Production of B cell stimulatory factor-2 and interferon gamma in the central nervous system during viral meningitis and encephalitis. Evaluation in a murine model infection and in patients

Inducible nitric-oxide synthase plays a minimal role in lymphocytic choriomeningitis virus-induced, T cell-mediated protective immunity and immunopathology

By using mice with a targetted disruption in the gene encoding inducible nitric-oxide synthase (iNOS), we have studied the role of nitric oxide (NO) in lymphocytic choriomeningitis virus (LCMV)-induced, T cell-mediated protective immunity and immunopathology. The afferent phase of the T cell-mediated immune response was found to be unaltered in iNOS-deficient mice compared with wild-type C57BL/6 mice, and LCMV- induced general immunosuppression was equally pronounced in both strains. In vivo analysis revealed identical kinetics of virus clearance, as well as unaltered clinical severity of systemic LCMV infection in both strains. Concerning the outcome of intracerebral infection, no significant differences were found between iNOS-deficient and wild-type mice in the number or composition of mononuclear cells found in the cerebrospinal fluid on day 6 post-infection. Likewise, NO did not influence the up-regulation of proinflammatory cytokine/chemokine genes significantly, nor did it influence the development of fatal meningitis. However, a reduced virus-specific delayed-type hypersensitivity reaction was observed in iNOS-deficient mice compared with both IFN-gamma-deficient and wild-type mice. This might suggest a role of NO in regulating vascular reactivity in the context of T cell-mediated inflammation. In conclusion, these findings indicate a minimal role for iNOS/NO in the host response to LCMV. Except for a reduced local oedema in the knockout mice, iNOS/NO seems to be redundant in controlling both the afferent and efferent phases of the T cell-mediated immune response to LCMV infection.

CSF and serum levels of soluble interleukin-6 receptors (sIL-6R and sgp130), but not of interleukin-6 are altered in multiple sclerosis

Interleukin-6 (IL-6) has recently been implicated in multiple sclerosis (MS), since IL-6 deficient mice were resistant to a demyelinating form of experimental autoimmune encephalomyelitis and IL-6 expression was upregulated in MS. The cytokine IL-6 and its action mediating soluble receptors (sIL-6R and sgp130) were measured in cerebrospinal fluid (CSF) and serum of 61 MS patients and 39 controls. In the presence of unchanged IL-6 concentrations, sIL-6R and sgp130 serum levels were significantly increased in MS and correlated with disease severity. Furthermore, sgp130 CSF levels were decreased in MS, suggesting a possibly altered IL-6 regulation in the CSF.

MHC Class II Engagement in Brain Endothelial Cells Induces Protein Kinase A-Dependent IL-6 Secretion and Phosphorylation of cAMP Response Element-Binding Protein

Activated endothelial cells can directly participate in immune responses by interacting with immunocompetent cells via class II MHC proteins. We show here that, after induction of MHC class II molecule expression by IFN-γ, rat brain endothelial cells responded to MHC class II ligands, anti-MHC class II Abs, or superantigens by expression of IL-6 transcript and IL-6 secretion. This response was not affected by protein kinase C depletion but was mimicked by the cAMP-elevating agent forskolin and completely blocked by H89, an inhibitor of cAMP-dependent protein kinase (PKA). Involvement of a cAMP/PKA signaling pathway in response to MHC class II ligands was further demonstrated by measure of a dose-dependent increase in cAMP level and phosphorylation of the transcription factor cAMP response element-binding protein (CREB). Our results indicate that MHC class II engagement in brain endothelial cells is directly coupled to IL-6 production via a cAMP/PKA-dependent intracellular pathway.

Neuroglial activation repertoire in the injured brain: graded response, molecular mechanisms and cues to physiological function

Damage to the central nervous system (CNS) leads to cellular changes not only in the affected neurons but also in adjacent glial cells and endothelia, and frequently, to a recruitment of cells of the immune system. These cellular changes form a graded response which is a consistent feature in almost all forms of brain pathology. It appears to reflect an evolutionarily conserved program which plays an important role in the protection against infectious pathogens and the repair of the injured nervous system. Moreover, recent work in mice that are genetically deficient for different cytokines (MCSF, IL1, IL6, TNFalpha, TGFbeta1) has begun to shed light on the molecular signals that regulate this cellular response. Here we will review this work and the insights it provides about the biological function of the neuroglial activation in the injured brain.

Leukemia inhibitory factor, Interleukin 6, and other cytokines using the GP130 transducing receptor: roles in inflammation and injury

Inflammation refers to a complex set of mechanisms by which tissues respond to injury and infection. Among the many soluble mediators associated with this process, cytokines are known to be crucial in regulating a variety of cellular and molecular events. Leukemia inhibitory factor (LIF), interleukin 6 (IL-6), IL-11, and possibly other members of this cytokine family are key mediators in various inflammatory processes such as the acute-phase reaction, tissue damage, and infection. These cytokines can act in both pro-inflammatory and anti-inflammatory ways, depending on a number of variables. We emphasize here recent work utilizing knockout mice, which has highlighted the roles of LIF and IL-6, particularly in interactions between the immune and nervous systems.

Expression of granulocyte colony-stimulating factor in recurrent glial tumors is inversely correlated with tumor progression

We have previously reported that in vivo-expression of granulocyte colony-stimulating factor (G-CSF) is a characteristic feature of reactive and neoplastic astrocytes. The aim of the present study was to analyze the expression of G-CSF protein in primary and recurrent astroglial, oligodendroglial and mixed glial-differentiated tumors. G-CSF expression was present in all GFAP-positive tumors excepting glioblastomas. G-CSF expression was significantly reduced in recurrent tumors more dedifferentiated than their primary counterparts. G-CSF expression was absent in all GFAP-negative tumors such as oligodendrogliomas. Our results demonstrate that G-CSF is a highly sensitive differentiation marker of neoplastic astrocytes, which is lost during tumor progression.

Increased interleukin-6 expression by microglia from brain of aged mice

Over expression of inflammatory cytokines in the brain may establish a state that is permissive to the onset of neurodegenerative disease. Because the occurrence of certain neurodegenerative diseases increases with age, in the present study we examined the expression of the inflammatory cytokine, interleukin-6 (IL-6), in the brain of aged mice. In an initial experiment, IL-6 was measured in crude protein extracts from brains of juvenile (1-month-old), adult (3-month-old), and aged (24-month-old) male BALB/c mice. The concentration of IL-6 in crude protein extracts from the cerebellum, cerebral cortex, and hippocampus increased with age. The increase in IL-6 was discrete, as levels in the hypothalamus were not age-dependent. To begin evaluating spontaneous IL-6 production in aging, glial cells were cultured from brains of neonate, adult, and aged mice. An age-associated increase in IL-6 mRNA and supernatant IL-6 concentration was evident, indicating glia from aged mice spontaneously express high levels of IL-6 relative to glia from adult and neonate mice. Flow cytometric analysis revealed that cultures established from aged brain compared to either adult or neonate brain comprised more microglia (i.e., MAC-1-positive cells). Furthermore, the proportion of microglia that was positive for IL-6 increased with age, whereas the proportion of astrocytes that were positive for IL-6 was not age-dependent. The present results suggest that IL-6 increases in the mouse brain with age, and that microglia cultured from aged mice spontaneously produce more IL-6 than those from neonate or adult mice. Therefore, microglia may contribute to the increased level of IL-6 present in aged brain.

Role of the proteasome and NF-kappaB in streptococcal cell wall-induced polyarthritis

The transcription factor NF-kappaB activates a number of genes whose protein products are proinflammatory. In quiescent cells, NF-kappaB exists in a latent form and is activated via a signal-dependent proteolytic mechanism in which the inhibitory protein IkappaB is degraded by the ubiquitin-proteasome pathway. Consequently, inhibition of the proteasome suppresses activation of NF-kappaB. This suppression should therefore decrease transcription of many genes encoding proinflammatory proteins and should ultimately have an anti-inflammatory effect. To this end, a series of peptide boronic acid inhibitors of the proteasome, exemplified herein by PS-341, were developed. The proteasome is the large multimeric protease that catalyzes the final proteolytic step of the ubiquitin-proteasome pathway. PS-341, a potent, competitive inhibitor of the proteasome, readily entered cells and inhibited the activation of NF-kappaB and the subsequent transcription of genes that are regulated by NF-kappaB. Significantly, PS-341 displayed similar effects in vivo. Oral administration of PS-341 had anti-inflammatory effects in a model of Streptococcal cell wall-induced polyarthritis and liver inflammation in rats. The attenuation of inflammation in this model was associated with an inhibition of IkappaBalpha degradation and NF-kappaB-dependent gene expression. These experiments clearly demonstrate that the ubiquitin-proteasome pathway and NF-kappaB play important roles in regulating chronic inflammation and that, as predicted, proteasome inhibition has an anti-inflammatory effect.

IL-6 deficiency leads to increased emotionality in mice: evidence in transgenic mice carrying a null mutation for IL-6

The role of interleukin-6 (IL-6) on emotional behavior was studied in two experiments using transgenic mice carrying a null mutation for IL-6 (IL-6(-/-)). In the first experiment, IL-6(-/-) mice were compared with the two wild-type strains contributing to the genetic background of the transgenic mice, namely C57BL/6J and 129/SvJ, as well as with the F2 offspring of C57BL/6J x 129/SvJ mice. The two parental strains differed substantially in terms of emotional reactivity, suggesting that the F2 offspring were more appropriated for analyzing the effect of the null mutation. IL-6(-/-) mice showed lower levels of ambulation in the holeboard, and lower levels of exploration of the open arms of the plus-maze, than the wild-type F2 C57BL/6J x 129/SvJ mice. In the second experiment, IL-6(-/-) mice were backcrossed for 10 generations to C57BL/6J mice to decrease the uncertainty of the effect of the genetic background, and when compared with wild-type C57BL/6J mice in the holeboard and the plus-maze, the same results were obtained. Therefore, IL-6(-/-) mice seem to be more emotional than their appropriate controls, suggesting that the major cytokine IL-6 is involved in the control of emotionality.

Role of interferon-gamma in the pathogenesis of LCMV-induced meningitis: unimpaired leucocyte recruitment, but deficient macrophage activation in interferon-gamma knock-out mice

Generally, interferon-gamma (IFN-gamma) is considered a critical regulator of T cell mediated inflammation. For this reason, we investigated the pathogenesis of lymphocytic choriomeningitis in mice with a targeted defect of the gene encoding this cytokine. Our results revealed that IFN-gamma is redundant in the afferent phase of the antiviral T cell response as well as a local mediator of this T cell mediated inflammatory disease. However, IFN-gamma may play an indirect role as it is involved in reducing extraneural infection that may compete with CNS for available effector cells. Analysis of the inflammatory exudate disclosed that leucocyte recruitment was unimpaired in the absence of IFN-gamma as was the upregulation of ICAM-1 and VCAM-1 on endothelium at the inflammatory site. However, local macrophage activation (production of tumor necrosis-alpha and NO) was significantly impaired. Notably, a viral peptide could also elicit a T cell mediated inflammatory response in virus-primed IFN-gamma knock-out mice, indicating that redundancy of this cytokine as a proinflammatory mediator is not restricted to inflammatory reactions triggered by an active infection. Thus, T cell mediated inflammation may be induced in the absence of IFN-gamma and local macrophage activation.

Cytokine and chemokine production in HSV-1 latently infected trigeminal ganglion cell cultures: effects of hyperthermic stress

The establishment of a primary trigeminal ganglion (TG) cell culture latently infected with herpes simplex virus type 1 (HSV-1) has been useful in studying stress-induced reactivation of the latent virus. However, the immune profile of this culture system prior to and after stress has never been established. In the present manuscript, cytokine and chemokine production were measured in primary cultures of TG cells obtained from uninfected and HSV-1 latently infected mice. Supernates from TG cell cultures contained detectable interleukin (IL)-6 but not IL-1beta, IL-2, IL-10, interferon (IFN)-gamma or tumor necrosis factor (TNF)-alpha as determined by ELISA. The basal level of IL-6 in uninfected TG cell cultures was 20.5 +/- 2.3 ng/ml, whereas latently infected TG cells produced significantly less IL-6 (12.1 +/- 1.9 ng/ml). Supernates from TG cell cultures also contained detectable levels of C-10, MCP-1 and eotaxin but little to no MIP-1alpha, MIP-1beta, or MIP-2. While there were no differences in the basal level of MCP-1 and eotaxin in TG cell cultures from HSV-1-infected and uninfected mice, C10 levels were significantly higher in TG cultures originating from infected mice compared to uninfected ones (5.86 +/- 0.61 ng/ml compared to 1.18 +/- 0.16 ng/ml). Hyperthermic stress (43 degrees C, 180 min), which induces reactivation of latent HSV-1 from TG cell cultures, significantly reduced IL-6 and C-10 levels from both uninfected and latently infected TG cell cultures. However, there was no correlation between cytokine/chemokine levels and HSV-1 reactivation. Immunofluorescent studies showed TG cell cultures contained 10% MAC-3+ staining cells (macrophage specific) but no dendritic cells. By comparison, cells from freshly isolated TG contained 6% positive dendritic cells but < 1% MAC-3 + cells. Both in vivo and in vitro TG consisted of a low percentage of CD3+ and CD8+ cells. Hyperthermic stress (43 degrees C for 3 h) eliminated the lymphocyte population as determined by RT-PCR. Whereas no spontaneous reactivation has been reported in mice, spontaneous reactivation occurred in 4.5% (10/220) of TG cell cultures surveyed over a 20 day period. Collectively, the dichotomy between HSV-1 replication and reactivation comparing the in vitro and in vivo HSV-1 latency models may reside, in part, to the differences in the levels of cytokines, chemokines and immune cell populations within the microenvironment of the in vitro and in vivo TG.

Transgenic mice and cytokine actions in the brain: bridging the gap between structural and functional neuropathology

Deciphering the neurobiological consequences of cerebral cytokine expression in vivo represents an important research objective which has implications for our understanding of the pathogenesis and treatment of many significant neurological disorders. In our own pursuit of this objective, studies by us have utilized a transgenic strategy employing the GFAP promoter to direct the chronic expression of the cytokines IL-3, IL-6, IFN-alpha or TNF-alpha to astrocytes in mice. Transgenic expression of each cytokine produces a unique spectrum of neuropathological and functional alterations, thereby directly implicating these mediators in the pathogenesis of CNS disease. Moreover, as exemplified here with the GFAP-IL6 transgenic mice, these models are valuable tools in which to perform multi-level analysis to link molecular and cellular alterations to specific electrophysiological, neuroendocrine and behavioral outcomes. Integrative studies such as described here in the GFAP-cytokine transgenic mice, are providing a more thorough understanding of the actions of cytokines in the CNS and bridge the gap between structural and functional neuropathology.

Structural and functional impact of the transgenic expression of cytokines in the CNS

Cytokines are powerful mediators of biologic responses in the CNS and may contribute to cellular injury in pathophysiologic states. In order to better understand the actions of cytokines in the intact mammalian CNS, a transgenic approach was employed that targeted the expression of different cytokines to astrocytes in mice. Fusion gene constructs consisting of a GFAP expression vector into which was inserted the DNA encoding the cytokines interleukin-6 (IL-6), IL-3, or TNF-alpha were used to generate transgenic mice. Expression of the transgene-encoded cytokines in astrocytes was confirmed at both the RNA and protein levels. Transgenic mice were subject to multilevel analysis to determine the extent of structural and functional CNS alterations. Transgenic mice exhibited distinct adult-onset, chronic-progressive neurological disorders that correlated with the level and anatomic distribution of transgene-encoded cytokine expression. The principal findings were neurodegeneration and cognitive decline due to IL-6 expression, macrophage/microglial-mediated primary demyelination with motor disease resulting from IL-3 expression, and lymphocytic meningoencephalomyelitis with paralysis induced by TNF-alpha expression. These transgenic models (1) indicate that expression of cytokines per se in the intact CNS is pathogenic, with cytokine-specific neural cell injury leading to unique functional deficits; (2) recapitulate many of the structural and functional changes seen in human inflammatory neurological disorders; (3) provide a valuable tool for advancing our understanding of the CNS pathobiology of cytokines; and (4) offer a unique resource for the development and testing of therapies aimed at abrogating the harmful actions of these important mediators.

Interleukin-6 levels are not increased in women with postpartum thyroid dysfunction

Postpartum thyroid dysfunction (PPTD) is an autoimmune-mediated thyroid destructive process. Human interleukin-6 (IL-6) is a cytokine found to be increased in subacute thyroiditis, amiodarone-induced thyrotoxicosis, Graves' disease, and other thyroid destructive processes. We report serum IL-6 levels in PPTD in two independent studies. New York Study: In a previous prospective study we demonstrated that PPTD occurred in 25% (7/28) of women with type 1 diabetes mellitus. IL-6 determinations were made on the frozen serum samples of these 28 women during each trimester of their pregnancy and at 1.5, 3, 6, 9, and 12 months postpartum. IL-6 levels were found to be similar in women with PPTD compared with women without PPTD (mean 3.06+/-2.25 vs. 2.51+/-2.21 pg/mL; p = 0.15). No difference in IL-6 levels was found between the pre- and the postpartum periods (mean 2.67+/-1.82 vs. 3.04+/-2.44 pg/mL; p = 0.30) in all 28 women. Cardiff Study: Serum IL-6 levels were measured on frozen serum samples of 30 women with PPTD. IL-6 levels were below the detection limit (25 fmol/L or 0.65 pg/mL) in 94 (67%) of these samples. No significant difference in the mean serum IL-6 levels were found between any time points in the study. There was no correlation between serum IL-6 levels, thyroid peroxidase (TPO)- antibodies and serum thyrotropin (TSH) levels at any time point. IL-6 levels during pregnancy or postpartum were not found to be significantly different in women with PPTD compared with women without PPTD.

Chemokines and chemotaxis of leukocytes in infectious meningitis

Chemokines constitute a constantly growing family of small inflammatory cytokines. They have been implied in many different diseases of the CNS including trauma, stroke and inflammation, e.g., multiple sclerosis. In this review we focus on the role of chemokines in infectious meningitis of bacterial or viral origin. In experimental bacterial meningitis induced by Listeria monocytogeneses both CXC and CC chemokines namely MIP-1alpha, MIP-1beta and MIP-2 are produced intrathecally by meningeal macrophages and leukocytes which infiltrate into the CNS. In patients with bacterial meningitis, IL-8, GROalpha, MCP-1, MIP-1alpha and MIP-1beta are detectable in the CSF. These chemokines contribute to CSF mediated chemotaxis on neutrophils and PBMC in vitro. In viral meningitis IL-8, IP-10 and MCP-1 are identified in the CSF to be responsible for chemotactic activity on neutrophils, PBMC and activated T cells. Taken collectively these data indicate that the recruitment of leukocytes in infectious meningitis involves the intrathecal production of chemokines.

Cerebrospinal fluid interleukin 6 in amyotrophic lateral sclerosis: immunological parameter and comparison with inflammatory and non-inflammatory central nervous system diseases

We assayed IL-6 in 105 cerebrospinal fluid (CSF) samples from patients with ALS, MS, HTLV-1 associated myelopathy (HAM), and controls. There was considerable overlap in IL-6 levels in all patient groups. The mean IL-6 in 27 patients with ALS was significantly higher than in 21 patients in the other neurological disease (OND) group (P=0.0075). There were no significant differences in MS or HAM and the OND control group. Overall, CSF IL-6 correlated with protein concentration but not with percentage IgG or IgG-albumin index. Patients with CSF oligoclonal bands were no more likely to have detectable IL-6 than patients without oligoclonal bands. Similarly, IL-6 did not correlate with clinical disease activity in MS when subgroups of patients were compared or when an individual patient was followed over time. The elevated IL-6 in ALS may reflect an ongoing humoral immune response, or IL-6 may be non-specifically expressed in these patients as a putative neurotrophic factor in response to nerve cell degeneration.

Cytokine mRNA profiles during the course of experimental Haemophilus influenzae bacterial meningitis

Intraperitoneal inoculation of Haemophilus influenzae type b (Hib) to 3-week-old Sprague-Dawley rats resulted in nonlethal meningitis with high levels of leukocytes in the cerebrospinal fluid (CSF) and positive bacterial culture. Using in situ hybridization, levels of cytokine mRNA-expressing cells were determined in the brain, CSF, and spleen from Hib-inoculated and uninfected control rats. IFN-gamma, IL-1 beta, IL-4, IL-6, IL-10, IL-12, and TNF-alpha mRNA levels were elevated at 12 hr postinoculation (pi) in spleen and CSF. At this time point, strong expression of IL-6 and TGF-beta was detected in the brain, and also of IL-10 at 48 hr while IFN-gamma and IL-12 were expressed at very low levels throughout the observation time. Delayed cytokine induction occurred in CSF compared to spleen and brain. TGF-beta was high in CSF at 48 hr, and some elevation of IL-1 beta, IL-6, IL-10, TNF-alpha, IFN-gamma, and IL-12 was evident at 72 hr pi. This may suggest measures that promote production of TGF-beta and/or IL-10 should be evaluated in treatment of bacterial meningitis.

Physiological and pathological roles of interleukin-6 in the central nervous system

The cytokine interleukin-6 (IL-6) is an important mediator of inflammatory and immune responses in the periphery. IL-6 is produced in the periphery and acts systemically to induce growth and differentiation of cells in the immune and hematopoietic systems and to induce and coordinate the different elements of the acute-phase response. In addition to these peripheral actions, recent studies indicate that IL-6 is also produced within the central nervous system (CNS) and may play an important role in a variety of CNS functions such as cell-to-cell signaling, coordination of neuroimmune responses, protection of neurons from insult, as well as neuronal differentiation, growth and survival. IL-6 may also contribute to the etiology of neuropathological disorders. Elevated levels of IL-6 in the CNS are found in several neurological disorders including AIDS dementia complex, Alzheimer's disease, multiple sclerosis, systemic lupus erythematosus, CNS trauma, and viral and bacterial meningitis. Moreover, several studies have shown that chronic overexpression of IL-6 in transgenic mice can lead to significant neuroanatomical and neurophysiological changes in the CNS similar to that commonly observed in various neurological diseases. Thus, it appears that IL-6 may play a role in both physiological and pathophysiological processes in the CNS.

Activated astrocytes induce nitric oxide synthase-2 in cerebral endothelium via tumor necrosis factor alpha

Astrocytes under pathological conditions become activated and produce a variety of cytokines and low molecular weight signal molecules. Previously we demonstrated that activated astrocytes release nitric oxide which can downregulate the expression of nitric oxide synthase (NOS)-2 in co-cultured cerebral endothelium, and also release a transcriptionally regulated factor that can induce NOS-2 expression in endothelium (Borgerding and Murphy: J Neurochem 65:1342, 1995). The activity of this NOS-2-inducing factor was impeded by inhibitors of tyrosine kinases and NF-kappaB activation. Tumor necrosis factor (TNF alpha) alone, or in combination with IL-6, induced NOS-2 expression in endothelial cells. A neutralizing antibody against TNF alpha attenuated the NOS-2 expression in endothelial cells exposed to activated astrocytes. These results imply that cytokine-activated astrocytes release TNF alpha which can induce NOS-2 expression in endothelium and suggest that activated astrocytes within the CNS may induce expression of NOS-2 in cells of the adjacent microvasculature. The ensuing alterations in blood-brain barrier properties may be either beneficial or detrimental.

Chemotactic activity on mononuclear cells in the cerebrospinal fluid of patients with viral meningitis is mediated by interferon-gamma inducible protein-10 and monocyte chemotactic protein-1

In viral meningitis the inflammatory response involves activated T cells and monocytes which are recruited into the subarachnoid space. To identify the chemotactic signals attracting the cells to the site of infection in the meninges, we measured the levels of two CXC chemokines, interferon-gamma (IFN-gamma) inducible protein (IP)-10 and monokine induced by IFN-gamma, four CC chemokines, monocyte chemotactic protein (MCP)-1, RANTES, macrophage inflammatory protein (MIP)-1 alpha and MIP-1 beta, as well as the cytokines interleukin (IL)-15 and IL-16 in the cerebrospinal fluid (CSF) of patients suffering from viral meningitis. The results point to an involvement of two chemokines, MCP-1 and IP-10, since (1) unlike the other cytokines, MCP-1 and IP-10 were present in 97% and 79% of the CSF, respectively, at concentrations sufficient to induce chemotaxis of mononuclear cells; (2) more than 90% of the CSF of viral meningitis induced chemotaxis of peripheral blood mononuclear cells (PBMC) and all of them induced chemotaxis of activated T cells, and (3) the CSF-mediated chemotaxis of PBMC was inhibited by anti-MCP-1 antibodies and chemotaxis of activated T cells was abolished by the combination of anti-MCP-1 and anti-IP-10 antibodies. Our data provide evidence that MCP-1 and IP-10 lead to accumulation of activated T cells and monocytes in the CSF compartment in viral meningitis.

Quinolinic acid production by macrophages stimulated with IFN-gamma, TNF-alpha, and IFN-alpha

Quinolinic acid (QUIN) has been associated with several inflammatory neurologic disorders, including AIDS dementia complex (ADC). Recent studies suggest that activation of macrophages with either HIV-1 or interferon-gamma (IFN-gamma) can lead to QUIN production. However, the importance of other cytokines, especially those related to the macrophage and that are especially important in ADC pathogenesis, remains unclear. We, therefore, sought to determine the role of tumor necrosis factor-alpha (TNF-alpha) and IFN-alpha in the production of QUIN. Primary human macrophages were stimulated with two different concentrations of these cytokines alone, in combination with each other, and with IFN-gamma. QUIN concentrations in the supernatants were then measured by mass spectrometry at 24, 48, and 72 hs. Results at 72 h showed significant increases in QUIN production in the cells stimulated with IFN-gamma (10297 +/- 170 nmol/L) and also in those stimulated with IFN-alpha (3600 +/- 113 nmol/L), whereas TNF-alpha-stimulated macrophages produced low levels of QUIN (1108 +/- 23 nmol/L). Macrophages stimulated with the cytokine combinations TNF-alpha and IFN-gamma, IFN-alpha, and IFN-gamma, and TNF-alpha and IFN-alpha also resulted in increases in QUIN production (11471 +/- 77.6 nmol/L, 16656 +/- 184 nmol/L, and 3369 +/- 120.5 nmol/L, respectively). The increases in QUIN production in all of the cytokine treatments approached or exceeded in vivo concentrations of QUIN that have been shown to be neurotoxic. These data further support a role for QUIN in cytokine-mediated neuronal death in inflammatory disorders of the brain, especially ADC.

Identification of interleukin-6 producing fibroblastoid cells in cerebrospinal fluid from patients with leukemic meningitis

Cytokine producing native cells in cerebrospinal fluid (CSF) have not been identified. So, we investigated the cytokine producing ability of floating cells in CSF from patients with leukemic meningitis. Morphologic study revealed that established cell lines were polygonal or elongated in shape and had an abundant and irregular branched cytoplasm. Immunocytochemical analysis demonstrated positive reactivity with monoclonal anti-fibroblast antibody only. Interleukin-6 (IL-6) was constitutively produced in vitro by these cell lines; both interleukin-1 and lipopolysaccharides significantly increased its synthesis. These findings imply that these fibroblastoid cells are floating in CSF of patients with leukemic meningitis and produce IL-6 in response to various inflammatory stimulations in vivo.

Interleukin-6 (IL-6)--a molecule with both beneficial and destructive potentials

Interleukin-6 (IL-6), a member of the neuropoietic cytokine family, initially was described in terms of its activities in the immune system and during inflammation. Accumulating evidence supports an essential role of IL-6 in the development, differentiation, regeneration and degeneration of neurons in the peripheral and central nervous system. Major sites of IL-6 synthesis are neurons and glial cells. Interleukin-6 functions are mediated by a specific receptor system composed of a binding site and a signal transducer. This receptor system can be modulated by a complex of IL-6 and soluble IL-6 receptor acting as agonist. The IL-6 can exert completely opposite actions on neurons, triggering either neuronal survival after injury or causing neuronal degeneration and cell death in disorders such as Alzheimer's disease. Development of selective IL-6 agonists and antagonists, as well as the usage of soluble IL-6 receptors, offers new possibilities for the treatment of neurodegenerative disorders. Furthermore, optimized genetic mouse models, including transgenic and knockout animals, should help to define the physiological and pathophysiological role of IL-6 in the nervous system.

Immunologically induced electrophysiological dysfunction: implications for inflammatory diseases of the CNS and PNS

During inflammation of the central or peripheral nervous system, a high number of immunologically active molecules, including bacterial or viral products as well as host-derived cytokines, are released. Patients suffering from inflammatory CNS or PNS diseases often develop transient symptoms with a rapid recovery, which obviously cannot be accounted for by immunologically induced tissue damage. These observations led to the hypothesis that immunologically active molecules can affect directly the electrophysiological functions of neurons and glial cells. Evidence for this hypothesis came from in vitro studies showing that cytokines, such as interleukins or tumor necrosis factors, arachidonic acid and its metabolites, interfere with electrophysiological properties of neurons or glial cells. These molecules affect ion currents, intracellular Ca2+ homeostasis, membrane potentials, and suppress or enhance the induction and maintenance of long-term potentiation. Similarly, virus proteins from human immunodeficiency virus type I were found to alter intracellular Ca2+ concentrations of neurons and astrocytes by modulating either transmitter receptors and channels or membrane transporters. Cerebrospinal fluid from MS patients contains factors which increase Na+ current inactivation and thereby reduce neuronal excitability. Immunoglobulins in sera of patients suffering from multifocal motor neuropathy and from acquired neuromyotonia interfere with nerve fibers, inducing alterations of conduction. Increased knowledge of these mechanisms will help to explain the pathogenesis of neurological symptoms and may provide a rationale for new therapeutic strategies.

Nerve growth factor levels in cerebrospinal fluid from patients neurologic disorders

Nerve growth factor levels were measured in the cerebrospinal fluid from 73 patients with neurologic disorders and non-neurologic acute illnesses by a two-site enzyme immunoassay. Elevated nerve growth factor levels in cerebrospinal fluid were demonstrated in 2 of 7 patients with bacterial meningitis, 7 of 14 patients with viral meningitis or encephalitis, and 1 with multiple sclerosis. Follow-up examinations of the 3 patients (1 with bacterial meningitis, 1 with viral meningitis, and 1 with multiple sclerosis) at convalescent stage showed diminished nerve growth factor levels in cerebrospinal fluid. None of the other patients showed elevation of nerve growth factor levels in cerebrospinal fluid. Nerve growth factor levels in cerebrospinal fluid were not correlated with cell numbers in patients with meningitis or encephalitis. No relationship was observed between nerve growth factor levels and outcome in patients with viral meningitis or encephalitis and bacterial meningitis. Nerve growth factor in cerebrospinal fluid may play a role in neuronal recovery or function as an immunomodulator in children with inflammatory and immune-mediated neurologic disorders.

Modification of the Sendai virus-specific antibody and CD8+ T-cell responses in mice homozygous for disruption of the interleukin-4 gene

Homozygous disruption (-/-) of the interleukin-4 (IL-4) gene did not obviously modify the severity of Sendai virus infection in the highly susceptible 129/J mouse strain. The virus was cleared from the respiratory tract, and potent cytotoxic T lymphocyte (CTL) effectors were present in the cell population recovered by bronchoalveolar lavage. However, the prevalence of virus-specific CTL precursors (p) was consistently diminished in the spleen and regional lymph nodes of the IL-4 -/- mice at day 7 after infection. Also, virus-specific serum immunoglobulin G1 (IgG1) levels were greatly reduced and few IgG1-producing cells were detected in the lymphoid tissue. The effect on IgG1 class switching was to be expected, but the decrease in CTLp numbers has not been observed previously for a virus-specific immune response.

Nitric oxide synthase type II expression by different cell types in MHV-JHM encephalitis suggests distinct roles for nitric oxide in acute versus persistent virus infection

Intranasal inoculation with mouse hepatitis virus strain JHM (MHV-JHM) results in acute meningoencephalitis. We found NOS II mRNA expression in brains of acutely infected animals on days 5 through 7 after infection. In situ hybridization and immunohistochemistry demonstrated NOS II message and protein in infiltrating macrophages. Persistent infection with MHV-JHM results in chronic demyelinating encephalomyelitis. NOS II mRNA was detected in persistently infected spinal cords. In situ hybridization and immunohistochemistry showed expression of NOS II in astrocytes in and around demyelinated lesions. These results suggest the role of NO release in acute versus persistent infection with this virus, and its contribution to the resulting pathology, may be different.

CD40 mediated activation of gingival and periodontal ligament fibroblasts

CD40 is a 50 kDa transmembrane protein important for regulating B lymphocyte proliferation and differentiation. This novel activation antigen is primarily expressed by hematopoietic cells including B lymphocytes, follicular dendritic cells, and monocytes. Recently, human fibroblasts from a variety of tissues were shown to display CD40; however, its function was unknown. Cellular responses mediated by CD40 are naturally triggered by its counter-receptor, the CD40 ligand, which is displayed on activated T cells, mast cells, eosinophils, basophils, and B lineage cells. This study investigated the functional significance of CD40 expression on periodontal fibroblasts, in the context of periodontal inflammation. The experiments reported herein demonstrate constitutive CD40 expression on cultured periodontal ligament (PDL) and gingival fibroblasts. Interestingly, cells of gingival origin displayed up to 13-fold higher constitutive levels of CD40, versus fibroblasts from PDL. Interferon gamma (IFN gamma) treatment enhanced CD40 expression on PDL and gingival fibroblasts, with up to 61-fold induction of expression. Immunohistochemical staining was used to detect CD40 on fibroblastic cells in both normal and acutely inflamed gingival tissue. Expression of CD40 in inflamed tissue was significantly higher than in uninflamed tissue. Western blot analysis of anti-CD40 triggered cells revealed the induction of tyrosine phosphorylation on a 50 kDa protein in PDL and gingival fibroblasts. These results indicate that CD40 is an active signaling conduit in periodontal fibroblasts. This concept was further substantiated by the fact that CD40 engagement stimulated interleukin 6 (IL-6) production by gingival fibroblasts, but not periodontal ligament fibroblasts. Overall, these results demonstrate that CD40 on periodontal fibroblasts may functionally interact with CD40L-expressing cells. This CD40/CD40L interaction can stimulate fibroblast activation and synthesis of the proinflammatory cytokine IL-6.

Interleukin 6 in cerebrospinal fluid of patients with meningitis is not a useful diagnostic marker in the differential diagnosis of meningitis

We assayed interleukin 6 (IL-6) concentrations in cerebrospinal fluid (CSF) from patients affected by meningitis of different aetiologies, and verified whether IL-6 can be used as a diagnostic marker in the differential diagnosis of meningitis. We used a monoclonal antibody enzyme immunoassay to test 98 CSF samples classified as pyogenic (15), viral (15), self-resolving aseptic meningitis (20), other infectious meningitis (9), neoplastic (4) and normal CSF from patients with (20) and without (15) non-infectious neurological diseases. CSF IL-6 concentrations were increased in pyogenic meningitis (100%) and in more than 50% of viral and other subarachnoid space infections, and rarely in patients without central nervous system infections. Though patients affected by pyogenic meningitis showed the highest levels of CSF IL-6, only a cut-off point > or = 10000 pg/mL was able to discriminate pyogenic meningitis from those of other aetiologies with a specificity > or = 94% and a positive predictive value of > or = 0.75 but the sensitivity was < or = 60%. Therefore, CSF IL-6 concentration is not a good diagnostic marker in the differential diagnosis of meningitis.

Progressive decline in avoidance learning paralleled by inflammatory neurodegeneration in transgenic mice expressing interleukin 6 in the brain

Inflammation with expression of interleukin 6 (IL-6) in the brain occurs in many neurodegenerative disorders. To better understand the role of IL-6 in such disorders, we examined performance in a learning task in conjunction with molecular and cellular neuropathology in transgenic mice that express IL-6 chronically from astrocytes in the brain. Transgenic mice exhibited dose- and age-related deficits in avoidance learning that closely corresponded with specific progressive neuropathological changes. These results establish a link between the central nervous system expression of IL-6, inflammatory neurodegeneration, and a learning impairment in transgenic mice. They suggest a critical role for a proinflammatory cytokine in the cognitive deficits and associated neuroinflammatory changes that have been documented in neurodegenerative diseases such as Alzheimer disease and AIDS.

Cytokine and nitric oxide production in the acute phase of bacterial cell wall-induced arthritis

We have investigated the temporal relationship among proinflammatory cytokine expression, nitric oxide (NO) production and joint inflammation in the acute phase of bacterial cell wall-derived peptidoglycan polysaccharide (PG/PS)-induced arthritis. Acute joint inflammation was induced in female LEW/N rats by a single intraperitoneal injection of PG/PS. Arthritis index and paw volume were quantified and joint histopathology was evaluated during acute joint inflammation (0-10 days). Tumor necrosis factor (TNF), interleukin-1 (IL-1) and interleukin-6 (IL-6) were determined by bioassay whereas nitric oxide (NO) was quantified by measuring serum nitrate/nitrite levels via the Griess procedure. We found that serum levels of TNF and serum IL-1 preceded the increase in IL-6 and NO production. Furthermore, the production of these proinflammatory cytokines and NO preceded bone erosion and osteoclast activity. Erosion of subchondral bone preceded pannus formation and cellular synovitis in the acute phase of PG/PS-induced arthritis. The temporal expression of TNF, IL-1, IL-6 and NO suggest a cascade of inflammatory mediators in which monocytes and macrophages respond to PG/PS with enhanced synthesis of TNF and IL-1, which may in turn promote the synthesis of IL-6 and NO. We postulate that one or more of these inflammatory events are responsible for initiating the subchondral bone erosion observed in acute joint inflammation.

Interleukin-6 in the injured patient. Marker of injury or mediator of inflammation?

OBJECTIVE

The effects of interleukin (IL)-6 in the injured patient are examined in an attempt to clarify the potential pathophysiologic role of IL-6 in the response to injury.

SUMMARY BACKGROUND DATA

Interleukin-6 is an integral cytokine mediator of the acute phase response to injury and infection. However, prolonged and excessive elevations of circulating IL-6 levels in patients after trauma, burns, and elective surgery have been associated with complications and mortality. The mechanistic role of IL-6 in mediating these effects is unclear.

METHODS

A review of current literature is performed to summarize the origins, mechanisms of action, and biologic effects of IL-6 and to characterize the IL-6 response to injury.

RESULTS

Interleukin-6 is a multifunctional cytokine expressed by a variety of cells after a multitude of stimuli, under complex regulatory control mechanisms. The IL-6 response to injury is uniquely consistent and related to the magnitude of the insult. Moreover, the early postinjury IL-6 response correlates with complications as well as mortality.

CONCLUSIONS

Interleukin-6 appears to play an active role in the postinjury immune response, making it an attractive therapeutic target in attempts to control hyperinflammatory provoked organ injury.

Effect of the bradykinin B2 receptor antagonist Hoe140 in experimental pneumococcal meningitis in the rat

To elucidate the role of bradykinin in the complex pathophysiology of bacterial meningitis we investigated the effect of the bradykinin B2 receptor antagonist Hoe140, icatibant (D-Arg[Hyp3-Thi5-D-Tic7-Oic8]-bradykinin), on pathophysiological alterations in experimental pneumococcal meningitis. Untreated rats injected intracisternally (i.c.) with heat-killed pneumococci developed an increase of regional cerebral blood flow (185.4 +/- 27.4%, baseline 100%, mean +/- S.D.), brain water content (79.16 +/- 0.23%), intracranial pressure (21.4 +/- 6.0 mm Hg), and white blood cell count in the cerebrospinal fluid (CSF) (4621 +/- 1894 cells/microliter) within 6 h after i.c. challenge. Treatment with Hoe140 (0.1 mg/kg i.v. at baseline and 0.05 mg/kg s.c. at 2 h after i.c. challenge) attenuated the increase of brain water content (78.53 +/- 0.28%; P < 0.05), intracranial pressure (7.5 +/- 2.2 mm Hg; P < 0.05), and regional cerebral blood flow (128.6 +/- 23.1%; P < 0.05), and reduced CSF pleocytosis (2690 +/- 1898 cells/microliter. N.S.). When treatment was started 4 h after i.c. challenge Hoe140 reduced intracranial pressure (P < 0.05), but was no more capable to significantly influence the other pathophysiological parameters. Treatment with lower (0.01 mg/kg i.v. at baseline, followed by 0.005 mg/kg s.c. at 2 h) and higher (2 mg/kg i.v., followed by 1 mg/kg s.c. at 2 h) concentrations of Hoe140 was ineffective. Likewise, i.c. injection of Hoe140, at different dosages (4 nmol, 40 nmol, 400 nmol) did not significantly alter the pathophysiological parameters in pneumococci-induced meningitis, but caused changes in mean arterial blood pressure at dosages greater than 4 nmol. We conclude that bradykinin is involved as an inflammatory mediator of microvascular changes, brain edema, and increased intracranial pressure during the early phase of experimental pneumococcal meningitis.

Molecular cloning and sequencing of interleukin 6 cDNA fragments from the harbor seal (Phoca vitulina), killer whale (Orcinus orca), and Southern sea otter (Enhydra lutris nereis)

Using polymerase chain reaction, interleukin-6 (IL-6) cDNA fragments from harbor seal (Phoca vitulina), killer whale (Orcinus orca), and Southern sea otter (Enhydra lutris nereis) were cloned and sequenced. For all three species, a continuous open reading frame encoding 203 residues for harbor seal, 199 residues for killer whale, and 201 residues for sea otter with stop codons located at analogous positions were identified. These fragments correspond to nucleotides 71 - 753 of the human IL-6 transcript and represent 96% of the complete coding nucleotides. Comparison of these marine mammal sequences with other published mammalian IL-6 cDNA demonstrated that both harbor seal and sea otter IL-6 had most similarity to that of other terrestrial carnivores (Mustelidae and Canidae), while killer whale had highest identity with ruminants (Bovidae and Ovidae). Among the three marine mammal species characterized, as well as cDNA sequences from nine other species, 40 invariant amino acids, including a number of residues situated at the putative gp80 and gp130 receptor binding sites, were identified. The presence of invariant amino acids within the receptor-binding portion of IL-6 for twelve different species suggests these positions are essential for biological activity of IL-6 and, moreover, likely account for the cross-reactivity among different mammalian IL-6-like activities in mouse bioassays. An additional significant finding was the presence of several variant residues only within the mouse putative IL-6 receptor binding region, which may account for observations of restricted cross-reactivity of mouse IL-6-like activity in human bioassays. Together, these findings provide insights into the evolution of the mammalian IL-6 gene and additional valuable information regarding amino acid residues essential for the biological activity of mammalian IL-6.

Immunohistochemical localization of interleukin-6-like immunoreactivity to peripheral nerve-like structures in normal and inflamed human skin

Interleukin-6-like (IL-6-like) immunoreactivity was sought in inflamed and normal human skin using the same immunohistochemical technique as for detection of neuropeptides. Such immunoreactivity was found in dermal and in a few intraepidermal nerve-like fibres in biopsy specimens from inflamed skin from patients with positive epicutaneous patch-test reactions to nickel sulphate, and in skin specimens from patients with atopic dermatitis and prurigo nodularis. However, IL-6-like immunoreactivity was also found in nerve-like fibres in specimens from nonlesional skin. In skin from patients with positive epicutaneous patch-test reactions there was a statistically significantly (P < 0.01) higher number of IL-6-positive nerve fibres in the epidermis than in normal skin, in contrast to the papillary dermis, in which no difference was found. Moreover, there were clusters of nerve-like fibres with IL-6-like immunoreactivity in the dermis of prurigo nodularis lesions. In these nerve-like fibres, the colocalization of the immunoreactivities for IL-6 and calcitonin gene-related peptide was indicated. Localization of immunoreactivity to nerve-like structures surrounding the eccrine sweat glands indicates that IL-6 is present in autonomic as well as in sensory nerve fibres.

Accelerated Nerve Regeneration in Mice by upregulated expression of interleukin (IL) 6 and IL-6 receptor after trauma

In this study we aimed to examine a role for interleukin 6 (IL-6) and its receptor (IL-6R) in peripheral nerve regeneration in vivo. We first observed that cultured mouse embryonic dorsal root ganglia exhibited dramatic neurite extension by simultaneous addition of IL-6 and soluble IL-6R (sIL-6R), a complex that is known to interact with and activate a signal transducing receptor component, gp130. After injury in the hypoglossal nerve in adult mice by ligation, immunoreactivity to IL-6 was upregulated in Schwann cells at the lesional site as well as in the cell bodies of hypoglossal neurons in the brain stem. In the latter, upregulation of the immunoreactivity to IL-6R was also observed. Regeneration of axotomized hypoglossal nerve in vivo was significantly retarded by the administration of anti-IL-6R antibody. Surprisingly, accelerated regeneration of the axotomized nerve was achieved in transgenic mice constitutively expressing both IL-6 and IL-6R, as compared with nontransgenic controls. These results suggest that the IL-6 signal may play an important role in nerve regeneration after trauma in vivo.

Interleukin-6 released in human cerebrospinal fluid following traumatic brain injury may trigger nerve growth factor production in astrocytes

Cytokines are involved in nerve regeneration by modulating the synthesis of neurotrophic factors. The role played by interleukin-6 (IL-6) in promoting nerve growth factor (NGF) after brain injury was investigated by monitoring the release of IL-6 and NGF in ventricular cerebrospinal fluid (CSF) of 22 patients with severe traumatic brain injuries. IL-6 was found in the CSF of all individuals and remained elevated for the whole study period. NGF appeared in the CSF if IL-6 levels reached high concentrations and was often detected simultaneously with or following an IL-6 peak. The amounts of NGF correlated with the severity of the injury, as indicated by the clinical outcome of the patients. The functional relationship of IL-6 and NGF was investigated utilizing cultured mouse astrocytes. The CSF of 8 patients containing IL-6 induced NGF production in astrocytes, whereas control CSF without IL-6 had no effect. The induction of NGF was inhibited up to 100% by adding anti-IL-6 antibodies. These results were corroborated when astrocytes were exposed to recombinant IL-6 at different concentrations resulting in NGF production. Thus, the production of IL-6 within the injured brain may likely contribute to the release of neurotrophic factors by astrocytes.

Relationship of interleukin-8 and colony-stimulating factors to neutrophil migration in aseptic meningitis

Polymorphonuclear neutrophilic leucocyte (PMNL) migration into the subarachnoid space in aseptic meningitis of probable enteroviral aetiology was evaluated in relation to cerebrospinal fluid and serum levels of interleukin-8 (IL-8), macrophage colony-stimulating factor (M-CSF) and granulocyte colony-stimulating factor (G-CSF). IL-8 levels reached a plateau within 12h of onset, while M-CSF and G-CSF levels reached a peak between 12 and 24 h after onset, corresponding to the peak increase in PMNL count. G-CSF levels had the closest correlation with PMNL count. M-CSF levels were weakly correlated with PMNL count. IL-8 levels were not correlated with PMNL count except within 12 h of onset. IL-8 and G-CSF were detected predominantly in cerebrospinal fluid, while the M-CSF levels in the two compartments were not different except between 12 and 24 h after onset. It is considered that IL-8 triggers rapid and transient migration of PMNL, and that G-CSF then promotes gradual and consistent infiltration of PMNL.

Determination of the presence of interleukin-6 in bile after orthotopic liver transplantation. Its role in the diagnosis of acute rejection

OBJECTIVE

The authors evaluated the significance of interleukin-6 (IL-6) in bile in the diagnosis of acute rejection after liver transplantation.

SUMMARY BACKGROUND DATA

Interleukin-6 in blood has not been shown to be useful as a marker of acute rejection in clinical liver transplantation. In a rat liver transplantation model, the authors have found that bile IL-6 levels correlated well with the severity of rejection as determined histologically, whereas kinetics of serum IL-6 differed among rats without any definite feature related to graft rejection.

METHODS

Fifty-one patients who underwent orthotopic liver transplantation between May 1990 and February 1991 at the University of California, Los Angeles, were included in the study. After liver transplantation, bile and blood were collected daily, and IL-6 levels were measured by the enzyme-linked immunosorbent assay.

RESULTS

Bile IL-6 increased to 1228 +/- 317 pg/mL on the day of transplantation and decreased to 50 pg/mL or less within 48 hours. Patients who had uneventful postoperative courses had low levels of bile IL-6 throughout their hospitalization. In patients with acute rejection, bile IL-6 significantly increased (1090 +/- 990 pg/mL; p<0.05), but decreased in response to antirejection therapy. In patients who had liver dysfunction due to ischemic change or sepsis, bile IL-6 did not increase. Patients with cholangitis had significantly increased levels of bile IL-6 (146 +/- 47; p<0.05). Interleukin-6 in blood increased with many kinds of complications other than rejection and seemed to be less specific than that in bile.

CONCLUSIONS

Measurement of IL-6 in bile may be a useful, noninvasive tool for diagnosing acute rejection.

Increased interleukin-6 mRNA expression in blood and cerebrospinal fluid mononuclear cells in multiple sclerosis

The increased intrathecal production of immunoglobulins within the cerebrospinal fluid (CSF) compartment commonly observed in multiple sclerosis (MS) implicates participation of B cell activating factors. One effect of the cytokine interleukin (IL)-6 is induction of immunoglobulin production by activated B cells. Employing in situ hybridization (ISH) with synthetic oligonucleotide probes, we measured numbers of IL-6 mRNA-expressing mononuclear cells (MNC) in blood and CSF from patients with MS, aseptic meningo-encephalitis (AM), and in blood from patients with other neurological diseases (OND) and healthy subjects. Numbers of IL-6 mRNA-expressing MNC were elevated in blood (mean frequency 1 per 33,000 MNC) and even further enriched in the CSF (1 per 10,000 MNC) of MS patients, and to a similar extent in AM patients' blood. Cultivation in the presence of myelin basic protein and proteolipid protein revealed strong augmentation of IL-6 mRNA-positive cells in MS but not in OND. The results suggest that IL-6 is one of several cytokines which are upregulated in MS, in particular locally in the CSF. A role of IL-6 in MS, whether disease- promoting or protective, remains unclear.

Role of interleukin 6 in epithelial hyperproliferation and bone resorption in middle ear cholesteatomas

Locally produced pro-inflammatory cytokines are considered to play an important role in the initiation and/or maintenance of inflammatory diseases. In cholesteatomatous lesions there are increased levels of some cytokines and inflammatory mediators like interleukin 1, tumor necrosis factor and colony-stimulating factor, etc. Interleukin 6 (IL-6) can be produced by different cells present in cholesteatoma (e.g. keratinocytes, lymphocytes, fibroblasts and macrophages). Until now, no data have been available on the role of IL-6 in cholesteatoma. In this study we used immunohistochemistry to investigate the presence and distribution of IL-6 in tissue samples from cholesteatoma patients. Levels of the cytokine were quantified in tissue extracts using an enzyme-linked immunosorbent assay. Finally, the presence of biologically active IL-6 was analyzed in the murine cell line 7TD1. Human skin samples obtained from the external ear canal were used as controls. Using the anti-IL-6 antibody in an alkaline phosphatase anti alkaline phosphatase technique, a moderate diffuse staining of the whole epidermis was observed in sections of normal skin. In cryostat sections of cholesteatoma samples, a stronger staining of the whole epithelium was observed. Many of the cells infiltrating the cholesteatoma stroma also showed positive immunostainings. The concentration of IL-6 in relation to the total protein concentration in cholesteatoma (119.33 +/- 30) were higher than in human skin (9.16 +/- 13). While IL-6 activity was not detected in skin samples, two of the ten cholesteatoma samples studied showed a stimulatory effect when incubated with the cell line 7TD1. The overexpression of IL-6 in middle ear cholesteatoma suggests a participation of this cytokine in some of the clinical features seen: epithelial hyperproliferation and bone resorption. The absence of biological activity in the majority of the cholesteatoma samples points to the presence of natural inhibitors for IL-6.

IL-6 expression in neurons of transgenic mice causes reactive astrocytosis and increase in ramified microglial cells but no neuronal damage

Growing evidence suggests that aberrant production of inflammatory cytokines within the central nervous system (CNS) contributes to the development of pathological conditions. To test the cause-effect relationship between the overproduction of interleukin-6 (IL-6) in the CNS and the onset of neuropathological changes, we have generated transgenic mice in which human IL-6 expression has been targeted to the neurons by using the rat neuron-specific enolase promoter. These mice develop reactive astrocytosis and an increase in ramified microglial cells but do not show histological or behavioural signs of neuron damage at the light microscope level. We thus conclude that a constant release of human IL-6 by neuronal subpopulations in mice is sufficient to activate cells potentially capable of modulating the local immune response, but at the same time is compatible with normal neuron functions.

Significance of elevated levels of soluble factors in the cerebrospinal fluid in patients with adult T-cell leukemia

Although it has been recognized previously that several markers are present in the cerebrospinal fluid (CSF), their clinical usefulness of these markers in the diagnosis of malignant lymphoma infiltrating to the CNS has not yet been established. In order to determine their diagnostic usefulness as markers of meningeal infiltration by lymphoma cells in patients with adult T-cell leukemia (ATL), we measured some soluble factors in the CSF of patients with ATL and non-ATL patients. Soluble CD4 (sCD4) was highly elevated in all patients with ATL and meningeal infiltration. The CSF level of the soluble interleukin-2 receptor (sIL-2R; sCD25) was markedly elevated in 13 (72.2%) of 18 patients with ATL and meningeal infiltration. Levels of sCD4 and sCD25 in the CSF of patients with ATL and meningeal infiltration were significantly higher than in non-ATL patients (p < .01 and p < .001, respectively). These findings indicate that levels of sCD4 and sCD25 in the CSF are probably associated with meningeal infiltration by leukemia cells expressing CD4 and CD25 on surface membranes. CSF levels of sCD4 in 14 (60.9%) of 23 ATL patients and sCD25 in 13 (72.2%) of 18 ATL patients without meningeal infiltration were moderately elevated. These findings suggest that a small number of leukemic cells which were not detected by conventional CSF examination may have infiltrated the meninges in these patients. Sequential measurements of sCD4 and sCD25 in CSF obtained from patients with meningeal infiltration by leukemic cells showed that sCD4 and sCD25 levels reflected the activity of leukemic meningitis and correlated with the number of cells in CSF. However, the levels of sCD4 in CSF did not fall below the limit of detection even when the number of cells in CSF became normal. It is thought that the level of sCD4 in CSF is a more sensitive marker for detecting the infiltration of leukemic cells in CSF than the number of cells present in the CSF considering the clinical course of two patients with acute type ATL. Therefore, ATL patients with meningeal infiltration should receive treatments until sCD4 levels become normal and not just until the number of cells become normal. Our results also suggest that measurement of CSF levels of sCD4 and sCD25 is useful for the differential diagnosis of aseptic meningitis and meningeal infiltration by leukemic cells in patients with smoldering ATL. We conclude that measurement of soluble factors in CSF plays an important role in diagnosis, prophylaxis and treatment of meningitis in patients with ATL.

Cytokines and tumors of the central nervous system

Cytokines are a group of molecules with an extremely broad range of activities on a variety of target cells. This review summarizes the known cytokine and cytokine receptor expression in primary brain tumors and derived cell lines. These expression patterns are compared with those occurring in other CNS diseases, such as virus or bacterial infections, experimental allergic encephalitis, multiple sclerosis, and trauma. A variety of cytokines are expressed during CNS neoplasia; their potential involvement in tumor growth through a variety of mechanisms, such as autocrine or paracrine growth stimulation, angiogenesis, and immune surveillance evasion, are discussed. Finally, results of preliminary therapeutic approaches with cytokines are critically evaluated.

Administration of neutralizing antibodies to interleukin-6 (IL-6) reduces experimental autoimmune encephalomyelitis and is associated with elevated levels of IL-6 bioactivity in central nervous system and circulation

BACKGROUND

We previously demonstrated the local production of the pleiotropic cytokine interleukin-6 (IL-6) in the central nervous system (CNS) in experimental autoimmune encephalomyelitis (EAE), an animal model for the human disease multiple sclerosis.

MATERIALS AND METHODS

To assess the role of IL-6 in autoimmune CNS inflammation, we administered neutralizing antibodies to IL-6 in the EAE model. Their effect was examined at the clinical and histopathological level. Levels of administered antibody and IL-6 bioactivity were followed in serum and cerebrospinal fluid (CSF).

RESULTS

Systemically administered antibodies penetrated into the fluid CSF in animals in which EAE was induced. Administration of anti-IL-6 reduced the development of actively induced as well as adoptively transferred EAE and was associated with increased levels of IL-6 activity in the CSF and to a lesser extent in the serum. Anti-IL-6 was still effective when given 1 day before the onset of disease signs in adoptively transferred EAE. The disease-reducing effect of anti-IL-6 was also reflected at the pathological level by the absence of inflammatory infiltrates in the CNS.

CONCLUSIONS

Our study indicates that IL-6 plays an important role in autoimmune CNS inflammation. However, due to the complex nature of the in vivo interactions of administered antibodies, the disease-reducing effect of the anti-IL-6 antibodies could be caused by neutralization of IL-6 activity or by enhancement of IL-6 activity via induction of higher IL-6 levels in the CNS.

Virus-activated T cells regulate expression of adhesion molecules on endothelial cells in sites of infection

To study the role of cell adhesion molecules in the fatal CD8+ T-cell mediated meningitis which is induced by intracerebral infection with lymphocytic choriomeningitis virus, the expression of relevant molecules on inflammatory cells and local endothelium was analyzed immunohistochemically. Most inflammatory cells were strongly positive for LFA-1, VLA-4, Pgp-1 and ICAM-1. Expression of ICAM-1 and VCAM-1 was upregulated on the endothelial cells in immunocompetent mice, but not in T-cell deficient nude mice. Analysis of mice deficient in either CD4+ or CD8+ T cells, revealed that not only was the inflammatory reaction dependent on the presence of CD8+ cells, but these cells also appeared to be required for maximal upregulation of ICAM-1 and VCAM-1 on the endothelial cells. These results indicate that virus-specific CD8+ T cells are crucially involved in regulating the inflammatory reaction through effects on endothelial expression of adhesion molecules.