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.     

Induction of interleukin-6 (IL-6) autoantibodies through vaccination with an engineered IL-6 receptor antagonist

Neutralization of cytokine activity by monoclonal antibodies or receptor antagonists is beneficial in the treatment of immune and neoplastic diseases, but the necessity for continuous parenteral delivery of these anticytokine agents poses considerable practical limitations. A viable alternative is to induce a neutralizing antibody response. Using transgenic mice with high circulating levels of human interleukin-6 (hIL-6), we show that injection of the hIL-6 receptor antagonist Sant1 (an IL-6 variant with seven amino-acid substitutions) induces a strong anti-hIL-6 antibody response. The elicited antibodies bind circulating hIL-6 with very high affinity, totally masking it, and neutralize hIL-6 bioactivity both in vitro and in vivo.     

Serum levels of interleukin 6 in patients with lung cancer

Serum interleukin 6 (IL-6) levels were measured in 75 patients with lung cancer and in 20 patients with benign lung diseases. IL-6 was detectable in 29 patients with lung cancer (39%), but was not detectable in any of the patients with benign lung diseases. Serum C-reactive protein levels and plasma fibrinogen levels were significantly higher and serum albumin concentration was significantly lower in lung cancer patients with detectable serum IL-6 levels than in those without detectable serum IL-6 levels and in patients with benign lung diseases. On the other hand, no significant difference was observed in blood platelet counts in these three groups. Moreover, serum IL-6 levels were not significantly different in lung cancer patients with or without clinically demonstrated distant metastasis. These results suggest that IL-6 may be a mediator of various reactions including an inflammatory response in lung cancer patients.     

Prostaglandin E2 induces interleukin-6 synthesis in human astrocytoma cells

Prostaglandins (PGs) and cytokines, such as interleukin-1 (IL-1) and interleukin-6 (IL-6), have been implicated in the etiopathology of various inflammatory and degenerative disorders, including Alzheimer's disease (AD) and prion diseases. Nonsteroidal antiinflammatory drugs (NSAIDs), potent inhibitors of PG synthesis, appear to be beneficial in the treatment of AD. To assess whether PGs are able to induce IL-6 synthesis in cells of the CNS, IL-6 mRNA and protein syntheses were measured in a human astrocytoma cell line after stimulation with different PGs. PGE1 and PGE2, but not PGD2 and PGF2 alpha, led to a rapid and transient induction of IL-6 mRNA, followed by IL-6 protein synthesis. Furthermore, PGE2 potentiated IL-1 beta-induced IL-6 mRNA synthesis. These results are discussed with respect to the participation of PGs in neurodegenerative diseases (and its inhibition by NSAIDs) by affecting cytokine expression.     

Serum dehydroepiandrosterone (DHEA) and DHEA sulfate are negatively correlated with serum interleukin-6 (IL-6), and DHEA inhibits IL-6 secretion from mononuclear cells in man in vitro: possible link between endocrinosenescence and immunosenescence

Interleukin-6 (IL-6) is one of the pathogenetic elements in inflammatory and age-related diseases such as rheumatoid arthritis, osteoporosis, atherosclerosis, and late-onset B cell neoplasia. In these diseases or during aging, the decrease in production of sex hormones such as dehydroepiandrosterone (DHEA) is thought to play an important role in IL-6-mediated pathogenetic effects in mice. In humans, we investigated the correlation of serum levels of DHEA, DHEA sulfate (DHEAS), or androstenedione (ASD) and IL-6, tumor necrosis factor-alpha, or IL-2 with age in 120 female and male healthy subjects (15-75 yr of age). Serum DHEA, DHEAS, and ASD levels significantly decreased with age (all P < 0.001), whereas serum IL-6 levels significantly increased with age (P < 0.001). DHEA/DHEAS and IL-6 (but not tumor necrosis factor-alpha or IL-2) were inversely correlated (all patients: r = -0.242/-0.312; P = 0.010/0.001). In female and male subjects, DHEA and ASD concentration dependently inhibited IL-6 production from peripheral blood mononuclear cells (P = 0.001). The concentration-response curve for DHEA was U shaped (maximal effective concentration, 1-5 x 10(-8) mol/L), which may be the optimal range for immunomodulation. In summary, the data indicate a functional link between DHEA or ASD and IL-6. It is concluded that the increase in IL-6 production during the process of aging might be due to diminished DHEA and ASD secretion. Immunosenescence may be directly related to endocrinosenescence, which, in turn, may be a significant cofactor for the manifestation of inflammatory and age-related diseases.     

Interleukin 6-producing malignant mesothelioma

Systemic amyloidosis of the amyloid A (AA) type, is occasionally associated with various neoplasms, but the cause is still unclear. We obtained interleukin 6 (IL-6)-producing cells designated YO from a primary culture of a malignant peritoneal mesothelioma of epithelial type obtained from a 62-year-old woman. Post mortem examination revealed that the patient had systemic amyloidosis of the AA type. The supernatant media of YO cells, as well as recombinant human IL-6, successfully induced nonneoplastic liver cells to produce serum AA (SAA). Our data suggest that IL-6 produced by the tumor cells may have played an important role in the paraneoplastic syndrome of AA amyloidosis in this patient.     

Interleukin-10 production by human carcinoma cell lines and its relationship to interleukin-6 expression

Recent data indicate a major role for IL-10 in suppressing immune and inflammatory reactions. To date, expression of human IL-10 has been attributed primarily to helper T lymphocytes, activated monocytes, and neoplastic B cells, and was often found to be associated with IL-6 expression. In this study we sought to determine whether non-hematopoietic human tumor cell lines produce IL-10 and, if so, what is the relationship between IL-10 and IL-6. Using ELISA, we determined IL-10 and IL-6 levels in culture supernatants of 48 cell lines established from carcinomas of the kidney, colon, breast and pancreas, malignant melanomas and neuroblastomas. IL-6 protein was secreted by 28 of the tumor cell lines; IL-10 was measurable in 15 cell lines. IL-6 secretion was maximal and most frequent in renal-cancer cell lines, while IL-10 production was found to be highest and most common among cell lines derived from colon carcinomas. IL-10 in conditioned medium of one of the colon carcinoma cell lines (CCL222) was bio-active, as demonstrated in the mouse MC/9 mast-cell-line assay and in human mixed-lymphocyte reactions. In both assays, IL-10 bio-activity was neutralized by an anti-IL-10 monoclonal antibody. Expression of IL-6 and IL-10 was confirmed by RNA analysis using message amplification by PCR and sequencing of amplified cDNA. LPS, IL-1 alpha, and TNF-alpha strongly enhanced the release of IL-6 by RCC cells, but only marginally affected IL-10 production in colon-carcinoma cells. IL-10 secretion by colon-carcinoma cells was moderately stimulated by IFN-gamma and IL-4. Dexamethasone suppressed the release of IL-6, but had no inhibitory effect on IL-10 secretion. Our results demonstrate that tumor cell lines established from certain types of human carcinomas are capable of expressing and releasing IL-6 and/or IL-10, suggesting a role of these cytokines in solid-tumor development and anti-tumor immunity.     

The IL-2 receptor complex: expression and function on normal and leukemic B cells

The interleukin 2 receptor (IL-2R) is composed of at least three different chains that may be variably expressed on normal and neoplastic lymphocytes. While considerable knowledge has been gained on the expression of the IL-2R alpha chain on human leukemic cells of different origin, less is known of the beta and gamma chains. In view of the highly pleiotropic functions exerted by IL-2, the IL-2-IL-2R interactions may play an important role in various leukemias. In this review we focus on the expression and function of the IL-2R complex on human normal and leukemic B cells. Possible implications in the expansion of the neoplastic clone and in the clinical course of the disease are discussed.     

Interleukin-6 downregulates factor XII production by human hepatoma cell line (HepG2)

Involvement of the contact system of coagulation in the pathogenesis of various inflammatory diseases is suggested by reduced plasma levels of factor XII (Hageman factor) and prekallikrein generally considered to result from activation of the contact system. However, in many of these diseases patients develop an acute-phase response and, therefore, an alternative explanation for the decreased levels of factor XII could be the downregulation of factor XII gene expression in the liver as described for negative acute-phase proteins. We report here that interleukin-6 (IL-6), the principal cytokine mediating the synthesis of most acute-phase proteins in the liver, downregulates the production of factor XII by the human hepatoma cell line HepG2 by up to 75%. The decrease in protein secretion correlated with an equivalent decrease of factor XII mRNA likely indicating a pretranslational control of factor XII gene expression by IL-6. Downregulation of factor XII production by IL-6 in vitro parallelled that of transthyretin, a known negative acute-phase protein. Moreover, we show that, in patients developing an acute-phase response after immunotherapy with IL-2, plasma levels of factor XII correlate (r = .76, P < .0001) with those of transthyretin. Taken together, these results suggest that factor XII behaves as a negative acute-phase protein.     

Chronic interleukin-6 alters NMDA receptor-mediated membrane responses and enhances neurotoxicity in developing CNS neurons

Recent studies show that the cytokine interleukin-6 (IL-6) is expressed at elevated levels in the CNS in several disease states and contributes to the neuropathological process. The mechanisms through which IL-6 exerts its CNS effects are primarily unknown. We have investigated the pathophysiological effects of IL-6 on developing CNS neurons using a culture model system and a chronic treatment paradigm. Here, we show, using current- and voltage-clamp recordings, that chronic IL-6 treatment of developing cerebellar granule neurons increases the membrane and current response to NMDA and that these effects are the primary mechanism through which IL-6 produces an enhanced calcium signal to NMDA. We also show that calcium influx through voltage-sensitive calcium channels contributes to the enhanced calcium signal to NMDA in the IL-6-treated neurons in a developmentally regulated manner and that the membrane depolarization to NMDA is more sensitive to the NMDA receptor antagonist ifenprodil in the IL-6-treated neurons compared with control neurons at a late developmental stage, consistent with a larger proportion of NMDA receptors containing the NMDAR2B subunit in the IL-6-treated neurons. Additional studies show that IL-6 treatment reduces the number of granule neurons in culture and enhances neurotoxicity involving NMDA receptors. These results support a pathological role for IL-6 in the CNS and indicate that NMDA receptor-mediated functions are likely to play a critical role in neuropathological changes observed in CNS diseases associated with elevated CNS levels of IL-6.     

Variations in interleukin-2 and interleukin-6 due to surgical trauma in cancer patients

Inflammatory response after surgical trauma, which is necessary for infection control and tissue repairing, can actually produce some cytokines suppressive of the antitumoral immunity response. In this study the authors evaluate pre- and post-operative IL-2 (antitumor response activator) and IL-6 (lymphocytic response inhibitor and tumor growth factor) levels in 26 cancer patients undergoing resective surgery. Analysis of the results showed a significative IL-6 increase and a tendency to IL-2 decrease in the post-operative period. It is thus confirmed, even on the basis of the cytokines, the meaningful immunosuppressive effect of the surgical trauma on neoplastic growth control.     

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.     

Oncostatin M, but not interleukin-6 or leukemia inhibitory factor, stimulates expression of alpha1-proteinase inhibitor in A549 human alveolar epithelial cells

Alpha-1 proteinase inhibitor (A1-Pi) is the main serine proteinase inhibitor found in human plasma and is a potent elastase inhibitor in various tissues, including lung. A1-Pi is expressed and induced in liver during inflammatory responses but can also be produced by epithelial cells. Since hepatocyte A1-Pi production is stimulated by interleukin-6 (IL-6) and other gp130-cytokines, such as leukemia inhibitory factor (LIF) and oncostatin M (OM), we investigated the role of these cytokines in regulating A1-Pi in lung epithelial cells. We show that OM, a monocyte and T cell product, can specifically and potently induce A1-Pi production in lung-derived A549 alveolar (epithelial) cells, as well as in liver-derived HepG2 cells. Both A1-Pi protein (as detected by ELISA and Western blots) and mRNA levels were enhanced 20-fold to 30-fold in A549 cells. OM was also able to stimulate the expression of tissue inhibitor of metalloproteinase-1 in these cells. Interestingly, other members of the IL-6 family (IL-6 and LIF) had little or no effect on A549 cells, and proinflammatory cytokines, such as IL-1 beta and tumor necrosis factor-alpha (TNF-alpha) also had no stimulatory effect on A1-Pi synthesis in A549 cells. Costimulation with IL-1 beta resulted in a decrease in A1-Pi production from OM-stimulated A549 cells. However, IL-6 production was synergistically enhanced. OM was also able to stimulate A1-Pi production from a bronchial epithelial primary cell line, whereas an intestinal epithelial cell line HT29 responded to IL-6 but not OM. These results suggest that lung levels A1-Pi could be derived not only from liver and inflammatory cells but also from epithelial cells, which can be upregulated on stimulation by OM. This may have implications for regulation of local activity of human neutrophil elastase (HNE) in such diseases as emphysema and cystic fibrosis.     

Human herpesvirus 8 encodes a homolog of interleukin-6

Kaposi's sarcoma is a multifocal lesion that is reported to be greatly influenced by cytokines such as interleukin-6 (IL-6) and oncostatin M. DNA sequences of a novel human gammaherpesvirus, termed human herpesvirus 8 (HHV-8) or Kaposi sarcoma-associated herpesvirus, have been identified in all epidemiological forms of Kaposi's sarcoma with high frequency. The presence of HHV-8 DNA is also clearly associated with certain B-cell lymphomas (body cavity-based lymphomas) and multicentric Castleman's disease. Sequence analysis of a 17-kb fragment revealed that adjacent to a block of conserved herpesvirus genes (major DNA-binding protein, glycoprotein B, and DNA polymerase), the genome of HHV-8 encodes structural homolog of IL-6. This cytokine is involved not only in the pathogenesis of Kaposi's sarcoma but also in certain B-cell lymphomas and multicentric Castleman's disease. The viral counterpart of IL-6 (vIL-6) has conserved important features such as cysteine residues involved in disulfide bridging or an amino-terminal signal peptide. Most notably, the region known to be involved in receptor binding is highly conserved in vIL-6. This conservation of essential features and the remarkable overlap between diseases associated with HHV-8 and diseases associated with IL-6 disregulation clearly suggest that vIL-6 is involved in HHV-8 pathogenesis.     

Interleukin 6 is an autocrine growth factor for normal human pleural mesothelial cells

Interleukin 6 (IL-6) is a multifunctional inflammatory cytokine whose abnormal production has been implicated in a variety of diseases. Our previous study demonstrated that exudative pleural effusions contain a large amount of IL-6, and the levels of IL-6 in pleural effusion have diagnostic and pathophysiologic values. Although IL-6 is produced by a variety of cells, the origin of IL-6 in pleural effusion has not been determined clearly. We hypothesized that pleural mesothelial cells (PMCs) are an important source of IL-6 in pleural diseases. In this study, we tried to demonstrate whether PMCs could produce IL-6 and to characterize the modulation of its production. PMCs were established from patients with nonmalignant pleural effusion. Immunoreactive IL-6 could be detected in cultured supernatants of all PMCs from five patients, and all IL-6 detected in the supernatants were biologically active. IL-6 production was augmented by the addition of interleukin 1 alpha (IL-1 alpha) in a dose-dependent manner and suppressed by dexamethasone. Expression of IL-6 mRNA was spontaneously observed and was increased by IL-1 alpha. PMCs also expressed mRNA for IL-6 receptors gp80 and gpl30. Spontaneous cell growth and DNA synthesis of PMCs were inhibited by the addition of a neutralizing anti-IL-6 monoclonal antibody and were promoted by the addition of IL-6 to the culture. These results suggest that IL-6 is an autocrine growth factor for PMCs.