Th1 cell-mediated resistance to cutaneous infection with Leishmania major is independent of P- and E-selectins

Studies in several models of inflammation have underscored the importance of P- and E-selectins in the migration of T cells to inflamed tissues. However, the role of the endothelial selectins in infection-induced cutaneous inflammation and host-protective immunity has not been investigated. In this study, we demonstrate that CD4(+) T cells recruited to the cutaneous compartment during infection with Leishmania major express P- and E-selectin ligands. Furthermore, expression of P- and E-selectin ligands correlates with activated Leishmania-specific Th1 cells and is dependent upon IL-12. To investigate the functional role of the endothelial selectins during leishmaniasis, we infected mice either singly or doubly deficient in the expression of P- and E- selectins. Mice lacking both P- and E-selectins developed significantly less inflammation at the site of a primary and secondary infection, and exhibited an impaired delayed-type hypersensitivity response. Surprisingly, the absence of the endothelial selectins had no effect on the control of parasite replication or immunity to reinfection. Thus, these data demonstrate that although the endothelial selectins contribute to the inflammatory response, they are not required for protective immunity to L. major. Moreover, these data suggest that by blocking P- and E-selectins, the immune pathology associated with cutaneous leishmaniasis might be ameliorated without compromising immunity to infection.     

Size-selective loosening of the blood-brain barrier in claudin-5-deficient mice

Tight junctions are well-developed between adjacent endothelial cells of blood vessels in the central nervous system, and play a central role in establishing the blood-brain barrier (BBB). Claudin-5 is a major cell adhesion molecule of tight junctions in brain endothelial cells. To examine its possible involvement in the BBB, claudin-5-deficient mice were generated. In the brains of these mice, the development and morphology of blood vessels were not altered, showing no bleeding or edema. However, tracer experiments and magnetic resonance imaging revealed that in these mice, the BBB against small molecules (<800 D), but not larger molecules, was selectively affected. This unexpected finding (i.e., the size-selective loosening of the BBB) not only provides new insight into the basic molecular physiology of BBB but also opens a new way to deliver potential drugs across the BBB into the central nervous system.     

A cell culture model of the blood-brain barrier

Endothelial cells that make up brain capillaries and constitute the blood-brain barrier become different from peripheral endothelial cells in response to inductive factors found in the nervous system. We have established a cell culture model of the blood-brain barrier by treating brain endothelial cells with a combination of astrocyte-conditioned medium and agents that elevate intracellular cAMP. These cells form high resistance tight junctions and exhibit low rates of paracellular leakage and fluid-phase endocytosis. They also undergo a dramatic structural reorganization as they form tight junctions. Results from these studies suggest modes of manipulating the permeability of the blood-brain barrier, potentially providing the basis for increasing the penetration of drugs into the central nervous system.     

Human TH17 lymphocytes promote blood-brain barrier disruption and central nervous system inflammation

T(H)17 lymphocytes appear to be essential in the pathogenesis of numerous inflammatory diseases. We demonstrate here the expression of IL-17 and IL-22 receptors on blood-brain barrier endothelial cells (BBB-ECs) in multiple sclerosis lesions, and show that IL-17 and IL-22 disrupt BBB tight junctions in vitro and in vivo. Furthermore, T(H)17 lymphocytes transmigrate efficiently across BBB-ECs, highly express granzyme B, kill human neurons and promote central nervous system inflammation through CD4+ lymphocyte recruitment.     

RAGE mediates a novel proinflammatory axis: a central cell surface receptor for S100/calgranulin polypeptides.

S100/calgranulin polypeptides are present at sites of inflammation, likely released by inflammatory cells targeted to such loci by a range of environmental cues. We report here that receptor for AGE (RAGE) is a central cell surface receptor for EN-RAGE (extracellular newly identified RAGE-binding protein) and related members of the S100/calgranulin superfamily. Interaction of EN-RAGEs with cellular RAGE on endothelium, mononuclear phagocytes, and lymphocytes triggers cellular activation, with generation of key proinflammatory mediators. Blockade of EN-RAGE/RAGE quenches delayed-type hypersensitivity and inflammatory colitis in murine models by arresting activation of central signaling pathways and expression of inflammatory gene mediators. These data highlight a novel paradigm in inflammation and identify roles for EN-RAGEs and RAGE in chronic cellular activation and tissue injury.     

Identification of initiator B cells, a novel subset of activation-induced deaminase-dependent B-1-like cells that mediate initiation of contact sensitivity

Contact sensitivity (CS) is related to delayed-type hypersensitivity and is a well-characterized prototype of T cell-mediated inflammation. However, the inflammatory response associated with CS is additionally dependent on Ag-specific IgM produced by a subpopulation of B cells in response to sensitization. Upon re-exposure to hapten, this IgM mediates rapid vascular activation and subsequent recruitment of proinflammatory T cells to the local site. Interference with this pathway prevents the full development of the classic delayed inflammatory response and is therefore termed the "CS initiation" pathway. In this study, we show that CS initiation is defective in mice deficient in activation-induced deaminase, an enzyme central to the process of somatic hypermutation. Using adoptive transfer experiments, we demonstrate that the defect is specific to a B-1-like population of B cells and that transfer of WT cells reconstitutes CS initiation mechanisms in deficient recipients. We went on to identify a novel subpopulation of Ag-binding B cells in the spleens of sensitized mice that possess initiation activity (CD19(+)CD5(+)Thy-1(int)IgM(high)IgD(high)) that we name "initiator B cells." Analysis of BCR H chain genes isolated from these cells revealed evidence of activation-induced deaminase-mediated somatic hypermutation. The sensitivity of CS initiation to very low amounts of sensitizing hapten suggests that the responsible B cells have increased IgM receptor gene mutations enabling selection to generate Abs with sufficient affinity to mediate the response.     

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.     

Cysteinyl leukotrienes regulate Th2 cell-dependent pulmonary inflammation

The Th2 cell-dependent inflammatory response is a central component of asthma, and the ways in which it is regulated is a critical question. The cysteinyl leukotrienes (cys-LTs) are 5-lipoxygenase pathway products implicated in asthma, in particular, by their function as smooth muscle constrictors of airways and microvasculature. To elucidate additional roles for cys-LTs in the pathobiology of pulmonary inflammation, we used an OVA sensitization and challenge protocol with mice lacking leukotriene C(4) synthase (LTC(4)S), the terminal enzyme for cys-LT generation. Ag-induced pulmonary inflammation, characterized by eosinophil infiltration, goblet cell hyperplasia with mucus hypersecretion, and accumulation and activation of intraepithelial mast cells was markedly reduced in LTC(4)S(null) mice. Furthermore, Ag-specific IgE and IgG1 in serum, Th2 cell cytokine mRNA expression in the lung, and airway hyperresponsiveness to methacholine were significantly reduced in LTC(4)S(null) mice compared with wild-type controls. Finally, the number of parabronchial lymph node cells from sensitized LTC(4)S(null) mice and their capacity to generate Th2 cell cytokines ex vivo after restimulation with Ag were also significantly reduced. In contrast, delayed-type cutaneous hypersensitivity, a prototypic Th1 cell-dependent response, was intact in LTC(4)S(null) mice. These findings provide direct evidence of a role for cys-LTs in regulating the initiation and/or amplification of Th2 cell-dependent pulmonary inflammation.     

Regulation of lymphokine response during reinfection by influenza virus. Production of a factor that inhibits lymphokine activity

Mononuclear cells, obtained from the spleens and lungs of influenza virus-seropositive C57BL/6 mice at 2 to 4 days after re-infection with homologous virus (strain A/Bangkok/1/79), produced a low m.w. factor in vitro that prevents the biologic expression, but not production, of the lymphokine, leukocyte migration inhibition factor (LIF). The low m.w. factor inhibited LIF activity without destroying the LIF molecule inasmuch as simple dialysis restored lymphokine activity to culture supernatants. Production of the low m.w. factor was observed from 2 to 4 days after re-infection, at which time the delayed-type hypersensitivity response to viral Ag was suppressed. In contrast, LIF was produced by splenocytes and lung mononuclear cells obtained at all times tested after re-infection (from 2 to 30 days). Production of the low m.w. factor required re-infection of influenza A virus-seropositive mice with type A virus; re-infection with influenza B virus failed to induce production. Ag specificity was also required in vitro for splenocytes to produce the factor; cells from type A virus-re-infected mice required type A Ag stimulation. Cell depletion studies with mAb plus C revealed that macrophages and T cells along with Ag stimulation were required for factor production by spleen cells. However, mononuclear cells obtained within 4 days from the lungs of re-infected mice did not require in vitro Ag stimulation for production of the low m.w. factor, and factor production was dependent upon the presence of CD4+ (L3T4) cells in the culture. Fractionation of culture supernatants over a Sephadex G-50 column indicated that the factor had a molecular mass of 2 to 3 kDa, and by FPLC chromatofocusing over a Mono P column, the factor eluted at a pH of approximately 8.2. Thus, re-exposure of influenza virus-seropositive mice to homologous virus resulted in the production of a low m.w. factor that prevented the biologic expression of LIF, but not its production. Lymphokines are an important component of the delayed-type hypersensitivity response; the presence of mononuclear cells secreting a low m.w. factor and LIF concomitantly at the site of virus replication (lungs) and the capacity of the factor to block the biologic expression of LIF in vitro suggest that the factor may have a role in the regulation of a delayed-type hypersensitivity response in vivo during re-infection.     

B-1 B cells mediate required early T cell recruitment to elicit protein-induced delayed-type hypersensitivity

We define the initiation of elicited delayed-type hypersensitivity (DTH) as a series of processes leading to local extravascular recruitment of effector T cells. Responses thus have two sequential phases: 1) 2-h peaking initiation required for subsequent recruitment of T cells, and 2) the late classical 24-h component mediated by the recruited T cells. We analyzed DTH initiation to protein Ags induced by intradermal immunization without adjuvants. Ag-spceific initiating cells are present by 1 day in spleen and lymph nodes. Their phenotypes, determined by depletion of cell transfers by mAb and complement, are CD5(+), CD19(+), CD22(+), B220(+), Thy1(+), and Mac1(+), suggesting that they are B-1 B cells. DTH initiation is absent in micro MT B cell and xid B-1 cell deficient mice, is impaired in mice unable to secrete IgM, and is reconstituted with 1 day immune serum, suggesting that early B-1 cell-derived IgM is responsible. Study of complement C5a receptor-deficient mice, anti-C5 mAb neutralization, or mast cell deficiency suggests that DTH initiation depends on complement and mast cells. ELISPOT assay confirmed production of Ag-specific IgM Abs at days 1 and 4 in wild-type mice, but not in B-1 cell-deficient xid mice. We conclude that rapidly activated B-1 cells produce specific IgM Abs which, after local secondary skin challenge, form Ag-Ab complexes that activate complement to generate C5a. This stimulates C5a receptors on mast cells to release vasoactive substances, leading to endothelial activation for the 2-h DTH-initiating response, allowing local recruitment of DTH-effector T cells.     

Cu/Zn superoxide dismutase plays important role in immune response

Activation of macrophages leads to the secretion of cytokines and enzymes that shape the inflammatory response and increase metabolic processes. This, in turn, results in increased production of reactive oxygen species. The role of Cu/Zn superoxide dismutase (SOD-1), an important enzyme in cellular oxygen metabolism, was examined in activated peritoneal elicited macrophages (PEM) and in several inflammatory processes in vivo. LPS and TNF-alpha induced SOD-1 in PEM. SOD-1 induction by LPS was mainly via extracellular signal-regulated kinase-1 activation. Transgenic mice overexpressing SOD-1 demonstrated a significant increase in the release of TNF-alpha and of the metalloproteinases MMP-2 and MMP-9 from PEM. Disulfiram (DSF), an inhibitor of SOD-1, strongly inhibited the release of TNF-alpha, vascular endothelial growth factor, and MMP-2 and MMP-9 from cultured activated PEM. These effects were prevented by addition of antioxidants, further indicating involvement of reactive oxygen species. In vivo, transgenic mice overexpressing SOD-1 demonstrated a 4-fold increase in serum TNF-alpha levels and 2-fold stronger delayed-type hypersensitivity reaction as compared with control nontransgenic mice. Conversely, oral administration of DSF lowered TNF-alpha serum level by 4-fold, lowered the delayed-type hypersensitivity response in a dose-dependent manner, and significantly inhibited adjuvant arthritis in Lewis rats. The data suggest an important role for SOD-1 in inflammation, establish DSF as a potential inhibitor of inflammation, and raise the possibility that regulation of SOD-1 activity may be important in the treatment of immune-dependent pathologies.     

Transgenic Expression of IFN-γ in the Eye as a Model for Studying Ocular Inflammatory Disease

To study the effects of IFN-γ on intraocular inflammation we used mice with transgenic expression of IFN-γ in the retina of the eye. These transgenic mice (rhoγ) were challenged intraocularly with soluble and cellular antigens and then studied for development of uveitis and delayed-type hypersensitivity reaction after a second intracutaneous challenge with the same antigen. Further experiments tested the influence of IFN-γ on infection with herpes simplex (HSV) by intraocular virus inoculation in rhoγ mice and rhoγ mice crossed with MHC class I or class II deficient mice. Pathology was studied by morphology immunocytochemistry and electron microscopy. Growth of HSV was assessed by plaque assay on Vero cells. Rhoγ transgenic mice produced IFN-γ in the photoreceptors of the retina and secreted the cytokine into the vitreous of the eye. These animals suffered from cellular infiltration of the eyes, cataracts, and degeneration of the photoreceptors. In contrast to control mice, transgenic mice had increased uveal inflammation and developed delayed-type hypersensitivity after intraocular challenge with alloantigens such as allogeneic splenocytes and inactivated virus. Rhoγ mice also experienced protection from infection with herpes simplex virus-1 (HSV-1) and HSV-2, suffering a less severe course of disease than control mice. Cytokine-induced protection was not based on viral replication block and did not require simultaneous expression of MHC class I and class II. The rhoγ transgenic mouse provided a model suitable for testing mechanisms of IFN-γ action in the eyein vivo.The surprising results offer new arguments in the evaluation of cytokine effects.     

Characterization of Theiler's murine encephalomyelitis virus (TMEV)-specific delayed-type hypersensitivity responses in TMEV-induced demyelinating disease: correlation with clinical signs

After intracerebral inoculation of Theiler's murine encephalomyelitis virus (TMEV), certain mouse strains develop a persistent central nervous system (CNS) infection and inflammatory demyelinating lesions containing infiltrates of mononuclear cells and macrophages. Previous findings demonstrating a strong correlation between disease incidence, the presence of particular H-2 region genotypes, and development of high levels of TMEV-specific delayed-type hypersensitivity (DTH) supported an immune-mediated basis for myelin breakdown. These findings led us to examine whether a possible causal relationship would be supported by a temporal analysis comparing the onset of clinical disease and the development of TMEV-specific cellular or humoral immune responses in susceptible and resistant strains. In susceptible SJL/J mice, TMEV-specific DTH and T cell proliferative (Tprlf) responses developed within 10 to 14 days postinfection, preceded the onset of clinical signs, and remained elevated for 6 mo. In contrast, resistant BALB/c mice developed low levels of TMEV-specific Tprlf and no measurable DTH. However, both strains attained comparable levels of TMEV-specific serum antibody responses with parallel kinetics. Both DTH and Tprlf responses in susceptible SJL/J mice were shown to be specific for TMEV and mediated by L3T4+, Lyt-1+2-, class II-restricted T cells. A model is proposed implicating an effector role for TMEV-specific DTH, wherein lymphokine release by virus-specific DTH T cells leads to the recruitment, accumulation, and activation of macrophages in CNS tissue, which cause bystander myelin destruction and provide a permissive population of host cells for TMEV persistence.     

Critical role for mast cells in the pathogenesis of 2,4-dinitrobenzene-induced murine colonic hypersensitivity reaction

The immunological mechanisms underlying the role of mast cells in the pathogenesis of inflammatory bowel disease (IBD) are poorly defined. In this study, non-IgE mediated colonic hypersensitivity responses in BALB/c mice induced by skin sensitization with dinitrofluorobenzene (DNFB) followed by an intrarectal challenge with dinitrobenzene sulfonic acid featured as a model to study the role of mast cells in the development of IBD. Vehicle- or DNFB-sensitized mice were monitored for clinical symptoms and inflammation 72 h after dinitrobenzene sulfonic acid challenge. DNFB-sensitized mice developed diarrheic stool, increased colonic vascular permeability, hypertrophy of colonic lymphoid follicles (colonic patches), and showed cellular infiltration at the microscopic level. Increased numbers of mast cells were found in the colon of DNFB-sensitized mice located in and around colonic patches associated with elevated levels of mouse mast cell protease-1 in plasma indicating mast cell activation. Colonic patches of DNFB mice, stimulated in vitro with stem cell factor indicated that an increase in TNF-alpha levels in the colon is mainly mast cell originated. Finally, neutrophil infiltration was observed in the colon of DNFB-sensitized mice. Induction of this model in mast cell-deficient WBB6F(1) W/W(v) mice shows a profound reduction of characteristics of the colonic hypersensitivity reaction. Reconstitution with bone marrow-derived mast cells in WBB6F(1) W/W(v) mice fully restored the inflammatory response. This study demonstrates the importance of mast cells in the development of clinical symptoms and inflammation in the presented murine model for IBD.     

Suppression of Brain Mast Cells Degranulation Inhibits Microglial Activation and Central Nervous System Inflammation

Brain inflammation has a critical role in the pathophysiology of brain diseases. Microglia, the resident immune cells in the brain, play an important role in brain inflammation, while brain mast cells are the “first responder” in the injury rather than microglia. Functional aspects of mast cell-microglia interactions remain poorly understood. Our results demonstrated that site-directed injection of the “mast cell degranulator” compound 48/80 (C48/80) in the hypothalamus induced mast cell degranulation, microglial activation, and inflammatory factor production, which initiated the acute brain inflammatory response. “Mast cell stabilizer” disodium cromoglycate (cromolyn) inhibited this effect, including decrease of inflammatory cytokines, reduced microglial activation, inhibition of MAPK and AKT pathways, and repression of protein expression of histamine receptor 1 (H₁R), histamine receptor 4 (H₄R), protease-activated receptor 2 (PAR2), and toll-like receptor 4 (TLR4) in microglia. We also demonstrated that C48/80 had no effect on microglial activation in mast cell-deficient Kit^W-sh/W-sh mice. These results implicate that activated brain mast cells trigger microglial activation and stabilization of mast cell inhibits microglial activation-induced central nervous system (CNS) inflammation. Interactions between mast cells and microglia could constitute a new and unique therapeutic target for CNS immune inflammation-related diseases.     

Critical role of corneal Langerhans cells in the CD4- but not CD8-mediated immunopathology in herpes simplex virus-1-infected mouse corneas.

Previous studies have revealed that the RE strain of HSV type 1 (HSV-1) induces a tissue-destructive inflammatory response in the mouse cornea that is mediated by CD4 T lymphocytes, whereas the KOS strain of HSV-1 preferentially activates CD8 T lymphocytes in the cornea. Langerhans cells (LC) normally reside only at the periphery of the cornea but can migrate centripetally after HSV-1 infection. We studied the relative contribution of LC to the corneal inflammation induced by the KOS and RE strains of HSV-1. Ten days after infection, the central one-third of RE HSV-1-infected corneas contained an average of 5.7 LC/high-power field compared with 0.6 LC/high-power field in KOS-infected corneas. We hypothesized that the increased density of LC in RE HSV-1-infected corneas at the time of T lymphocyte infiltration contributed to the preferential activation of CD4 T lymphocytes in these corneas. To test this hypothesis, we gave mice a low dose of UV-B corneal irradiation (150 mJ/cm2) 1 day before infection with HSV-1. UV-B irradiation effectively prevented the migration of LC into the central cornea when measured 10 or 21 days after corneal infection with either HSV-1 strain. UV-B corneal irradiation had no effect on the CTL response to HSV-1 Ag in the regional lymph nodes after corneal infection with KOS or RE HSV-1. The delayed-type hypersensitivity response induced by both strains of virus, when measured 8 and 14 days after corneal infection, was significantly reduced by UV-B irradiation. UV-B irradiation significantly reduced the incidence (p = 0.0023) and severity (p = 0.0008) of corneal stromal disease induced by RE HSV-1 but did not significantly affect the stromal disease induced by KOS HSV-1. To distinguish between the effect of UV-B treatment on the afferent and efferent arms of the Ir in mice, we administered UV-B treatment to one eye, followed 24 h later by RE HSV-1 infection of both eyes. These mice developed a normal delayed-type hypersensitivity response, and stromal inflammation developed normally in the untreated eye. However, stromal inflammation was significantly reduced in the treated eye. Our findings suggest that LC play a critical role in the activation of HSV-reactive CD4 T lymphocytes in the cornea. Moreover, the type of corneal inflammation induced by different strains of HSV-1 may reflect their differential capacity to induce LC migration into the central cornea.     

Abolishment of TNBS-induced visceral hypersensitivity in mast cell deficient rats

Mucosal mast cells are implicated in visceral hypersensitivity associated with irritable bowel syndrome (IBS). In this study, we investigated the role of mast cells in the development of visceral hypersensitivity by using mast cell deficient (Ws/Ws) rats and their control (W+/W+). In W+/W+ rats, an injection of 2,4,6-trinitrobenzene sulfonic acid (TNBS) into the proximal colon produced a significant decrease in pain threshold of the distal colon. Severe mucosal necrosis and inflammatory cell infiltration with concomitant increase in tissue myeloperoxidase activity were observed in the proximal colon that was directly insulted by TNBS, whereas neither necrosis nor increased myeloperoxidase activity occurred in the distal colon, indicating that TNBS-induced hypersensitivity is not caused by the local tissue damage or inflammation in the region of the gut where distention stimuli were applied. On the other hand, TNBS failed to elicit visceral hypersensitivity in Ws/Ws rats. This finding indicates that mast cells are essential for development of TNBS-induced visceral hypersensitivity in rats. Since the severity of TNBS-induced proximal colon injury and MPO activity was not affected by mast cell deficiency, it is unlikely that abolishment of visceral hypersensitivity in mast cell deficient rats was a result of altered development of the primary injury in the proximal colon. There was no difference between sham-operated Ws/Ws and W+/W+ rats in colonic pain threshold to distention stimuli, indicating that mast cells play no modulatory roles in normal colonic nociception. The present results support the view that mucosal mast cells play key roles in the pathogenesis of IBS.     

Characterization of the inflammatory response in the central nervous system of mice susceptible or resistant to demyelination by Theiler's virus

Intracerebral inoculation of mice with Theiler's murine encephalomyelitis virus results in an intense inflammatory response of mononuclear leukocytes which infiltrate into the central nervous system. Resistant strains of mice have the ability to clear virus whereas susceptible strains become infected persistently and are associated with chronic demyelination which is proposed to be immune-mediated. In an attempt to better understand the role of the immune response during demyelination, mononuclear leukocytes were isolated from the central nervous system of infected mice and stained by an immunoperoxidase technique with anti-Thy-1.2, anti-L3T4, anti-Lyt-2 and anti-MAC-1 mAb. Infection of susceptible SJL/J mice resulted in a biphasic immune response which peaked on days 7 and 27 post-infection. In contrast, a single peak (day 7) was observed in resistant C57BL/10SNJ mice. The presence of Thy-1.2, L3T4, and MAC-1+ cells was similar between the two strains. However, although the number of Lyt-2+ cells peaked on day 7 in C57BL/10SNJ mice, they were not detected in SJL/J mice until 14 days post-infection and gradually increased in number over the course of infection. To further study the role of T cells in demyelination, serial frozen sections of brain and spinal cord were stained for the presence of Lyt-2 and L3T4+ cells in the lesions of chronically infected SJL/J mice. L3T4+ cells were observed predominantly in perivascular regions while Lyt-2+ cells were observed infiltrating the parenchyma. These results provide further evidence that Lyt-2+ lymphocytes are important in the mechanism of susceptibility/resistance to Theiler's murine encephalomyelitis virus-induced demyelination.     

Invariant NKT Cells Regulate the CD8 T Cell Response during Theiler's Virus Infection

Invariant NKT cells are innate lymphocytes with a broad tissue distribution. Here we demonstrate that iNKT cells reside in the central nervous system (CNS) in the absence of inflammation. Their presence in the CNS dramatically augments following inoculation of C57Bl/6 mice with the neurotropic Theiler''s murine encephalomyelitis virus (TMEV). At the peak of inflammation the cellular infiltrate comprises 45 000 iNKT cells for 1 250 CD8 T cells specific for the immunodominant TMEV epitope. To study the interaction between these two T cell subsets, we infected both iNKT cell deficient Jα18^-/- mice and iNKT cell enriched Vα14 transgenic mice with TMEV. The CD8 T cell response readily cleared TMEV infection in the iNKT cell deficient mice. However, in the iNKT cell enriched mice TMEV infection persisted and was associated with significant mortality. This was caused by the inhibition of the CD8 T cell response in the cervical lymph nodes and spleen after T cell priming. Taken together we demonstrate that iNKT cells reside in the CNS in the absence of inflammation and that their enrichment is associated with the inhibition of the anti-viral CD8 T cell response and an augmented mortality during acute encephalomyelitis.