Immune modulation within the brain: recruitment of inflammatory cells and increased major histocompatibility antigen expression following intracerebral injection of interferon-gamma

Pathogenic T cell cytokines in multiple sclerosis

Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the central nervous system that is believed to have an autoimmune etiology. As MS is the most common nontraumatic disease that causes disability in young adults, extensive research has been devoted to identifying therapeutic targets. In this review, we discuss the current understanding derived from studies of patients with MS and animal models of how specific cytokines produced by autoreactive CD4 T cells contribute to the pathogenesis of MS. Defining the roles of these cytokines will lead to a better understanding of the potential of cytokine-based therapies for patients with MS.

Interferons: A molecular switch between damage and repair in ageing and Alzheimer's disease

Alzheimer's disease was first described over 100 years ago, yet it remains incurable and affects 44 million people worldwide. Traditionally, research has largely focused on the amyloid cascade hypothesis, but interest in the importance of inflammation in the progression of the disease has recently been increasing. Interferons, a large family of cytokines that trigger the immune system, are believed to play a crucial role in the pathology of Alzheimer's disease. This review focuses on how interferons affect the brain during ageing and whether they could be candidate therapeutic targets for the treatment of Alzheimer's disease.

Comparative Immunopathology of Cetacean morbillivirus Infection in Free-Ranging Dolphins From Western Mediterranean, Northeast-Central, and Southwestern Atlantic

Cetacean morbillivirus (CeMV; Paramyxoviridae) causes epizootic and interepizootic fatalities in odontocetes and mysticetes worldwide. Studies suggest there is different species-specific susceptibility to CeMV infection, with striped dolphins (Stenella coeruleoalba), bottlenose dolphins (Tursiops truncatus), and Guiana dolphins (Sotalia guianensis) ranking among the most susceptible cetacean hosts. The pathogenesis of CeMV infection is not fully resolved. Since no previous studies have evaluated the organ-specific immunopathogenetic features of CeMV infection in tissues from infected dolphins, this study was aimed at characterizing and comparing immunophenotypic profiles of local immune responses in lymphoid organs (lymph nodes, spleen), lung and CNS in CeMV-molecularly (RT-PCR)-positive cetaceans from Western Mediterranean, Northeast-Central, and Southwestern Atlantic. Immunohistochemical (IHC) analyses targeted molecules of immunologic interest: caspase 3, CD3, CD20, CD57, CD68, FoxP3, MHCII, Iba1, IFNγ, IgG, IL4, IL10, lysozyme, TGFβ, and PAX5. We detected consistent CeMV-associated inflammatory response patterns. Within CNS, inflammation was dominated by CD3⁺ (T cells), and CD20⁺ and PAX5⁺ (B cells) lymphocytes, accompanied by fewer Iba1⁺, CD68⁺, and lysozyme⁺ histiocytes, mainly in striped dolphins and bottlenose dolphins. Multicentric lymphoid depletion was characterized by reduced numbers of T cells and B cells, more pronounced in Guiana dolphins. Striped dolphins and bottlenose dolphins often had hyperplastic (regenerative) phenomena involving the aforementioned cell populations, particularly chronically infected animals. In the lung, there was mild to moderate increase in T cells, B cells, and histiocytes. Additionally, there was a generalized increased expression of caspase 3 in lymphoid, lung, and CNS tissues. Apoptosis, therefore, is believed to play a major role in generalized lymphoid depletion and likely overt immunosuppression during CeMV infection. No differences were detected regarding cytokine immunoreactivity in lymph nodes, spleen, and lung from infected and non-infected dolphins by semiquantitative analysis; however, there was striking immunoreactivity for IFNγ in the CNS of infected dolphins. These novel results set the basis for tissue-specific immunophenotypic responses during CeMV infection in three highly susceptible delphinid species. They also suggest a complex interplay between viral and host's immune factors, thereby contributing to gain valuable insights into similarities, and differences of CeMV infection's immunopathogenesis in relation to body tissues, CeMV strains, and cetacean hosts.

Cytokine networks in neuroinflammation

Cytokines provide cells with the ability to communicate with one another and orchestrate complex multicellular behaviour. There is an emerging understanding of the role that cytokines play in normal homeostatic tissue function and how dysregulation of these cytokine networks is associated with pathological conditions. The central nervous system (CNS), where few blood-borne immune cells circulate, seems to be particularly vulnerable to dysregulated cytokine networks. In degenerative diseases, such as proteopathies, CNS-resident cells are the predominant producers of pro-inflammatory cytokines. By contrast, in classical neuroinflammatory diseases, such as multiple sclerosis and encephalitides, pro-inflammatory cytokines are mainly produced by tissue-invading leukocytes. Whereas the effect of dysregulated cytokine networks in proteopathies is controversial, cytokines delivered to the CNS by invading immune cells are in general detrimental to the tissue. Here, we summarize recent observations on the impact of dysregulated cytokine networks in neuroinflammation.

Efficacy and Safety of Fingolimod in an Unselected Patient Population

BACKGROUND

Fingolimod is a first in class oral compound approved for the treatment of relapsing-remitting multiple sclerosis (RR-MS). The aim of this study was to evaluate clinical and neuroradiological responses to fingolimod as well as the safety and tolerability in RR-MS patients in clinical practice. In addition, a panel of pro-inflammatory serum cytokines was explored as potential biomarker for treatment response.

METHODS

We conducted a retrospective, non-randomized, open-label, observational study in 105 patients with RR-MS and measured cytokines in longitudinal serum samples.

RESULTS

Compared to the year before fingolimod start the annualized relapse rate was reduced by 44%. Also, the percentage of patients with a worsening of the EDSS decreased. Accordingly, the fraction of patients with no evidence of disease activity (no relapse, stable EDSS, no new active lesions in MRI) increased from 11% to 38%. The efficacy and safety were comparable between highly active patients or patients with relevant comorbidities and our general patient population.

CONCLUSIONS

The efficacy in reducing relapses was comparable to that observed in the phase III trials. In our cohort fingolimod was safe and efficacious irrespective of comorbidities and previous treatment.

Opposing Roles of Interferon-Gamma on Cells of the Central Nervous System in Autoimmune Neuroinflammation

Multiple sclerosis (MS) is the principal cause of autoimmune neuroinflammation in humans, and its animal model, experimental autoimmune encephalomyelitis (EAE), is widely used to gain insight about their immunopathological mechanisms for and the development of novel therapies for MS. Most studies on the role of interferon (IFN)-γ in the pathogenesis and progression of EAE have focused on peripheral immune cells, while its action on central nervous system (CNS)-resident cells has been less explored. In addition to the well-known proinflammatory and damaging effects of IFN-γ in the CNS, evidence has also endowed this cytokine both a protective and regulatory role in autoimmune neuroinflammation. Recent investigations performed in this research field have exposed the complex role of IFN-γ in the CNS uncovering unexpected mechanisms of action that underlie these opposing activities on different CNS-resident cell types. The mechanisms behind these two-faced effects of IFN-γ depend on dose, disease phase, and cell development stage. Here, we will review and discuss the dual role of IFN-γ on CNS-resident cells in EAE highlighting its protective functions and the mechanisms proposed.

The interdependent, overlapping, and differential roles of type I and II IFNs in the pathogenesis of experimental autoimmune encephalomyelitis

Type I IFNs (IFN-α and IFN-β) and type II IFN (IFN-γ) mediate both regulation and inflammation in multiple sclerosis, neuromyelitis optica, and in experimental autoimmune encephalomyelitis (EAE). However, the underlying mechanism for these Janus-like activities of type I and II IFNs in neuroinflammation remains unclear. Although endogenous type I IFN signaling provides a protective response in neuroinflammation, we find that when IFN-γ signaling is ablated, type I IFNs drive inflammation, resulting in exacerbated EAE. IFN-γ has a disease stage-specific opposing function in EAE. Treatment of mice with IFN-γ during the initiation phase of EAE leads to enhanced severity of disease. In contrast, IFN-γ treatment during the effector phase attenuated disease. This immunosuppressive activity of IFN-γ required functional type I IFN signaling. In IFN-α/β receptor-deficient mice, IFN-γ treatment during effector phase of EAE exacerbated disease. Using an adoptive transfer EAE model, we found that T cell-intrinsic type I and II IFN signals are simultaneously required to establish chronic EAE by encephalitogenic Th1 cells. However, in Th17 cells loss of either IFN signals leads to the development of a severe chronic disease. The data imply that type I and II IFN signals have independent but nonredundant roles in restraining encephalitogenic Th17 cells in vivo. Collectively, our data show that type I and II IFNs function in an integrated manner to regulate pathogenesis in EAE.

Central nervous system vasculitis: still more questions than answers

The central nervous system (CNS) may be involved by a variety of inflammatory diseases of blood vessels. These include primary angiitis of the central nervous system (PACNS), a rare disorder specifically targeting the CNS vasculature, and the systemic vasculitides which may affect the CNS among other organs and systems. Both situations are severe and convey a guarded prognosis. PACNS usually presents with headache and cognitive impairment. Focal symptoms are infrequent at disease onset but are common in more advanced stages. The diagnosis of PACNS is difficult because, although magnetic resonance imaging is almost invariably abnormal, findings are non specific. Angiography has limited sensitivity and specificity. Brain and leptomeningeal biopsy may provide a definitive diagnosis when disclosing blood vessel inflammation and are also useful to exclude other conditions presenting with similar findings. However, since lesions are segmental, a normal biopsy does not completely exclude PACNS. Secondary CNS involvement by systemic vasculitis occurs in less than one fifth of patients but may be devastating. A prompt recognition and aggressive treatment is crucial to avoid permanent damage and dysfunction. Glucocorticoids and cyclophosphamide are recommended for patients with PACNS and for patients with secondary CNS involvement by small-medium-sized systemic vasculitis. CNS involvement in large-vessel vasculitis is usually managed with high-dose glucocorticoids (giant-cell arteritis) or glucocorticoids and immunosuppressive agents (Takayasu's disease). However, in large vessel vasculitis, where CNS symptoms are usually due to involvement of extracranial arteries (Takayasu's disease) or proximal portions of intracranial arteries (giant-cell arteritis), revascularization procedures may also have an important role.

Immunostimulants for malignant gliomas

Several immunostimulant approaches have been studied in the treatment of gliomas. The advent of recombinant DNA technology led to a nonspecific immunostimulation via systemic administration of cytokines. Recently, in attempts to more closely mimic their natural activity, cytokines have been delivered by implanting genetically transduced cells or by using in vivo gene transfer techniques. The latest efforts have focused on immunostimulatory agents that act directly on antigen-presenting cells and effector cells of the immune system via pattern recognition receptors. Combining these strategies with more than one mode of immunotherapy may provide better clinical results.

Acute in vivo exposure to interferon-gamma enables resident brain dendritic cells to become effective antigen presenting cells

Dendritic cells (DC) are the professional antigen presenting cells (APC) that bridge the innate and adaptive immune system. Previously, in a CD11c/EYFP transgenic mouse developed to study DC functions, we anatomically mapped and phenotypically characterized a discrete population of EYFP(+) cells within the microglia that we termed brain dendritic cells (bDC). In this study, we advanced our knowledge of the function of these cells in the CD11c/EYFP transgenic mouse and its chimeras, using acute stimuli of stereotaxically inoculated IFNgamma or IL-4 into the CNS. The administration of IFNgamma increased the number of EYFP(+)bDC but did not recruit peripheral DC into the CNS. IFNgamma, but not IL-4, upregulated the expression levels of major histocompatibility class II (MHC-II). In addition, IFNgamma-activated EYFP(+)bDC induced antigen-specific naïve CD4 T cells to proliferate and secrete Th1/Th17 cytokines. Activated bDC were also able to stimulate naïve CD8 T cells. Collectively, these data reveal the Th1 cytokine IFNgamma, but not the Th2 cytokine IL4, induces bDC to up-regulate MHC-II and become competent APC.

Current immunotherapeutic strategies for central nervous system tumors

Immunotherapy has emerged as a promising tool in the management of malignant central nervous system tumors. Despite improvement in patient survival, traditional approaches, which consist mostly of surgery, radiotherapy, and chemotherapy, have been largely unsuccessful in permanently controlling these aggressive tumors. Immunotherapeutic strategies offer not only a novel approach but also an advantage in a way other modalities have been failing. Specifically, the capabilities of the immune system to recognize altered cells while leaving normal cells intact offer tremendous advantage over the conventional therapeutic approaches. This article summarizes our current understanding of immunotherapeutic treatment modalities used in clinical trials for management of malignant central nervous system tumors.

Loss of IFN-gamma enables the expansion of autoreactive CD4+ T cells to induce experimental autoimmune encephalomyelitis by a nonencephalitogenic myelin variant antigen

MHC variant peptides are analogues of immunogenic peptides involving alterations of the MHC-binding residues, thereby altering the affinity of the peptide for the MHC molecule. Recently, our laboratory demonstrated that immunization of WT B6 mice with 45D, a low-affinity MHC variant peptide of MOG(35-55), results in significantly attenuated experimental autoimmune encephalomyelitis (EAE), yet IFN-gamma production is comparable to myelin oligodendrocyte glycoprotein (MOG)(35-55)-immunized mice. In light of these findings, we asked whether IFN-gamma was required for the reduced encephalitogenicity of the weak ligand 45D in EAE. In this study, we report that immunization of mice deficient in IFN-gamma or its receptor with 45D exhibit significant EAE signs compared with 45D-immunized wild-type B6 mice. Moreover, 45D-immunized IFN-gamma(-/-) and IFN-gammaR(-/-) mice demonstrate MOG tetramer-positive CD4(+) T cells within the CNS and display substantial numbers of MOG-specific CD4(+) T cells in the periphery. In contrast, wild-type mice immunized with 45D exhibit reduced numbers of MOG-specific CD4(+) T cells in the periphery and lack MOG tetramer- positive CD4(+) T cells in the CNS. Importantly, the increased encephalitogenicity of 45D in mice lacking IFN-gamma or IFN-gammaR was not due to deviation toward an enhanced IL-17-secreting phenotype. These findings demonstrate that IFN-gamma significantly attenuates the encephalitogenicity of 45D and are the first to highlight the importance of IFN-gamma signaling in setting the threshold level of responsiveness of autoreactive CD4(+) T cells to weak ligands.

Targeting inflammatory demyelinating lesions to sites of Wallerian degeneration

In Theiler's murine encephalomyelitis virus (TMEV) infection, an animal model for multiple sclerosis (MS), axonal injury precedes inflammatory demyelinating lesions, and the distribution of axonal damage present during the early phase of infection corresponds to regions where subsequent demyelination occurs during the chronic phase. We hypothesized that axonal damage recruits inflammatory cells to sites of Wallerian degeneration, leading to demyelination. Three weeks after TMEV infection, axonal degeneration was induced in the posterior funiculus of mice by injecting the toxic lectin Ricinus communis agglutinin (RCA) I into the sciatic nerve. Neuropathology was examined 1 week after lectin injection. Control mice, infected with TMEV but receiving no RCA I, had inflammatory demyelinating lesions in the anterior/lateral funiculi. Other control mice that received RCA I alone did not develop inflammatory lesions. In contrast, RCA I injection into TMEV-infected mice induced lesions in the posterior funiculus in addition to the anterior/lateral funiculi. We found no differences in lymphoproliferative responses or antibody titers against TMEV among the groups. This suggests that axonal degeneration contributes to the recruitment of inflammatory cells into the central nervous system by altering the local microenvironment. In this scenario, lesions develop from the axon (inside) to the myelin (outside) (Inside-Out model).

IFN-gamma-induced chemokines synergize with pertussis toxin to promote T cell entry to the central nervous system

Inflammation of the CNS, which occurs during multiple sclerosis and experimental autoimmune encephalomyelitis, is characterized by increased levels of IFN-gamma, a cytokine not normally expressed in the CNS. To investigate the role of IFN-gamma in CNS, we used intrathecal injection of a replication-defective adenovirus encoding murine IFN-gamma (AdIFNgamma) to IFN-gamma-deficient (GKO) mice. This method resulted in stable, long-lived expression of IFN-gamma that could be detected in cerebrospinal fluid using ELISA and Luminex bead immunoassay. IFN-gamma induced expression in the CNS of message and protein for the chemokines CXCL10 and CCL5, to levels comparable to those seen during experimental autoimmune encephalomyelitis. Other chemokines (CXCL2, CCL2, CCL3) were not induced. Mice lacking the IFN-gammaR showed no response, and a control viral vector did not induce chemokine expression. Chemokine expression was predominantly localized to meningeal and ependymal cells, and was also seen in astrocytes and microglia. IFN-gamma-induced chemokine expression did not lead to inflammation. However, when pertussis toxin was given i.p. to mice infected with the IFN-gamma vector, there was a dramatic increase in the number of T lymphocytes detected in the CNS by flow cytometry. This increase in blood-derived immune cells in the CNS did not occur with pertussis toxin alone, and did not manifest as histologically detectable inflammatory pathology. These results show that IFN-gamma induces a characteristic glial chemokine response that by itself is insufficient to promote inflammation, and that IFN-gamma-induced CNS chemoattractant signals can synergize with a peripheral infectious stimulus to drive T cell entry into the CNS.

Immunotherapy for malignant glioma: current approaches and future directions

Traditional therapies for the treatment of malignant glioma have failed to make appreciable gains regarding patient outcome in the last decade. Therefore, immunotherapeutic approaches have become increasingly popular in the treatment of this cancer. This article reviews general immunology of the central nervous system and the immunobiology of malignant glioma to provide a foundation for understanding the rationale behind current glioma immunotherapies. A review of currently implemented immunological treatments is then provided with special attention paid to the use of vaccines, gene therapy, cytokines, dendritic cells and viruses. Insights into future and developing avenues of glioma immunotherapy, such as novel delivery systems, are also discussed.

Expression of a dominant negative IFN-gammareceptor on mouse oligodendrocytes

The interferon-gamma (IFN-gamma) receptor is expressed by all nucleated cells, and binding of its cognate ligand, IFN-gamma, induces a wide variety of biological functions. Transgenic mice expressing a dominant negative IFN-gamma receptor 1 (IFN-gammaR1DeltaIC) on oligodendrocytes under control of the myelin proteolipid protein promoter are described. The mRNA encoding the transgene was only detected in the nervous system and protein expression was confirmed by immunohistochemistry. Transgenic receptor expression does not alter myelination and the mice exhibited no clinically apparent phenotype. Consistent with the restricted nervous system expression of the transgene, no alterations in peripheral immune responses were detected. Flow cytometric analysis demonstrated constitutive expression of both the IFN-gammaR1DeltaIC transgene and the endogenous IFN-gamma receptor 2 at high levels on oligodendrocytes derived from the transgenic mice. These oligodendrocytes also exhibited decreased STAT1 phosphorylation in response to IFN-gamma, confirming dominant negative transgene function. Transgenic mice in which oligodendrocytes have a diminished ability to respond to IFN-gamma showed delayed virus clearance from oligodendroglia compared with wild-type mice. This model will allow evaluation of oligodendrocyte responses to this critical cytokine during CNS inflammation.

IL-1 type I receptor plays a key role in mediating the recruitment of leukocytes into the central nervous system

This study investigates the role of type I IL-1 receptor (IL-1R1) in mediating the recruitment of leukocytes into the brain parenchyma in mice. Intracerebroventricular (icv) injection of interleukin IL-1beta induced infiltration of leukocytes between 8 and 72 h after the injection. Leukocytes were rarely found in the brain tissue of saline-injected animals. At 8h after IL-1beta injection, leukocytes were seen lining the blood vessels of the brain and sparsely scattered infiltration of leukocytes was found in the cortex. Peak infiltration of leukocytes, which distributed evenly throughout the brain, was seen at 16 h post-injection. The number of leukocytes in the brain declined thereafter and no leukocytes were found 72 h post-injection. This phenomenon was replicated in mice deficient in lymphotoxin-alpha (LT(alpha)), IL-6, interferon (IFN)-gamma receptor, or the tumor necrosis factor (TNF)-alpha receptor, but abrogated in animals deficient in IL-1R1. ICV injection of IFN-gamma or TNF-alpha, but not IL-6 or IL-12, also induced leukocyte infiltration into the brain. Injection of IL-1beta, IFN-gamma, TNF-alpha, IL-6, and IL-12 induced IL-1beta expression in the brain, with IL-6 and IL-12 being the least effective. Leukocyte infiltration induced by icv IFN-gamma and TNF-alpha was also abrogated in IL-1R1-knockout animals. The induced infiltrating leukocytes were identified as neutrophils. Chronic infection with Trypanosoma brucei resulted in the recruitment of T cells, but no other cell types, into the brain. This did not occur in IL-1R1-knockout mice. Thus, IL-1R1 appears to be important for the recruitment of leukocytes across the blood-brain barrier.

Critical Roles of CXC Chemokine Ligand 16/Scavenger Receptor that Binds Phosphatidylserine and Oxidized Lipoprotein in the Pathogenesis of Both Acute and Adoptive Transfer Experimental Autoimmune Encephalomyelitis

The scavenger receptor that binds phosphatidylserine and oxidized lipoprotein (SR-PSOX)/CXCL16 is a chemokine expressed on macrophages and dendritic cells, while its receptor expresses on T and NK T cells. We investigated the role of SR-PSOX/CXCL16 on acute and adoptive experimental autoimmune encephalomyelitis (EAE), which is Th1-polarized T cell-mediated autoimmune disease of the CNS. Administration of mAb against SR-PSOX/CXCL16 around the primary immunization decreased disease incidence of acute EAE with associated reduced infiltration of mononuclear cells into the CNS. Its administration was also shown to inhibit elevation of serum IFN-gamma level at primary immune response, as well as subsequent generation of Ag-specific T cells. In adoptive transfer EAE, treatment of recipient mice with anti-SR-PSOX/CXCL16 mAb also induced not only decreased clinical disease incidence, but also diminished traffic of mononuclear cells into the CNS. In addition, histopathological analyses showed that clinical development of EAE correlates well with expression of SR-PSOX/CXCL16 in the CNS. All the results show that SR-PSOX/CXCL16 plays important roles in EAE by supporting generation of Ag-specific T cells, as well as recruitment of inflammatory mononuclear cells into the CNS.

Identification of HLA a*0201 glioblastoma multiforme cell lines for immunotherapy by PCR-SSP and DNA sequencing

Most tumor specific antigens characterized to date are restricted by HLA a*0201, which is the major HLA subtype in many ethnic groups. Cancer cells that express tumor antigens in association with the HLA a*0201 subtype have been shown to be responsive to various immunotherapies. We therefore sought to identify glioma cell lines that also express this HLA subtype and determine whether they had the molecular properties needed for tumor-peptide presentation. The HLA a*0201 allele was identified with PCR using sequence-specific primers followed by DNA sequencing. With this method, we screened 15 glioma cell lines to determine if they were of the HLA a*0201 genotype. Glioma cell lines that express the HLA a*0201 subtype were further studied for the expression of MHC class I and beta-2-microglobulin (beta2m) molecules by flow cytometry, and peptide presentation molecules TAP-1, TAP-2, and tapasin by RT-PCR. We identified six out of fifteen cell lines that were of the HLA a*0201 subtype. These cell lines are U87, T98, U373, U138, CRL2365 and UMN-4. All these six cell lines exhibited high levels of MHC class I and beta2m molecules. In addition, these cell lines all expressed molecules required for peptide presentation as shown by the presence of peptide presentation-related molecules TAP-1, TAP-2 and tapasin. The identification of glioma cell lines that express the HLA a*0201 subtype along with the necessary molecules for peptide-presentation will enable their use in developing new immunotherapeutic approaches for treating brain tumors. The method used to identify HLA a*0201 glioma cells is rapid and inexpensive, and suitable for screening tumor cells.

Human alloreactive CTL interactions with gliomas and with those having upregulated HLA expression from exogenous IFN-gamma or IFN-gamma gene modification

By flow cytometry, a panel of 18 primary glioma cell explants exhibited high expression of class I HLA-A, B, C, but class II HLA-DR expression was absent. Freshly isolated normal brain cells displayed little or no HLA antigens. Alloreactive cytotoxic T lymphocytes (aCTL), sensitized to the HLA of the patient, were generated in a one-way mixed lymphocyte response (MLR). The specificity of aCTL was confirmed to be to target cells (patient glioma cells or lymphoblasts) expressing the relevant HLA antigens. However, nontumor patient-specific aCTL did not lyse normal brain cells. Titration of antibodies to HLA class I into cytotoxicity assays blocked lysis of gliomas by aCTL, confirming aCTL T cell receptor (TCR) interactions with the class I antigen on gliomas. Furthermore, aCTL interactions with glioma cells caused their apoptosis. Coincubations of aCTL with gliomas resulted in upregulated cytokine secretion. Importantly, dexamethasone, an immunosuppressive steroid used for brain edema, did not affect aCTL lytic function against tumor, indicating that steroid-dependent patients may benefit from the immunotherapy. We also explored the use of interferon-gamma (IFN-gamma) to increase aCTL tumor recognition. Coincubation of gliomas with exogenous IFN-gamma (500 U/ml, 48 h) caused a 3-fold upregulation of HLA class I and a slight induction of class II antigen expression. Gene-modified glioma cells producing IFN-gamma similarly displayed upregulated HLA expression. Glioma cells incubated with exogenous IFN-gamma or IFN-gamma-transduced glioma cells were more susceptible to lysis by aCTL than their parental counterparts, thus supporting the concept of combining IFN-gamma cytokine gene therapy with adoptive aCTL immunotherapy for brain tumor treatment.

CD134 plays a crucial role in the pathogenesis of EAE and is upregulated in the CNS of patients with multiple sclerosis

We investigated the role of the CD134 (also named OX40) molecule in experimental allergic encephalomyelitis (EAE) and multiple sclerosis (MS). We examined the susceptibility of Cd134(-/-) mice to EAE, an autoimmune murine model that is dependent on infiltrating CD4+ T lymphocytes reactive to myelin proteins. EAE induced by myelin oligodendrocyte glycoprotein (MOG) injection in Cd134(-/-) mice showed less severe clinical signs of disease and markedly reduced inflammatory infiltrates within the central nervous system (CNS). Resistance was associated with a strong reduction of pathogenic IFNgamma-producing T cells infiltrating the CNS of Cd134(-/-) mice. Furthermore, analysis of CNS tissue sections from EAE animals and MS patients revealed the presence of CD134+ cells that were localized in active lesions, mainly in perivascular infiltrates. The presence of CD134-expressing T cells in brain tissue of MS patients and EAE affected mice, together with the functional evidence provided by the significant decrease in disease score obtained in Cd134(-/-) mice, indicate that interfering with the CD134 molecule in T cells may be an appropriate target for therapeutic intervention in active MS.

Cytokine-induced enhancement of autoimmune inflammation in the brain and spinal cord: implications for multiple sclerosis

Multiple sclerosis and experimental autoimmune encephalomyelitis (EAE) are autoimmune inflammatory diseases in which cytokines are intimately involved. Here we test the hypothesis that injection of pro-inflammatory cytokines, tumour necrosis factor-alpha (TNFalpha) and interferon gamma (IFNgamma) into the brain of animals in the prodromal phase of EAE significantly enhances inflammation in the central nervous system (CNS). We were particularly interested to learn whether a local increase in cytokines influenced the pathology locally, or more extensively, within the CNS. EAE was induced in female adult Lewis rats. Eight days post-inoculation, TNFalpha or INFgamma was injected into one cerebral hemisphere. Days 11 and 13 post-inoculation (3 and 5 days after the injection of cytokine) inflammation was quantified by the number of perivascular cuffs and the degree of major histocompatibility complex (MHC) class II expression by microglia. Normal animals injected with cytokines, and EAE animals with saline injection served as controls.

RESULTS

microglial activation was increased three- to fourfold in the brain and eightfold in the spinal cord (P </= 0.05); lymphocyte invasion was increased sixfold in the brain and three- to fourfold in the spinal cord (P </= 0.01) following injections of TNFalpha or INFgamma in EAE animals compared with controls. Significant axonal damage was observed in white matter associated with the perivascular cuffs.

CONCLUSION

local changes in the release of pro-inflammatory cytokines within the brain in EAE results in the widespread enhancement of autoimmune inflammation within the brain and cord, and exacerbation of clinical symptoms.

Robust ability of IFN-gamma to upregulate class II MHC antigen expression in tumor bearing rat brains

T cells are attractive for delivering therapy to brain tumor, especially disseminated micro-tumor. However, to trigger effector function, tumor antigen must be re-presented to T cells, via major histocompatibility complex (MHC) proteins, at the tumor site. In normal brain, MHC+ antigen-presenting cells (APC) are rare, but abundant after gamma interferon (IFN-gamma) injection. Here we studied tumor-bearing brains. IFN-gamma (or buffer) was injected stereotactically into brains with established tumors from a panel of immunologically varied glioma cell lines, some expressing b-galactosidase as a micro-tumor marker. Four days later, cryostat sections were stained for tumor and MHC proteins. In phosphate-buffered saline-injected controls, class II MHC+ potential APC (microglia, macrophages) were seen only at (some) tumor sites. In rats that received IFN-gamma, class II+ potential APC were widespread, including all actual and potential micro-tumor sites and all tumor-free areas. In the same slides, neither class I nor class II MHC antigen was detected in neural cells or most tumor cells. This MHC pattern favors indirect re-presentation of tumor antigen, by tumor-adjacent APC. The robust response to IFN-gamma might also be exploited in other ways: activated microglia and macrophages can attack tumor directly, and class II+ APC may help mark micro-tumor sites.

Gamma interferon transduced 9L gliosarcoma. Cytokine gene therapy and its relevance to cellular therapy with alloreactive cytotoxic T lymphocytes

In earlier studies, we demonstrated that intratumoral infusions of alloreactive cytotoxic T lymphocytes (aCTL), sensitized to the major histocompatibility complex (MHC) antigens of the host, effectively retarded the intracranial growth of Fischer 9L gliosarcoma. We further demonstrated that continuous in vitro exposure to gamma-interferon (gammaIFN) upregulates MHC on 9L gliosarcoma cells and that they were better targets of anti-Fischer aCTL. We hypothesized that the efficacy of cellular therapy with aCTL could be further improved by in situ transduction of the tumor with retroviral vectors coding for gammaIFN, which would generate continuous secretion of the cytokine and maintain upregulated MHC expression by the tumor cells. 9L gliosarcoma and Herpes simplex virus thymidine kinase (tk) transductants of those cells were transduced with a retrovirus carrying the murine gammaIFN gene. By limiting dilution, clones of these cells, designated 9Lgamma 7, 9Lgamma tk8, and 9Lgamma tk10, which produced similar levels of gammaIFN (383-411 ng gammaIFN/10(6) cells/24 h) were isolated. The production of gammaIFN by one clone, 9Lgamma 7, was stable when monitored over 6 weeks in vitro. The clones also demonstrated upregulated MHC class I expression, and the tk-transduced clones maintained their sensitivity to ganciclovir. Compared to the wildtype cells, 9Lgamma 7 had approximate 6- and 1.5-fold increases in the relative antigen densities of MHC I and II, respectively. Addition of exogenous gammaIFN to 9Lgamma 7 cultures did not significantly increase the MHC expression. In cytotoxicity assays, 9Lgamma 7 cells, or 9Lgamma 7 incubated with exogenous gammaIFN, were better targets of aCTL than the parental 9L cells. The growth rate of 9Lgamma-transduced cells was decreased compared to the wildtype cells both in vitro and in vivo. Proliferation studies with transwell plated 9L, 9Lgamma 7, and 9Lgamma tk10 cells in various combinations revealed that the secreted cytokine itself caused a decrease in proliferation. However, the transduced cells exhibited a much reduced growth rate, which likely was a consequence of redirected metabolic activity of the cells. In vivo growth of the 9L and 9Lgamma 7 tumors in rat brains given identical inoculums similarly demonstrated significantly reduced 9Lgamma 7 tumor volumes at various timepoints, indicative of slower growth of the gammaIFN-producing tumors.

Immunology and immunotherapy in neurosurgical disease

OBJECTIVE

For many years, the central nervous system (CNS) has been described as "immunologically privileged" and devoid of conventional immune reactivity. However, our more current understanding of neuroimmunology supports a different view. Although immune mechanisms within the CNS may behave differently from those located at peripheral anatomic sites, it is now widely accepted that biologically relevant immune responses can and do occur within the brain and that these responses can play important roles in CNS disease. The objective of this present review is to explore key aspects of recent insights into the cellular interactions involved in neuroimmunology, which may suggest more rational approaches to the immunotherapy of neurosurgical disorders.

CONCLUSION

Modern advances in molecular medicine and basic immunology have yielded a plethora of new data about CNS immunobiology. The design of effective immunotherapeutic strategies for CNS diseases requires a contemporary understanding of the basic tenets of how the immune system works. The current renaissance in this field may give neurosurgeons hope that, in the future, immunotherapy-based paradigms may be able to successfully treat neurosurgical diseases that are currently refractory to traditional therapies.

Effects of IFN-gamma and interleukin-1beta on major histocompatibility complex antigen and intercellular adhesion molecule-1 expression by 9L gliosarcoma: relevance to its cytolysis by alloreactive cytotoxic T lymphocytes

To enhance the efficacy of cellular immunotherapy for gliomas, we tested the concept of using proinflammatory cytokine treatment with interferon-gamma (IFN-gamma) or interleukin-1beta (IL-1beta) or both to render glioma cells more susceptible to cytolysis by alloreactive cytotoxic T lymphocytes (aCTL). The cytokines, separately or in combination, were able to upregulate major histocompatibility complex (MHC) class I antigen or intercellular adhesion molecule-1 (ICAM-1) on Fischer rat 9L gliosarcoma cells. 9L cells were incubated in vitro for 24, 48, or 72 h with varying concentrations of rat IFN-gamma (0-2000 U/ml) or recombinant human IL-1 (rHUIL-1) (0-1000 U/ml) or both. By 48 h, IFN-gamma (500 U/ml) maximally induced the percentage of positive expressing cells and the relative antigen density of MHC class I and ICAM-1 on 9L cells, whereas IL-1 induced only ICAM-1 expression. Simultaneous incubation of IL-1 with IFN-gamma did not further affect the induction of class I on 9L cells more than that achieved with IFN-gamma alone. 9L cells with upregulated MHC class I and ICAM-1 expression were more sensitive to lysis by aCTL in in vitro cytotoxicity assays, regardless of whether the precursor aCTL came from naive or from 9L-immunized rats. Furthermore, inhibition of 9L cytotoxicity in assays that included blocking antibodies to MHC class I or to ICAM-1 revealed that T cell receptor (TCR) interactions with MHC class I and that ICAM-1 interactions with lymphocyte function-associated-1 (LFA-1) antigen account for a portion of the glioma lysis by aCTL.

Substance P antagonist blocks leakage and reduces activation of cytokine-stimulated rat brain endothelium

We recently demonstrated that substance P mediates increased permeability of brain endothelium exposed to HIV-1 gp120. To test whether substance P is involved in immune processes at the blood-brain barrier (BBB), we stimulated rat brain endothelial cultures prepared from cerebral microvessels with Interferon-gamma (IFN-gamma) and Tumor necrosis factor-alpha (TNF-alpha), two proinflammatory cytokines that alter the BBB and measured permeability to albumin and expression of adhesion molecule ICAM-1 and MHC class II antigen in the presence and absence of spantide, a powerful substance P antagonist. In a dose-dependent manner, spantide completely neutralized increased permeability induced by TNF-alpha and IFN-gamma and expression of MHC class II molecule induced by IFN-gamma and prevented associated cell morphological changes as revealed by scanning electron microscope. Spantide also reduced expression of ICAM-1 induced by TNF-alpha and IFN-gamma by 35% and 30%, respectively. Substance P mRNA was found in unstimulated brain endothelial cells and was upregulated after stimulation with TNF-alpha and IFN-gamma. These in vitro findings demonstrate that substance P plays a major pathogenetic role in damaging and activating the BBB vascular component in the presence of proinflammatory cytokines.

Interferon-gamma regulates oxidative stress during experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an induced inflammatory and demyelinating disease of the central nervous system which shares many clinical and pathological features with and is considered the animal model of multiple sclerosis. There is extensive evidence that EAE is a Th1 disease eliciting secretion of proinflammatory cytokines like IFN-gamma or TNF-alpha, and it has been suggested that cytokine-induced oxidative stress could have a role in EAE neuropathology. However, the individual roles of these and other cytokines in the pathogenesis of the disease are still uncertain. Here we analyze the role of IFN-gamma during EAE by using both IFN-gamma receptor-knockout (IFN-gamma R(-/-)) and wild-type mice, both strains immunized with peptide 40-55 from rat myelin oligodendrocyte glycoprotein. The levels of oxidative stress were determined through the analysis of immunoreactivity for inducible NO synthase, nitrotyrosine, and malondialdehyde, as well as through the expression of the tissue-protective antioxidant factors metallothionein I+II (MT-I+II). We also examined the number of cells undergoing apoptosis as judged by using the TUNEL technique. The levels of oxidative stress, MT-I+II, and apoptotic cell death by EAE were significantly increased in all mice, though more so in IFN-gamma R(-/-) mice compared with wild-type mice. These data support the notion that IFN-gamma has a protective role against EAE.

Treatment with anti-interferon-gamma monoclonal antibodies modifies experimental autoimmune encephalomyelitis in interferon-gamma receptor knockout mice

The role of interferon-gamma (IFN-gamma) in the pathogenesis of multiple sclerosis and experimental autoimmune encephalomyelitis (EAE) is still controversial. We have studied the function of IFN-gamma and its receptor in the EAE model using two different IFN-gamma receptor knockout (IFN-gamma R(-/-)) mouse types: C57Bl/6x129Sv, with a disruption of the IFN-gamma receptor cytoplasmic domain, and 129Sv, homozygous for a disrupted IFN-gamma receptor gene. Mice were immunized with peptide 40-55 from rat myelin oligodendrocyte glycoprotein. A subgroup of mice was treated with anti-IFN-gamma monoclonal antibodies (mAb) on day 8 postimmunization. Clinical scoring and both histological and immunohistochemical studies were undertaken for all groups. We hereby show that treatment with anti-IFN-gamma mAb worsened the disease course of 129Sv wild-type mice. However, it decreased the mean daily score in IFN-gamma R(-/-) 129Sv and the incidence of the disease down to 50% in C57Bl/6x129Sv IFN-gamma R(-/-) mice. Moreover, after anti-IFN-gamma mAb treatment, oxidative stress levels, metallothionein I and II antioxidant protein expression, and apoptoticneuronal death were increased in wild-type mice while decreased in IFN-gamma R(-/-) mice. These results suggest a putative alternative mechanism of action of this cytokine that works independent of its receptor.

New animal models to probe brain tumor biology, therapy, and immunotherapy: advantages and remaining concerns

New genetic models provide better biological mimics of human tumors. The new models can give deeper insight into tumorigenesis and provide better targets for testing therapies. To use the new models most successfully, it is useful to keep in mind limitations that are harder to overcome by genetic manipulation. These include biochemical and anatomical differences between species, as well as differences in scale, both spatial and temporal. Three approaches to new genetic brain tumor models are described in the following articles. This essay provides a context, bringing out both advantages and remaining concerns. Examples are taken from work in brain tumor immunobiology and immunotherapy. The complementarity of different models, and the dichotomy between general principles and model-specific details are stressed.

Local immune regulation in the central nervous system by substance P vs. glutamate

The response of parenchymal microglia to interferon-gamma (IFN-gamma) varies across the brain. To ask if local neurochemicals contribute to site-specific control, the influence of substance P (SP) and glutamate was evaluated in brainstem vs. hippocampus. In brainstem, stereotaxic injection of SP increased class II MHC upregulation by IFN-gamma, while a SP receptor antagonist (Spantide I) prevented it. In hippocampus, where the baseline response to IFN-gamma was lower, SP was ineffective, but blocking glutamate enhanced the response in a proportion of rats. Attempts to understand and control immune activity in the CNS should take the local neurochemical environment into account.

Cerebellar dysfunction is associated with overexpression of proinflammatory cytokine genes in lupus

Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown etiology accompanied by central nervous system involvement in up to 60% of patients. The current study chronicles the expression of cerebellar dysfunction in SLE using MRL-lpr/lpr mice as the experimental model. These mice spontaneously develop an illness that has immunological and clinical features of human lupus. We found that MRL-lpr/lpr mice manifest severe and progressive behavioral disturbances indicative of cerebellar dysfunction beginning at 11 weeks of age. Although the lpr gene is known to induce autoimmune features, immunologically normal mice rendered congenic for lpr failed to exhibit disturbances in cerebellar function. Because lupus is a cytokine-driven disease and overexpression of certain proinflammatory cytokines has been associated with neurodegeneration, the relationship between cerebellar dysfunction and cytokine gene expression was examined. Relative to immunologically normal CBA/J mice, the cerebellum of young (11-15 weeks of age) MRL-lpr/lpr mice contained high levels of interleukin (IL)-6 and interferon-gamma (IFNgamma) mRNA, which became even more pronounced in old (22-30 weeks of age) autoimmune mice. mRNA levels for the cytokines IL-1beta and IL-10 were elevated in the cerebellum of old, but not young, MRL-lpr/lpr mice relative to CBA/J. In contrast, the levels of cerebellar transcripts for IL-3 and tumor necrosis factor-alpha were comparable in autoimmune and normal mice, indicating that enhanced gene expression of IL-6, IFNgamma, IL-1beta, and IL-10 was selective. These results suggest a potential role for certain proinflammatory cytokines in the pathogenesis of cerebellar disturbances in SLE.

Cellular inflammatory response associated with breakdown of the blood-brain barrier after closed head injury in rats

This study reports a widespread microglial response characterized by an upregulation of surface antigens, such as complement type 3 receptors (CR3) and major histocompatibility complex (MHC) class II antigens on these cells following closed head injury. Increased expression of CR3 (OX-42) and MHC class II antigens (OX-6) was observed in rats killed at 1, 3, and 5 days after injury. Intense OX-42 immunoreactivity was observed in microglial cells throughout the brain with a smaller number of them being OX-6 positive. In addition to microglial reaction, astrocytic activation reflected in cellular hypertrophy and increased immunoreactivity for glial fibrillary acidic protein (GFAP) was observed at 5 days after head injury. Together with the above, a diffuse perivascular and intraneuronal immunostaining for immunoglobulin G (IgG) was observed primarily in the cerebral cortex. This was accompanied by an enhanced expression of both endothelial nitric oxide synthase (eNOS) in blood vessels and inducible nitric oxide synthase (iNOS) in brain macrophages. In rats subjected to closed head injury followed by a single intraperitoneal (i.p.) injection of rhodamine isothiocyanate (RhIc), seepage of the fluorescent dye into the neuropil was observed. This had resulted in the labelling of the cortical neurons clearly demonstrating a breakdown of the blood-brain barrier (BBB). In the latter, it is conceivable that the ensuing leakage of plasma immunoglobulins and other serum-derived materials could induce the expression of MHC class II antigens on microglia. The mechanism causing the BBB dysfunction is not clear, although present results suggest that excessive release of nitric oxide (NO) may be a contributory factor. The widespread activation of microglia in rats after head injury suggests their involvement in increased endocytosis and immunological responses.

Genetic models for CNS inflammation

The use of transgenic technology to over-express or prevent expression of genes encoding molecules related to inflammation has allowed direct examination of their role in experimental disease. This article reviews transgenic and knockout models of CNS demyelinating disease, focusing primarily on the autoimmune disease multiple sclerosis, as well as conditions in which an inflammatory response makes a secondary contribution to tissue injury or repair, such as neurodegeneration, ischemia and trauma.

Amelioration of CR-EAE with lisofylline: effects on mRNA levels of IL-12 and IFN-gamma in the CNS

CR-EAE is a Th1-mediated inflammatory autoimmune demyelinating disease of the CNS and serves as a model of human multiple sclerosis. Our previous studies have shown the protective effect of orally administered lisofylline in the prevention of active and passively induced acute EAE. In our present studies we have examined the efficacy and mechanism of action of lisofylline on CR-EAE. Lisofylline decreased the number and severity of paralytic attacks in mice with relapsing EAE. The reduction of clinical disease correlated with decreased levels of mRNA levels of IFN-gamma but not of mRNA levels of IL-12. These studies suggest that lisofylline may be an effective therapeutic for established Th1 mediated autoimmune disease and that it acts by blocking IL-12R signaling and not IL-12 production in vivo.

Early and specific expression of monocyte chemoattractant protein-1 in the thalamus induced by cortical injury

For many years it has been known that retrograde degeneration of thalamic neurons occurs following damage to the cerebral cortex, however, the molecular mechanisms which control this process are unknown. Recent studies have demonstrated microglial activation in thalamic nuclei well before the onset of retrograde neuronal cell death. Activated monocytes and microglia synthesize factors detrimental to neuronal survival as well as phagocytose damaged and dying neurons. Our previous studies demonstrated that monocyte chemoattractant protein-1 (MCP-1), a beta chemokine which attracts cells of monocytic origin to sites of injury, is rapidly expressed in the brain following visual cortical lesions. The present study examined the expression of MCP-1 messenger RNA and protein in the thalamus following a visual cortical lesion. Aspiration lesions of visual cortex were made in adult mice. At specific times after lesion, brains were harvested and dissected into specific regions. MCP-1 message as detected using northern analysis was absent in uninjured brain, but was elevated in the ipsilateral thalamus as rapidly as 1 h following the lesion. In situ hybridization localized MCP-1 message to subpial glial cells of the lateral geniculate nucleus (LGN) of the ipsilateral thalamus after injury. ELISA showed that MCP-1 protein levels were significantly elevated in the ipsilateral thalamus at 6 h, peaked at 12 h, and remained above baseline levels for at least 1 week post lesion. In addition, anti-GFAP staining demonstrated activated astrocytes localized to the ipsilateral LGN at 24 and 72 h after injury. The early expression and regional localization of MCP-1 mRNA and protein strongly suggest that MCP-1 is a critical molecule in the regulation of thalamic retrograde neuronal degeneration.

Lens injury stimulates axon regeneration in the mature rat optic nerve

In mature mammals, retinal ganglion cells (RGCs) are unable to regenerate their axons after optic nerve injury, and they soon undergo apoptotic cell death. However, a small puncture wound to the lens enhances RGC survival and enables these cells to regenerate their axons into the normally inhibitory environment of the optic nerve. Even when the optic nerve is intact, lens injury stimulates macrophage infiltration into the eye, Müller cell activation, and increased GAP-43 expression in ganglion cells across the entire retina. In contrast, axotomy, either alone or combined with intraocular injections that do not infringe on the lens, causes only a minimal change in GAP-43 expression in RGCs and a minimal activation of the other cell types. Combining nerve injury with lens puncture leads to an eightfold increase in RGC survival and a 100-fold increase in the number of axons regenerating beyond the crush site. Macrophage activation appears to play a key role, because intraocular injections of Zymosan, a yeast cell wall preparation, stimulated monocytes in the absence of lens injury and induced RGCs to regenerate their axons into the distal optic nerve.

Interferon-gamma induces apoptosis and augments the expression of Fas and Fas ligand by microglia in vitro

Activation of microglia by interferon-gamma (IFN-gamma) has been implicated in a number of central nervous system (CNS) inflammatory disease processes. Because IFN-gamma has also been shown to play a role in programmed cell death, we investigated its cytotoxicity and its effect on the Fas apoptotic pathway in microglia. Flow cytometry was used to quantify the IFN-gamma-mediated apoptotic response and Fas and Fas ligand (FasL) expression in two well-characterized murine microglia cell lines (BV-2 and N9). Nuclear fragmentation, suggestive of apoptosis, was noted within 24 h of incubation of microglia with IFN-gamma (10 U/ml). After a 72-h incubation, almost every BV-2 and N9 microglia, but not GL261 glioma cells, underwent cell death and detached from the culture plates. This cytotoxicity occurred even at low IFN-gamma concentrations (1 U/ml) and was inhibited by BAF, a pan-caspase inhibitor. Incubation of BV-2 and N9 microglia, but not GL261 glioma cells, with IFN-gamma also potentiated the expression of Fas and FasL in a similar dose-response and time-course manner, as seen for the apoptotic response. Whereas Fas expression increased by 100% in both microglia cells, FasL upregulation was more pronounced and increased by as much as 200% in the N9 cells. These findings suggest that in addition to its role as a microglia activator, IFN-gamma may also induce apoptosis of microglia, possibly through simultaneous upregulation of Fas and FasL. Interferon-gamma modulation of the Fas pathway and apoptosis in microglia may be important in the pathogenesis of inflammatory CNS disease processes.

Local neurochemicals and site-specific immune regulation in the CNS

Although it is often described as "immunologically privileged," the brain can display vigorous immune activity, both clinically and experimentally. The underlying control mechanisms are under active study. Here we shift attention from the brain as a whole to its diverse microenvironments. We review evidence that immune regulation in the brain is site-specific, and that local neurochemicals contribute to the site-specific control. Key points are illustrated by recent work from a rat model in which local injection of the proinflammatory cytokine, IFN-gamma, was used to modulate 2 essential aspects of the cell-mediated immune response: T cell entry from the blood, and expression of the MHC proteins that are needed to present antigen to the newly entered T cells. A growing number of neurologic disorders are known to be exacerbated by the immune/inflammatory network. Understanding the factors that influence local immune function may help explain the distribution of localized CNS damage and, more importantly, may suggest new therapeutic approaches for both desirable and unwanted responses.

Studies in B7-deficient mice reveal a critical role for B7 costimulation in both induction and effector phases of experimental autoimmune encephalomyelitis

The importance of B7 costimulation in regulating T cell expansion and peripheral tolerance suggests that it may also play a significant regulatory role in the development of autoimmune disease. It is unclear whether B7 costimulation is involved only in the expansion of autoreactive T cells in the periphery, or if it is also required for effector activation of autoreactive T cells in the target organ for mediating tissue injury and propagating autoimmune disease. In this study, the role of B7-CD28 costimulation and the relative importance of B7 costimulators for the induction and effector phases of experimental autoimmune encephalomyelitis (EAE) induced by myelin oligodendrocyte glycoprotein (MOG) peptide were examined. Wild-type, B7-1/B7-2-deficient mice, or CD28-deficient C57BL/6 mice were immunized with MOG 35-55 peptide. Mice lacking both B7-1 and B7-2 or CD28 showed no or minimal clinical signs of EAE and markedly reduced inflammatory infiltrates in the brain and spinal cord. However, mice lacking either B7-1 or B7-2 alone developed clinical and pathologic EAE that was comparable to EAE in wild-type mice, indicating overlapping functions for B7-1 and B7-2. Resistance to EAE was not due to a lack of induction of T helper type 1 (Th1) cytokines, since T cells from B7-1/B7-2(-/-) mice show reduced proliferative responses, but greater interferon gamma production compared with T cells from wild-type mice. To study the role of B7 molecules in the effector phase of the disease, MOG 35-55-specific T lines were adoptively transferred into the B7-1/B7-2(-/-) and wild-type mice. Clinical and histologic EAE were markedly reduced in B7-1/B7-2(-/-) compared with wild-type recipient mice. These results demonstrate that B7 costimulation has critical roles not only in the initial activation and expansion of MOG-reactive T cells, but also in the effector phase of encephalitogenic T cell activation within the central nervous system.

Site-specific control of T cell traffic in the brain: T cell entry to brainstem vs. hippocampus after local injection of IFN-gamma

Although it is known that neurotransmitters and neuropeptides can affect immune function in vitro, less is understood about how the neural environment affects immune function in the brain. Previously, we showed that regulation of parenchymal class II MHC after local injection of IFN-gamma is site-specific. In this companion study, we defined the effect of local IFN-gamma on the entry of class II-restricted T cells to the brain parenchyma. To activate endogenous T cells, adult CDF rats were immunized with a normal neural antigen (MBP). Two weeks later, the proinflammatory cytokine IFN-gamma (100 to 10,000 U/site) was injected stereotaxically into two neurochemically and anatomically distinct sites, the hippocampus (area CAI) and brainstem (nucleus of the solitary tract). Monoclonal R73 was used to detect T cells on cryostat sections. The greatest difference was seen 48 h after 300 U IFN-gamma was injected at each site, when there were several-fold more parenchymal T cells in the brainstem than in the hippocampus. Most parenchymal T cells were CD4+ /class II-restricted. Thus, parenchymal T cell entry and parenchymal class II up-regulation show the same hierarchy (brainstem >> hippocampus) after local IFN-gamma injection, although T cell entry was more sensitive to the IFN-gamma dose. We suggest that the local regulatory environment contributes to site-specific immune regulation, and discuss implications for the distribution of MS plaques and other aspects of local immune control. Further, in interpreting the many previous studies of cytokine-mediated immune changes in the CNS, the possibility of site-specific differences should be considered.

Leukocyte traffic in the central nervous system: the participants and their roles

While the central nervous system has long been considered immunologically privileged, over the past decade it has become evident that a wide variety of leukocyte types traffic through the nervous system. It is also apparent that the rules governing the trafficking of these disparate cell types are different for each. Some arrive, and probably depart, continuously as part of normal physiology. Others only appear to seek a specific antigen or in response to tissue damage. In this review the nature and function of individual cell types are discussed and our current knowledge regarding the parameters governing their entry into the CNS is examined.

Site-specific immune regulation in the brain: differential modulation of major histocompatibility complex (MHC) proteins in brainstem vs. hippocampus

Although neurotransmitters and neuropeptides are known to affect immune function in vitro and in non-neural tissues, little is known about how the local mix of neurochemicals affects immune function in the brain. Here, we study local modulation of the class II major histocompatibility complex (MHC) proteins, which present antigen to T cells in a key pathway for cell-mediated immune activity. Two sites that are well-separated anatomically and have very different neuroregulatory environments, the brainstem and hippocampus, were compared. The class II-upregulating cytokine, gamma interferon (IFN-gamma, 0.1 to 10,000 U/site), was injected stereotaxically into the hippocampus and contralateral brainstem of adult Charles-derived Fischer rats. Four days later, monoclonal antibody staining was used to detect class II MHC proteins on cryostat sections, followed by computer-assisted image analysis. As compared to hippocampus, the brainstem showed enhanced class II expression at lower IFN-gamma doses, and reached a higher plateau. Site-specific class II modulation was also seen within the layers of the hippocampus, and among other brain sites. Injection of marker protein to visualize the spread of injected protein, plus injection of IFN-gamma into alternative sites, suggested that preferential flow cannot explain all of the site-specific effects. We suggest that the local neuroregulatory environment and/or intrinsic differences among target microglia are likely to play a role. Implications for the distribution of pathological changes, such as multiple sclerosis plaques, and for local immunotherapy are discussed.

Oligodendroglial response to the immune cytokine interferon gamma

In the human demyelinating disorder multiple sclerosis, and its animal model experimental allergic encephalomyelitis, there is a breakdown of the blood-brain barrier and an infiltration of immune cells into the CNS. Infiltrating T lymphocytes and macrophages are believed to be key mediators of the disease process. Considerable circumstantial and experimental evidence has suggested that the pleiotropic cytokine interferon gamma (IFN-gamma), which is exclusively expressed by T cells and natural killer cells, is a deleterious component of the immune response in these disorders. When experimentally introduced into the CNS IFN-gamma promotes many of the pathological changes that occur in immune-mediated demyelinating disorders. In vitro, this cytokine elicits a number of effects on oligodendrocytes, including cell death. The harmful actions of IFN-gamma on CNS myelin are likely mediated through direct effects on the myelinating cells, as well as through the activation of macrophages and microglia. In this review we summarize relevant studies concerning the action of IFN-gamma in demyelinating disorders and discuss possible mechanisms for the observed effects.

Non-coding plasmid DNA induces IFN-gamma in vivo and suppresses autoimmune encephalomyelitis

Regulatory sequences used in plasmids for naked DNA vaccination can modulate cytokine production in vivo. We demonstrate here that injection of plasmid DNA can suppress the prototypic T cell-mediated autoimmune disease, experimental autoimmune encephalomyelitis, by inducing IFN-gamma.

Prevention of Experimental Allergic Encephalomyelitis via Inhibition of IL-12 Signaling and IL-12-Mediated Th1 Differentiation: An Effect of the Novel Anti-Inflammatory Drug Lisofylline

Experimental allergic encephalomyelitis (EAE) is an inflammatory, CD4+ Th1-mediated autoimmune disease, which serves as a model for multiple sclerosis. We examined the effect of a novel anti-inflammatory drug, lisofylline (LSF), on EAE induced either by injection of mouse spinal cord homogenate or following transfer of myelin basic protein-reactive T cells. Orally administered LSF significantly inhibited EAE in both cases, decreasing peak clinical scores by &gt;70% and &gt;80%, respectively. In addition, analysis of representative spinal cord sections from LSF-treated mice showed complete lack of demyelination and lymphocyte infiltration. The reduction in EAE correlated with the inhibition of Th1 differentiation by LSF in vivo, as indicated by a reduction in T cell IFN-γ production ex vivo after Ag restimulation. The inhibition of Th1 differentiation in vivo is consistent with a block in IL-12 receptor signaling, because LSF blocked IL-12-driven Th1 differentiation and T cell proliferation in vitro, yet had no effect on IL-12 secretion from APCs ex vivo or in vitro.

Distribution and temporal regulation of the immune response in the rat brain to intracerebroventricular injection of interferon-gamma

The response to intracerebroventricular administration of interferon (IFN)-gamma was examined in the adult Wistar rat brain: major histocompatibility complex (MHC) antigens class I and II, CD8 and CD4 antigens, and the macrophage/microglia antigen OX42 were analyzed in respect to saline-injected cases over 1 week. The glial cell type expressing MHC antigens was characterized with double labeling. IFN-gamma was thus found to induce MHC class I and II expression in microglia, identified by tomato lectin histochemistry, and not in GFAP-immunostained astrocytes. MHC antigen-expressing microglia was detected in the periventricular parenchyma, several fields of the cerebral cortex, cerebellum, major fiber tracts, and brainstem superficial parenchyma. Different gradients of density and staining intensity of the MHC-immunopositive elements were observed in these regions, in which MHC class I antigens persisted up to 1 week, when MHC class II induction had declined. Quantitative analysis pointed out the proliferation of OX42-immunoreactive cells in periventricular and basal brain regions. CD8+ T cells were observed in periventricular regions, basal forebrain, and fiber tracts 3 days after IFN-gamma injection and their density markedly increased by 7 days. CD4+ T cells were also seen and they were fewer than CD8+ ones. However, numerous CD4+ microglial cells were observed in periventricular and subpial regions, especially 1 week after IFN-gamma injection. Our data indicate that this proinflammatory cytokine mediates in vivo microglia activation and T cell infiltration in the brain and that the cells involved in this immune response display a regional selectivity and a different temporal regulation of antigen expression.