Recruitment kinetics and composition of antibody-secreting cells within the central nervous system following viral encephalomyelitis

Infection by the neurotropic JHM strain of mouse hepatitis virus produces an acute demyelinating encephalomyelitis. While cellular immunity initially eliminates infectious virus, CNS viral persistence is predominantly controlled by humoral immunity. To better understand the distinct phases of immune control within the CNS, the kinetics of humoral immune responses were determined in infected mice. Early during clearance of the JHM strain of mouse hepatitis virus, only few virus-specific Ab-secreting cells (ASC) were detected in the periphery or CNS, although mature B cells and ASC without viral specificity were recruited into the CNS concomitant with T cells. Serum antiviral Ab and CNS virus-specific ASC became prominent only during final elimination of infectious virus. Virus-specific ASC peaked in lymphoid organs before the CNS, suggesting peripheral B cell priming and maturation. Following elimination of infectious virus, virus-specific ASC continued to increase within the CNS and then remained stable during persistence, in contrast to declining T cell numbers. These data comprise three novel findings. Rapid recruitment of B cells in the absence of specific Ab secretion supports a potential Ab-independent effector function involving lysis of virus-infected cells. Delayed recruitment relative to viral clearance and subsequent maintenance of a stable CNS ASC population demonstrate differential regulation of T and B lymphocytes within the infected CNS. This supports a critical role of humoral immunity in regulating viral CNS persistence. Lastly, altered antiviral ASC specificities following clearance of infectious virus suggest ongoing recruitment of peripheral memory cells and/or local B cell differentiation.     

Type I interferons are essential in controlling neurotropic coronavirus infection irrespective of functional CD8 T cells

Neurotropic coronavirus infection induces expression of both beta interferon (IFN-beta) RNA and protein in the infected rodent central nervous system (CNS). However, the relative contributions of type I IFN (IFN-I) to direct, cell-type-specific virus control or CD8 T-cell-mediated effectors in the CNS are unclear. IFN-I receptor-deficient (IFNAR(-/-)) mice infected with a sublethal and demyelinating neurotropic virus variant and those infected with a nonpathogenic neurotropic virus variant both succumbed to infection within 9 days. Compared to wild-type (wt) mice, replication was prominently increased in all glial cell types and spread to neurons, demonstrating expanded cell tropism. Furthermore, increased pathogenesis was associated with significantly enhanced accumulation of neutrophils, tumor necrosis factor alpha, interleukin-6, chemokine (C-C motif) ligand 2, and IFN-gamma within the CNS. The absence of IFN-I signaling did not impair induction or recruitment of virus-specific CD8 T cells, the primary adaptive mediators of virus clearance in wt mice. Despite similar IFN-gamma-mediated major histocompatibility complex class II upregulation on microglia in infected IFNAR(-/-) mice, class I expression was reduced compared to that on microglia in wt mice, suggesting a synergistic role of IFN-I and IFN-gamma in optimizing class I antigen presentation. These data demonstrate a critical direct antiviral role of IFN-I in controlling virus dissemination within the CNS, even in the presence of potent cellular immune responses. By limiting early viral replication and tropism, IFN-I controls the balance of viral replication and immune control in favor of CD8 T-cell-mediated protective functions.     

CXCR3 mediates region-specific antiviral T cell trafficking within the central nervous system during West Nile virus encephalitis

Regional differences in inflammation during viral infections of the CNS suggest viruses differentially induce patterns of chemoattractant expression, depending on their cellular targets. Previous studies have shown that expression of the chemokine CXCL10 by West Nile virus (WNV)-infected neurons is essential for the recruitment of CD8 T cells for the purpose of viral clearance within the CNS. In the current study we used mice deficient for the CXCL10 receptor, CXCR3, to evaluate its role in leukocyte-mediated viral clearance of WNV infection within various CNS compartments. WNV-infected CXCR3-deficient mice exhibited significantly enhanced mortality compared with wild-type controls. Immunologic and virologic analyses revealed that CXCR3 was dispensable for control of viral infection in the periphery and in most CNS compartments but, surprisingly, was required for CD8 T cell-mediated antiviral responses specifically within the cerebellum. WNV-specific, CXCR3-expressing T cells preferentially migrated into the cerebellum, and WNV-infected cerebellar granule cell neurons expressed higher levels of CXCL10 compared with similarly infected cortical neurons. These results indicate that WNV differentially induces CXCL10 within neuronal populations and suggest a novel model for nonredundancy in chemokine-mediated inflammation among CNS compartments.     

Contributions of CD8+ T cells and viral spread to demyelinating disease

Acute and chronic demyelination are hallmarks of CNS infection by the neurotropic JHM strain of mouse hepatitis virus. Although infectious virus is cleared by CD8+ T cells, both viral RNA and activated CD8+ T cells remain in the CNS during persistence potentially contributing to pathology. To dissociate immune from virus-mediated determinants initiating and maintaining demyelinating disease, mice were infected with two attenuated viral variants differing in a hypervariable region of the spike protein. Despite similar viral replication and tropism, one infection was marked by extensive demyelination and paralysis, whereas the other resulted in no clinical symptoms and minimal neuropathology. Mononuclear cells from either infected brain exhibited virus specific ex vivo cytolytic activity, which was rapidly lost during viral clearance. As revealed by class I tetramer technology the paralytic variant was superior in inducing specific CD8+ T cells during the acute disease. However, after infectious virus was cleared, twice as many virus-specific IFN-gamma-secreting CD8+ T cells were recovered from the brains of asymptomatic mice compared with mice undergoing demyelination, suggesting that IFN-gamma ameliorates rather than perpetuates JHM strain of mouse hepatitis virus-induced demyelination. The present data thus indicate that in immunocompetent mice, effector CD8+ T cells control infection without mediating either clinical disease or demyelination. In contrast, demyelination correlated with early and sustained infection of the spinal cord. Rapid viral spread, attributed to determinants within the spike protein and possibly perpetuated by suboptimal CD8+ T cell effector function, thus ultimately leads to the process of immune-mediated demyelination.     

Mechanisms of central nervous system viral persistence: the critical role of antibody and B cells.

Contributions of humoral and cellular immunity in controlling neurotropic mouse hepatitis virus persistence within the CNS were determined in B cell-deficient J(H)D and syngeneic H-2(d) B cell+ Ab-deficient mice. Virus clearance followed similar kinetics in all mice, confirming initial control of virus replication by cellular immunity. Nevertheless, virus reemerged within the CNS of all Ab-deficient mice. In contrast to diminished T cell responses in H-2(b) B cell-deficient muMT mice, the absence of B cells or Ab in the H-2(d) mice did not compromise expansion, recruitment into the CNS, or function of virus-specific CD4+ and CD8+ T cells. The lack of B cells and lymphoid architecture thus appears to manifest itself on T cell responses in a genetically biased manner. Increasing viral load did not enhance frequencies or effector function of virus-specific T cells within the CNS, indicating down-regulation of T cell responses. Although an Ab-independent antiviral function of B cells was not evident during acute infection, the presence of B cells altered CNS cellular tropism during viral recrudescence. Reemerging virus localized almost exclusively to oligodendroglia in B cell+ Ab-deficient mice, whereas it also replicated in astrocytes in B cell-deficient mice. Altered tropism coincided with distinct regulation of CNS virus-specific CD4+ T cells. These data conclusively demonstrate that the Ab component of humoral immunity is critical in preventing virus reactivation within CNS glial cells. B cells themselves may also play a subtle role in modulating pathogenesis by influencing tropism.     

Melanoma differentiation-associated gene 5 is critical for protection against Theiler's virus-induced demyelinating disease

Infection of dendritic and glial cells with Theiler's murine encephalomyelitis virus (TMEV) induces various cytokines via Toll-like receptor- and melanoma differentiation-associated gene 5 (MDA5)-dependent pathways. However, the involvement and role of MDA5 in cytokine gene activation and the pathogenesis of TMEV-induced demyelinating disease are largely unknown. In this study, we demonstrate that MDA5 plays a critical role in the production of TMEV-induced alpha interferon (IFN-α) during early viral infection and in protection against the development of virus-induced demyelinating disease. Our results indicate that MDA5-deficient 129SvJ mice display significantly higher viral loads and apparent demyelinating lesions in the central nerve system (CNS) accompanied by clinical symptoms compared with wild-type 129SvJ mice. During acute viral infection, MDA5-deficient mice produced elevated levels of chemokines, consistent with increased cellular infiltration, but reduced levels of IFN-α, known to control T cell responses and cellular infiltration. Additional studies with isolated CNS glial cells from these mice suggest that cells from MDA5-deficient mice are severely compromised in the production of IFN-α upon viral infection, which results in increased cellular infiltration and viral loads in the CNS. Despite inadequate stimulation, the overall T cell responses to the viral determinants were significantly elevated in MDA5-deficient mice, reflecting the increased cellular infiltration. Therefore, the lack of MDA5-mediated IFN-α production may facilitate a massive viral load and elevated cellular infiltration in the CNS during early viral infection, leading to the pathogenesis of demyelinating disease.     

Selective tropism of a neurotropic coronavirus for ependymal cells, neurons, and meningeal cells.

The ability of a neurotropic virus, mouse hepatitis virus type 3 (MHV3), to invade the central nervous system (CNS) and to recognize cells selectively within the brain was investigated in vivo and in vitro. In vivo, MHV3 induced in C3H mice a genetically controlled infection of meningeal cells, ependymal cells, and neurons. In vitro, purified MHV3 bound to the surface of isolated ependymal cells and cultured cortical neurons but not to oligodendrocytes or cultured astrocytes. MHV3 replicated within cultured cortical neurons and neuroblastoma cells (NIE 115); infected cultured neurons nonetheless survived and matured normally for a 7-day period postinfection. On the other hand, MHV3 had a low affinity for cortical glial cells or glioma cells (C6 line), both of which appear to be morphologically unaltered by viral infection. Finally, MHV3 infected and disrupted cultured meningeal cells. This suggests that differences in the affinity of cells for MHV3 are determinants of the selective vulnerability of cellular subpopulations within the CNS. In vivo, a higher titer of virus was needed for CNS penetration in the genetically resistant (A/Jx) mice than in the susceptible (C57/BL6) mouse strain. However, in spite of viral invasion, no neuropathological lesions developed. In vitro viral binding to adult ependymal cells of susceptible and resistant strains of mice was identical. Genetic resistance to MHV3-CNS infection appeared to be mediated both by a peripheral mechanism limiting viral penetration into the CNS and by intra-CNS mechanisms, presumably at a stage after viral attachment to target cells.     

Impaired T cell immunity in B cell-deficient mice following viral central nervous system infection

CD8(+) T cells are required to control acute viral replication in the CNS following infection with neurotropic coronavirus. By contrast, studies in B cell-deficient (muMT) mice revealed Abs as key effectors in suppressing virus recrudescence. The apparent loss of initial T cell-mediated immune control in the absence of B cells was investigated by comparing T cell populations in CNS mononuclear cells from infected muMT and wild-type mice. Following viral recrudescence in muMT mice, total CD8(+) T cell numbers were similar to those of wild-type mice that had cleared infectious virus; however, virus-specific T cells were reduced at least 3-fold by class I tetramer and IFN-gamma ELISPOT analysis. Although overall T cell recruitment into the CNS of muMT mice was not impaired, discrepancies in frequencies of virus-specific CD8(+) T cells were most severe during acute infection. Impaired ex vivo cytolytic activity of muMT CNS mononuclear cells, concomitant with reduced frequencies, implicated IFN-gamma as the primary anti viral factor early in infection. Reduced virus-specific CD8(+) T cell responses in the CNS coincided with poor peripheral expansion and diminished CD4(+) T cell help. Thus, in addition to the lack of Ab, limited CD8(+) and CD4(+) T cell responses in muMT mice contribute to the ultimate loss of control of CNS infection. Using a model of virus infection restricted to the CNS, the results provide novel evidence for a role of B cells in regulating T cell expansion and differentiation into effector cells.     

Perforin and gamma interferon-mediated control of coronavirus central nervous system infection by CD8 T cells in the absence of CD4 T cells

Infection of the central nervous system (CNS) with the neurotropic JHM strain of mouse hepatitis virus produces acute and chronic demyelination. The contributions of perforin-mediated cytolysis and gamma interferon (IFN-gamma) secretion by CD8(+) T cells to the control of infection and the induction of demyelination were examined by adoptive transfer into infected SCID recipients. Untreated SCID mice exhibited uncontrolled virus replication in all CNS cell types but had little or no demyelination. Memory CD8(+) T cells from syngeneic wild-type (wt), perforin-deficient, or IFN-gamma-deficient (GKO) donors all trafficked into the infected CNS in the absence of CD4(+) T cells and localized to similar areas. Although CD8(+) T cells from all three donors suppressed virus replication in the CNS, GKO CD8(+) T cells expressed the least antiviral activity. A distinct viral antigen distribution in specific CNS cell types revealed different mechanisms of viral control. While wt CD8(+) T cells inhibited virus replication in all CNS cell types, cytolytic activity in the absence of IFN-gamma suppressed the infection of astrocytes, but not oligodendroglia. In contrast, cells that secreted IFN-gamma but lacked cytolytic activity inhibited replication in oligodendroglia, but not astrocytes. Demyelination was most severe following viral control by wt CD8(+) T cells but was independent of macrophage infiltration. These data demonstrate the effective control of virus replication by CD8(+) T cells in the absence of CD4(+) T cells and support the necessity for the expression of distinct effector mechanisms in the control of viral replication in distinct CNS glial cell types.     

CD8+ T lymphocytes control murine cytomegalovirus replication in the central nervous system of newborn animals

Human CMV infection of the neonatal CNS results in long-term neurologic sequelae. To define the pathogenesis of fetal human CMV CNS infections, we investigated mechanisms of virus clearance from the CNS of neonatal BALB/c mice infected with murine CMV (MCMV). Virus titers peaked in the CNS between postnatal days 10-14 and infectious virus was undetectable by postnatal day 21. Congruent with virus clearance was the recruitment of CD8(+) T cells into the CNS. Depletion of CD8(+) T cells resulted in death by postnatal day 15 in MCMV-infected animals and increased viral loads in the liver, spleen, and the CNS, suggesting an important role for these cells in the control of MCMV replication in the newborn brain. Examination of brain mononuclear cells revealed that CD8(+) T cell infiltrates expressed high levels of CD69, CD44, and CD49d. IE1(168)-specific CD8(+) T cells accumulated in the CNS and produced IFN-gamma and TNF-alpha but not IL-2 following peptide stimulation. Moreover, adoptive transfer of brain mononuclear cells resulted in decreased virus burden in immunodepleted MCMV-infected syngeneic mice. Depletion of the CD8(+) cell population following transfer eliminated control of virus replication. In summary, these results show that functionally mature virus-specific CD8(+) T cells are recruited to the CNS in mice infected with MCMV as neonates.     

Age-dependent resistance to lethal alphavirus encephalitis in mice: analysis of gene expression in the central nervous system and identification of a novel interferon-inducible protective gene,mouse ISG12

Several different mammalian neurotropic viruses produce an age-dependent encephalitis characterized by more severe disease in younger hosts. To elucidate potential factors that contribute to age-dependent resistance to lethal viral encephalitis, we compared central nervous system (CNS) gene expression in neonatal and weanling mice that were either mock infected or infected intracerebrally with a recombinant strain, dsTE12Q, of the prototype alphavirus Sindbis virus. In 1-day-old mice, infection with dsTE12Q resulted in rapidly fatal disease associated with high CNS viral titers and extensive CNS apoptosis, whereas in 4-week-old mice, dsTE12Q infection resulted in asymptomatic infection with lower CNS virus titers and undetectable CNS apoptosis. GeneChip expression comparisons of mock-infected neonatal and weanling mouse brains revealed developmental regulation of the mRNA expression of numerous genes, including some apoptosis regulatory genes, such as the proapoptotic molecules caspase-3 and TRAF4, which are downregulated during development, and the neuroprotective chemokine, fractalkine, which is upregulated during postnatal development. In parallel with increased neurovirulence and increased viral replication, Sindbis virus infection in 1-day-old mice resulted in both a greater number of host inflammatory genes with altered expression and greater changes in levels of host inflammatory gene expression than infection in 4-week-old mice. Only one inflammatory response gene, an expressed sequence tag similar to human ISG12, increased by a greater magnitude in infected 4-week-old mouse brains than in infected 1-day-old mouse brains. Furthermore, we found that enforced neuronal ISG12 expression results in a significant delay in Sindbis virus-induced death in neonatal mice. Together, our data identify genes that are developmentally regulated in the CNS and genes that are differentially regulated in the brains of different aged mice in response to Sindbis virus infection.     

Antibody is required for clearance of infectious murine hepatitis virus A59 from the central nervous system, but not the liver.

Intracerebral inoculation with mouse hepatitis virus strain A59 results in viral replication in the CNS and liver. To investigate whether B cells are important for controlling mouse hepatitis virus strain A59 infection, we infected muMT mice who lack membrane-bound IgM and therefore mature B lymphocytes. Infectious virus peaked and was cleared from the livers of muMT and wild-type mice. However, while virus was cleared from the CNS of wild-type mice, virus persisted in the CNS of muMT mice. To determine how B cells mediate viral clearance, we first assessed CD4(+) T cell activation in the absence of B cells as APC. CD4(+) T cells express wild-type levels of CD69 after infection in muMT mice. IFN-gamma production in response to viral Ag in muMT mice was also normal during acute infection, but was decreased 31 days postinfection compared with that in wild-type mice. The role of Ab in viral clearance was also assessed. In wild-type mice plasma cells appeared in the CNS around the time that virus is cleared. The muMT mice that received A59-specific Ab had decreased virus, while mice with B cells deficient in Ab secretion did not clear virus from the CNS. Viral persistence was not detected in FcR or complement knockout mice. These data suggest that clearance of infectious mouse hepatitis virus strain A59 from the CNS requires Ab production and perhaps B cell support of T cells; however, virus is cleared from the liver without the involvement of Abs or B cells.     

Decreased antiviral immune response within the central nervous system of aged mice is associated with increased lethality of West Nile virus encephalitis

West Nile virus (WNV) is an emerging pathogen that causes disease syndromes ranging from a mild flu‐like illness to encephalitis. While the incidence of WNV infection is fairly uniform across age groups, the risk of lethal encephalitis increases with advanced age. Prior studies have demonstrated age‐related, functional immune deficits that limit systemic antiviral immunity and increase mortality; however, the effect of age on antiviral immune responses specifically within the central nervous system (CNS) is unknown. Here, we show that aged mice exhibit increased peripheral organ and CNS tissue viral burden, the latter of which is associated with alterations in activation of both myeloid and lymphoid cells compared with similarly infected younger animals. Aged mice exhibit lower MHCII expression by microglia, and higher levels of PD1 and lower levels of IFNγ expression by WNV‐specific CD8⁺ T cells in the CNS and CD8⁺CD45⁺ cells. These data indicate that the aged CNS exhibits limited local reactivation of T cells during viral encephalitis, which may lead to reduced virologic control at this site.     

禽流感H5N1亚型病毒对五个不同品系小鼠致病性的比较(英文)

目的比较了不同遗传背景小鼠对禽流感H5N1亚型病毒的致病敏感性,为H5N1禽流感模型制作和机理研究提供依据。方法近交系BALB/c、C57BL/6和封闭群ICR、NIHSwiss和KMSwiss共五个不同品系小鼠。每个品系实验动物30只,分接毒组20只,空白对照组10只,每组雌雄各半。病毒株为A/Goose/Guangdong/NH/2003(H5N1),经测定TCID50为10-4.875/mL。接毒组通过鼻腔接种0.1mL病毒液,对照组接种正常鸡胚尿囊液。小鼠接毒后连续观察14d,观察记录临床症状、体温、体重变化,对在实验期间死亡和实验14d结束后仍然存活的小鼠均进行组织器官病理取材,进行RT-PCR病毒分离检测、HE染色及H5N1抗原特异性免疫组化染色。结果①临床症状:H5N1禽流感病毒能感染五个品系的小鼠,引起呼吸急促等症状和一过性体重、体温下降。②死亡情况:小鼠在接毒后第1天即出现死亡,死亡的高峰期集中在接毒后第3～6天。五个品系小鼠死亡率存在差异,BALB/c为70%,ICR为50%,NIHSwiss为40%,C57BL/6为25%,KMSwiss为10%;③病毒分离:各组接毒小鼠在死亡后均进行了病毒分离,死亡小鼠的肺脏均分离到病毒,其他脏器未分离到病毒。④病理变化:实验期间五个品系死亡小鼠肺脏病理改变相近。大体观:死亡小鼠肺部淤血,呈暗红色,体积增大,局部肺组织实变。镜下观:死亡小鼠的共同病理改变为间质性肺炎,具体表现为肺泡腔及间质出血、炎性细胞浸润;间质增生,肺泡隔增宽;肺泡腔中见纤维素性渗出,透明膜形成。⑤免疫组化结果 :在死亡小鼠的气管上皮细胞和肺巨噬细胞可观察到H5N1禽流感病毒阳性表达。结论小鼠作为H5N1禽流感病毒模型具有普适性,不同品系小鼠感染鹅源H5N1禽流感病毒的临床症状、病程和病理变化与人禽流感病例相似。不同品系小鼠的死亡比例有明显差别,可以根据不同的实验目的 ,选择不同品系的小鼠制作H5N1禽流感动物模型。不同品系的遗传特性对禽流感易感性产生明显的影响,遗传背景可能与H5N1禽流感病毒感染应答机理存在联系:BALB/c和C57BL/6均为近交系,其中BALB/c小鼠的品系特征之一表现为干扰素产量低,接种H5N1病毒后表现为高死亡率(70%),而C57BL/6小鼠的干扰素产量高,接种H5N1病毒后表现为低死亡率(25%),提示不同遗传背景小鼠的干扰素水平与H5N1感染致死具相关性。为进一步研究H5N1禽流感病毒易感性相关基因以及其与宿主免疫反应的关系提供了一个研究基础。     

Mode of spread to and within the central nervous system after oral infection of neonatal mice with the DA strain of Theiler's murine encephalomyelitis virus.

Theiler's murine encephalomyelitis virus is a neurotropic enterovirus known to cause biphasic neural disease after intracerebral inoculation into adult mice. The present study characterizes a neonatal mouse model with a high disease incidence for the study of the acute phase of the pathogenesis of the DA strain of Theiler's murine encephalomyelitis virus after oral infection. The route of viral spread to and within the central nervous system (CNS) was determined by examining the kinetics of viral replication in various organs and by performing histopathological analysis. Viral antigen was detected widely in the neonatal CNS, mainly in the gray matter, and it was asymmetrical and multifocal in its distribution, with considerable variation in lesion distribution from animal to animal. Necrotizing lesions appeared to expand by direct extension from infected cells to their close neighbors, with a general disregard of neuroanatomical boundaries. The diencephalon showed particular susceptibility to viral infection. Other areas of the CNS, including the cerebellum and dentate gyrus of the hippocampus, were consistently spared. Neurons with axons extending peripherally to other organs or receiving direct input from the peripheral nervous system were not preferentially affected. The kinetics of viral replication in the liver, spleen, and CNS and the histopathological findings indicate that viral entry to the CNS is via a direct hematogenous route in orally infected neonatal mice and that the disease then progresses within the CNS mainly by direct extension from initial foci.     

The interferon-inducible gene viperin restricts West Nile virus pathogenesis

Type I interferon (IFN) signaling coordinates an early antiviral program in infected and uninfected cells by inducing IFN-stimulated genes (ISGs) that modulate viral entry, replication, and assembly. However, the specific antiviral functions in vivo of most ISGs remain unknown. Here, we examined the contribution of the ISG viperin to the control of West Nile virus (WNV) in genetically deficient cells and mice. While modest increases in levels of WNV replication were observed for primary viperin(-/-) macrophages and dendritic cells, no appreciable differences were detected in deficient embryonic cortical neurons or fibroblasts. In comparison, viperin(-/-) adult mice infected with WNV via the subcutaneous or intracranial route showed increased lethality and/or enhanced viral replication in central nervous system (CNS) tissues. In the CNS, viperin expression was induced in both WNV-infected and adjacent uninfected cells, including activated leukocytes at the site of infection. Our experiments suggest that viperin restricts the infection of WNV in a tissue- and cell-type-specific manner and may be an important ISG for controlling viral infections that cause CNS disease.     

Antibody prevents virus reactivation within the central nervous system.

The neurotropic JHM strain of mouse hepatitis virus (JHMV) produces an acute CNS infection characterized by encephalomyelitis and demyelination. The immune response cannot completely eliminate virus, resulting in persistence associated with chronic ongoing CNS demyelination. The contribution of humoral immunity to viral clearance and persistent infection was investigated in mice homozygous for disruption of the Ig mu gene (IgM-/-). Acute disease developed with equal kinetics and severity in IgM-/- and syngeneic C57BL/6 (wt) mice. However, clinical disease progressed in IgM-/- mice, while wt mice recovered. Viral clearance during acute infection was similar in both groups, supporting a primary role of cell-mediated immunity in viral clearance. In contrast to wt mice, in which infectious virus was reduced to below detection following acute infection, increasing infectious virus was recovered from the CNS of the IgM-/- mice following initial clearance. No evidence was obtained for selection of variant viruses nor was there an apparent loss of cell-mediated immunity in the absence of Ab. Passive transfer of anti-JHMV Ab following initial clearance prevented reactivation of infectious virus within the CNS of IgM-/- mice. These data demonstrate the clearance of infectious virus during acute disease by cell-mediated immunity. However, immunologic control is not maintained in the absence of anti-viral Ab, resulting in recrudescence of infectious virus. These data suggest that humoral immunity plays no role in controlling virus during acute infection, but plays an important role in establishing and maintaining CNS viral persistence.     

Mouse adenovirus type 1 causes a fatal hemorrhagic encephalomyelitis in adult C57BL/6 but not BALB/c mice.

Mouse adenovirus type 1 (MAV-1) produces a lethal disease in newborn or suckling mice characterized by infectious virus and viral lesions in multiple organs. Previous reports of MAV-1 infection of adult mice generally described serologic evidence of infection without morbidity or mortality. However, our current results demonstrate that MAV-1 causes a fatal illness in adult C57BL/6(B6) mice (50% lethal dose, [LD50], 10(3.0) PFU) but not in adult BALB/c mice at all of the doses tested (LD50, > or = 10(5.0) PFU). Adult (BALB/c x B6)F1 mice were intermediately susceptible (LD50, 10(4.5) PFU). Clinically, the sensitive B6 mice showed symptoms of acute central nervous system (CNS) disease, including tremors, seizures, ataxia, and paralysis. Light microscopic examination of CNS tissue from the B6 animals revealed petechial hemorrhages, edema, neovascularization, and mild inflammation in the brain and spinal cord. Analysis by electron microscopy showed evidence of inflammation, such as activated microglia, as well as swollen astrocytic endfeet and perivascular lipid deposition indicative of blood-brain barrier dysfunction. Outside of the CNS, the only significant pathological findings were foci of cytolysis in the splenic white pulp. Assessment of viral replication from multiple tissues was performed by using RNase protection assays with an antisense MAV-1 early region 1a probe. The greatest amounts of viral mRNA in MAV-1-infected B6 animals were located in the brain and spinal cord. Less viral message was detected in the spleen, lungs, and heart. No viral mRNA was detected in BALB/c mouse tissue, with the exception of low levels in the heart. Viral titers of organ tissues were also determined and were concordant with RNase protection findings on the brain and spinal cord but failed to demonstrate significant infectious virus in additional organs. Our experiments demonstrate that MAV-1 has a striking tropism for the CNS that is strain dependent, and this provides an informative in vivo model for the study of adenoviral pathogenesis.     

The Production of Antibody by Invading B Cells Is Required for the Clearance of Rabies Virus from the Central Nervous System

Background

The pathogenesis of rabies is associated with the inability to deliver immune effectors across the blood-brain barrier and to clear virulent rabies virus from CNS tissues. However, the mechanisms that facilitate immune effector entry into CNS tissues are induced by infection with attenuated rabies virus.

Methodology/Principal Findings

Infection of normal mice with attenuated rabies virus but not immunization with killed virus can promote the clearance of pathogenic rabies virus from the CNS. T cell activity in B cell–deficient mice can control the replication of attenuated virus in the CNS, but viral mRNA persists. Low levels of passively administered rabies virus–neutralizing antibody reach infected cells in the cerebellum of B cell–deficient mice but are not sufficient to mediate virus clearance. Production of rabies virus-specific antibody by B cells invading CNS tissues is required for this process, and a substantial proportion of the B cells that accumulate in the CNS of mice infected with attenuated rabies virus produce virus-specific antibodies.

Conclusions/Significance

The mechanisms required for immune effectors to enter rabies virus-infected tissues are induced by infection with attenuated rabies virus but not by infection with pathogenic rabies viruses or immunization with killed virus. T cell activities can inhibit rabies virus replication, but the production of rabies virus–specific antibodies by infiltrating B cells, as opposed to the leakage of circulating antibody across the BBB, is critical to elimination of the virus. These findings suggest that a pathogenic rabies virus infection may be treatable after the virus has reached the CNS tissues, providing that the appropriate immune effectors can be targeted to the infected tissues.