated as primary triggers of demyelinating diseases. Specifically, the association of Epstein-Barr virus (EBV) infection with development of multiple sclerosis (MS) has re-ignited an interest in virus induced autoimmune responses to CNS antigens. Nevertheless, demyelination may also be caused by immune mediated bystander pathology in an attempt to control direct infection in the CNS. Tissue damage as a result of anti-viral responses or low level viral persistence may lead to immune activation manifesting in demyelinating lesions, axonal damage and clinical symptoms. This review focuses on the neurotropic mouse coronavirus induced demyelination model to highlight how immune responses activated during the acute phase pave the way to dampen pathology and promote repair. We specifically discuss the role of immune dampening factors programmed cell death ligand 1 (PD-L1) and interleukin (IL)-10, as well as microglia and triggering receptor expressed on myeloid cells 2 (Trem2), in limiting demyelination independent of viral persistence.

IL-10 suppresses T cell expansion while promoting tissue-resident memory cell formation during SARS-CoV-2 infection in rhesus macaques

The regulation of inflammatory responses and pulmonary disease during SARS-CoV-2 infection is incompletely understood. Here we examine the roles of the prototypic pro- and anti-inflammatory cytokines IFNγ and IL-10 using the rhesus macaque model of mild COVID-19. We find that IFNγ drives the development of 18fluorodeoxyglucose (FDG)-avid lesions in the lungs as measured by PET/CT imaging but is not required for suppression of viral replication. In contrast, IL-10 limits the duration of acute pulmonary lesions, serum markers of inflammation and the magnitude of virus-specific T cell expansion but does not impair viral clearance. We also show that IL-10 induces the subsequent differentiation of virus-specific effector T cells into CD69+CD103+ tissue resident memory cells (Trm) in the airways and maintains Trm cells in nasal mucosal surfaces, highlighting an unexpected role for IL-10 in promoting airway memory T cells during SARS-CoV-2 infection of macaques.

An important call: Suggestion of using IL-10 as therapeutic agent for COVID-19 with ARDS and other complications

The global coronavirus disease 2019 (COVID-19) pandemic has a detrimental impact on public health. COVID-19 usually manifests as pneumonia, which can progress into acute respiratory distress syndrome (ARDS) related to uncontrolled TH17 immune reaction. Currently, there is no effective therapeutic agent to manage COVID-19 with complications. The currently available anti-viral drug remdesivir has an effectiveness of 30% in SARS-CoV-2-induced severe complications. Thus, there is a need to identify effective agents to treat COVID-19 and the associated acute lung injury and other complications. The host immunological pathway against this virus typically involves the THαβ immune response. THαβ immunity is triggered by type 1 interferon and interleukin-27 (IL-27), and the main effector cells of the THαβ immune response are IL10-CD4 T cells, CD8 T cells, NK cells, and IgG1-producing B cells. In particular, IL-10 exerts a potent immunomodulatory or anti-inflammatory effect and is an anti-fibrotic agent for pulmonary fibrosis. Concurrently, IL-10 can ameliorate acute lung injury or ARDS, especially those caused by viruses. Owing to its anti-viral activity and anti-pro-inflammatory effects, in this review, IL-10 is suggested as a possible treatment agent for COVID-19.

The multifaceted nature of IL-10: regulation, role in immunological homeostasis and its relevance to cancer, COVID-19 and post-COVID conditions

Interleukin-10 (IL-10) is a pleiotropic cytokine that has a fundamental role in modulating inflammation and in maintaining cell homeostasis. It primarily acts as an anti-inflammatory cytokine, protecting the body from an uncontrolled immune response, mostly through the Jak1/Tyk2 and STAT3 signaling pathway. On the other hand, IL-10 can also have immunostimulating functions under certain conditions. Given the pivotal role of IL-10 in immune modulation, this cytokine could have relevant implications in pathologies characterized by hyperinflammatory state, such as cancer, or infectious diseases as in the case of COVID-19 and Post-COVID-19 syndrome. Recent evidence proposed IL-10 as a predictor of severity and mortality for patients with acute or post-acute SARS-CoV-2 infection. In this context, IL-10 can act as an endogenous danger signal, released by tissues undergoing damage in an attempt to protect the organism from harmful hyperinflammation. Pharmacological strategies aimed to potentiate or restore IL-10 immunomodulatory action may represent novel promising avenues to counteract cytokine storm arising from hyperinflammation and effectively mitigate severe complications. Natural bioactive compounds, derived from terrestrial or marine photosynthetic organisms and able to increase IL-10 expression, could represent a useful prevention strategy to curb inflammation through IL-10 elevation and will be discussed here. However, the multifaceted nature of IL-10 has to be taken into account in the attempts to modulate its levels.

Olfactory Bulb and Amygdala Gene Expression Changes in Subjects Dying with COVID-19

In this study we conducted RNA sequencing on two brain regions (olfactory bulb and amygdala) from subjects who died from COVID-19 or who died of other causes. We found several-fold more transcriptional changes in the olfactory bulb than in the amygdala, consistent with our own work and that of others indicating that the olfactory bulb may be the initial and most common brain region infected. To some extent our results converge with pseudotime analysis towards common processes shared between the brain regions, possibly induced by the systemic immune reaction following SARS-CoV-2 infection. Changes in amygdala emphasized upregulation of interferon-related neuroinflammation genes, as well as downregulation of synaptic and other neuronal genes, and may represent the substrate of reported acute and subacute COVID-19 neurological effects. Additionally, and only in olfactory bulb, we observed an increase in angiogenesis and platelet activation genes, possibly associated with microvascular damages induced by neuroinflammation. Through coexpression analysis we identified two key genes (CAMK2B for the synaptic neuronal network and COL1A2 for the angiogenesis/platelet network) that might be interesting potential targets to reverse the effects induced by SARS-CoV-2 infection. Finally, in olfactory bulb we detected an upregulation of olfactory and taste genes, possibly as a compensatory response to functional deafferentation caused by viral entry into primary olfactory sensory neurons. In conclusion, we were able to identify transcriptional profiles and key genes involved in neuroinflammation, neuronal reaction and olfaction induced by direct CNS infection and/or the systemic immune response to SARS-CoV-2 infection.

The Immunopathogenesis of Neuroinvasive Lesions of SARS-CoV-2 Infection in COVID-19 Patients

The new coronavirus disease COVID-19 was identified in December 2019. It subsequently spread across the world with over 125 M reported cases and 2.75 M deaths in 190 countries. COVID-19 causes severe respiratory distress; however, recent studies have reported neurological consequences of infection by the COVID-19 virus SARS-CoV-2 even in subjects with mild infection and no initial neurological effects. It is likely that the virus uses the olfactory nerve to reach the CNS and that this transport mechanism enables virus access to areas of the brain stem that regulates respiratory rhythm and may even trigger cell death by alteration of these neuronal nuclei. In addition, the long-term neuronal effects of COVID-19 suggest a role for SARS-CoV-2 in the development or progression of neurodegerative disease as a result of inflammation and/or hypercoagulation. In this review recent findings on the mechanism(s) by which SARS-CoV-2 accesses the CNS and induces neurological dysregulation are summarized.

Mapping of SARS-CoV-2 Brain Invasion and Histopathology in COVID-19 Disease

The coronavirus SARS-CoV-2 (SCV2) causes acute respiratory distress, termed COVID-19 disease, with substantial morbidity and mortality. As SCV2 is related to previously-studied coronaviruses that have been shown to have the capability for brain invasion, it seems likely that SCV2 may be able to do so as well. To date, although there have been many clinical and autopsy-based reports that describe a broad range of SCV2-associated neurological conditions, it is unclear what fraction of these have been due to direct CNS invasion versus indirect effects caused by systemic reactions to critical illness. Still critically lacking is a comprehensive tissue-based survey of the CNS presence and specific neuropathology of SCV2 in humans. We conducted an extensive neuroanatomical survey of RT-PCR-detected SCV2 in 16 brain regions from 20 subjects who died of COVID-19 disease. Targeted areas were those with cranial nerve nuclei, including the olfactory bulb, medullary dorsal motor nucleus of the vagus nerve and the pontine trigeminal nerve nuclei, as well as areas possibly exposed to hematogenous entry, including the choroid plexus, leptomeninges, median eminence of the hypothalamus and area postrema of the medulla. Subjects ranged in age from 38 to 97 (mean 77) with 9 females and 11 males. Most subjects had typical age-related neuropathological findings. Two subjects had severe neuropathology, one with a large acute cerebral infarction and one with hemorrhagic encephalitis, that was unequivocally related to their COVID-19 disease while most of the 18 other subjects had non-specific histopathology including focal β-amyloid precursor protein white matter immunoreactivity and sparse perivascular mononuclear cell cuffing. Four subjects (20%) had SCV2 RNA in one or more brain regions including the olfactory bulb, amygdala, entorhinal area, temporal and frontal neocortex, dorsal medulla and leptomeninges. The subject with encephalitis was SCV2-positive in a histopathologically-affected area, the entorhinal cortex, while the subject with the large acute cerebral infarct was SCV2-negative in all brain regions. Like other human coronaviruses, SCV2 can inflict acute neuropathology in susceptible patients. Much remains to be understood, including what viral and host factors influence SCV2 brain invasion and whether it is cleared from the brain subsequent to the acute illness.

Neurological involvement of COVID-19: from neuroinvasion and neuroimmune crosstalk to long-term consequences

As the coronavirus disease 2019 (COVID-19) pandemic continues to be a multidimensional threat to humanity, more evidence of neurological involvement associated with it has emerged. Neuroimmune interaction may prove to be important not only in the pathogenesis of neurological manifestations but also to prevent systemic hyperinflammation. In this review, we summarize reports of COVID-19 cases with neurological involvement, followed by discussion of possible routes of entry, immune responses against coronavirus infection in the central nervous system and mechanisms of nerve degeneration due to viral infection and immune responses. Possible mechanisms for neuroprotection and virus-associated neurological consequences are also discussed.

Co-infection of Malassezia sympodialis With Bacterial Pathobionts Pseudomonas aeruginosa or Staphylococcus aureus Leads to Distinct Sinonasal Inflammatory Responses in a Murine Acute Sinusitis Model

Host-associated bacteria and fungi, comprising the microbiota, are critical to host health. In the airways, the composition and diversity of the mucosal microbiota of patients are associated with airway health status. However, the relationship between airway microbiota and respiratory inflammation is not well-understood. Chronic rhinosinusitis (CRS) is a complex disease that affects up to 14% of the US population. Previous studies have shown decreased microbial diversity in CRS patients and enrichment of either Staphylococcus aureus or Pseudomonas aeruginosa. Although bacterial community composition is variable across CRS patients, Malassezia is a dominant fungal genus in the upper airways of the majority of healthy and CRS subjects. We hypothesize that distinct bacterial-fungal interactions differentially influence host mucosal immune response. Thus, we investigated in vitro and in vivo interactions between Malassezia sympodialis, P. aeruginosa, and S. aureus. The in vitro interactions were evaluated using the modified Kirby-Bauer Assay, Crystal Violet assay for biofilm, and FISH. A pilot murine model of acute sinusitis was used to investigate relationships with the host immune response. S. aureus and P. aeruginosa were intranasally instilled in the presence or absence of M. sympodialis (n = 66 total mice; 3–5/group). Changes in the microbiota were determined using 16S rRNA gene sequencing and host immune response was measured using quantitative real-time PCR (qRT-PCR). In vitro, only late stage planktonic P. aeruginosa and its biofilms inhibited M. sympodialis. Co-infection of mice with M. sympodialis and P. aeruginosa or S. aureus differently influenced the immune response. In co-infected mice, we demonstrate different expression of fungal sensing (Dectin-1), allergic responses (IL-5, and IL-13) and inflammation (IL-10, and IL-17) in murine sinus depending on the bacterial species that co-infected with M. sympodialis (p < 0.05). The pilot results suggest that species-specific interactions in airway-associated microbiota may be implicated driving immune responses. The understanding of the role of bacterial-fungal interactions in CRS will contribute to development of novel therapies toward manipulation of the airway microbiota.

IL-15 immunotherapy is a viable strategy for COVID-19

Coronavirus disease 2019 (COVID-19) is a pulmonary inflammatory disease induced by a newly recognized coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 infection was detected for the first time in the city of Wuhan in China and spread all over the world at the beginning of 2020. Several millions of people have been infected with SARS-CoV-2, and almost 382,867 human deaths worldwide have been reported so far. Notably, there has been no specific, clinically approved vaccine or anti-viral treatment strategy for COVID-19. Herein, we review COVID-19, the viral replication, and its effect on promoting pulmonary fibro-inflammation via immune cell-mediated cytokine storms in humans. Several clinical trials are currently ongoing for anti-viral drugs, vaccines, and neutralizing antibodies against COVID-19. Viral clearance is the result of effective innate and adaptive immune responses. The pivotal role of interleukin (IL)-15 in viral clearance involves maintaining the balance of induced inflammatory cytokines and the homeostatic responses of natural killer and CD8+ T cells. This review presents supporting evidence of the impact of IL-15 immunotherapy on COVID-19.

Increased Pathogenicity and Virulence of Middle East Respiratory Syndrome Coronavirus Clade B In Vitro and In Vivo

Middle East respiratory syndrome coronavirus (MERS-CoV) causes severe acute respiratory disease in humans. MERS-CoV strains from early epidemic clade A and contemporary epidemic clade B have not been phenotypically characterized to compare their abilities to infect cells and mice. We isolated the clade B MERS-CoV ChinaGD01 strain from a patient infected during the South Korean MERS outbreak in 2015 and compared the phylogenetics and pathogenicity of MERS-CoV EMC/2012 (clade A) and ChinaGD01 (clade B) in vitro and in vivo Genome alignment analysis showed that most clade-specific mutations occurred in the orf1ab gene, including mutations that were predicted to be potential glycosylation sites. Minor differences in viral growth but no significant differences in plaque size or sensitivity to beta interferon (IFN-β) were detected between these two viruses in vitro ChinaGD01 virus infection induced more weight loss and inflammatory cytokine production in human DPP4-transduced mice. Viral titers were higher in the lungs of ChinaGD01-infected mice than with EMC/2012 infection. Decreased virus-specific CD4⁺ and CD8⁺ T cell numbers were detected in the lungs of ChinaGD01-infected mice. In conclusion, MERS-CoV evolution induced changes to reshape its pathogenicity and virulence in vitro and in vivo and to evade adaptive immune response to hinder viral clearance.IMPORTANCE MERS-CoV is an important emerging pathogen and causes severe respiratory infection in humans. MERS-CoV strains from early epidemic clade A and contemporary epidemic clade B have not been phenotypically characterized to compare their abilities to infect cells and mice. In this study, we showed that a clade B virus ChinaGD01 strain caused more severe disease in mice, with delayed viral clearance, increased inflammatory cytokines, and decreased antiviral T cell responses, than the early clade A virus EMC/2012. Given the differences in pathogenicity of different clades of MERS-CoV, periodic assessment of currently circulating MERS-CoV is needed to monitor potential severity of zoonotic disease.

TIGIT limits immune pathology during viral infections

Co-inhibitory pathways have a fundamental function in regulating T cell responses and control the balance between promoting efficient effector functions and restricting immune pathology. The TIGIT pathway has been implicated in promoting T cell dysfunction in chronic viral infection. Importantly, TIGIT signaling is functionally linked to IL-10 expression, which has an effect on both virus control and maintenance of tissue homeostasis. However, whether TIGIT has a function in viral persistence or limiting tissue pathology is unclear. Here we report that TIGIT modulation effectively alters the phenotype and cytokine profile of T cells during influenza and chronic LCMV infection, but does not affect virus control in vivo. Instead, TIGIT has an important effect in limiting immune pathology in peripheral organs by inducing IL-10. Our data therefore identify a function of TIGIT in limiting immune pathology that is independent of viral clearance.

Fine Tuning the Cytokine Storm by IFN and IL-10 Following Neurotropic Coronavirus Encephalomyelitis

The central nervous system (CNS) is vulnerable to several viral infections including herpes viruses, arboviruses and HIV to name a few. While a rapid and effective immune response is essential to limit viral spread and mortality, this anti-viral response needs to be tightly regulated in order to limit immune mediated tissue damage. This balance between effective virus control with limited pathology is especially important due to the highly specialized functions and limited regenerative capacity of neurons, which can be targets of direct virus cytolysis or bystander damage. CNS infection with the neurotropic strain of mouse hepatitis virus (MHV) induces an acute encephalomyelitis associated with focal areas of demyelination, which is sustained during viral persistence. Both innate and adaptive immune cells work in coordination to control virus replication. While type I interferons are essential to limit virus spread associated with early mortality, perforin, and interferon-γ promote further virus clearance in astrocytes/microglia and oligodendrocytes, respectively. Effective control of virus replication is nonetheless associated with tissue damage, characterized by demyelinating lesions. Interestingly, the anti-inflammatory cytokine IL-10 limits expansion of tissue lesions during chronic infection without affecting viral persistence. Thus, effective coordination of pro- and anti-inflammatory cytokines is essential during MHV induced encephalomyelitis in order to protect the host against viral infection at a limited cost.

Interleukin-10 Modulation of Virus Clearance and Disease in Mice with Alphaviral Encephalomyelitis

Alphaviruses are an important cause of mosquito-borne outbreaks of arthritis, rash, and encephalomyelitis. Previous studies in mice with a virulent strain (neuroadapted SINV [NSV]) of the alphavirus Sindbis virus (SINV) identified a role for Th17 cells and regulation by interleukin-10 (IL-10) in the pathogenesis of fatal encephalomyelitis (K. A. Kulcsar, V. K. Baxter, I. P. Greene, and D. E. Griffin, Proc Natl Acad Sci U S A 111:16053-16058, 2014, https://doi.org/10.1073/pnas.1418966111). To determine the role of virus virulence in generation of immune responses, we analyzed the modulatory effects of IL-10 on disease severity, virus clearance, and the CD4+ T cell response to infection with a recombinant strain of SINV of intermediate virulence (TE12). The absence of IL-10 during TE12 infection led to longer morbidity, more weight loss, higher mortality, and slower viral clearance than in wild-type mice. More severe disease and impaired virus clearance in IL-10-/- mice were associated with more Th1 cells, fewer Th2 cells, innate lymphoid type 2 cells, regulatory cells, and B cells, and delayed production of antiviral antibody in the central nervous system (CNS) without an effect on Th17 cells. Therefore, IL-10 deficiency led to more severe disease in TE12-infected mice by increasing Th1 cells and by hampering development of the local B cell responses necessary for rapid production of antiviral antibody and virus clearance from the CNS. In addition, the shift from Th17 to Th1 responses with decreased virus virulence indicates that the effects of IL-10 deficiency on immunopathologic responses in the CNS during alphavirus infection are influenced by virus strain.IMPORTANCE Alphaviruses cause mosquito-borne outbreaks of encephalomyelitis, but determinants of outcome are incompletely understood. We analyzed the effects of the anti-inflammatory cytokine IL-10 on disease severity and virus clearance after infection with an alphavirus strain of intermediate virulence. The absence of IL-10 led to longer illness, more weight loss, more death, and slower viral clearance than in mice that produced IL-10. IL-10 influenced development of disease-causing T cells and entry into the brain of B cells producing antiviral antibody. The Th1 pathogenic cell subtype that developed in IL-10-deficient mice infected with a less virulent virus was distinct from the Th17 subtype that developed in response to a more virulent virus, indicating a role for virus strain in determining the immune response. Slow production of antibody in the nervous system led to delayed virus clearance. Therefore, both the virus strain and the host response to infection are important determinants of outcome.

The neonatal anti-viral response fails to control measles virus spread in neurons despite interferon-gamma expression and a Th1-like cytokine profile

Neonates are highly susceptible to viral infections in the periphery, potentially due to deviant cytokine responses. Here, we investigated the role of interferon-gamma (IFNγ), a key anti-viral in the neonatal brain. We found that (i) IFNγ, which is critical for viral control and survival in adults, delays mortality in neonates, (ii) IFNγ limits infiltration of macrophages, neutrophils, and T cells in the neonatal brain, (iii) neonates and adults differentially express pathogen recognition receptors and Type I interferons in response to the infection, (iv) both neonates and adults express IFNγ and other Th1-related factors, but expression of many cytokines/chemokines and IFNγ-responsive genes is age-dependent, and (v) administration of IFNγ extends survival and reduces CD4 T cell infiltration in the neonatal brain. Our findings suggest age-dependent expression of cytokine/chemokine profiles in the brain and distinct dynamic interplays between lymphocyte populations and cytokines/chemokines in MV-infected neonates.

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The role of the anti-viral cytokine interferon-gamma (IFNγ) is investigated during a neonatal viral infection in CNS neurons.

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IFNγ did not prevent mortality in neonates, but it slowed disease progression.

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IFNγ reduced infiltration of neutrophils, macrophages, and T cells in the neonatal CNS.

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Both adult and neonatal mice expressed Th1-like cytokines, including IFNγ and some IFNγ-stimulated genes, during infection.

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Despite a Th1-like cytokine profile in the neonatal CNS, the cytokine milieu is ineffective at controlling viral spread.

Roles of regulatory T cells and IL-10 in virus-induced demyelination

Neurotropic viruses are important causes of morbidity and mortality in human populations. Some of these viruses preferentially infect oligodendrocytes in the white matter, causing either direct lysis of infected cells, or more commonly myelin damage as a consequence of the host immune response to the virus. Virus-induced demyelination has similarities to the human disease multiple sclerosis. To study this disease process in experimental animals, mice are infected, most commonly, with neurotropic strains of mouse hepatitis virus, a coronavirus or Theiler's murine encephalomyelitis, a picornavirus. While the diseases caused by these two viruses differ in some aspects, in both cases demyelination is a major consequence of the infection. As in autoimmune disease, therapeutic interventions that diminish an overactive immune response would be useful. However, unlike autoimmune disease, complete suppression would result in unchecked virus replication, generally leading to more severe disease. Here we discuss two approaches that dampen but do not fully suppress the host immune response. Regulatory T cells, especially those that are specific for antigens recognized by pathogenic T cells, and IL-10 are two anti-inflammatory/pro-resolution factors that demonstrate efficacy in experimental models of virus-induced demyelination and may be useful in patients infected with viruses that cause demyelination.

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MHV and TMEV are common causes of virus-induced demyelination in mice

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Virus-induced demyelination is often host cell-mediated.

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Virus-specific Treg dampen pathogenic T cells responding to cognate epitope

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IL-10 expressed by Tregs and Tr1 cells dampens pathogenic T cell responses

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Tregs and IL-10 suppress pathogenic T cells without broad immunosuppression

Viral Infection of the Central Nervous System Exacerbates Interleukin-10 Receptor Deficiency-Mediated Colitis in SJL Mice

Theiler´s murine encephalomyelitis virus (TMEV)-infection is a widely used animal model for studying demyelinating disorders, including multiple sclerosis (MS). The immunosuppressive cytokine Interleukin (IL)-10 counteracts hyperactive immune responses and critically controls immune homeostasis in infectious and autoimmune disorders. In order to investigate the effect of signaling via Interleukin-10 receptor (IL-10R) in infectious neurological diseases, TMEV-infected SJL mice were treated with IL-10R blocking antibody (Ab) in the acute and chronic phase of the disease. The findings demonstrate that (i) Ab-mediated IL-10 neutralization leads to progressive colitis with a reduction in Foxp3+ regulatory T cells and increased numbers of CD8+CD44+ memory T cells as well as activated CD4+CD69+ and CD8+CD69+ T cells in uninfected mice. (ii) Concurrent acute TMEV-infection worsened enteric disease-mediated by IL-10R neutralization. Virus-triggered effects were associated with an enhanced activation of CD4+ T helper cells and CD8+ cytotoxic T lymphocytes and augmented cytokine expression. By contrast, (iii) IL-10R neutralization during chronic TMEV-infection was not associated with enhanced peripheral immunopathology but an increased CD3+ T cell influx in the spinal cord. IL-10R neutralization causes a breakdown in peripheral immune tolerance in genetically predisposed mice, which leads to immune-mediated colitis, resembling inflammatory bowel disease. Hyperactive immune state following IL-10R blockade is enhanced by central nervous system-restricted viral infection in a disease phase-dependent manner.

Immune Surveillance of the CNS following Infection and Injury

The central nervous system (CNS) contains a sophisticated neural network that must be constantly surveyed in order to detect and mitigate a diverse array of challenges. The innate and adaptive immune systems actively participate in this surveillance, which is critical for the maintenance of CNS homeostasis and can facilitate the resolution of infections, degeneration, and tissue damage. Infections and sterile injuries represent two common challenges imposed on the CNS that require a prompt immune response. While the inducers of these two challenges differ in origin, the resultant responses orchestrated by the CNS share some overlapping features. Here, we review how the CNS immunologically discriminates between pathogens and sterile injuries, mobilizes an immune reaction, and, ultimately, regulates local and peripherally-derived immune cells to provide a supportive milieu for tissue repair.

T cell-derived interleukin-10 is an important regulator of the Th17 response during lethal alphavirus encephalomyelitis

Neuroadapted Sindbis virus infection of mice causes T cell-mediated fatal encephalomyelitis. In the absence of IL-10, pathogenic Th17 cells are increased and disease is accelerated. Lymphoid and myeloid cell contributions to IL-10 production were determined using VertX IL-10 transcriptional eGFP reporter mice. Effector and regulatory CD4(+) and CD8(+) T cells in the brain, but not the cervical lymph nodes, were the primary producers of IL-10. Th17 and Th1/Th17 cells were increased in mice that lacked T cell IL-10 production, although less than in the absence of IL-10. Morbidity and mortality were not affected suggesting an IL-10 threshold for disease exacerbation.

Immune Responses to Viruses in the CNS

For recovery from infection, the immune response in the central nervous system (CNS) must eliminate or control virus replication without destroying nonrenewable, essential cells. Thus, upon intracellular virus detection, the infected cell must initiate clearance pathways without triggering neuronal cell death. As a result, the inflammatory response must be tightly regulated and unique mechanisms contribute to the immune response in the CNS. Early restriction of virus replication is accomplished by the innate immune response upon activation of pattern recognition receptors in resident cells. Infiltrating immune cells enter from the periphery to clear virus. Antibodies and interferon-γ are primary contributors to noncytolytic clearance of virus in the CNS. Lymphocytes are retained in the CNS after the acute phase of infection presumably to block reactivation of virus replication.

Effect of cadmium on the expression levels of interleukin-1α and interleukin-10 cytokines in human lung cells

Cadmium is an environmentally hazardous metal, which causes toxicity in humans. Inhalation of cigarette smoke and industrial fumes containing cadmium are sources of cadmium exposure. It is responsible for the malfunction of various organs, leading to disease particularly in the lungs, liver and kidneys. In the present study, the effect of cadmium chloride (CdCl2) on cell viability, and the expression levels of interleukin (IL)‑1α and IL‑10 cytokines at various concentrations and incubation durations were assessed in MRC‑9 human normal lung and A549 human lung cancer cells to elucidate the mechanism of cadmium toxicity. Cell viability was measured using a crystal violet dye binding assay. The expression levels of the cytokines were measured by cytokine specific enzyme‑linked immunosorbent assay kits. The viability assay results revealed higher sensitivity of the A549 lung cancer cells to CdCl2 compared with the normal MRC‑9 lung cells. In the normal MRC‑9 lung cells, higher expression levels of the cytokines were observed at the lowest CdCl2 concentration at a shorter exposure time compared with the lung cancer cells. Higher levels of the cytokines were observed in the A549 lung cancer cells at all other times and concentrations compared with the MRC‑9 cells, indicating higher levels of inflammation. The cytokine levels were reduced at higher CdCl2 concentrations and longer exposure durations, demonstrating the toxic effect of cadmium. The results indicated that CdCl2 affected the expression levels of the cytokines and led to cytotoxicity in human lung cells, and suggested that compounds which reduce inflammation may prevent cadmium toxicity.

Distinct Immune Responses in Resistant and Susceptible Strains of Mice during Neurovirulent Alphavirus Encephalomyelitis

Susceptibility to alphavirus encephalomyelitis is dependent on a variety of factors, including the genetic background of the host. Neuroadapted Sindbis virus (NSV) causes uniformly fatal disease in adult C57BL/6 (B6) mice, but adult BALB/c (Bc) mice recover from infection. In B6 mice, fatal encephalomyelitis is immune mediated rather than a direct result of virus infection. To identify the immunological determinants of host susceptibility to fatal NSV-induced encephalomyelitis, we compared virus titers and immune responses in adult B6 and Bc mice infected intranasally with NSV. B6 mice had higher levels of virus replication, higher levels of type I interferon (IFN), and slower virus clearance than did Bc mice. B6 mice had more neuronal apoptosis, more severe neurologic disease, and higher mortality than Bc mice. B6 mice had more infiltration of inflammatory cells and higher levels of IL1b, IL-6, TNFa, Csf2, and CCL2 mRNAs and interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), IFN-γ, and C-C motif ligand 2 (CCL2) protein in brains than Bc mice. However, Bc mice had more brain antibody at day 7 and a higher percentage of CD4(+) T cells. CD4(+) T cells in the brains of Bc mice included fewer Th17 cells and more regulatory T cells (Tregs) producing IL-10 than B6 mice, accompanied by higher levels of Il2 and Cxcl10 mRNAs. In the absence of IL-10, resistant Bc mice became susceptible to fatal encephalomyelitis after NSV infection. These studies demonstrate the importance of the immune response and its regulation in determining host survival during alphavirus encephalomyelitis.

IMPORTANCE

Mosquito-borne alphavirus infections are an important cause of encephalomyelitis in humans. The severity of disease is dependent both on the strain of the virus and on the age and genetic background of the host. A neurovirulent strain of Sindbis virus causes immune-mediated fatal encephalomyelitis in adult C57BL/6 mice but not in BALB/c mice. To determine the host-dependent immunological mechanisms underlying the differences in susceptibility between these two strains of mice, we compared their immune responses to infection. Resistance to fatal disease in BALB/c mice was associated with better antibody responses, more-rapid virus clearance, fewer Th17 cells, and more-potent regulatory T cell responses than occurred in susceptible C57BL/6 mice. In the absence of interleukin-10, a component of the regulatory immune response, resistant mice became susceptible to lethal disease. This study demonstrates the importance of the immune response and its regulation for host survival during alphavirus encephalomyelitis.

Interleukin 10 modulation of pathogenic Th17 cells during fatal alphavirus encephalomyelitis

Mosquito-borne alphaviruses are important causes of epidemic encephalomyelitis. Neuronal cell death during fatal alphavirus encephalomyelitis is immune-mediated; however, the types of cells involved and their regulation have not been determined. We show that the virus-induced inflammatory response was accompanied by production of the regulatory cytokine IL-10, and in the absence of IL-10, paralytic disease occurred earlier and mice died faster. To determine the reason for accelerated disease in the absence of IL-10, immune responses in the CNS of IL-10(-/-) and wild-type (WT) mice were compared. There were no differences in the amounts of brain inflammation or peak virus replication; however, IL-10(-/-) animals had accelerated and increased infiltration of CD4(+)IL-17A(+) and CD4(+)IL-17A(+)IFNγ(+) cells compared with WT animals. Th17 cells infiltrating the brain demonstrated a pathogenic phenotype with the expression of the transcription factor, Tbet, and the production of granzyme B, IL-22, and GM-CSF, with greater production of GM-CSF in IL-10(-/-) mice. Therefore, in fatal alphavirus encephalomyelitis, pathogenic Th17 cells enter the CNS at the onset of neurologic disease and, in the absence of IL-10, appear earlier, develop into Th1/Th17 cells more often, and have greater production of GM-CSF. This study demonstrates a role for pathogenic Th17 cells in fatal viral encephalitis.

Differential responses of disease-resistant and disease-susceptible primate macrophages and myeloid dendritic cells to simian hemorrhagic fever virus infection

Simian hemorrhagic fever virus (SHFV) causes a fatal hemorrhagic fever in macaques but an asymptomatic, persistent infection in baboons. To investigate factors contributing to this differential infection outcome, the targets of SHFV infection, macrophages (MΦs) and myeloid dendritic cells (mDCs), were differentiated from macaque and baboon peripheral blood monocytes and used to compare viral replication and cell responses. SHFV replicated in >90% of macaque MΦs but in only ∼10% of baboon MΦs. Although SHFV infected ∼50% of macaque and baboon mDCs, virus replication was efficient in macaque but not in baboon mDCs. Both types of macaque cultures produced higher virus yields than baboon cultures. A more efficient type I interferon response and the production of proinflammatory cytokines, including interleukin-1β (IL-1β), IL-6, IL-12/23(p40), tumor necrosis factor alpha (TNF-α), and macrophage inflammatory protein 1α (MIP-1α), in response to SHFV infection were observed in macaque but not baboon cultures, suggesting less efficient counteraction of these responses by viral proteins in macaque cells. Baboon cultures produced higher levels of IL-10 than macaque cultures both prior to and after SHFV infection. In baboon but not macaque cell cultures, SHFV infection upregulated IL-10R1, a subunit of the IL-10 receptor (IL-10R), and also SOCS3, a negative regulator of proinflammatory cytokine production. Incubation of macaque cultures with human IL-10 before and/or after SHFV infection decreased production of IL-6, IL-1β, and MIP-1α but not TNF-α, suggesting a role for IL-10 in suppressing SHFV-induced proinflammatory cytokine production in macaques.

Cytokine and chemokine responses in the blood and cerebrospinal fluid of patients with human herpesvirus 6B-associated acute encephalopathy with biphasic seizures and late reduced diffusion

Acute encephalopathy with biphasic seizures and late reduced diffusion has become increasingly common among various types of human herpesvirus 6B (HHV-6B) encephalitis at the time of primary viral infection. The aim of the present study is to explore the pathophysiology of HHV-6B-associated acute encephalopathy with biphasic seizures and late reduced diffusion. Five cytokines and five chemokines were measured in serum and cerebrospinal fluid (CSF) obtained from 12 HHV-6B-associated acute encephalopathy with biphasic seizures and late reduced diffusion patients and 19 control exanthem subitum (without complications) patients. Serum interleukin (IL)-10 (P = 0.007) and IL-8 (P = 0.025) were significantly higher in the patients with the disease than controls. Serum IL-1β (P = 0.034) and monocyte chemoattractant protein (MCP)-1 (P = 0.002) were significantly higher in the controls than patients with the disease. In patients with the disease, IL-10 (P = 0.012), regulated on activation normal T cell expressed and secreted (RANTES; P = 0.001), and monokine induced by interferon γ (MIG; P = 0.001) were significantly higher in serum than CSF, meanwhile IL-6 (P = 0.034), IL-8 (P = 0.034), and MCP-1 (P = 0.001) were significantly higher in CSF than serum. Additionally, serum IL-10 was significantly higher in the disease patients with sequelae than those without sequelae (P = 0.016). Several cytokines and chemokines may be associated with the pathogenesis of acute encephalopathy with biphasic seizures and late reduced diffusion. Moreover, the regulation of cytokine networks appears to be different between peripheral blood (systemic) and central nervous system.

Role of CD25(+) CD4(+) T cells in acute and persistent coronavirus infection of the central nervous system

The influence of CD25(+)CD4(+) regulatory T cells (Treg) on acute and chronic viral infection of the central nervous system (CNS) was examined using a glial tropic murine coronavirus. Treg in the CNS were highest during initial T cell mediated virus control, decreased and then remained relatively stable during persistence. Anti-CD25 treatment did not affect CNS recruitment of inflammatory cells. Viral control was initially delayed; however, neither the kinetics of viral control nor viral persistence were affected. By contrast, the absence of Treg during the acute phase resulted in increased demyelination during viral persistence. These data suggest that CNS inflammation, progression of viral control and viral persistence are relatively independent of CD25(+)CD4(+) Treg. However, their absence during acute infection alters the ability of the host to limit tissue damage.

Mucosal vaccines to prevent porcine reproductive and respiratory syndrome: a new perspective

Porcine reproductive and respiratory syndrome (PRRS) is an economically important infectious disease of swine. Constant emergence of variant strains of PRRS virus (PPRSV) and virus-mediated immune evasion followed by viral persistence result in increased incidence and recurrence of PRRS in swine herds. Current live and killed PRRSV vaccines administered by a parenteral route are ineffective in inducing complete protection. Thus, new approaches in design and delivery of PRRSV vaccines are needed to reduce the disease burden of the swine industry. Induction of an effective mucosal immunity to several respiratory pathogens by direct delivery of a vaccine to mucosal sites has proven to be effective in a mouse model. However, there are challenges in eliciting mucosal immunity to PRRS due to our limited understanding of safe and potent mucosal adjuvants, which could potentiate the mucosal immune response to PRRSV. The purpose of this review is to discuss methods for induction of protective mucosal immune responses in the respiratory tract of pigs. The manuscript also discusses how PRRSV modulates innate, adaptive and immunoregulatory responses at both mucosal and systemic sites of infected and/or vaccinated pigs. This information may help in the design of innovative mucosal vaccines to elicit superior cross-protective immunity against divergent field strains of PRRSV.