Tumor necrosis factor-alpha enhances interferon-gamma-mediated class II antigen expression on astrocytes

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.

Divergent roles for tumor necrosis factor-alpha in the brain

Proinflammatory cytokines and chemokines have been implicated in the pathogenesis of several neurological and neurodegenerative disorders. Prominent among such factors is the pleiotropic cytokine, tumor necrosis factor (TNF)-alpha. Under normal physiological conditions, TNF-alpha orchestrates a diverse array of functions involved in immune surveillance and defense, cellular homeostasis, and protection against certain neurological insults. However, paradoxical effects of this cytokine have been observed. TNF-alpha is elicited in the brain following injury (ischemia, trauma), infection (HIV, meningitis), neurodegeneration (Alzheimer's, Parkinson's), and chemically induced neurotoxicity. The multifarious identity for this cytokine appears to be influenced by several mechanisms. Among the most prominent are the regulation of TNFalpha-induced NF-kappaB activation by adapter proteins such as TRADD and TRAF, and second, the heterogeneity of microglia and their distribution pattern across brain regions. Here, we review the differential role of TNF-alpha in response to brain injury, with emphasis on neurodegeneration, and discuss the possible mechanisms for such diverse and region-specific effects.

Differential expression, shedding, cytokine regulation and function of TNFR1 and TNFR2 in human fetal astrocytes

Tumor necrosis factor (TNF)-alpha induces pleiotropic cellular effects through a 55kDa, type 1 receptor (TNFR1) and a 75kDa type 2 receptor (TNFR2). Moreover, it participates in the pathogenesis of several CNS diseases, including demyelinating diseases. TNF-alpha receptors are differentially expressed and are regulated in many cell types. However, data regarding the TNF-alpha receptor expression and regulation in human astrocytes is limited to date. We investigated TNF- receptor expression, its regulation by cytokines, and its functional role in primary cultured human fetal astrocytes, which are the most abundant cellular population in the central nervous system and are known to be immunologically active. In this study, astrocytes were found to constitutively and predominantly transcribe, translate and shed TNFR1 rather than TNFR2, but TNFR2 expression was increased by adding TNF-alpha, IL-1, and IFN-gamma, but not by adding LPS. To determine the functional roles of TNFR1 and TNFR2 on TNF induction, we investigated NF-kappaB activation and TNF-alpha induction after neutralizing TNFR1 and TNFR2 by an antibody treatment. We found that NF-kappaB activation and TNF-alpha induction are blocked by TNFR1 neutralizing antibody treatments.

Tumor necrosis factor-α mediates the proliferation of rat C6 glioma cells via β-adrenergic receptors

In the present study, we observed that isoproterenol, a beta-adrenergic receptor (beta-AR) agonist, stimulated rat C6 glioma cell proliferation, while propranolol, a beta-AR blocker, greatly reduced the proliferative effect of TNF-alpha on C6 cells. The gene and protein expressions of both beta1- and beta2-ARs were enhanced in C6 cells after TNF-alpha treatment, and the increase in beta-AR was due to an increased number of binding sites and not due to increase in receptor affinity. We further showed that protein kinase C (PKC) was involved in the TNF-alpha-induced beta-AR expression. Collectively, our results indicate that TNF-alpha-induced proliferation in C6 glioma cells might be via the induction and activation of beta-ARs.

Inhibitor of kappaB kinase is required to activate a subset of interferon gamma-stimulated genes

IkappaB kinase (IKK), discovered as the major activator of NF-kappaB, plays additional roles in signaling. By using mouse embryo fibroblasts (MEFs) lacking both the alpha and beta subunits of IKK, we find that these proteins are required for induction of a major subset of IFNgamma-stimulated genes and that this requirement is independent of NF-kappaB activation. Furthermore, there is no defect in IFNgamma-stimulated signal transducer and activator of transcription 1 (Stat1) activation or function in the IKKalpha/beta-null MEFs. Therefore, although activated Stat1 dimers are necessary for the activation of these genes in response to IFNgamma, they are not sufficient. These results reveal an important additional pathway for IFNgamma-stimulated gene expression in which an NF-kappaB-independent function of IKK is required.

Sex differences in in vitro pro-inflammatory cytokine production from peripheral blood of multiple sclerosis patients

We compared the patterns of the pro-inflammatory cytokines, interferon-gamma (IFN-gamma), interleukin-2 (IL-2) and tumor necrosis factor-alpha (TNF-alpha), and the anti-inflammatory cytokines, interleukin-10 (IL-10) and tumor growth factor-beta (TGF-beta) from peripheral blood of male and female patients with relapsing-remitting (RR) and secondary progressive (SP) forms of multiple sclerosis (MS). The relationships between pro-inflammatory cytokines and disability (expanded disability status scale, EDSS) were also examined. Peripheral blood anti-coagulated with heparin was obtained from 47 MS patients (30 women and 17 men) and activated with phorbol-12-myristate 13 acetate (PMA) and ionomycin in the presence of brefeldin A and stained for flow cytometry with fluorescently labeled antibodies against intracellular IFN-gamma, TNF-alpha, IL-2, IL-4 and IL-10. The T cells were delineated with peridinin chlorophyll protein (Per-CP) labeled anti-CD3 antibody. The stained samples were analyzed on a flow cytometer to assess the intracellular pro-inflammatory cytokine patterns. The levels of interleukin-10 (IL-10) and tumor growth factor-beta (TGF-beta) were measured in plasma using enzyme-linked immunoassay. The percentage of TNF-alpha-producing CD3 positive cells was significantly higher (P=0.045) in men (mean+/-S.D., 39+/-13%) than in women (mean+/-S.D., 29+/-13%) RR-MS patients. The percentage of CD3 positive cells producing IFN-gamma was significantly correlated with EDSS in females but not in males (Spearman rank correlation r(S)=0.49, P=0.018). The secretion of the pro-inflammatory cytokines, IFN-gamma and TNF-alpha, is influenced by gender in MS patients and may contribute to the sexual dimorphism of MS.

Expression of chemokines and their receptors in human and simian astrocytes: evidence for a central role of TNF alpha and IFN gamma in CXCR4 and CCR5 modulation

Chemokines are key mediators of the selective migration of leukocytes that occurs in neurodegenerative diseases and related inflammatory processes. Astrocytes, the most abundant cell type in the CNS, have an active role in brain inflammation. To ascertain the role of astrocytes during neuropathological processes, we have investigated in two models of primary cells (human fetal and simian adult astrocytes) the repertoire of chemokines and their receptors expressed in response to inflammatory stimuli. We demonstrated that, in the absence of any stimulation, human fetal and simian adult astrocytes express mRNA for receptors APJ, BOB/GPR15, Bonzo/CXCR6, CCR2, CCR3, CCR5, CCR8, ChemR23, CXCR3/GPR9, CXCR4, GPR1, and V28/CX3CR1. Moreover, TNFalpha and IL-1beta significantly increase BOB/GPR15, CCR2, and V28/CX3CR1 mRNA levels in both models. Furthermore, TNFalpha and IFNgamma act synergistically to induce expression of the major coreceptors for HIV infection, CXCR4 and CCR5, at both the mRNA and protein levels in human and simian astrocytes, whereas CCR3 expression was not affected by cytokine treatment. Finally, TNFalpha/IFNgamma was the most significant cytokine combination in leading to a pronounced upregulation in a comparable, time-dependent manner of the production of chemokines IP-10/CXCL10, RANTES/CCL5, MIG/CXCL9, MCP-1/CCL2, and IL-8/CXCL8. In summary, these data suggest that astrocytes serve as an important source of chemokines under the dependence of a complex cytokine regulation, and TNFalpha and IFNgamma are important modulators of chemokines and chemokine receptor expression in human as well as simian astrocytes. Finally, with the conditions we used, there was no difference between species or age of tissue.

SunghyangJungki-San Ga Pogongyoung inhibits IL-1 mediated tumour necrosis factor-alpha secretion in astrocytes

Astrocytes play an important role in initiating and modulating inflammatory responses within the central nervous system (CNS). Extensive studies in rodents have shown that substance P induces inflammatory cytokine production in astrocytes. In this study we have examined whether an aqueous extract of SunghyangJungki-San Ga Pogongyoung (SSGP) inhibits the secretion of TNF-alpha from primary cultures of rat astrocytes. SSGP (10-1,000 microg/mL) significantly inhibited the TNF-alpha secretion by astrocytes stimulated with lipopolysaccharide (LPS) and substance P (SP). Interleukin-1 (IL-1) has been shown to elevate TNF-alpha secretion from LPS-stimulated astrocytes while having no effect on astrocytes in the absence of LPS. We therefore examined whether IL-1 mediated inhibition of TNF-alpha secretion from primary astrocytes by SSGP. Treatment with SSGP (10-1,000 microg/mL) to astrocytes stimulated with both LPS and SP decreased IL-1 secretion significantly. Moreover, the secretion of TNF-alpha by LPS and SP in astrocytes was progressively inhibited with an increasing amount of IL-1 neutralizing antibody. Our results suggest that SSGP may inhibit TNF-alpha secretion by inhibiting IL-1 secretion and that SSGP has an antiinflammatory activity in the CNS.

Zaprinast, an inhibitor of cGMP-selective phosphodiesterases, enhances the secretion of TNF-alpha and IL-1beta and the expression of iNOS and MHC class II molecules in rat microglial cells

Proinflammatory cytokines produced by activated glial cells may in turn augment the immune/inflammatory reactions of glial cells through autocrine and paracrine routes. The NO/cGMP signaling represents one of the reactions of activated glial cells. We investigated whether the production of proinflammatory cytokines by glial cells is affected by NO-dependent downstream cGMP signaling. In primary cultures of mixed astrocytes and microglial cells, zaprinast (0.1 mM), an inhibitor of cGMP-selective phosphodiesterases, enhanced the basal and LPS (1.0 microg/ml)-induced secretion of TNF-alpha and IL-1beta. Zaprinast also enhanced NO production induced by LPS or IFN-gamma (100 U/ml), and in microglial cell cultures, but not in astrocyte cultures, zaprinast enhanced the basal and the IFN-gamma-induced production of the cytokines, TNF-alpha and IL-1beta, and of NO. This upregulation by zaprinast was partially inhibited by KT5823 (1.0 microM), an inhibitor of protein kinase G. The LPS-induced production of TNF-alpha, IL-1beta, and NO was inhibited by ODQ (50 microM), an inhibitor of soluble guanylyl cyclase, and by KT5823. Immunohistochemical analysis of mixed glial cell cultures showed that LPS/IFN-gamma-induced iNOS expression and the enhanced expression of iNOS by zaprinast were restricted to microglial cells. Zaprinast enhanced the IFN-gamma (200 U/ml)-induced expression of MHC Class II molecules in astrocytes and microglial cells in mixed cultures, but did not enhance this IFN-gamma-induced expression in pure astrocytes, which lacked paracrine TNF-alpha from microglial cells. Summarizing, zaprinast, which is associated with cGMP/protein kinase G signaling, may augment central immune/inflammatory reactions, possibly via the increased production of TNF-alpha and IL-1beta by activated microglial cells.

Inhibition of tumour necrosis factor-alpha secretion from rat astrocytes by Sesim-Tang

Substance P (SP) can stimulate secretion of tumour necrosis factor-alpha (TNF-alpha) from astrocytes stimulated with lipopolysaccharide (LPS). In this study, we have examined whether an aqueous extract of Sesim-Tang inhibits the secretion of TNF-alpha from primary cultures of rat astrocytes. Sesim-Tang (10-1000 microg/mL) significantly inhibited the TNF-alpha secretion by astrocytes stimulated with LPS and SP. Interleukin-1 (IL-1) has been shown to elevate TNF-alpha secretion from LPS-stimulated astrocytes while having no effect on astrocytes in the absence of LPS. We therefore examined whether IL-1 mediated inhibition of TNF-alpha secretion from primary astrocytes by Sesim-Tang. Treatment with Sesim-Tang (10-1000 microg/mL) of astrocytes stimulated with both LPS and SP decreased IL-1 secretion significantly. Moreover, the secretion of TNF-alpha by LPS and SP in astrocytes was progressively inhibited with increasing amounts of IL-1 neutralizing antibody. Our results suggest that Sesim-Tang may inhibit TNF-alpha secretion by inhibiting IL-1 secretion and that Sesim-Tang has an antiinflammatory activity in the central nervous system.

Selective abrogation of major histocompatibility complex class II expression on extrahematopoietic cells in mice lacking promoter IV of the class II transactivator gene

MHC class II (MHCII) molecules play a pivotal role in the induction and regulation of immune responses. The transcriptional coactivator class II transactivator (CIITA) controls MHCII expression. The CIITA gene is regulated by three independent promoters (pI, pIII, pIV). We have generated pIV knockout mice. These mice exhibit selective abrogation of interferon (IFN)-gamma-induced MHCII expression on a wide variety of non-bone marrow-derived cells, including endothelia, epithelia, astrocytes, and fibroblasts. Constitutive MHCII expression on cortical thymic epithelial cells, and thus positive selection of CD4(+) T cells, is also abolished. In contrast, constitutive and inducible MHCII expression is unaffected on professional antigen-presenting cells, including B cells, dendritic cells, and IFN-gamma-activated cells of the macrophage lineage. pIV(-/-) mice have thus allowed precise definition of CIITA pIV usage in vivo. Moreover, they represent a unique animal model for studying the significance and contribution of MHCII-mediated antigen presentation by nonprofessional antigen-presenting cells in health and disease.

Immunocompetent astrocytes and microglia display major differences in the processing of the invariant chain and in the expression of active cathepsin L and cathepsin S

The role of astrocytes and microglia as antigen-presenting cells in the brain is still controversial. In this study we have analyzed and compared aspects of the molecular machinery that underlies MHC class II trafficking in immunocompetent astrocytes and microglia. We show that IFN-gamma-stimulated microglia possess active cathepsin L and cathepsin S, and efficiently degrade the invariant chain, unlike IFN-gamma-stimulated astrocytes that express cathepsin L but not cathepsin S. The lack of cathepsin S proves to be dramatic for the antigen-presentation capacity of astrocytes, which is nearly abolished when these cells are stimulated by a combination of IFN-gamma and TNF-alpha. TNF-alpha indeed decreases cathepsin L activity as we show here, leading to alterations in invariant chain processing, and hence in MHC class II trafficking in astrocytes. Cystatin C inhibits cathepsin L activity in astrocytes, but does not regulate cathepsin L and cathepsin S activity in microglia. We therefore identify cathepsin L and cathepsin S as key components in the regulation of the immune potential of astrocytes and microglia, and provide evidence for a cell-specific regulation exerted by IFN-gamma and TNF-alpha on the expression and activity of cathepsins.

Inhibitory effect of tumor necrosis factor-alpha secretion from rat astrocytes by Chilbokeum

Substance P (SP) can stimulate secretion of tumor necrosis factor-alpha (TNF-alpha) from astrocytes stimulated with lipopolysaccharide (LPS). In this study, we have examined whether an aqueous extract of Chilbokeum inhibits secretion of TNF-alpha from primary cultures of rat astrocytes. Chilbokeum (10 microg/ml) significantly inhibited the TNF-alpha secretion by astrocytes stimulated with LPS and SP. Interleukin-1 (IL-1) has been shown to elevate TNF-alpha secretion from LPS-stimulated astrocytes while having no effect on astrocytes in the absence of LPS. We therefore examined whether IL-1 mediated inhibition of TNF-alpha secretion from primary astrocytes by Chilbokeum. Treatment of Chilbokeum (10 and 100 microg/ml) to astrocytes stimulated with both LPS and SP decreased IL-1 secretion significantly. Moreover, the secretion of TNF-alpha by LPS and SP in astrocytes was progressively inhibited with increasing amount of IL-1 neutralizing antibody. Our results suggest that Chilbokeum may inhibit TNF-alpha secretion by inhibiting IL-1 secretion and that Chilbokeum has an antiinflammatory activity in the central nervous system.

Taraxacum officinale inhibits tumor necrosis factor-alpha production from rat astrocytes

Substance P (SP) can stimulate production of tumor necrosis factor-alpha (TNF-alpha) from astrocytes stimulated with lipopolysaccharide (LPS). The objective of the current study was to determine the effect of Taraxacum officinale (TO) on the production of TNF-alpha from primary cultures of rat astrocytes. TO (100 and 1000 microg/ml) significantly inhibited the TNF-alpha production by astrocytes stimulated with LPS and SP. Interleukin-1 (IL-1) has been shown to elevate TNF-alpha production from LPS-stimulated astrocytes while having no effect on astrocytes in the absence of LPS. We therefore examined whether IL-1 mediated inhibition of TNF-alpha production from primary astrocytes by TO. Treatment of TO (100 and 1000 microg/ml) to astrocytes stimulated with both LPS and SP decreased IL-1 production significantly. Moreover, the production of TNF-alpha by LPS and SP in astrocytes was progressively inhibited with increasing amount of IL-1 neutralizing antibody. Our results suggest that TO may inhibit TNF-alpha production by inhibiting IL-1 production and that TO has an antiinflammatory activity in the central nervous system.

Strain specific variation in cytokine regulated ICAM-1 expression by rat brain-endothelial cells

Cytokine induced levels of ICAM-1 expressed by rat brain-endothelial cells were quantitated by enzyme immunoassay in response to stimulation by TNF-alpha in the presence or absence of IFN-gamma. The rat strains investigated differ in their susceptibility to experimental allergic encephalomyelitis; significantly less ICAM-1 was induced by BEC derived from the resistant PVG strain as compared to the susceptible LEW strain with both cytokine combinations. In contrast, despite the difference in disease susceptibility, equivalent levels of ICAM-1 were induced between the LEW and BN strain. Furthermore, evidence for a synergistic interaction of both TNF-alpha and IFN-gamma was observed in the BN strain. The results are discussed with relevance to the disease profile of each strain.

Dehydroepiandrosterone selectively inhibits production of tumor necrosis factor alpha and interleukin-6 [correction of interlukin-6] in astrocytes

Dehydroepiandrosterone (DHEA) is a native neurosteroid with immunomodulating activity. DHEA effectively protects animals from several viral, bacterial and parasitic infections and it was suggested that its age-associated decline is related with immunosenescence. In the present study we examined the ability of DHEA to inhibit the production of inflammatory mediators by mycoplasma-stimulated glial cells and to change the course of acute central nervous system (CNS) inflammatory disease in vivo. Addition of DHEA (10 microg/ml) markedly inhibited tumor necrosis factor alpha (TNFalpha) and interleukin-6 (IL-6) production (98 and 95%, respectively), whereas nitric oxide (NO) and prostaglandin E2 (PGE2) production was not affected. However, daily administration of 0.5 mg DHEA to mice or 5 mg to rats did not change the clinical outcome of experimental autoimmune encephalomyelitis (EAE).

Differential selectivity of CIITA promoter activation by IFN-gamma and IRF-1 in astrocytes and macrophages: CIITA promoter activation is not affected by TNF-alpha

During demyelinating disease of the central nervous system (CNS), locally elevated cytokine levels may induce upregulation of MHC class II molecules on otherwise low expressing or negative cell types such as microglia and astrocytes, since IFN-gamma has been shown to induce MHC class II expression on these cell types in vitro. While many transcription factors are involved with MHC class II expression, only the class II transactivator (CIITA) is tightly coordinated with IFN-gamma-inducibility. Control of CIITA gene expression is complex, involving four distinct promoters, two of which (promoters III and IV) are IFN-gamma-inducible in certain cell types. Here we demonstrate that IFN-gamma treatment of rat astrocytes induces only CIITA promoter IV activity in contrast to the murine macrophage cell line RAW 264.7 that uses both IFN-gamma-inducible promoters. In contrast to previously published reports, promoter IV activation is completely dependent upon an intact interferon regulatory factor-1 (IRF-1) but not STAT binding site using promoter constructs specifically mutated at these positions. Importantly, while TNF-alpha is able to synergize with IFN-gamma to increase astrocyte MHC class II expression in vitro, we show that treatment of rat astrocytes with TNF-alpha has no effect on CIITA promoter activity. These data demonstrate that TNF-alpha augments MHC class II expression through a mechanism downstream or independent of CIITA induction.

Tumor necrosis factor-alpha signals to the IFN-gamma receptor complex to increase Stat1alpha activation

We describe a novel mechanism of signaling interaction through which tumor necrosis factor-alpha (TNF-alpha) treatment augments interferon-gamma (IFN-gamma)-induced Stat1alpha DNA-binding complexes and transcriptional activation of a Stat-binding element. In TNF-alpha-treated cells, IFN-gamma-induced phosphorylation of Jak2 kinase is increased, Jak2 kinase activity is enhanced, and genetic studies indicate that TNF-alpha requires Jak2 kinase activity to enhance Stat1alpha tyrosine phosphorylation. Increased Jak2 and Stat1alpha phosphorylation are observed within minutes of coexposure to TNF-alpha/IFN-gamma, suggesting a direct signaling interaction. IFN-gamma receptor chain 1 (IFNGR-1) tyrosine phosphorylation is markedly enhanced in cells treated with TNF-alpha/IFN-gamma without alteration in receptor levels. Thus, there exists a direct signaling interaction between TNF-alpha and IFN-gamma, independent of cooperating enhancer elements, that may be relevant for cytokine action during immune-mediated host defense and inflammatory processes.

Flow cytometric analysis of in vitro proinflammatory cytokine secretion in peripheral blood from multiple sclerosis patients

The cytokines, interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and interleukin-2 (IL-2) are important endogenous proinflammatory proteins and have been linked to disease activity in multiple sclerosis. In this study, we use flow cytometric methodology to compare the secretion of IFN-gamma, IL-2, and TNF-alpha from peripheral blood-derived T cells of multiple sclerosis patients to the secretion in healthy controls. The percentages of IFN-gamma, IL-2, and TNF-alpha secreting cells are not significantly different between multiple sclerosis patients and controls. However, the TNF-alpha secreting CD3 cell percentage is correlated with the IFN-gamma and IL-2 secreting CD3 cell percentages in multiple sclerosis patients. In the controls, only the TNF-alpha secreting CD3 cell percentage is correlated with IFN-gamma. These findings show that correlated secretion of cytokines occurs in multiple sclerosis and suggest that concerted intercytokine interactions may play an important role in the disease.

IFN-γ Regulation of the Type IV Class II Transactivator Promoter in Astrocytes

The transcriptional activation of class II MHC genes requires the class II transactivator (CIITA) protein, a regulator that is essential for both constitutive and IFN-γ-inducible class II MHC expression. The CIITA gene is controlled by multiple independent promoters; two promoters direct constitutive expression, while another, the type IV CIITA promoter, mediates IFN-γ-induced expression. We investigated the molecular regulation of IFN-γ-induced type IV CIITA promoter activity in astrocytes. IFN-γ inducibility of the type IV CIITA promoter is dependent on three cis-acting elements contained within a 154-bp fragment of the promoter; the proximal IFN-γ activation sequence (GAS) element, the E box, and the proximal IFN regulatory factor (IRF) element. Two IFN-γ-activated transcription factors, STAT-1α and IRF-1, bind the proximal GAS and IRF elements, respectively. The E box binds upstream stimulating factor-1 (USF-1), a constitutively expressed transcription factor. Furthermore, STAT-1α binding to the proximal GAS element is dependent on the binding of USF-1 to the adjacent E box. Functionally, the proximal IRF element is essential for IFN-γ induction of type IV CIITA promoter activity, while the proximal GAS and E box elements contribute to the IFN-γ inducibility of this promoter. In astrocytes, TNF-α enhances IFN-γ-induced class II MHC transcription. Our results demonstrate that TNF-α does not enhance IFN-γ-induced transcriptional activation of the type IV CIITA promoter, indicating that the enhancing effect of TNF-α is mediated downstream of CIITA transcription. These results define the molecular basis of IFN-γ activation of the type IV CIITA promoter in astrocytes.

Suppression of experimental autoimmune encephalomyelitis by tyrphostin AG-556

Tyrosine kinase blockers from the AG 126/AG-556 tyrphostin family are shown to inhibit the lipopolysaccharide (LPS)-induced production of tumor necrosis factor alpha (TNFalpha), nitric oxide (NO), and prostaglandin E2 (PGE2) in primary rat astrocytes cultures. The tyrphostin AG-556 which was previously shown to be effective against sepsis in mice and dogs also show excellent efficacy in inhibiting experimental autoimmune encephalomyelitis (EAE) in mice. AG-556 does not block the activation of JNK/SAPK and of p38/HOG and therefore seems to act at a target down stream to these kinases which is activated in stress or at a target on an obligatory parallel pathway. These findings together with previous results showing inhibition of sepsis in mice and dogs suggest that protein tyrosine kinase (PTK) blockers of the AG-556 family may be considered in the management of human autoimmune disorders such as multiple sclerosis (MS).

The role of tumour necrosis factor, interleukin 6, interferon-gamma and inducible nitric oxide synthase in the development and pathology of the nervous system

Proinflammatory cytokines, tumour necrosis factor (TNF)-alpha, interferon (IFN)-gamma and interleukin (IL)-6, have multiple effects in the central nervous system (CNS) not strictly cytotoxic being involved in controlling neuronal and glial activation, proliferation, differentiation and survival, thus influencing neuronal and glial plasticity, degeneration as well as development and regeneration of the nervous system. Moreover, they can contribute to CNS disorders, including multiple sclerosis. Alzheimer's disease and human immunodeficiency virus-associated dementia complex. Recent results with deficient mice in the expression of those cytokines indicate that they are in general more sensible to insults resulting in neural damage. Some of the actions induced by TNF-alpha, and IFN-gamma, including both beneficial and detrimental, are mediated by inducible nitric oxide synthase (iNOS)-derived nitric oxide (NO) production. NO produced by iNOS may be beneficial by promoting the differentiation and survival of neurons. IL-6 does not induce iNOS, explaining why this cytokine is less often involved in this dual role protection pathology. Some of the proinflammatory as well as the neurotrophic effects of those cytokines also involve upregulation of cell adhesion molecules (CAM). Those apparently conflicting results may be reconciled considering that proinflammatory cytokines are involved in promoting the disease, mostly by inducing expression of CAM leading to alteration of the blood-brain barrier integrity, whereas they have a protective role once disease is established due to its immunosuppressive or neurotrophic role. Understanding the dichotomy pathogenesis/neuroprotection of those cytokines may provide a rationale for better therapeutic strategies.

Expression of interleukin 6 in the rat striatum following stereotaxic injection of quinolinic acid

Stereotaxic intrastriatal injection of the naturally occurring N-methyl-D-aspartate (NMDA) agonist quinolinic acid (QA) serves as a valuable in vivo model to study excitotoxic cell damage in the central nervous system (CNS). Although morphological changes such as neuronal loss, glial activation and remote reactions following QA injection have been described in some detail, much less is known about the molecular mechanisms mediating the accompanying glial response. Cytokines are known to play a crucial role in almost all kinds of CNS alterations. We now demonstrate that IL-6, a multifunctional glycoprotein which belongs to the family of neurokines, is expressed endogenously in the rat striatum following QA injection. Using Northern blot analysis, a massive but transient upregulation of IL-6 mRNA could be detected. This started 3 h after QA injection, reached a maximum at 6 h and disappeared within 24 h. That activated microglia are the most likely cellular source of the observed corresponding IL-6 protein expression could be concluded by comparing the immunocytochemical pattern of IL-6 expression and microglial activation. Interestingly, astrocytes initially downregulate their expression of glial fibrillary acidic protein (GFAP) in the excitotoxically injured striatum, but show a delayed increase in GFAP immunoreactivity starting in the periphery of the striatum, subsequently expanding to the core. The early transient IL-6 expression may play an important role in initiating the delayed astrocytic response following excitotoxic cell injury.

The effect of nitric oxide on cytokine-induced release of PGE2 by human cultured astroglial cells

1. The role of the L-arginine-nitric oxide (NO) pathway on the formation of prostaglandin E2 (PGE2) by human cultured astroglial cells incubated with interleukin-1beta (IL-1beta) and tumour necrosis factor-alpha (TNF-alpha) was investigated. 2. Incubation of T 67 astroglial cell line with IL-beta (10 ng ml(-1)) and TNF-alpha (500 u ml(-1)) produced a significant (P<0.05) increase of both nitrite (the breakdown product of NO), cyclic GMP and PGE2 levels in cell supernatants. N omega-nitro-L-arginine methyl ester (L-NAME; 20-300 microM), an inhibitor of NO synthase (NOS), inhibited the increase of cyclic GMP and nitrite levels found in supernatants of cytokine-treated astroglial cells and reduced the release of PGE2. The latter effect showed that the enhanced arachidonic acid (AA) metabolism subsequent to stimulation of astroglial cells with IL-1beta and TNF-alpha was, at least in part, induced by NO. This occurred also when sodium nitroprusside (SNP; 120 microM), an NO donor, was incubated with astroglial cells, an effect antagonized by oxyhaemoglobin (OxyHb; 10 microM). 3. The inhibition elicited by L-NAME on PGE2-release by cytokine-treated astroglial cells was reversed by adding AA (40 microM), showing that the effect of NO on cytokine-dependent PGE2 release occurred at the cyclo-oxygenase (COX) level. Furthermore, the release of PGE2 in cytokine-treated astroglial cells was inhibited by indomethacin (10 microM), a COX inhibitor as well as by preincubating cells with dexamethasone (20 microM), an inhibitor of inducible enzymes, showing that the inducible isoform of COX (COX-2) was involved. 4. On the other hand, pretreating astroglial cells with methylene blue (MB; 10 microM), an inhibitor of NO biological activity acting at the guanylate cyclase level, failed to affect PGE2 release in cytokine-treated astroglial cells, leading to the conclusion that cyclic GMP changes related to NO formation are not involved in the generation of AA metabolites. 5. The present experiments demonstrated that the release of PGE2 by astroglial cells pretreated with IL-1beta and TNF-alpha is due to enhanced COX-2 activity via activation of the L-arginine-NO pathway, and this may be relevant to the understanding of the pathophysiological mechanisms underlying neuroimmune disorders.

Distribution of endogenous tumour necrosis factor alpha in gliomas

AIMS

To determine the distribution and cellular origin of endogenous tumour necrosis factor alpha (TNF alpha) in the cellular components of human gliomas.

METHODS

Frozen sections of 26 gliomas (four astrocytomas (As); two oligoastrocytomas (OA); one ansplastic astrocytoma (AA); one anaplastic oligoastrocytoma (AOA); 18 glioblastomas (GB)) were examined immunohistochemically using antihuman TNF alpha and anti-Leu-M5 (CD11c) antibodies. Additional studies with double immunohistocchemical procedures were performed with anti-glial fibrillary acidic protein and anti-neurofilament antibodies.

RESULTS

Eighty per cent of the AA, AOA, and GB (16 of 20) had a positive reaction for TNF alpha, but only 17% of As and OA (one of six) were positive. Positive cells were seen in both the tumour tissue and adjacent brain tissues. TNF alpha protein was detected not only in the tumour cells but also in the endothelium of tumour vessels as well as reactive astrocytes and neurons.

CONCLUSIONS

Endogenous TNF alpha is present in cells of various origins in glial tumours including tumour vessels; however, the role of TNF alpha may be different in different types of cells or altered microenvironment.

Induction of adhesion/differentiation of human neuroblastoma cells by tumour necrosis factor-alpha requires the expression of an inducible nitric oxide synthase

Neuroblastoma cell lines (SK-N-SH and SK-N-MC) were induced to differentiate, as detected by the expression of neurofilament proteins of 68 and 200 kDa, and to express adhesion molecules (intercellular adhesion molecule-1 and vascular cell adhesion molecule) after stimulation with tumour necrosis factor-alpha (TNF-alpha). This induction was accompanied by the arrest of cell growth. The induction of neuroblastoma adhesion by TNF-alpha could be inhibited by the nitric oxide synthase inhibitors, L-N-monomethyl arginine (L-NMMA) and L-N6-(1-imidoethyl)-lysine (highly specific for the inducible enzyme), but not by the inactive enantiomer D-NMMA. These results indicate that TNF-alpha induces the adhesion of neuroblastoma cells via nitric oxide. This was confirmed by the finding that the adhesion/differentiation of SK-N-SH and SK-N-MC cells can be directly induced by the addition of nitric oxide donors, sodium nitroprusside and S-nitroso-N-acetyl-penicillamine, into the culture medium. The isoform of the nitric oxide synthase induced in human neuroblastoma cells by TNF-alpha treatment was identified enzymatically as isoform II by Western blotting and by the polymerase chain reaction. Thus TNF-alpha induces the in vitro adhesion/differentiation of human neuroblastoma cells through nitric oxide synthesized by a calcium-independent inducible form of nitric oxide synthase, clearly indicating that isoform II of nitric oxide synthase can be expressed in human neuronal cell types.

Distribution of tumor necrosis factor receptor messenger RNA in normal and herpes simplex virus infected trigeminal ganglia in the mouse

PURPOSE

to investigate the distribution of p55 and p75 tumor necrosis factor (TNF) receptor mRNA in normal murine trigeminal ganglia, and in murine trigeminal ganglia acutely infected with McKrae strain herpes simplex virus (HSV).

METHODS

in situ hybridization with antisense 35S-labeled riboprobes for mRNA encoding both the p55 and p75 TNF receptor (TNFR) subtypes was used in normal and HSV-infected murine trigeminal ganglia. Sense riboprobes were used as controls.

RESULTS

in situ hybridization with both p55 and p75 riboprobes produced a strong autoradiographic signal over many, but not all, trigeminal sensory neurons. Signal for mRNA encoding both TNFR subtypes was also present over the arachnoid layers surrounding trigeminal ganglia. Acute ocular HSV infection was accompanied by an intense leukocytic infiltrate into the ophthalmic portion of the trigeminal ganglia, and, in this setting, increased p55 and p75 mRNA signal was closely related to the location and number of infiltrating white blood cells. The distribution and number of trigeminal sensory neurons expressing mRNA for the two TNFR subtypes did not appear to change following infection. Signal over control sections hybridized with sense p55 and p75 TNFR cRNA probes was comparable to background.

CONCLUSIONS

the observed distribution of p55 and p75 TNFR mRNA over trigeminal sensory neurons and over the arachnoid layers surrounding trigeminal ganglia supports suggestions that TNF has a direct effect on neurons, either as a neuromodulator or neurotrophic factor, and that TNF may play a central role in blood-brain barrier regulation. Increased signal for TNFR mRNA in acutely infected trigeminal ganglia appears to reflect infiltration by receptor-bearing white blood cells.

Differential regulation of cytokine-induced major histocompatibility complex class II expression and nitric oxide release in rat microglia and astrocytes by effectors of tyrosine kinase, protein kinase C, and cAMP

Two glial cell populations of the CNS, astrocytes and microglia, were examined for expression of two immunologically important molecules, MHC class II and nitric oxide (NO), following treatment with cytokines. IFN-gamma induced both molecules in microglia at substantially higher levels than astrocytes. The addition of TNF-alpha to IFN-gamma elevated class II expression and NO in both cells. Genistein, an inhibitor of tyrosine kinases, and calphostin, an inhibitor of protein kinase C, diminished cytokine induction of class II MHC and NO in both glial populations. Forskolin was most effective in inhibiting class II MHC expression, but had little inhibitory effect on NO production. These results indicate microglia are more effective than astrocytes in producing cell-associated and secreted immune mediators in response to IFN-gamma and or TNF-alpha and multiple parallel, but distinct, signaling events are required for cytokine induced class II MHC or NO production.

Expression pattern and cellular origin of cytokines in the normal and Toxoplasma gondii-infected murine brain

In the normal brain, low levels of cytokines are observed, whereas inflammatory disorders of the central nervous system are characterized by an up-regulation of cytokine production. The cellular sources for cytokines in the central nervous system are largely undefined. In the present study, we have analyzed intracerebral cytokine production in normal and Toxoplasma gondii-infected mice using immunohistochemistry, in situ hybridization, flow cytometry of brain-derived leukocytes, and reverse transcriptase polymerase chain reaction detection in various subpopulations of inflammatory cells. In the normal brain, neurons and choroid plexus epithelia expressed interleukin (IL)-1 beta and IL-10. Microglia/macrophages produced IL-1 beta, IL-10, and tumor necrosis factor-alpha In Toxoplasma encephalitis, these cell types exhibited increased levels of the respective cytokines. In addition, microglia/macrophages showed a de novo expression of inducible nitric oxide synthase. CD4+ and CD8+ T cells, which were recruited to the brain, produced IL-2, IL-10, tumor necrosis factor-alpha, and interferon-gamma. IL-4 was exclusively detectable in CD4+ T cells, whereas CD8+ T cells showed expression of IL-1 beta. As chronic Toxoplasma encephalitis was not associated with neuronal degeneration and an up-regulation of neurotrophic factors, some cytokines may also exert neurotrophic and/or neuroprotective properties.

Systemic high-dose recombinant-alpha-2a-interferon therapy modulates lymphokine production in multiple sclerosis

Chronic systemic high-dose recombinant alpha 2a-interferon (rIFNA) therapy reduces exacerbation rate and MRI signs of disease activity in relapsing/remitting multiple sclerosis (RR MS) patients. In order to clarify the possible mechanisms underlying the clinical efficacy of rIFNA in MS, several immunologic studies were performed as a part of a pilot clinical trial. Twenty RR MS patients were treated with 9 x 10(6) IU of rIFNA (n = 12) or placebo (n = 8) intramuscularly every other day for 6 months. Cytokine production by cultured lymphocytes, major histocompatibility complex class II (MHC-II) antigen expression on cultured macrophages, peripheral blood (PB) and cerebrospinal fluid (CSF) lymphocyte phenotype, and IgG and beta 2 microglobulin levels were studied before therapy, after 6 months of therapy, and 6 months after stopping therapy. rIFNA therapy was associated with reduction of interferon-gamma and tumor necrosis factor-alpha production by PB lymphocytes (p < 0.04), and with slight, not significant, increase of transforming growth factor-beta 2 or interleukin (IL)-10 production. IL-4 was undetectable in the culture supernatants both before and after therapy. rIFNA therapy had no effect on macrophage MHC-II molecule expression. An increased percentage of CD8+, CD8+ high CD11b+ low, and CD3- CD16+ CD56+ cells, and of CD4+ absolute cell number was observed in CSF after rIFNA therapy. After rIFNA administration, IgG level significantly increased both systemically (p < 0.02) and intrathecally (p < 0.001). Serum beta 2 microglobulin level increased (p < 0.01), as well. Only 1 out of the 12 rIFNA treated patients developed neutralizing antibodies against rIFNA during therapy. Six months after stopping therapy all the immunologic changes returned to baseline. These data suggest that the beneficial effect of rIFNA therapy on MS disease activity is probably mediated by a downregulation of proinflammatory cytokine synthesis by PB lymphocytes rather than by macrophage MHC-II antigen expression. The immunologic effects of high-dose systemic rIFNA therapy are temporary and restricted to the period of drug administration.

Modulation of immune-associated surface markers and cytokine production by murine retinal glial cells

Murine retinal glia are normally negative for major histocompatibility complex (MHC) Class II antigens and express low levels of MHC Class I and intercellular adhesion molecule-1 (ICAM-1) as detected by avidin-biotin-peroxidase immunohistochemistry. These surface molecules associated with immune function were either induced (Class II) or upregulated (Class I and ICAM-1) on cultured retinal glial cells in a dose- and time-dependent manner following exposure to recombinant interferon-gamma (rIFN-gamma). MHC Class I and II expression by passaged and primary cells was maximal (> 90% positive) after incubation with 100 U/m1 of rIFN-gamma for 48 h. ICAM-1 expression by primary and passaged cells tripled between 48 and 72 h after exposure to 25 or 50 U/m1 of rIFN-gamma. By 72 h after exposure to 100 U/m1 of rIFN-gamma, 62% of the retinal glia were positive for ICAM-1, whereas under normal culture conditions these molecules were detected on < 3% of the retinal glia. Bacterial lipopolysaccharide (LPS), a known stimulator of central nervous system (CNS) astrocytes, increased ICAM-1 expression only 3-fold to 9% of cells staining positively, but neither MHC Class I nor Class II expression was altered from baseline levels. Surface expression of ICAM-1, MHC Class I, and MHC Class II was unaffected by exposure to either rTNF-alpha (1000 U/m1) or rIL-6 (100 U/m1) for 24 h. Under normal culture conditions, intracellular interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) were detected immunohistochemically. Exposure to either rIFN-gamma or LPS induced more intense staining which correlated with increased secreted levels of both cytokines in culture supernatants. Levels of secreted TNF-alpha increased 6-fold after stimulation with LPS for 24 h, while secreted IL-6 increased over 9-fold. These results support the hypothesis that retinal glia may participate in intraretinal immune processes following stimulation during inflammatory and infections processes via either cell surface-or soluble mediator-dependent mechanisms or a combination of both.

Brain injury and tumor necrosis factors induce calbindin D-28k in astrocytes: evidence for a cytoprotective response

Calbindin is a 28 kDa calcium-binding protein expressed in restricted neuronal populations in the mammalian brain where it may play a role in protecting neurons against excitotoxic insults. Recent findings indicate that electrical activity and some neurotrophic factors can induce the expression of calbindin in neurons. We now report that brain injury, effected by systemic administration of the excitotoxin kainate or mechanical trauma, induces expression of calbindin in cells of the corpus callosum and subcortical white matter. Immunohistochemical analysis using antibodies to the astrocyte-specific proteins (glial fibrillary acidic protein and S-100 beta) established the identity of calbindin immunoreactive cells as astrocytes. Because brain injury is known to induce the expression of several neurotrophic factors and cytokines, we employed cultures of hippocampal and neocortical astrocytes to test the hypothesis that such factors can induce expression of calbindin in astrocytes. Tumor necrosis factors (TNF alpha and TNF beta), cytokines that are expressed in response to brain injury, induced the expression of calbindin in cultured rat hippocampal and neocortical astrocytes. Two neurotrophic factors, basic fibroblast growth factor and nerve growth factor, did not induce calbindin in astrocytes. TNF-treated, calbindin-expressing astrocytes were resistant to acidosis and calcium ionophore toxicity, suggesting that TNFs and calbindin may serve a cytoprotective role in astrocytes in the injured brain.

Production and function of monocyte chemoattractant protein-1 and other beta-chemokines in murine glial cells

Monocyte chemoattractant protein-1 (MCP-1), formerly termed JE, is a member of the beta-chemokine (C-C chemokine) family and has been shown to be produced by a variety of cell types. Recently, mRNA of JE/MCP-1 was detected in astrocytes during the acute phase of experimental allergic encephalomyelitis (EAE). In addition, supernatants collected from human cultured astrocytes have recently been found to be chemotactic for monocytes. However, chemokine production and function in glial cells has not been fully examined. Using a sandwich ELISA assay, we have now quantitated MCP-1 levels and assessed MCP-1 function on murine glial cells. Lipopolysaccharide (LPS), interleukin (IL)-1 beta and tumor necrosis factor (TNF)-alpha induced MCP-1 secretion by astrocytes, but not microglia. In addition, pretreatment with interferon (IFN)-gamma significantly augmented MCP-1 production by either LPS or the above cytokines. In contrast, LPS preferentially induced production of another beta-chemokine, macrophage inflammatory protein-1 alpha (MIP-1 alpha) from microglial cells. MCP-1 induced chemotaxis of microglial cells and macrophages. Similarly, another beta-chemokine, TCA3, which is produced by encephalitogenic T lymphocytes, also induced chemotaxis of microglia and macrophages. These findings suggested that astrocytes and microglial cells differentially produce chemokines in the central nervous system, and that both astrocytes and T cells may facilitate recruitment and activation of microglial cells via production of beta-chemokines.

The receptor for tumor necrosis factor on murine astrocytes: characterization, intracellular degradation, and regulation by cytokines and Theiler's murine encephalomyelitis virus

Previous reports have shown that tumor necrosis factor (TNF) exerts a role on the physiology of astrocytes under inflammatory situations. The signalling for biological effects of this and other cytokines are usually exerted through cell surface receptors. In this study, we have demonstrated the presence of a surface TNF alpha receptor type I in murine astrocytes of both SJL/J and BALB/c origin, using 125I-labelled recombinant mouse TNF alpha. A linear Scatchard plot indicates the presence of only one type of receptor with a MW of 58 kDa (Type I TNF receptor) that binds the ligand with a Kd of 1 x 10(-9) M. There are 3,000 copies of this receptor on untreated astrocytes. The results also indicate that receptor-bound TNF is rapidly internalized at 37 degrees C and degraded intracellularly to a principal molecular species which elutes from HPLC reverse-phase columns at 38% acetonitrile rather than at 60%, as native TNF alpha does. The binding is up-regulated by increasing the number of receptors (but not its affinity) by treatments with Theiler's murine encephalomyelitis virus (TMEV), Con A and inflammatory cytokines such as IL-1 alpha, IL-6, and INF-gamma. It is not influenced by vaccinia virus, IL-2, or LPS. This receptor may contribute to the initiation of perpetuation of the immune response which mediates the demyelinating inflammation induced by Theiler's virus.

Brain beta 2-microglobulin levels are elevated in the striatum in Parkinson's disease

beta 2-Microglobulin (B2-MG) content was measured for the first time in the brain (caudate nucleus, putamen, and cerebral cortex) from control and parkinsonian patients by a highly sensitive sandwich enzyme immunoassay. The concentrations of B2-MG in dopaminergic striatal regions were significantly higher in parkinsonian patients than those in controls, whereas those in the cerebral cortex showed no significant difference between parkinsonian and control subjects. Tumor necrosis factor-alpha (TNF-alpha) concentrations were also increased in the striatum, confirming our previous findings, but not in the cerebral cortex. Since TNF-alpha may induce B2-MG expression, these results suggest that an immunological response may occur in the nigrostriatal dopaminergic regions in Parkinson's disease.

Survival, development, and electrical activity of central nervous system myelinated axons exposed to tumor necrosis factor in vitro

Spinal cord explants from CD-1 mouse embryos were cultured in Maximow slide assemblies to promote myelin development. At about 20 days in vitro, recombinant human or mouse tumor necrosis factor alpha (TNF alpha) was added. Observed 3-8 days later, myelin was largely intact. The myelin blistering and oligodendrocyte damage seen in other strains were generally absent. Axonal conduction was measured optically through the use of a voltage-sensitive dye. Action potential shape, conduction velocity, and refractory period were all unchanged by exposure to TNF alpha. Two series of explants were grown with TNF alpha present continuously throughout the culture period. Observed with light and electron microscopy, myelin developed in at least 50% of the explants treated with recombinant mouse TNF alpha and 80% of those exposed to recombinant human TNF alpha. Optically recorded action potentials were of normal shape and refractory period. Conduction velocities were slightly lower than controls. CD-1 mouse central nervous system contains TNF alpha receptors and yet was resistant to myelin damage. The apparent strain specificity of TNF alpha disruption of myelin may result from more indirect modes of action, including interaction with other cytokines produced by glial cells. Survival of axonal conduction suggests that Na+ channel function remains intact following TNF alpha exposure.

Measurement of immune markers in the serum and cerebrospinal fluid of multiple sclerosis patients during clinical remission

Magnetic resonance imaging of multiple sclerosis (MS) patients often shows active inflammatory lesions despite clinical remission. No immunological marker of disease activity has been identified in these patients. Concentrations of neopterin, interleukin-2 (IL-2), soluble interleukin-2 receptor (sIL-2R) and tumour necrosis factor-alpha (TNF-alpha) were measured in the serum and cerebrospinal fluid of 19 clinically-inactive MS patients and compared with those of 19 non-inflammatory controls. Cerebrospinal fluid (CSF) neopterin concentrations were significantly higher in the MS group than in controls (mean 9.1 mM vs 3.4 nM, P < 0.01) and 10 of 19 MS patients had levels above the control range. This finding provides evidence of ongoing T-cell-directed and interferon-gamma-mediated macrophage activation in the central nervous system. Analysis of IL-2, sIL-2R and TNF-alpha concentrations revealed no significant differences between MS patients and controls. We conclude that CSF neopterin concentration may correlate with disease activity in asymptomatic patients.

Release of nitric oxide from astroglial cells: a key mechanism in neuroimmune disorders

Astrocytes are glial cells able to release nitric oxide (NO) under basal conditions as well as following different neurochemical stimuli including cytokines, endotoxins and soluble antigens, thereby participating in neuroimmune responses. In particular, the inducible isoform of NO synthase seems to be activated during co-incubation of this cell type with cytokines as well as in the presence of the HIV coating gp120 glycoprotein, an effect which is associated with an enhancement of prostanoid release. This seems also to occur via activation of cyclooxygenase by NO. Thus, the L-arginine-NO pathway found in astrocytes may represent a novel approach in the treatment of neuroimmune disorders such as multiple sclerosis, Alzheimer's disease and AIDS.

Role of protein kinase C and tyrosine kinase activity in IFN-gamma-induced expression of the class II MHC gene

Astrocytes are induced by interferon-gamma (IFN-gamma) to express class II major histocompatibility complex (MHC) antigens. Our previous studies demonstrated that IFN-gamma-initiated signaling events important for class II expression include activation of protein kinase C (PKC) and the Na+/H+ antiporter. We have extended these studies and found that protein tyrosine kinase (PTK) activity is also required for class II expression. Treatment of astrocytes with inhibitors specific for PKC and PTK blocked INF-gamma-induced class II gene transcription, mRNA expression, and protein expression. Immunoblotting and immunoprecipitation experiments demonstrated that IFN-gamma induced tyrosine phosphorylation of the p91 component of ISGF3, which is blocked by preincubation of cells with PTK inhibitors. Treatment of astrocytes with IFN-gamma and either PKC and PTK inhibitors changed the mobility and intensity of a nuclear factor, IFN-gamma-enhanced factor X, which binds to the X box of the class II MHC promoter. Taken together, these data provide evidence that activation of both PTK and PKC is required for IFN-gamma-induced expression of the class II gene.

Induction of TH1- and TH2-associated cytokine mRNA in mouse bladder following intravesical growth of the murine bladder tumor MB49 and BCG immunotherapy

Productive immunity to murine and human parasites is associated with the development of a type I T cell response (interferon-gamma-producing) while type II responses (interleukin-4-producing) suppress the development of delayed-type hypersensitivity (DTH) and the elimination of the parasite. To determine if a similar regulatory pathway might exist in tumor systems and may be effected by immunotherapeutic manipulation, we have studied the localized cytokine response to the murine bladder tumor MB49 growing intravesically in syngeneic mice. Intravesical growth of MB49 results in the host-derived expression of mRNA for both interleukin-4 (IL-4) (TH2) and interferon gamma (IFN gamma) (TH1), as well as tumor necrosis factor alpha (TNF alpha) expression of indeterminate origin. Intravesical instillation of bacillus Calmette-Guérin (BCG), highly effective in eliminating bladder tumors clinically and in experimental systems, results in IFN gamma and TNF alpha mRNa production in the bladder wall, but no IL-4. Following BCG treatment of intravesical MB49, the number bladders expressing IL-4 mRNA decreases, while IFN gamma and TNF alpha expression remains constant. These results are consistent with the mechanism of action of BCG involving the generation of an enhanced TH1 immune milieu in the bladder wall, which may contribute to the generation of productive tumor-specific immunity.

TNF-alpha increases the frequency of spontaneous miniature synaptic currents in cultured rat hippocampal neurons

Tumor necrosis factor-alpha (TNF-alpha) is a cytokine secreted by activated astrocytes and is known to alter evoked synaptic activity in slices of adult rat hippocampus. In this paper we show that TNF-alpha increases the frequency of spontaneous miniature synaptic currents in cultured hippocampal neurons, acting at nanomolar concentrations. In addition, we show that the mRNA for the 55 kDa TNF-alpha receptor (TNF-R1) is detected in embryonic rat hippocampal cultures, as well as in acutely dissected embryonic and adult rat hippocampi. Possible transduction pathways mediating the TNF-alpha effect are discussed.

The astrocyte mitogen, tumor necrosis factor-alpha, inhibits the proliferative effect of more potent adult human astrocyte mitogens, gamma-interferon and activated T-lymphocyte supernatants

The proliferative response of adult human astrocytes to tumor necrosis factor-alpha (TNF-alpha) was examined. Applied alone, TNF-alpha was dependent on the content of serum in the feeding medium, being mitogenic only in conditions of over 15% serum in medium. In accordance with previous results, supernatants from activated human CD8+ T-lymphocytes (CD8 SN) and recombinant human interferon-gamma (IFN-gamma) enhanced proliferation of adult human astrocytes in 5% serum-containing medium. Simultaneous administration of TNF-alpha (10-1000 units), however, abrogated the mitogenic effects of either CD8 SN or IFN-gamma; the inhibitory effect of TNF-alpha was lost if applied 2 days following IFN-gamma treatment. These studies show that while TNF-alpha is an astrocyte mitogen under selected conditions, it inhibits proliferation induced by other mitogens. In this manner, TNF-alpha may be important in regulating the proliferative response of astrocytes during reactive astrogliosis in vivo.

Tumor necrosis factor-alpha (TNF-alpha), interferon-gamma, and interleukin-6 but not TNF-beta induce differentiation of neuroblastoma cells: the role of nitric oxide

Tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), and interleukin-6 (IL-6), but not TNF-beta, can induce the in vitro differentiation of the neuroblastoma cell line N103 in a dose-dependent manner. Differentiation of N103 was accompanied by the arrest of cell growth and neurite formation. The induction of neuroblastoma cell differentiation by TNF-alpha and IFN-gamma can be specifically inhibited by a nitric oxide (NO) synthase inhibitor, L-NG-monomethylarginine. In contrast, the differentiation of N103 cells by IL-6 was not affected by L-NG-monomethylarginine. These results indicate that TNF-alpha and IFN-gamma, but not IL-6, induce the differentiation of neuroblastoma cells via NO. This is confirmed by the finding that the culture supernatants of N103 cells induced by TNF-alpha and IFN-gamma, but not that by IL-6, contained high levels of NO2-, the production of which was inhibited by L-NG-monomethylarginine. Furthermore, the differentiation of N103 cells can be induced directly in a dose-dependent manner by the addition of nitroprusside, a generator of NO, into the culture medium. These data therefore indicate that NO may be an important mediator in the induction of neuronal cell differentiation by certain cytokines such as TNF-alpha and IFN-gamma and that neuronal cells, in addition to the macrophage-like brain cells, can be induced by immunological stimuli to produce large quantities of NO.