Interleukin-15 gene expression in human astrocytes and microglia in culture

Microglia in health and disease

Microglia, one of three glial cell types in the central nervous system (CNS), play an important role as resident immunocompetent and phagocytic cells in the CNS in the event of injury and disease. It was del Rio Hortega in 1927 who determined that microglia belong a distinct glial cell type apart from astrocytes and oligodendrocytes, and since 1970s there has been wide recognition that microglia are immune effectors in the CNS that respond to pathological conditions and participate in initiation and progression of neurological disorders including Alzheimer's disease, Parkinson's disease, multiple sclerosis, and acquired immune deficiency syndrome dementia complex by releasing potentially cytotoxic molecules such as proinflammatory cytokines, reactive oxygen intermediates, proteinases and complement proteins. There is also evidence to suggest that microglia are capable of secreting neurotrophic or neuron survival factors upon activation via inflammation or injury. It is thus timely to review current status of knowledge on biology and immunology of microglia, and consider new directions of investigation on microglia in health and disease.

Complementary contribution of CD4 and CD8 T lymphocytes to T-cell infiltration of the intact and the degenerative spinal cord

The central role of T cells in inflammatory reactions of the central nervous system (CNS) is well documented. However, there is little information about the few T cells found within the noninflamed CNS. In particular, the contribution of CD4+ and CD8+ T cells to the lymphocyte pool infiltrating the intact CNS, the location of these cells in CNS white and gray matter, and changes in the cellular composition of T-cell infiltrates coinciding with degeneration are primarily undefined. To address these points, we studied T cells in the intact and degenerative rat spinal cord. In the intact spinal cord, T cells were preferentially located within the gray matter. CD8+ T cells were more numerous than CD4+ lymphocytes. In cases of neuroaxonal degeneration or myelin degeneration/oligodendrocyte death, T cells were predominantly seen in areas of degeneration and were present in increased numbers. These effects were more pronounced for the CD4+ than for the CD8+ T-cell subset. Collectively, these data provide evidence for a clear cellular and compartmental bias in T-cell infiltration of the intact and degenerative spinal cord. This could indicate that CD4+ and CD8+ T cells might fulfill complementary roles in the intact and the diseased organ.

Changes in hippocampal IL-15, related cytokines, and neurogenesis in IL-2 deficient mice

Previous studies have demonstrated that interleukin-2 knockout (KO) mice exhibit alterations in hippocampal cytoarchitecture. Several lines of evidence suggest that these variations may result from immune dysregulation and/or autoimmunity. Thus, this study sought to compare adult IL-2 KO mice and wild-type littermates (8-12 weeks of age), the age where differences in hippocampal cytoarchitecture have previously been observed, for differences in measures of neuroimmunological status in the hippocampus. Furthermore, because IL-15 shares the same receptor subunits for signal transduction as IL-2 (IL-2/15Rbeta and gammac) that are enriched in the hippocampus and may induce inflammatory processes in IL-2 KO mice, we sought to test the hypothesis that IL-15 is elevated in the hippocampus of IL-2 KO mice. Compared to wild-type mice, IL-2 KO mice exhibited increased hippocampal protein concentrations of IL-15 as well as IL-12, IP-10, and MCP-1. These cytokine changes, however, did not correlate with levels in the peripheral circulation, and there were no T cells or an increase in MHCII-positive microglia in the hippocampus of IL-2 KO mice. Since elevated levels of certain inflammatory cytokines may impair hippocampal neurogenesis, we also tested the hypothesis that changes in neuroimmunological status would be associated with reductions in neurogenesis of neurons in the dentate gyrus of IL-2 KO mice. Contrary to this hypothesis, compared to wild-type mice, male IL-2 KO mice exhibited increased neurogenesis in both the infrapyramidal and suprapyramidal limbs of the granule cell layer of the dentate gyrus, differences that were not observed between females. These findings indicate that IL-2 gene deletion alters the neuroimmunological status of the mouse hippocampus through a dysregulation of cytokines produced by CNS cells, and in males, these changes are associated with increased hippocampal neurogenesis.

Cultured human adult microglia from different donors display stable cytokine, chemokine and growth factor gene profiles but respond differently to a pro-inflammatory stimulus

OBJECTIVES

Brain microglia are highly responsive cells in the central nervous system that exert key functions in host defense as well as in neuroprotection and regeneration. In this study the gene expression profiles for 268 cytokines, chemokines, growth factors and their receptors were examined in cultures of purified human adult microglia, using cDNA array profiling.

METHODS

Microglia from 9 different donors were compared, also following challenge of such microglia with the pro-inflammatory cytokines TNF-alpha and IFN-gamma.

RESULTS

A stable pattern was observed of genes abundantly expressed in the different cultures under standard conditions. Genes abundantly expressed in all microglia cultures include CCL2 (MCP-1), thymosin beta-10, migration-inhibitory factor-related protein 8 (MRP8), MRP14, corticotropin-releasing factor receptor 1 and endothelin 2. Abundant gene products novel to microglia were neuromodulin (GAP43) and Flt3 ligand. Yet, treatment with TNF-alpha and IFN-gamma led to widely different response profiles among the different cultures.

CONCLUSION

These data show a surprising level of heterogeneity among human adult microglia cultures in their response to a pro-inflammatory stimulus despite the standardized methodology to examine this response.

Coronavirus neurovirulence correlates with the ability of the virus to induce proinflammatory cytokine signals from astrocytes and microglia

The molecular and cellular basis of coronavirus neurovirulence is poorly understood. Since neurovirulence may be determined at the early stages of infection of the central nervous system (CNS), we hypothesize that it may depend on the ability of the virus to induce proinflammatory signals from brain cells for the recruitment of blood-derived inflammatory cells. To test this hypothesis, we studied the interaction between coronaviruses (mouse hepatitis virus) of different neurovirulences with primary cell cultures of brain immune cells (astrocytes and microglia) and mouse tissues. We found that the level of neurovirulence of the virus correlates with its differential ability to induce proinflammatory cytokines (interleukin 12 [IL-12] p40, tumor necrosis factor alpha, IL-6, IL-15, and IL-1beta) in astrocytes and microglia and in mouse brains and spinal cords. These findings suggest that coronavirus neurovirulence may depend on a novel discriminatory ability of astrocytes and microglia to induce a proinflammatory response in the CNS.

Cytokine, chemokine and growth factor gene profiling of cultured human astrocytes after exposure to proinflammatory stimuli

Astrocytes play key roles in CNS development, inflammation, and repair by producing a wide variety of cytokines, chemokines, and growth factors. Understanding the regulation of this network is important for a full understanding of astrocyte functioning. In this study, expression levels of 268 genes encoding cytokines, chemokines, growth factors, and their receptors were established in cultured human adult astrocytes using cDNA arrays. Also, changes in this gene profile were determined following stimulation with TNFalpha, IL-1beta, and IFNgamma. The data obtained reveal a highly reproducible pattern of gene expression not only between different astrocyte cultures from a single source, but also between astrocytes from different donors. They also identify several gene products not previously described for human astrocytes, including a.o. IL-17, CD70, CD147, and BIGH3. When stimulated with TNFalpha astrocytes respond with increased expression of several genes, notably including those encoding the chemokines CCL2 (MCP-1), CCL5 (RANTES), and CXCL8 (IL-8), growth factors including BMP-2A, BMP-3, neuromodulin (GAP43), BDNF, and G-CSF, and receptors such as the CRF receptor, the calcitonin receptor (CTR), and TKT. The response to IL-1beta involves largely the same range of genes, but responses were blunted in comparison to the TNFalpha response. Treatment with IFNgamma had no or only marginal effects on expression of any of the 268 genes analyzed. Astrocytes treated with a mixture of all three stimuli together displayed responses that are largely similar to those found in response to TNFalpha or IL-1beta alone, with only few additional synergistic effects.

Fractalkine and fractalkine receptors in human neurons and glial cells

Fractalkine has been identified as a novel chemokine that exhibits cell adhesion and chemoattractive properties in the central nervous system (CNS), and the fractalkine receptors, CX3CR1, are also expressed in the CNS. In the present study, the expression of fractalkine and fractalkine receptors was investigated in enriched populations of human CNS neurons, astrocytes, and microglia. In addition, the regulatory role played by protein kinase C (PKC) in fractalkine secretion in neurons was determined in A1 human hybrid neuronal cell line produced between a human cerebral neuron and a human neuroblastoma cell. Human neurons and astrocytes expressed fractalkine mRNA as determined by the revserse transcriptase-polymerase chain reaction (RT-PCR) analysis, while human microglia preparation did not express the fractalkine message. Human neurons and microglia expressed CX3CR1 mRNA, but astrocytes did not. These results suggest that fractalkine secreted by CNS neurons and astrocytes produce biological effects in neurons and microglia. Although phorbol ester did not change the expression of fractalkine mRNA level in A1 hybrid neurons, it did upregulate fractalkine secretion over unstimulated controls. This upregulation of fractalkine production was suppressed by the treatment with Ro32-0432, a PKC inhibitor. These results indicate that intracellular signals transduced by PKC play an important role in the regulation of soluble fractalkine at the post-transcriptional level in human neurons. As for the biological function of fractalkine, extracellularly applied fractalkine increased the number of bromodeoxyuridine-labeled microglia 3-fold over the untreated controls, indicating fractalkine induces proliferation of human microglia. These observations suggest that fractalkine released by injured neurons could induce proliferation, activation and/or migration of microglia at the injured brain sites.

Increased levels of IL-15 mRNA in relapsing--remitting multiple sclerosis attacks

IL-15 is a proinflammatory cytokine which has recently been implicated in multiple sclerosis (MS) pathogenesis, where it may play a role in the initiation and/or progression of the disease. We have used reverse transcriptase-polymerase chain reaction (RT-PCR) to study IL-15 mRNA levels in peripheral blood mononuclear cells (PBMC) from healthy controls and relapsing-remitting MS (RRMS) patients in a stable phase of the disease and during a bout, both before and after corticosteroid treatment (CST). IL-15 mRNA expression was found to be similar in controls and stable patients. We have detected an increased level of IL-15 mRNA in PBMC of patients with a relapse, which was maintained after CST. We have also found an inverse correlation between PBMC IL-15 mRNA levels at the onset of the relapse and the time elapsed since the previous attack, as well as an absence of correlation between IL-15 mRNA levels and the patient demographic and clinical characteristics. Results in the present work further suggest a role for IL-15 in MS pathophysiology.

Expression of IL-15 and IL-15 receptor isoforms in select structures of human fetal brain

IL-15, a key cytokine linking innate and acquired immunity, is expressed in many cell types and tissues. Recent data indicate constitutive expression of IL-15 in human neural cell lines and tissues. The aim of the present study was to examine the expression patterns of mRNA encoding IL-15 and IL-15 receptor alpha (IL-15Ralpha) isoforms in select structures of human fetal brain. We report that mRNA for IL-15 and IL-15Ralpha isoforms were expressed in all tested brain structures: cerebral cortex, cerebellum, hippocampus, and thalamus. However, the levels of IL-15 and IL-15Ralpha mRNA were higher in the hippocampus and cerebellum in comparison with cortex and thalamus. Moreover, higher levels of cytosol in comparison with membrane-bound IL-15 isoform were present in all brain structures. The constitutive, but distinct, expression of IL-15 and its receptors in select human fetal brain structures suggests that IL-15 plays a role in their development and physiology.

IL-2/15 receptor-beta gene deletion alters neurobehavioral performance

The common IL-2/15 receptor-beta (IL-2/15Rbeta) is an essential signaling subunit that is shared exclusively by IL-2 and IL-15, and is enriched in the hippocampal formation and related limbic regions. We have previously shown that mice lacking IL-2 exhibit alterations in hippocampal-dependent learning, sensorimotor gating and accompanying reductions in hippocampal infrapyramidal mossy neuronal fiber length. Although the effects of exogenous IL-2 on various aspects of forebrain neuronal function are well documented, it is unclear whether IL-15 has neuromodulatory actions. Here we sought to test the hypothesis that the combined loss of the ability of IL-2 and IL-15 to signal through IL-2/15Rbeta in the brain would influence neurobehavioral performance, in particular spatial learning and memory performance. To test this hypothesis, we compared several different domains of behavior in mice that had one or both IL-2/15Rbeta gene alleles deleted. Compared with C57BL/6-IL-2/15Rbeta+/+ wild-type and C57BL/6-IL-2/15Rbeta+/- heterozygote littermates, C57BL/6-IL-2/15Rbeta-/- knockout mice exhibited a deficit in prepulse inhibition of the acoustic startle reflex (PPI). The IL-2/15Rbeta knockout mice also showed significant reductions in acoustic startle reactivity, and modest differences in behavior in the elevated plus-maze test indicative of reduced levels of fearfulness in response to novelty. The IL-2/15Rbeta knockout mice did not differ in locomotor activity in either the plus-maze or the Morris water-maze, and contrary to our working hypothesis, they did not differ in spatial learning or memory performance in the water-maze. Further studies are required to determine if these behavioral alterations may be attributable to factors such as the loss of the ability of IL-15 and/or IL-2 to modulate limbic neurons, autoimmunity or genetic factors associated with IL-2/15Rbeta gene deletion.

Differential expression of interleukin-15, a pro-inflammatory cytokine and T-cell growth factor, and its receptor in human prostate

BACKGROUND

Pro-inflammatory interleukin (IL)-15 plays a major role in host defense and chronic inflammation by stimulating T-lymphocyte recruitment and growth. Expression of IL-15 and IL-15 receptor (IL-15R) in human prostate was examined.

METHODS

Normal and benign hyperplastic (BPH) prostate specimens (n = 23) were analyzed for IL-15 and IL-15Ralpha-chain expression by immunohistochemistry and Real-Time-PCR/RT-PCR. Regulation of prostatic stromal cell (PSC) IL-15 mRNA and effect of IL-15 on prostatic cell growth were analysed in vitro.

RESULTS

In normal prostate, anti-IL-15 and anti-IL-15Ralpha-chain reactivity were restricted to smooth muscle and stromal cells. However, in BPH, in addition epithelial cells frequently exhibited discrete anti-IL-15R and often intense, membranous anti-IL-15 reactivity. IL-15/IL-15R mRNA were detected in all prostatic cells types. In BPH tissues, IL-15 mRNA content was variable (15-fold). IL-15 mRNA synthesis of PSC was significantly up-regulated by IFN-gamma. Furthermore IL-15 strongly stimulated the growth of BPH-T-lymphocytes and weakly that of carcinoma cell lines, but not of stromal cells.

CONCLUSIONS

Overexpression of IL-15 and IL-15Ralpha-chain in BPH and massive proliferation of BPH-T-lymphocytes induced by IL-15 suggest a role for IL-15 in prostatic inflammation. Since IFN-gamma, a T-lymphocyte product, stimulates prostatic IL-15 production; chronic inflammation might be triggered by this paracrine loop.

Lipopolysaccharide-stimulated or granulocyte-macrophage colony-stimulating factor-stimulated monocytes rapidly express biologically active IL-15 on their cell surface independent of new protein synthesis

Although IL-15 shares many of the biological activities of IL-2, IL-2 expression is primarily under transcriptional regulation, while the mechanisms involved in the regulation of IL-15 are complex and not completely understood. In the current study, we found that CD14(+) monocytes constitutively exhibit both IL-15 mRNA and protein. IL-15 protein was found stored intracellularly and stimulation of CD14(+) monocytes with either LPS or GM-CSF resulted in mobilization of IL-15 stores to the plasma membrane. This rapidly induced surface expression was the result of a translocation of preformed stores, confirming that posttranslational regulatory stages limit IL-15, because it was not accompanied by an increase in IL-15 mRNA and occurred independent of de novo protein synthesis. After fixation, activated monocytes, but not resting monocytes, were found to support T cell proliferation, and this effect was abrogated by the addition of an IL-15-neutralizing Ab. The presence of preformed IL-15 stores and the ability of stimulated monocytes to mobilize these stores to their surface in an active form is a novel mechanism of regulation for IL-15.

Interleukin-15 and interleukin-2 enhance non-REM sleep in rabbits

Interleukin (IL)-15 and -2 share receptor- and signal-transduction pathway (Jak-STAT pathway) components. IL-2 is somnogenic in rats but has not been tested in other species. Furthermore, the effects of IL-15 on sleep have not heretofore been described. We investigated the somnogenic actions of IL-15 in rabbits and compared them with those of IL-2. Three doses of IL-15 or -2 (10, 100, and 500 ng) were injected intracerebroventriculary at the onset of the dark period. In addition, 500 ng of IL-15 and -2 were injected 3 h after the beginning of the light period. IL-15 dose dependently increased non-rapid eye movement sleep (NREMS) and induced fever. IL-15 inhibited rapid eye movement sleep (REMS) after its administration during the light period; however, all doses of IL-15 failed to affect REMS if given at dark onset. IL-2 also dose dependently increased NREMS and fever. IL-2 inhibited REMS, and this effect was observed only in the light period. IL-15 and -2 enhanced electroencephalographic (EEG) slow waves during the initial 9-h postinjection period, then, during hours 10-23 postinjection, reduced EEG slow-wave activity. Current data support the notion that the brain cytokine network is involved in the regulation of sleep.

Cloning the full-length IL-2/15 receptor-beta cDNA sequence from mouse brain: evidence of enrichment in hippocampal formation neurons

Numerous studies have implicated interleukin-2 (IL-2) in various brain processes, and more recently, several studies have also attributed neurobiological actions to interleukin-15 (IL-15). On lymphocytes, receptors for IL-2 and IL-15 share a common subunit, the IL-2/15 receptor-beta (IL-2/15Rbeta) that is essential for intracellular signaling. Although a short segment of IL-2/15Rbeta has been cloned (0.35 kb) from normal brain cells, attempts to isolate the full-length cDNA have been unsuccessful, suggesting the possibility that the genes expressed by brain cells and lymphocytes may differ. Using conventional and anchored PCR cloning strategies, we isolated the full-length cDNA of IL-2/15Rbeta (2038 bp) from well-perfused, normal mouse forebrain. The coding sequence and the adjacent 5' and 3' UTR sequences from brain and lymphocyte were found to be fully homologous. Although evidence of expression of IL-2/15Rbeta can be found in many brain regions using PCR, clear evidence of gene expression by in situ hybridization was detectable only in the hippocampal formation, habenula and piriform cortex. This same pattern of mRNA expression in situ was also observed for the common gamma subunit shared by IL-2 and IL-15. In the hippocampus, IL-2/15Rbeta expression was localized to neurons by high resolution in situ hybridization and evidence of IL-2 receptor protein expression was also detected by radioligand receptor binding using hippocampal homogenates. Comparison of undifferentiated and differentiated, immortalized H19-7 hippocampal neurons showed that IL-2/15Rbeta was constitutively expressed across disparate stages of hippocampal neuronal differentiation. These data indicate that IL-2/15Rbeta may serve to modulate neuronal processes in the hippocampus and associated limbic brain regions.

Erythropoietin and erythropoietin receptors in human CNS neurons, astrocytes, microglia, and oligodendrocytes grown in culture

Erythropoietin (EPO) is a hematopoietic growth factor that stimulates proliferation and differentiation of erythroid precursor cells and is also known to exert neurotrophic activity in the central nervous system (CNS). However, little is known about expression of EPO and EPO receptor (EPOR) in human CNS tissues. In the present study, we investigated the effects of proinflammatory cytokines on EPO and EPOR expression in highly purified cultures of human neurons, astrocytes, microglia, and oligodendrocytes using reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). EPO mRNA was demonstrated only in human astrocytes, while EPOR expression was found in human neurons, astrocytes, and microglia. Neither EPO nor EPOR expression was found in oligodendrocytes. In human astrocytes, EPO mRNA and secreted EPO protein levels were downregulated after exposure to proinflammatory cytokines (IL-1beta, IL-6, or TNF-alpha). In human neurons, TNF-alpha treatment markedly increased EPOR expression. These results suggest that proinflammatory cytokines regulate expression of EPO and EPOR in human neurons, astrocytes, and microglia and further facilitate interactions among different cell types in the human CNS.

Viral activation of interleukin-15 (IL-15): characterization of a virus-inducible element in the IL-15 promoter region

We identified an interferon regulatory factor motif (IRF-E) upstream of an NF-kappaB binding site in the interleukin-15 (IL-15) promoter. Since these two motifs are part of the virus-inducible enhancer region of the beta interferon promoter, we speculated that there might be similar responses of these two genes to stimuli such as viruses. To test this hypothesis, L929 cells were infected with Newcastle disease virus (NDV), which led to the induction of IL-15 mRNA and protein expression. Using IL-15 promoter-reporter deletion constructs, a virus-inducible region, encompassing IRF-E, NF-kappaB, and a 13-nucleotide sequence flanked by these two motifs, was mapped to the -295-to--243 position relative to the transcription initiation site. Using cotransfection studies, it was demonstrated that all three motifs were essential to achieve the maximum promoter activity induced by IRF-1 and NF-kappaB expression plasmids. The presence of a virus-inducible region in the IL-15 promoter suggests a role for IL-15 as a component of host antiviral defense mechanisms.

p38 map kinase regulates TNF-alpha production in human astrocytes and microglia by multiple mechanisms

In the vertebrate central nervous system (CNS), tumour necrosis factor-alpha (TNF-alpha) is produced by astrocytes and microglia and mediates cell injury in nerve cells and oligodendrocytes. In the present study, we have used a specific inhibitor of p38 MAP kinase, SB203580 to examine the role of p38 MAP kinase in regulation of TNF-alpha production in human astrocytes and microglia in terms of levels of mRNA and secreted protein. A reverse transcriptase polymerase chain reaction (RT-PCR) analysis showed that increased levels of TNF-alpha mRNA were induced in astrocytes by IL-1beta treatment, and in microglia by bacterial lipopolysaccharide (LPS). In microglia, treatment with SB203580 reduced the level of TNF-alpha mRNA, but in astrocytes it did not. However, the secretion of TNF-alpha by both astrocytes and microglia was markedly inhibited by SB203580 at a low concentration. TNF-alpha secretion was reduced approximately 80% in astrocytes and 85% in microglia. The results demonstrate a key role played by p38 MAP kinase in upregulation of TNF-alpha mRNA levels in LPS-activated human microglia, whereas p38 MAP kinase is involved in post-transcriptional regulation of TNF-alpha production at translational level in IL-1beta-activated human astrocytes.

The brain and thymus have much in common: a functional analysis of their microenvironments

Research into the neural and immune systems has begun to converge. Since the first reports that interleukins play important roles in both systems and that lymphocytes secrete neuronal factors, scientists have been surprised by the ever-increasing list of interactions. Here, Rolf Mentlein and Marion Kendall examine the major supporting cells of the brain and thymus - astrocytes and thymic epithelial cells - the similar neuroectodermal origin of which could explain such fundamental analogies.

Accessory role of human peritoneal mesothelial cells in antigen presentation and T-cell growth

BACKGROUND

To assess the role of human peritoneal mesothelial cells (HPMCs) in the generation of an immune response during peritonitis, we tested their ability to activate T-cells by antigen presentation (AP) and by the secretion of interleukin-15 (IL-15). IL-15 is a potent leukocyte activator that stimulates the proliferation of CD4+, CD8+, and B and natural killer (NK) cells.

METHODS

HPMCs and mononuclear cells were derived from six volunteer patients who underwent elective abdominal surgery. Flow cytometry was used to analyze human lymphocyte antigen-DR (HLA-DR), intercellular adhesion molecule-1 (ICAM-1), and B7 molecules on HPMCs. Affinity-purified CD4 cells were used for AP assays. We used a specific enzyme-linked immunosorbent assay to detect interferon-gamma (IFN-gamma), IL-2, and IL-15 protein and reverse transcription-polymerase chain reaction for mRNA analysis.

RESULTS

HPMCs expressed HLA-DR molecules following IFN-gamma treatment. ICAM-1 molecules were expressed at high levels, and B7-1 and B7-2 molecules could not be detected. The accessory function of HPMCs was assayed by T-cell stimulation using anti-CD3 antibodies (OKT3). HPMCs were essential for a significant OKT3-induced T-cell proliferation. Anti-ICAM-1 antibodies blocked OKT3-induced proliferation. HPMCs served as effective antigen-presenting cells when Tetanus toxoid (TT) or Staphylococcus aureus-alpha-toxin were used as antigens. IFN-gamma, IL-2, and IL-15 accumulated during AP reactions. We found that IL-15 is produced by HPMCs, and IFN-gamma up-regulated its mRNA levels and protein secretion in a dose-dependent manner. We also detected IL-15 in the peritoneal effluent of patients undergoing continuous peritoneal dialysis treatment. In patients suffering from peritonitis, IL-15 levels were elevated (35.0 +/- 6.0 pg/mL, N = 10) as compared with noninfected patients (16.2 +/- 4.0 pg/mL, N = 7).

CONCLUSIONS

HPMCs participate in the peritoneal immune response against invading pathogens by AP. For this process, ICAM-1 is the major accessory molecule. In addition, HPMCs may contribute to T-cell activation by secretion of IL-15.

A novel fluorescent GSH-adduct binds to the NMDA receptor

In an attempt to develop various fluorescent probes to label glutathione (GSH) receptors, we have serendipitously synthesized a probe that binds to and antagonizes the NMDA receptor. Probe 1, a GSH adduct, displaces the competitive NMDA antagonist [3H]-CGP 39653 with a higher affinity than NMDA or cysteine in rat synaptic membranes. In recording experiments from a rat cortical 'wedge' preparation, Probe 1 reversibly blocks both NMDA- and cysteine-induced depolarization. In mixed astrocyte-neuron tissue culture preparations, Probe 1 labels parts of both cell bodies as well as processes. The present data suggest that Probe 1 binds to the NMDA receptor and antagonizes channel function.

Involvement of IL-15 in the Pathogenesis of Human T Lymphotropic Virus Type I-Associated Myelopathy/Tropical Spastic Paraparesis: Implications for Therapy with a Monoclonal Antibody Directed to the IL-2/15Rβ Receptor

Human T lymphotropic virus type I (HTLV-I) is the causative agent of an inflammatory neurological disease termed HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). An ongoing lymphocyte activation exists in patients with HAM/TSP, which was demonstrated by the spontaneous proliferation of their PBMC ex vivo. It was shown that spontaneous proliferation present in HAM/TSP is due, in part, to an IL-2/IL-2R autocrine loop. However, addition of Abs against IL-2 or IL-2Rα only partially inhibited the spontaneous proliferation. Since IL-15 is a cytokine with similar functional characteristics to those of IL-2, we reasoned that IL-15 might be an additional growth factor that contributes to the spontaneous proliferation observed in HAM/TSP. In this study, we demonstrated that IL-15 mRNA expression was elevated in PBMC obtained from HAM/TSP patients when compared with those of the normal donors. Furthermore, we showed that the addition of blocking Abs against IL-15 or its receptor inhibited the spontaneous proliferation of HAM/TSP PBMC. Addition of Abs directed toward both IL-15 and IL-2, or their receptors, inhibited the proliferation almost completely. These data suggest the existence of two autocrine loops involving IL-15/IL-15R and IL-2/IL-2R, both contributing to the spontaneous proliferation of HAM/TSP PBMC.

Levels of interleukin-15-expressing blood mononuclear cells are elevated in multiple sclerosis

Interleukin-15 (IL-15) is a novel IL-2-like cytokine expressed by cells of the monocyte/macrophage and epithelial lineages. Cytokines might be involved in the pathogenesis of multiple sclerosis (MS). Using immunocytochemistry, we analysed spontaneous expression of IL-15 by peripheral blood (PB) and cerebrospinal fluid (CSF) mononuclear cells (MNC) from patients with MS, other neurological diseases (OND) and healthy controls. IL-15- positive peripheral blood mononuclear cells (PBMNC) were elevated in patients with MS compared to healthy controls (P < 0.05). The elevation of IL-15- positive PBMNC was restricted to patients with chronic progressive MS and not observed in patients studied during the relapsing-remitting phase of MS. The numbers of IL-15- expressing PBMNC correlated with the duration and disability of MS (r = 0.45, P < 0.001, and r = 0.39, P < 0.01, respectively). IL-15 was undetectable in CSF MNC, and ELISA showed low CSF levels of IL-15 in occasional patients with MS and OND. IL-15 is a potent growth factor for gammadelta T cells, but there was no correlation between IL-15 expression by PBMNC and percentage of gammadelta T cells in blood from the MS patients. Together, these data demonstrate that IL-15 expression by PBMNC is upregulated in the chronic stage of MS.

The multifaceted regulation of interleukin-15 expression and the role of this cytokine in NK cell differentiation and host response to intracellular pathogens

Interleukin-15 (IL-15) is a 14- to 15-kDa member of the 4 alpha-helix bundle family of cytokines. IL-15 expression is controlled at the levels of transcription, translation, and intracellular trafficking. In particular, IL-15 protein is posttranscriptionally regulated by multiple controlling elements that impede translation, including 12 upstream AUGs of the 5' UTR, 2 unusual signal peptides, and the C-terminus of the mature protein. IL-15 uses two distinct receptor and signaling pathways. In T and NK cells the IL-15 receptor includes IL-2/15R beta and gamma c subunits, which are shared with IL-2, and an IL-15-specific receptor subunit, IL-15R alpha. Mast cells respond to IL-15 with a receptor system that does not share elements with the IL-2 receptor but uses a novel 60- to 65-kDa IL-15RX subunit. In mast cells IL-15 signaling involves Jak2/STAT5 activation rather than the Jak1/Jak3 and STAT5/STAT3 system used in activated T cells. In addition to its other functional activities in immune and nonimmune cells, IL-15 plays a pivotal role in the development, survival, and function of NK cells. Abnormalities of IL-15 expression have been described in patients with rheumatoid arthritis or inflammatory bowel disease and in diseases associated with the retroviruses HIV and HTLV-I. New approaches directed toward IL-15, its receptor, or its signaling pathway may be of value in the therapy of these disorders.

Cytokine-induced production of macrophage inflammatory protein-1alpha (MIP-1alpha) in cultured human astrocytes

Macrophage inflammatory protein-1alpha (MIP-1alpha) is a member of a superfamily of inflammatory cytokines termed chemokines, and it has been implicated in the pathogenesis of several human diseases with inflammatory components. It has been known that MIP-1alpha plays a role in recruiting and activating mononuclear phagocytes in the central nervous system (CNS), and that astrocytes and microglia are sources of this chemokine. However, details of the regulation of MIP-1alpha production by these glial cells are not known. In the present study, expression of MIP-1alpha was determined in purified cultures of human astrocyte. MIP-1alpha mRNA levels in human astrocyte cell preparations were determined by reverse transcription polymerase chain reaction (RT-PCR) and amount of MIP-1alpha protein secreted into culture supernatants by human astrocytes was assayed by enzyme-linked immunosorbent assay (ELISA). Under the unstimulated conditions, human astrocytes did not express MIP-1alpha message or protein, indicating that human astrocytes do not constitutively carry MIP-1alpha message. Following treatment with interleukin-1beta (IL-1beta), human astrocytes demonstrated increased message and protein expression for MIP-1alpha, while other immune modulators such as interferon-gamma (IFN)-gamma, tumor necrosis factor-alpha (TNF-alpha), granulocyte-macrophage colony-stimulating factor (GM-CSF), lipopolysaccharide, or phorbol ester (a protein kinase C activator) did not induce MIP-1alpha expression in human astrocytes.

Regulation of the hypothalamic-pituitary-adrenal axis by cytokines: actions and mechanisms of action

Glucocorticoids are hormone products of the adrenal gland, which have long been recognized to have a profound impact on immunologic processes. The communication between immune and neuroendocrine systems is, however, bidirectional. The endocrine and immune systems share a common "chemical language," with both systems possessing ligands and receptors of "classical" hormones and immunoregulatory mediators. Studies in the early to mid 1980s demonstrated that monocyte-derived or recombinant interleukin-1 (IL-1) causes secretion of hormones of the hypothalamic-pituitary-adrenal (HPA) axis, establishing that immunoregulators, known as cytokines, play a pivotal role in this bidirectional communication between the immune and neuroendocrine systems. The subsequent 10-15 years have witnessed demonstrations that numerous members of several cytokine families increase the secretory activity of the HPA axis. Because this neuroendocrine action of cytokines is mediated primarily at the level of the central nervous system, studies investigating the mechanisms of HPA activation produced by cytokines take on a more broad significance, with findings relevant to the more fundamental question of how cytokines signal the brain. This article reviews published findings that have documented which cytokines have been shown to influence hormone secretion from the HPA axis, determined under what physiological/pathophysiological circumstances endogenous cytokines regulate HPA axis activity, established the possible sites of cytokine action on HPA axis hormone secretion, and identified the potential neuroanatomic and pharmacological mechanisms by which cytokines signal the neuroendocrine hypothalamus.

Induction of IL-15 mRNA and protein in A549 cells by pro-inflammatory cytokines

Interleukin-15 is a recently discovered cytokine which is functionally similar to IL-2. In order to learn more about possible targets for modulation of the expression of IL-15 we investigated the expression of IL-15 mRNA and protein in the A549 (human lung carcinoma) cell line. Constitutive expression of IL-15 mRNA was detected in A549 cells. Treatment with TNF-alpha or IL-1 beta (10 ng/ml each) induced an about 2-fold increase of IL-15 mRNA; IFN-gamma induced significant effects only at 100 ng/ml. Stimulation with a combination of TNF-alpha and IFN-gamma was not superior to stimulation with TNF-alpha alone. EGF, KGF and the combination thereof were without effects. IL-15 protein was detected in cellular lysates of unstimulated cells and was increased by stimulation with TNF-alpha or IL-1 beta. No significant amounts of IL-15 protein were detected in cellular supernatants.

Interleukin-15, a T-cell growth factor, is expressed in human neural cell lines and tissues

Interleukin-15 (IL-15) is a novel cytokine which shares activities and receptor components with IL-2. To investigate the biological roles of IL-15 in the human nervous system, we examined the expression of mRNAs for IL-15 and the IL-15 receptor three subunits (IL-15alpha, IL-2Rbeta and IL-2Rgamma) in human neural cell lines and tissues using reverse transcription-polymerase chain reaction and Southern blot analysis. The constitutive expression of high levels of IL-15 mRNA was observed in all the cell lines examined, including Y79 retinoblastoma, IMR-32 neuroblastoma, SK-N-SH neuroblastoma, U-373MG glioma, KG-1-C glioma, NTera2 teratocarcinoma and neurons derived from NTera2 cells following treatment with retinoic acid (RA). Among these cell lines, IL-15 protein was detectable at high levels in culture supernatants of SK-N-SH cells and NTera2-derived neurons. The expression of an alternatively-spliced transcript of the IL-15 gene was up-regulated in NTera2 cells during RA-induced neuronal differentiation, suggesting the existence of differentiation-dependent transcriptional regulation. The expression of IL-15 mRNA was also identified in the human cerebral and cerebellar tissues, peripheral nerve and skeletal muscle, while the mRNAs for the complete set of IL-15R components were detectable only in U-373MG cells, cerebral and cerebellar tissues at significant levels. These results indicate that the expression of IL-15 but not of IL-15R mRNA is universal in human neural cell lines and tissues and raise the possibility that IL-15 acts as a neuroimmune regulatory factor in the human central nervous system.

Human T cell lymphotropic virus type I Tax protein trans-activates interleukin 15 gene transcription through an NF-kappaB site

Interleukin 15 (IL-15) mRNA is expressed in a wide variety of tissue types. However, with the exception of some T cell lines, IL-15 transcript expression has not been described in T cells. Herein we demonstrate that IL-15 mRNA can be detected in freshly isolated normal T cells and T cell lines. Furthermore, its expression is 3- to 4-fold higher in human T cell lymphotropic virus type I (HTLV-I)-infected T cells. By using reporter constructs bearing the 5' regulatory region of the IL-15 gene, we observed a positive correlation between HTLV-I Tax protein expression and IL-15 promoter activity in HTLV-I-infected T cells. Additionally, by using a Jurkat T cell transfectant that expresses Tax under an inducible promoter, we demonstrated that the expression of IL-15 mRNA increased 3-fold as Tax was expressed, suggesting that the Tax protein activates IL-15 transcription. An NF-kappaB consensus sequence is located at the -75 and -65 region of the IL-15 5' regulatory region. Mutations in the NF-kappaB motif or deletion of this sequence abrogated the promoter activity in both HTLV-I-positive and Jurkat Tax-transfectant cells. These data represent evidence for trans-activation of the IL-15 gene by the HTLV-I Tax protein through an NF-kappaB motif and suggest a potential role for IL-15 in HTLV-I-associated diseases such as adult T cell leukemia and HTLV-I-associated myopathy/tropical spastic paraparesis.

IL-15 mRNA expression is up-regulated in blood and cerebrospinal fluid mononuclear cells in multiple sclerosis (MS)

IL-15, produced by monocytes and epithelial cells, is a novel cytokine with actions similar to IL-2. IL-15 induces T cell proliferation, B cell maturation and natural killer (NK) cell cytotoxicity, and is a chemoattractant for T cells. We investigated the expression of IL-15 mRNA in blood and cerebrospinal fluid (CSF) mononuclear cells (MNC) in MS, an inflammatory disease of the central nervous system where cytokines are involved. MS patients had higher numbers of IL-15 mRNA-expressing blood MNC than patients with aseptic meningo-encephalitis (AM) and healthy controls. In CSF, MS patients had even higher numbers of IL-15 mRNA-expressing cells than in blood. This discrepancy between IL-15 mRNA expression between blood and CSF MNC was not seen in AM patients. Patients examined during the secondary chronic-progressive phase of MS had higher numbers of IL-15 mRNA-expressing blood MNC compared with patients examined during the relapsing-remitting phase. Levels of IL-15 mRNA-positive blood MNC were similar in patients with AM, myasthenia gravis, non-inflammatory neurological diseases and healthy controls. Taken together these data indicate that IL-15 mRNA expression is up-regulated in MS, further suggesting a role for proinflammatory cytokines in the pathogenesis of MS.

Mouse brain microglia express interleukin-15 and its multimeric receptor complex functionally coupled to Janus kinase activity

The cytokine, interleukin (IL)-15, and the T cell growth factor, IL-2, exhibit a similar spectrum of immune effects and share the IL-2 receptor (IL-2R) subunits IL-2Rbeta and IL-2Rgamma for signaling in hematopoietic cells. Numerous neuroregulatory activities of IL-2 have been suggested, but its expression in the normal central nervous system (CNS) is apparently very low and regionally restricted. We show by RNA and protein detection that IL-15, its specific receptor molecule, IL-15Ralpha, and the signal-transducing receptor subunits, IL-2Rbeta and IL-2Rgamma, are constitutively present in various regions of the developing and adult mouse brain. We further demonstrate, also at the single-cell level, that IL-15 and the components for IL-15Ralpha/IL-2Rbetagamma receptors are expressed by microglia. Tyrosine phosphorylation data are presented showing that IL-15 signaling in microglia involves Janus kinase 1 activity. At doses of 0.1-10 ng/ml, IL-15 affected functional properties of these cells, such as the production of nitric oxide, and supported their growth in culture, suggestive of a role as an autocrine growth factor. Microglial IL-15 could thus play a pivotal role in the CNS and may participate in certain CNS and neuroendocrine functions previously ascribed to IL-2.

Ion channels of human microglia in culture

Macroscopic and microscopic currents have been recorded using human microglia isolated from fetal human brains (12-20 weeks gestation). Within a period of two days following plating of cells, inward K+ currents were small (mean amplitude of 0.3 nA at -100 mV) and outward K+ currents were not observed. For periods in excess of five days after adherence to substrate, an inactivating outward K+ current, sensitive to 4-aminopyridine, was expressed. A slowly rising current, blocked by tetraethylammonium, was also evident in a small population of human microglia. This current was activated with cell depolarization positive to +10 mV and had properties similar to those recently described for a proton current in mouse cells. In early adherent cells (days 1 or 2 after plating), treatment of microglia with interferon-gamma led to the expression of outward K+ current which was lacking in the absence of the treatment. In excised, inside-out patches, two high conductance channels were identified. A calcium-dependent K+ channel (unitary conductance of 106 pS with physiological levels of K+ across the patch) had an open probability of 0.5 with internal Ca2+ at 7 microM and the patch potential at 0 mV. In addition, an anion channel (unitary conductance of 280 pS) was transiently activated with depolarizing or hyperpolarizing steps applied from 0 mV. Characterization of the macroscopic and unitary properties of currents in microglia will have relevance to a description of putative cell functions in the human CNS. In particular, modification of cell electrophysiological properties by various activating stimuli may contribute to signalling processes in CNS pathology.