Heterogeneity of poly(I) x poly(C)-induced human fibroblast interferon mRNA species

LILRB3 Modulates Acute Myeloid Leukemia Progression and Acts as an Effective Target for CAR T-cell Therapy

Identifying novel cell surface receptors that regulate leukemia cell differentiation and can be targeted to inhibit cellular proliferation is crucial to improve current treatment modalities in acute myeloid leukemia (AML), especially for relapsed or chemotherapy-refractory leukemia. Leukocyte immunoglobulin-like receptor type B (LILRB) is an immunomodulatory receptor originally found to be expressed in myeloid cells. In this study, we found that LILRB receptors can be induced under inflammatory stimuli and chemotherapy treatment conditions. Blockade of LILRB3 inhibited leukemia cell proliferation and leukemia progression. In addition, treatment with LILRB3 blocking antibodies upregulated myeloid lineage differentiation transcription factors, including PU.1, C/EBP family, and IRF, whereas phosphorylation of proliferation regulators, for example, AKT, cyclin D1, and retinoblastoma protein, was decreased. Conversely, transcriptomic analysis showed LILRB3 activation by agonist antibodies may enhance leukemia survival through upregulation of cholesterol metabolism, which has been shown to promote leukemia cell survival. Moreover, LILRB3-targeted CAR T cells exhibited potent antitumor effects both in vitro and in vivo. Taken together, our results suggest that LILRB3 is a potentially potent target for multiple treatment modalities in AML.

SIGNIFICANCE

LILRB3 regulates differentiation and proliferation in acute myeloid leukemia and can be targeted with monoclonal antibodies and CAR T cells to suppress leukemia growth.

Biological functions and therapeutic opportunities of soluble cytokine receptors

Cytokines control the immune system by regulating the proliferation, differentiation and function of immune cells. They activate their target cells through binding to specific receptors, which either are transmembrane proteins or attached to the cell-surface via a GPI-anchor. Different tissues and individual cell types have unique expression profiles of cytokine receptors, and consequently this expression pattern dictates to which cytokines a given cell can respond. Furthermore, soluble variants of several cytokine receptors exist, which are generated by different molecular mechanisms, namely differential mRNA splicing, proteolytic cleavage of the membrane-tethered precursors, and release on extracellular vesicles. These soluble receptors shape the function of cytokines in different ways: they can serve as antagonistic decoy receptors which compete with their membrane-bound counterparts for the ligand, or they can form functional receptor/cytokine complexes which act as agonists and can even activate cells that would usually not respond to the ligand alone. In this review, we focus on the IL-2 and IL-6 families of cytokines and the so-called Th2 cytokines. We summarize for each cytokine which soluble receptors exist, were they originate from, how they are generated, and what their biological functions are. Furthermore, we give an outlook on how these soluble receptors can be exploited for therapeutic purposes.

Development of the field of structural physiology

Electron crystallography is especially useful for studying the structure and function of membrane proteins - key molecules with important functions in neural and other cells. Electron crystallography is now an established technique for analyzing the structures of membrane proteins in lipid bilayers that closely simulate their natural biological environment. Utilizing cryo-electron microscopes with helium-cooled specimen stages that were developed through a personal motivation to understand the functions of neural systems from a structural point of view, the structures of membrane proteins can be analyzed at a higher than 3 Å resolution. This review covers four objectives. First, I introduce the new research field of structural physiology. Second, I recount some of the struggles involved in developing cryo-electron microscopes. Third, I review the structural and functional analyses of membrane proteins mainly by electron crystallography using cryo-electron microscopes. Finally, I discuss multifunctional channels named "adhennels" based on structures analyzed using electron and X-ray crystallography.

Interleukin-6 and its receptors: a highly regulated and dynamic system

Interleukin-6 (IL-6) is a multifunctional cytokine with well-defined pro- and anti-inflammatory properties. Although only small amounts in the picogram range can be detected in healthy humans, IL-6 expression is highly and transiently up-regulated in nearly all pathophysiological states. IL-6 induces intracellular signaling pathways after binding to its membrane-bound receptor (IL-6R), which is only expressed on hepatocytes and certain subpopulations of leukocytes (classic signaling). Transduction of the signal is mediated by the membrane-bound β-receptor glycoprotein 130 (gp130). In a second pathway, named trans-signaling, IL-6 binds to soluble forms of the IL-6R (sIL-6R), and this agonistic IL-6/sIL-6R complexes can in principle activate all cells due to the uniform expression of gp130. Importantly, several soluble forms of gp130 (sgp130) are found in the human blood, which are considered to be the natural inhibitors of IL-6 trans-signaling. Most pro-inflammatory roles of IL-6 have been attributed to the trans-signaling pathway, whereas anti-inflammatory and regenerative signaling, including the anti-bacterial acute phase response of the liver, is mediated by IL-6 classic signaling. In this simplistic view, only a minority of cell types expresses the IL-6R and is therefore responsive for IL-6 classic signaling, whereas gp130 is ubiquitously expressed throughout the human body. However, several reports point towards a much more complex situation. A plethora of factors, including proteases, cytokines, chemical drugs, and intracellular signaling pathways, are able to modulate the cellular expression of the membrane-bound and soluble forms of IL-6R and gp130. In this review, we summarize current knowledge of regulatory mechanisms that control and regulate the dynamic expression of IL-6 and its two receptors.

Mouse and human lung fibroblasts regulate dendritic cell trafficking, airway inflammation, and fibrosis through integrin αvβ8-mediated activation of TGF-β

The airway is a primary portal of entry for noxious environmental stimuli that can trigger airway remodeling, which contributes significantly to airway obstruction in chronic obstructive pulmonary disease (COPD) and chronic asthma. Important pathologic components of airway remodeling include fibrosis and abnormal innate and adaptive immune responses. The positioning of fibroblasts in interstitial spaces suggests that they could participate in both fibrosis and chemokine regulation of the trafficking of immune cells such as dendritic cells, which are crucial antigen-presenting cells. However, physiological evidence for this dual role for fibroblasts is lacking. Here, in two physiologically relevant models - conditional deletion in mouse fibroblasts of the TGF-β-activating integrin αvβ8 and neutralization of αvβ8 in human COPD fibroblasts - we have elucidated a mechanism whereby lung fibroblast chemokine secretion directs dendritic cell trafficking, in a manner that is critically dependent on αvβ8-mediated activation of TGF-β by fibroblasts. Our data therefore indicate that fibroblasts have a crucial role in regulating both fibrotic and immune responses in the lung.

Structure of a chromosomal gene for human interferon beta

We have cloned and analyzed a chromosomal DNA segment containing the human interferon beta(1) gene from a human gene library. The nucleotide sequence of the protein-coding and the noncoding regions of the chromosomal gene was identical to the cDNA sequence reported previously. In the region upstream from the putative transcription initiation site, significant nucleotide sequence homology was observed between interferon beta(1) and alpha(1) genes. This region thus may play a role in expression of the interferon genes. From the sequence data and the result of nuclease S1 mapping experiments, we conclude that, like the interferon alpha(1) gene, the interferon beta(1) gene is devoid of intervening sequences.

Structure-function relationship of tumour necrosis factor and its mechanism of action

We have cloned the cDNAs of both human and mouse TNF and expressed them to high efficiency in Escherichia coli. Many transformed cell lines are sensitive to the cytotoxic action of TNF, especially in the presence of gamma-interferon, whereas normal cells either are unaffected or respond mitogenically. A number of human-mouse chimeric TNF genes have been constructed and expressed. All show biological activity but none of the chimeric proteins is neutralized by monoclonal antibodies to TNF. TNF has potent antitumour activity in nude mice carrying human xenografts or in mice bearing syngeneic tumours. In some systems direct effects can be demonstrated (in combination with species-specific gamma-interferon) but in others TNF acts indirectly. Combination of TNF with cytostatic drugs can also be effective in curing in vivo. The major limitation of the use of TNF is its toxicity. On many cell types TNF has an action similar to interleukin 1 (IL-1). At least some of the secondary, intracellular events may be identical for the two effectors. A possible mechanism of action of TNF is the release and metabolism of polyunsaturated fatty acids, which would explain the synthesis of prostaglandins and leukotrienes by many cell types after TNF treatment. The activation of the phospholipase can be blocked by corticoids. Some protease inhibitors protect cells from TNF-induced cytotoxicity but the target of these inhibitors has not been identified. Several genes are switched on by TNF (and by IL-1), including the gene for the 26 kDa protein recently identified as B cell stimulation factor 2. Events preceding death in rats include hypothermia, hypotension, acidosis and hypoglycaemia. All these effects can be largely eliminated by indomethacin pretreatment, with a resulting improvement in survival. As indomethacin does not inhibit the cytotoxic action of TNF on malignant cells it may form the basis for improved treatment protocols.

Learning from viruses: the necrotic bodies of tumor cells with intracellular synthetic dsRNA induced strong anti-tumor immune responses

PURPOSE

Coaxing dead tumor cells to induce specific immune responses is an attractive tumor therapy. However, there continues to be a need for adjuvants that can promote the cross-presentation of the dead tumor cells to induce specific anti-tumor response. Viral dsRNA has multiple mechanisms to promote the cross-presentation of viral antigens in virus-infected cells. We propose to learn from viruses by generating dead tumor cells having synthetic dsRNA delivered inside them to allow the dsRNA to promote the cross-presentation of dead tumor cells.

MATERIALS AND METHODS

Using synthetic dsRNA, poly(I:C), and the TC-1 cervical cancer model, we evaluated the extent to which the poly(I:C) can promote the necrotic bodies of TC-1 cells to induce specific anti-tumor immune response. The poly(I:C) was either simply mixed with the dead TC-1 cells or pre-loaded inside them.

RESULTS

Immunization of tumor-bearing mice with the necrotic bodies of tumor cells admixed with poly(I:C) significantly inhibited the tumor growth. More importantly, immunization with the necrotic bodies having poly(I:C) pre-loaded inside led to a significantly stronger anti-tumor response than when the necrotic bodies were simply admixed with the poly(I:C), apparently through a CD8(+) CTL response-mediated mechanism.

CONCLUSIONS

These findings are expected to be clinically relevant for devising improved whole cell-based tumor vaccines.

Type I interferons in combination with bacterial stimuli induce apoptosis of monocyte-derived dendritic cells

Both type I interferons (IFNs) as well as lipopolysaccharide (LPS) individually compromise selected monocytic or dendritic cell (DC) functions. This study investigates the influence of these agents on the differentiation and the regulation of cell death of monocyte-derived DCs generated in the presence of granulocyte-macrophage colony-stimulating factor plus interleukin-4 (IL-4). It is reported that excessive apoptosis occurred rapidly in monocyte-derived DC cultures, if IFN-alpha or IFN-beta was added in combination with LPS or lipoteichoic acid (LTA). The small fraction of cells surviving in such cultures displayed a mature DC phenotype with expression of CD83, CD80, and CD86. IL-10 was found in the supernatants of monocyte-derived DC cultures, if supplemented with LPS or IFN-alpha plus LPS but not in control cultures. When monocyte-derived DCs were generated in the presence of IFN-alpha without LPS, these cells displayed an immature DC phenotype with a reduction of cell recovery but no overt apoptosis. However, the addition of LPS, LTA, LPS plus IFN-gamma, or tumor necrosis factor alpha (TNF-alpha) plus prostaglandin E2 to such cells again resulted in the rapid induction of apoptosis in the majority of cells, together with a reduced production of IL-12 p70 and TNF-alpha. Together, these data indicate an exquisite sensitivity of monocyte-derived DCs to activation-induced cell death if generated in the presence of IFN-alpha, indicating the existence of an important mechanism of immunosuppression caused by IFN-alpha-inducing agents, such as viral or bacterial stimuli. (Blood. 2001;98:736-742)

Phase 1 trial of subcutaneous IL-6 in patients with refractory cancer: clinical and biologic effects

The authors evaluated the clinical and biologic effects of human recombinant interleukin-6 (rhIL-6) in patients with refractory cancer. A phase 1 trial using escalating doses of rhIL-6 (1-50 microg x kg(-1) x d(-1), Monday through Friday for 4 weeks) was performed in 30 patients. Toxicity was moderate and the maximum tolerated dose was determined to be 25 microg x kg(-1)x d(-1) based on cardiac and neurocortical toxicity in one patient each and thrombocytosis (platelets > 800,000/microL) in three patients. One patient with non-small-cell lung cancer had a partial response after three cycles of therapy. The biologic effects of rhIL-6 included anemia and dose-related thrombocytosis. Various proinflammatory activities were induced and included dose-related cyclical increases in peripheral blood monocytes and the CD14+/CD45RB+ +/- CD16C+ mononuclear cell populations. These increases were accompanied by increased levels of C-reactive protein, serum neopterin, and type I soluble tumor necrosis factor receptor. In contrast, rhIL-6 did not affect lymphocyte numbers or function (cytotoxicity, cytokine levels, immunoglobulin levels), with the possible exception of IL-2Ralpha mRNA induction in peripheral blood lymphocytes. rhIL-6 has pleiotropic proinflammatory actions in vivo and moderate toxicity when administered as long-term therapy.

The relationship between interleukin-6 and herpes simplex virus type 1: implications for behavior and immunopathology

Cytokines are hormones once thought to be restricted to the immune system produced solely by hematopoietic-derived cells and acting on receptors expressed by cells of the immune system. However, it is now clear that many cytokines are produced not only by lymphocytes, monocytes, granulocytes, and dendritic cells but are also synthesized by cells outside the realm of the immune system in response to stimuli that may not be associated with immune homeostasis. In fact, there is evidence supporting a role of selected cytokines modifying behavior and neuroendocrine function. Recently, a potential relationship between the cytokine interleukin (IL)-6 and herpes simplex virus type 1 (HSV-1) reactivation has been found. This article discusses the relevance of these findings and considers the potential impact that HSV-1 infection has on behavior and chronic inflammatory processes that can occur in the nervous system during "latent" virus infection as a result of chronic IL-6 expression.

Culture of human amniotic cells: a system to study interferon production

This study investigated whether primary culture of human amniotic membrane cells (PCHAM) could be used as an in vitro model system for the study of interferon (IFN) production. PCHAM cells infected with Newcastle disease virus (NDV) produced the two antigenic types of IFN, previously shown in a amniotic membrane cells (HAM) system. PCHAM IFN was detected as early as 2 h after NDV infection and was composed by two antigenically distinct fractions, one neutralized with anti-HuIFN beta antibody and another that is not related to IFN beta, -alpha and -gamma. These fractions correspond respectively to 80 and 20 per cent of the IFN produced 4 h after virus induction, 55 and 45 per cent of the IFN produced from 4 to 12 h and 67 and 33 per cent of the IFN produced 12 h after virus induction. A cDNA library, established from PCHAM with or without NDV infection, was screened for IFN alpha and -beta using specific primers. The PCR product, amplified by IFN beta primers, was cloned, sequenced and expressed in Escherichia coli M15. The sequences of several cloned cDNAs were identical to HuIFN beta gene and the antiviral activity of the expressed protein was neutralized only by antiHuIFN-beta antibody. The other IFN fraction not neutralized by polyclonal antibodies anti-IFN beta, -alpha and -gamma is now being studied.

Leukaemia inhibitory factor and interleukin 6 are expressed at very low levels in the normal adult mouse and are induced by inflammation

We have assessed the limitations of the polymerase chain reaction (PCR) as a semiquantitative technique for assessing very low level gene expression. Using PCR, the in vivo expression patterns of the cytokines Leukaemia Inhibitory Factor (LIF) and Interleukin 6 (IL-6) in the normal adult mouse, have been examined. We show that both LIF and IL-6 mRNA are constitutively expressed, albeit at extremely low levels, in most tissues. While it is unclear whether this low level of expression is of biological significance, it is possible that it reflects a local mode of action of these potent polyfunctional molecules. Lipopolysaccharide, the bacterial cell wall product responsible for endotoxic shock, when administered in vivo, was capable of inducing the expression of both LIF and IL-6 in all of the tissues examined. In addition, LIF and IL-6 expression was induced in lung tissue by in vitro culturing in serum-free media. This induction of LIF and IL-6, by LPS and culturing, may reflect the role of these molecules as mediators of the acute phase response to tissue damage.

Cyclosporin A does not inhibit IL-1 alpha-induced epithelial cell IL-6 secretion

Trauma and infection activated a murine mucosal IL-6 response in different ways: the IL-6 response to bacteria was sensitive to Cyclosporin A (CsA); the IL-6 response to trauma was not. The aim of the present study was to identify possible activators of the CsA-insensitive IL-6 secretion at the epithelial cell level. Two human epithelial cell lines from the kidney (A498) and bladder (J82) were exposed to Escherichia coli Hu734, interleukin-1 alpha (IL-1 alpha) and tumour necrosis factor alpha (TNF-alpha). The E. coli strain had been used for the in vivo experiments which led to this study, and IL-1 alpha and TNF-alpha were likely to be released during infections and trauma. The secretion of IL-6 into the supernatants was compared between cells stimulated in the presence or absence of CsA. E. coli Hu734, IL-1 alpha and TNF-alpha stimulated an IL-6 response in the two epithelial cell lines. The IL-1 alpha-induced IL-6 response was rapid, and the secreted IL-6 levels were significantly higher than those induced by E. coli Hu734 or TNF-alpha. The IL-6 response to IL-1 alpha was insensitive to CsA. By contrast, the IL-6 response to E. coli Hu734 and TNF-alpha was inhibited by CsA. These results demonstrated that the inhibitory effect of CsA depends on the stimulus triggering the IL-6 response. IL-1 alpha may play a role in the induction of trauma-associated CsA-insensitive IL-6 secretion.

Recombinant human tumour necrosis factor-alpha (rhTNF-alpha) and rhTNF-alpha analogue enhance amyloid deposition in the Syrian hamster

Tumour necrosis factor-alpha (TNF-alpha) is one of the cytokines that stimulate the production of serum amyloid A (SAA), the precursor of AA amyloid. The role of TNF-alpha in amyloidogenesis was investigated in experimental hamsters using purified recombinant human TNF-alpha (rhTNF-alpha) and rhTNF-alpha analogue different from the normal molecule by two amino acid substitutions. Daily injections of 1 microgram rhTNF-alpha resulted in elevated SAA levels but even in the presence of amyloid enhancing factor (AEF) no amyloid was deposited, indicating that apart from the AEF and one particular SAA stimulating factor an additional factor is needed to result in amyloid deposition. This factor is generated by repeated injections of E. coli lipopolysaccharide (LPS). A single intraperitoneal injection of 12.5 micrograms or more of rhTNF-alpha followed by seven daily subcutaneous injections of LPS resulted in enhanced amyloid deposition. Heat denaturation of rhTNF-alpha did abolish its AEF activity. The rhTNF-alpha analogue, having one-fifth of the cytotoxic activity of the normal rhTNF-alpha, showed a similar reduction in its SAA-inducing capacity and its amyloidogenicity. This suggests the AEF activity to be closely related to TNF-alpha activity. However, poly(I)-poly(C) (a potent inducer of IL-6) also showed AEF activity, suggesting that not a single cytokine but rather a certain combination of different cytokines could be decisive in AA amyloidogenesis.

Functional significance of human vascular smooth muscle cell-derived interleukin 1 in paracrine and autocrine regulation pathways

Interleukin 1 (IL1), a key mediator in the cytokine network, alters many pathophysiologically important functions of blood vessel wall cells. Vascular cells, such as endothelial cells and smooth muscle cells (SMC) can themselves transcribe IL1 genes, raising the possibility that IL1 regulates blood vessel wall functions by local autocrine or paracrine mechanisms. However, IL1 lacks a recognizable signal sequence and it is still unclear how vascular cells might release IL1 or if IL1 derived from vascular cells can actually produce autocrine or paracrine effects. We explored these issues in human vascular SMC, the most numerous cell type in arteries and veins, using cultured SMC and short term organoid cultures. SMC treated with lipopolysaccharide recombinant tumor necrosis factor (recTNF), or recIL1 itself ("activated SMC") elaborated thymocyte costimulatory activity, a biological activity traditionally ascribed to IL1. However, neutralization experiments with monospecific antibodies disclosed that the more recently recognized cytokine IL6 rather than IL1 accounted for most of the soluble thymocyte costimulatory activity released by activated SMC. Using the D10S assay that distinguishes IL1 from IL6 and TNF we found that the culture supernatant of activated SMC contained little or no IL1, but that the cytosol and surface of these cells did exhibit this activity. Antiserum to recIL1 alpha inhibited stimulation of D10S cells by surface-associated IL1 of activated SMC, while treatment with acid to elute receptor- or nonspecifically bound IL1 did not abrogate this D10S proliferation. Short term organoid cultures of both normal veins and human arteriosclerotic plaque also expressed tissue-associated IL1 activity upon stimulation with LPS but did not release significant soluble IL1 activity. To establish further the biological functions of cell-associated IL1, we incubated stimulated or unstimulated SMC that were fixed with paraformaldehyde and washed extensively (fixed SMC) with overlayered viable SMC of the same donor (responder SMC). Contact with fixed SMC that bore surface IL1 following TNF or IL1 stimulation evoked up to 20-fold higher IL6 release from responder SMC than did exposure to unstimulated SMC (57 vs 1052 ng/ml/day). Addition of anti-IL1 antibody inhibited the release of IL6 from the responder SMC. These results demonstrate that cytokine-activated SMC express biologically active IL1 on their cell surface and illustrate how these cells might actually participate in autocrine and paracrine signaling in the vessel wall. The requirement for direct intercellular contact for IL1 effects could facilitate local information exchange among vascular wall cells and/or infiltrating leukocytes and permit costimulation while limiting undue propagation of inflammatory stimuli.

High circulating levels of interleukin-6 in patients with septic shock: evolution during sepsis, prognostic value, and interplay with other cytokines. The Swiss-Dutch J5 Immunoglobulin Study Group

PURPOSE AND PATIENTS

We measured the serum concentrations of interleukin-6 (IL-6) in 70 patients with established septic shock caused predominantly by gram-negative bacteria. The aims of the study were to determine whether and for how long IL-6 was detectable in the circulation of these patients, to assess whether IL-6 levels were associated with patients' outcomes, and, finally, to examine the interplay between IL-6, tumor necrosis factor (TNF), interleukin-1 beta (IL-1 beta), and interferon-gamma (IFN-gamma).

RESULTS

IL-6 was detected in 64% of the patients at study entry but in only 18% on Day 1 and 2% on Day 10. Serum levels of IL-6 were higher (median: 3.5 ng/mL, range: less than 0.1 to 305 ng/mL) in patients dying of fulminant septic shock than in those surviving (median: 0.5 ng/mL, range: less than 0.1 to 135 ng/mL; p = 0.003) or in those with a transient reversal of shock but who ultimately died of a relapse of shock (median: less than 0.1 ng/mL, range: less than 0.1 to 12.5 ng/mL; p = 0.005). However, no cutoff values of IL-6 confidently predicted the outcome of an individual patient. The serum concentrations of IL-6 measured at study entry correlated with the duration of survival (r = -0.51, p = 0.004) and with the levels of TNF-alpha (r = 0.53; p less than 0.0001) but not with the levels of either IL-1 beta (r = 0.01, p = 0.90) or IFN-gamma (r = 0.06, p = 0.60).

CONCLUSIONS

These results indicate that circulating levels of IL-6 are detectable in a majority of patients with gram-negative septic shock. Concentrations of IL-6 peaked near the onset of shock and rapidly decreased to undetectable levels within approximately 24 hours in most patients. Levels of IL-6 measured at study entry correlated with levels of TNF and with patients' outcomes. Yet, IL-6 does not appear to be a clinically useful laboratory test for predicting the outcome of an individual patient.

The role of interleukin-6 in mitogenic T-cell activation: detection of interleukin-2 heteronuclear RNA by polymerase chain reaction

It has been documented that interleukin-6 (IL-6) supports the proliferation of purified, anti-CD3-stimulated murine T cells. We found that stimulation of human peripheral blood mononuclear cells (PBMCs) with anti-CD3 induced a significant accumulation of IL-6 mRNA, indicating that antigen-mediated T-cell activation may involve IL-6 release from accessory cells. Phytohemagglutinin (PHA) had little effect upon IL-6 gene expression. In keeping with these findings, anti-IL-6 reduced but did not abolish anti-CD3-mediated proliferation of PBMCs, but had no significant effect upon PHA-stimulated proliferation. The addition of recombinant (r) IL-6 enhanced the proliferation of anti-CD3-stimulated PBMCs and increased the accumulation of IL-2 mRNA in PHA-stimulated PBMCs during the first 5 hr of culture. Nuclear run-off experiments did not reveal significant changes in IL-2 transcription in PHA plus rIL-6-treated PBMCs attempting to assume that IL-6 mediates stabilization of IL-2 mRNA. However, monitoring of partially spliced IL-2 mRNA by polymerase chain reaction revealed a clear increase in IL-2 heteronuclear RNA. Thus IL-6 increases the rate of IL-2 transcription which was not detectable by conventional in vitro transcription assays. We conclude that anti-CD3 triggers T-cell proliferation through a process that is partially but not entirely dependent upon release of IL-6. IL-6, in turn, supports IL-2 transcription. Insofar as anti-CD3 mimics antigen-triggered activation of the T-cell receptor complex, IL-6 appears to support the early immune response by augmenting antigen-triggered IL-2 gene expression.

Expression and function of interleukin-6 in epithelial cells

Epithelial cells both produce and are affected by interleukin-6 (IL-6). Experiments with an adenocarcinoma-derived cell line (HeLa) reveal that activation of the transfected human IL-6 promoter occurs largely through two partially overlapping second messenger (cAMP, phorbol ester)- and cytokine (IL-1, TNF, serum)-responsive enhancer elements (MRE 1, -173 to -151 and MRE II, -158 to -145). MRE I contains the typical GACGTCA cAMP and phorbol ester-responsive (CRE-TRE) motif, whereas MRE II defines a new CRE/TRE motif that contains an imperfect dyad repeat. The mechanism of dexamethasone-mediated repression of IL-6 gene expression in epithelial cells involves occlusion of the entire MRE enhancer region and of the core-promoter elements (TATA-box and RNA start site) by ligand-activated glucocorticoid receptor. Enhanced levels of IL-6 expression are observed in many solid tumors and in the hyperproliferative (and glucocorticoid-suppressible) lesions of psoriasis. In cell culture, IL-6 enhances, inhibits, or has no effect on the proliferation of epithelial cells depending upon the cell-type examined. IL-6 enhances proliferation of keratinocytes but inhibits that of breast carcinoma cell lines ZR-75-1 and T-47D. In these breast carcinoma cells, IL-6 elicits a major change in cell phenotype which is characterized by a fibroblastoid morphology, enhanced motility, increased cell-cell separation, and decreased adherens type junctions (desmosomes and focal adhesions). The new data identify IL-6 as a regulator of epithelial cell growth and of cell-cell association.

Measurement of interleukin-6 in bronchoalveolar lavage fluid by radioimmunoassay: differences between patients with interstitial lung disease and control subjects

Bronchoalveolar lavage fluid (BALF) from subjects with a variety of interstitial lung diseases (active sarcoidosis, pigeon breeders' disease (PBD), asymptomatic pigeon breeders, patients with idiopathic pulmonary fibrosis) and from control subjects were assayed for interleukin-6 (IL-6) using a novel radioimmunoassay system. IL-6 was detectable in BALF from all groups, with disease groups showing significantly increased IL-6 levels compared with controls (P less than 0.01 in all cases). When these results were standardized, using urea to compensate for dilution effects in the BALF, only the asymptomatic pigeon breeders had significantly higher IL-6 levels than the controls (P less than 0.025), with all other groups showing no difference. When albumin was used for standardization, both the PBD group (P less than 0.001) and the sarcoidosis patients (P less than 0.01) had considerably lower levels of IL-6 than the control subjects. Using either albumin or urea for standardization, the PBD patients had significantly lower levels of IL-6 than do their asymptomatic counterparts (P less than 0.001 in both cases). This is contrasted by the finding of greatly elevated levels of IgG in the BALF of the PBD patients compared with asymptomatics (P less than 0.001). There was, however, no relation between IL-6 and IgG in any patient group, although the PBD patients had the lowest IL-6 and highest IgG as a group. These findings may suggest a mechanism by which asymptomatic subjects remain free from clinical complaints.

Induction and regulation of interleukin-6 gene expression in rat astrocytes

Cells that produce interleukin-6 (IL-6) require the presence of signaling molecules since this cytokine is not normally constitutively expressed. It is now established that astrocytes produce IL-6; however, the precise inducing molecules and the kinetics of their action have not yet been clearly identified. In the current study, we show that either interleukin-1 beta (IL-1 beta) or tumor necrosis factor-alpha (TNF-alpha) exert a strong inducing signal for IL-6 in primary rat astrocytes. When the two cytokines are added together the response is synergistic, suggesting that each cytokine may induce IL-6 gene expression by different pathways. Interferon-gamma (IFN-gamma) does not affect IL-6 expression although if it is added in conjunction with IL-1 beta, an augmented induction of IL-6 occurs. In addition to the cytokines, bacterial lipopolysaccharide (LPS) and the calcium ionophore, A23187, induce IL-6 expression. IL-6 expression can be blocked by the glucocorticoid analogue, dexamethasone. IL-6 induction by LPS/Ca2+ ionophore is more sensitive to the suppressive effects of dexamethasone than is IL-6 induction by TNF-alpha/IL-1 beta. Cycloheximide (CHX), an inhibitor of protein synthesis, markedly increased levels of IL-6 mRNA in both unstimulated and stimulated astrocytes, indicating that ongoing protein synthesis is not required for astrocyte IL-6 gene expression. We propose that astrocyte-produced IL-6 may have a role in augmenting intracerebral immune responses in neurological diseases such as multiple sclerosis (MS), AIDS dementia complex (ADC), and viral infections. These diseases are characterized by infiltration of lymphoid and mononuclear cells into the central nervous system (CNS), and intrathecal production of immunoglobulins. IL-6 may act to promote terminal differentiation of B cells in the CNS, leading to immunoglobulin synthesis.

Kinetics of interleukin-2 and interleukin-6 synthesis following major mechanical trauma

Although it is known that mitogen-induced lymphocyte proliferation and interleukin-2 (IL-2) synthesis are depressed following mechanical trauma, it is not known whether these defects are due to high levels of circulating prostaglandin E2 released by macrophages, suppressor T-lymphocytes, and serum suppressive factors or due to intracellular defects in T-lymphocytes. Moreover, the kinetic of interleukin-6 (IL-6), a new multifunctional cytokine, following trauma is not known. To study this, highly purified T-cell cultures were prepared from 21 patients with major mechanical trauma on Days 3, 7, 10, 14, and 21 post-trauma and assayed for proliferative response to phytohemagglutinin, IL-2, and IL-6 synthesis. T-lymphocyte proliferation of patients was unaltered on all days post-trauma compared to that of healthy controls. Interleukin-2 synthesis of patients showed a significant (P less than 0.01) reduction ranging from 23% of control values on Day 3 to 40% on Day 21. Interleukin-6 synthesis in contrast was markedly increased (P less than 0.05) in the patient group on all days up to sixfold (Day 3) with a tendency toward normalization on Day 21. High levels of IL-6 correlated with the appearance of infectious complications in the post-traumatic course. These data indicate that the alterations in T-cell proliferation and IL-2 synthesis following major injury found in earlier studies are caused by different suppressor mechanisms. While T-cell proliferation is only decreased by extracellular components, IL-2 synthesis is suppressed mainly by an intracellular defect. The role of highly increased IL-6 levels and its effect on the immune response are so far unknown.

Identification of interleukin-6 as an autocrine growth factor for Epstein-Barr virus-immortalized B cells

Autocrine growth factors are believed to be important for maintenance of an immortalized state by Epstein-Barr virus (EBV), because cell-free supernatants of EBV-immortalized cell lines promote the proliferation of autologous cells and permit their growth at low cell density. In this study, we provide evidence for the existence of two autocrine growth factor activities produced by EBV-immortalized lines distinguished by size and biological activities. Much of the autocrine growth factor activity in lymphoblastoid cell line supernatants resided in a low-molecular-weight (less than 5,000) fraction. However, up to 20 to 30% of the autocrine growth factor activity resided in the high-molecular-weight (greater than 5,000) fraction. While the nature of the low-molecular-weight growth factor activity remains undefined, the high-molecular-weight growth factor activity was identified as interleukin-6 (IL-6). Culture supernatants from six EBV-induced lymphoblastoid cell lines tested contained IL-6 activity, because they promoted proliferation in the IL-6-dependent hybridoma cell line B9. In addition, a rabbit antibody to human IL-6 neutralized the capacity of the high-molecular-weight (greater than 5,000) fraction of a lymphoblastoid cell line supernatant to promote growth both in autologous EBV-immortalized cells and in B9 cells. Similarly, this high-molecular-weight autocrine growth factor activity was neutralized by a monoclonal antibody to human IL-6. Furthermore, characteristic bands, attributable to IL-6, were visualized in supernatants of each of four EBV-induced lymphoblastoid cell lines after immunoprecipitation with a rabbit antiserum to human IL-6. Thus, in addition to its previously reported properties, IL-6 is an autocrine growth factor for EBV-immortalized B cells cultured under serum-free conditions.

Interleukin-6: historical background, genetics and biological significance

Interleukin-6 (IL-6) is a pleiotropic cytokine previously known as B cell stimulatory factor (BSF-2), interferon-beta 2 (IFN-beta 2), 26-kDa protein, and hepatocyte stimulating factor (HSF). The name IL-6 was proposed when the nucleotide sequences of the cDNAs for these proteins had been determined and the molecules were found to be identical. IL-6 production can be induced by a wide variety of agents in a wide range of cells, although IL-6 gene expression seems to be regulated in a tissue and stimulus specific manner. At least 3 different signal pathways regulate IL-6 gene expression, emphasizing its multiply inducible nature. The currently known activities of IL-6 include regulatory functions in hematopoiesis, immune reactions and acute phase responses. IL-6 appears to be a key member of the IL family; however, it is still poorly understood how IL-6 interacts with other lymphokines within the network. The anti-viral activity of IL-6 seems to be negligible. Elevated IL-6 levels have been found in diseases like rheumatoid arthritis, multiple myeloma and systemic lupus erythematosus. The abnormal expression and dysregulation of IL-6 in certain disorders may be a typical feature of this cytokine, making it the first cytokine that may be directly related to pathogenesis.

Proliferating or interleukin 1-activated human vascular smooth muscle cells secrete copious interleukin 6

The cells that make up blood vessel walls appear to participate actively in local immune and inflammatory responses, as well as in certain vascular diseases. We tested here whether smooth muscle cells (SMC) can produce the important inflammatory mediator IL6. Unstimulated SMC in vitro elaborated 5 X 10(3) pg recIL6/24h (i.e., biological activity equivalent to 5 X 10(3) pg recombinant IL6 (recIL6), as determined in B9-assay with a recIL6 standard). Several pathophysiologically relevant factors augmented IL6 release from SMC including 10 micrograms LPS/ml (10(4) pg recIL6), 10 ng tumor necrosis factor/ml (4 X 10(4) pg recIL6), and most notably 10 ng IL1/ml (greater than or equal to 3.2 X 10(5) pg recIL6). Production of IL6 activity corresponded to IL6 mRNA accumulation and de novo synthesis. SMC released newly synthesized IL6 rapidly, as little metabolically labeled material remained cell-associated. In supernatants of IL1-stimulated SMC, IL6 accounted for as much as 4% of the secreted proteins. In normal vessels SMC seldom divide, but SMC proliferation can occur in hypertension or during atherogenesis. We therefore tested the relationship between IL6 production and SMC proliferation in response to platelet-derived growth factor (PDGF) in vitro. Quiescent SMC released scant IL6 activity, whereas PDGF (1-100 ng/ml) produced concentration-dependent and coordinate enhancement of SMC proliferation and IL6 release (linear regression of growth vs. IL6 release yielded r greater than 0.9). IL6 itself neither stimulated nor inhibited SMC growth or IL6 production. Intact medial strips studied in short-term organoid culture produced large quantities of IL6, similar to the results obtained with cultured SMC. These findings illustrate a new function of vascular SMC by which these cells might participate in local immunoregulation and in the pathogenesis of various important vascular diseases as well as in inflammatory responses generally.

Interleukin-6 and the acute phase response

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Adult human vascular endothelial cells express the IL6 gene differentially in response to LPS or IL1

We investigated the regulation of IL6 biological activity, de novo synthesis, and mRNA levels in adult vascular endothelial cells (EC) by bacterial endotoxin or inflammatory cytokines. Cells incubated without stimulus released scant IL6 activity. IFN gamma, IL2, or PDGF did not augment IL6 release from EC. LPS, lipid A, and TNF increased IL6 release modestly (5 to 20-fold), while recombinant IL1s (rIL1s) stimulated this process 100 to 400-fold. Differential release of IL6 from EC treated with LPS or rIL1 continued for at least 144 hr. Exposure to LPS or rIL1 caused EC to synthesize IL6 de novo. EC secreted the newly synthesized IL6 into the supernatant, rather than retaining it within or bound to cells. EC accumulated IL6 mRNA after 3 hr of exposure to rIL1. However, we could only detect IL6 message in cells incubated with LPS under "superinduction" conditions with cycloheximide, consistent with lower levels of IL6 biological activity in response to LPS compared to IL1 stimulation. We propose that local production of IL6 by vascular EC, which comprise the barrier between tissues and the blood, may influence regional immune and inflammatory responses.

Interleukin-6 and its receptor during homeostasis, inflammation, and tumor growth

This review focuses on describing the specific role of interleukin-6 within the network of inflammatory mediators in man. Sites of interleukin-6 synthesis, regulation of its expression, and the biological functions of this molecule are here outlined. The potential role of interleukin-6 as a diagnostic monitor is discussed. Particular attention is paid to experimental evidence that interleukin-6 and its receptor may be involved in the pathogenesis of autocrine tumor growth. A recently proposed therapeutical use of cytotoxic interleukin-6 fusion proteins in order to selectively, destroy certain interleukin-6 receptor bearing tumor cells is discussed in the light of the finding, that not only hepatocytes, but also normal peripheral blood monocytes express the interleukin-6 receptor.

Activation of neutrophils by recombinant interleukin 6

The cytokine interleukin 6 (IL-6) has been shown to have multiple biological activities against many cellular targets. The present studies were designed to determine whether these activities extended to the neutrophil (PMN). Initially, we investigated the ability of IL-6 to modulate PMN-mediated antibody-dependent cellular cytotoxicity. The presence of IL-6 stimulated 51Cr release from labeled, opsonized targets by 67.1% (from 21.6 +/- 1.4% to 36.1 +/- 1.3% at 10 U of IL-6 (P less than 0.01)). IL-6 was not directly toxic to the target cells and stimulation of ADCC was shown to occur across a range of effector-to-target ratios. To investigate the basis of the capacity of IL-6 to stimulate PMN, we studied the effects of IL-6 on PMN chemotaxis, degranulation, and the respiratory burst. IL-6 was not chemotactic or chemokinetic for PMN. However, IL-6 stimulated lysozyme secretion from 14.1 +/- 2.5 to 23.7 +/- 3.6% at 100 U (P less than 0.01). IL-6 was a complete secretagogue, being able to induce the secretion of both the secretory granule marker lactoferrin (11.2 +/- 2.0 to 23.5 +/- 2.2%) and the primary granule marker beta-glucuronidase (5.0 +/- 1.0 to 18.2 +/- 4.0%). IL-6 was not able to directly stimulate the PMN respiratory burst. However, IL-6 did "prime" PMN, enhancing superoxide secretion by fMLP (10(-7) M)-treated PMN by 50.8% (5.9 +/- 1.0 to 8.9 +/- 1.5 nmol superoxide at 100 U of IL-6; P less than 0.01) and PMA (5.0 nM) by 54.3% (8.1 +/- 2.6 to 12.5 +/- 3.6 nmol; P less than 0.05). In conclusion, IL-6 is a PMN stimulant, enhancing the toxicity of PMN in an antibody-dependent cellular cytotoxicity assay. Enhanced cytotoxicity may have been mediated, at least in part, by the stimulation of secretion of toxic components from PMN targets and by the priming of stimulating respiratory burst activity.

Host defense against infections and inflammations: role of the multifunctional IL-6/IFN-beta 2 cytokine

IL-6/IFN-beta 2 appears to be one of the important mediators of the response to viral and bacterial infections and to shock. The biological effects now associated with IL-6/IFN-beta 2 include: stimulation of immunoglobulin secretion by mature B lymphocytes (BSF-2 activity), growth stimulation of plasmacytomas and hybridomas (HGF activity), activation of T cells, stimulation of hepatic acute phase protein synthesis (HSF activity), stimulation of hematopoiesis, cell differentiation (DIF activity), inhibition of tumor cell growth (AP activity) and other IFN-like effects. As a typical cytokine, IL-6/IFN-beta 2 is secreted by many cell types and acts in various combinations with other interleukins and interferons.

Interaction of interferon with other cytokines

Interferons interact with other cytokines to exert their antiviral, cell growth regulatory and immunomodulatory activities. Growth factors, tumor necrosis factors, colony stimulating factors, interleukins and interferons have pleiotropic effects and form a parallel network of intercellular signals. These signals are transduced at the cell surface through specific receptors with intrinsic enzymatic activity or with the capacity to regulate intracellular enzymes through interactive effects with G-proteins. This leads to regulated gene transcription of intracellular and secreted, functional and structural proteins. Although much is known about the interaction of cytokines with their receptors and about the regulation of transcription at the genomic level the various steps linking these two phenomena deserve further research.

Interleukin 6 stimulates synthesis of complement proteins factor B and C3 in human skin fibroblasts

Human interleukin (IL) 6 is a multifunctional cytokine which is synthesized by fibroblasts in response to many stimuli, including bacterial lipopolysaccharide (LPS). During acute-phase response, liver cells secrete a specific group of proteins among which components of the complement system and IL 6 appear to be an important mediator of this response. Human skin fibroblasts also synthesize at least seven proteins of the complement system. Each of these seems to be characteristically regulated by soluble mediators of the inflammatory process. Here we report that in fibroblasts, IL 6 induces increases in the rate of synthesis of factor B and C3, activator proteins of the alternative pathway of complement activation. The increases in factor B and C3 were concentration dependent reaching about 40- and 15-fold, respectively. The protein increases were observed within 4 h after IL 6 addition to the cells and were accompanied by increase in factor B and C3 mRNA. The data suggest that the induction of factor B and C3 by LPS may be mediated, at least in part, by IL 6 induced by LPS. This new function of IL 6 could provide a local protection against invading agents through activation of the antibody-independent alternative pathway of complement activation.

Regulation of interleukin-6 receptor expression in human monocytes and hepatocytes

Human blood monocytes normally express the interleukin-6 receptor. Treatment of cultured monocytes with endotoxin, interleukin-1 beta, or interleukin-6 results in a decrease in interleukin-6 receptor mRNA levels. Glucocorticoids aso cause a drop in monocytic interleukin-6 receptor mRNA levels. We also found interleukin-6 receptor expression in cultured human hepatocytes, but in contrast to monocytes, where interleukin-6 receptor mRNA is presented by the ligand and by interleukin-1, treatment of hepatocytes with interleukin-6 or interleukin-1 resulted in increased interleukin-6 receptor mRNA levels. Induction of interleukin-6 receptor mRNA in hepatocytes was less pronounced when glucocorticoids were omitted from the culture medium. We conclude that during noninflammatory homeostasis, blood monocytes are involved in binding of trace amounts of circulating interleukin-6. During inflammatory events, the main target of interleukin-6 may be changed from the monocytic population not only to activated B-cells, but also to the hepatocytes.

Interleukin 6 primes human neutrophil and monocyte oxidative burst response

Interleukin 6 (IL-6), a 26-kDa inducible protein, is a cytokine with multiple biological activities. This paper reports on the regulatory role of rIL-6 on the function of human polymorphonuclear and mononuclear leukocytes, a property not described previously. rIL-6 by itself did not exhibit any chemotactic activity and it could not activate these cells for an oxidative burst response. Preincubation of both cell types with rIL-6 at concentrations of 5 and 50 ng/ml primed the cells for enhanced generation of oxygen radicals following stimulation with the chemotactic peptide f-Met-Leu-Phe or the phorbol ester PMA. The enhancement of the oxidative burst response occurred both at the level of superoxide anion generation, an early step in the activation pathway, and at the level of the hydrogen peroxide-myeloperoxidase mediated response, a later step in the oxidative burst pathway. The priming ability was abolished by heat treatment of rIL-6 at 100 degrees C but not at 70 degrees C. Stimulation of B cell growth and immunoglobulin production combined with enhancement of oxidative burst response of phagocytic cells by IL-6 provide an effective mechanism of fighting against invading micro-organisms.

Interleukin 6 primes human neutrophil and monocyte oxidative burst response

Interleukin 6 (IL-6), a 26-kDa inducible protein, is a cytokine with multiple biological activities. This paper reports on the regulatory role of rIL-6 on the function of human polymorphonuclear and mononuclear leukocytes, a property not described previously. rIL-6 by itself did not exhibit any chemotactic activity and it could not activate these cells for an oxidative burst response. Preincubation of both cell types with rIL-6 at concentrations of 5 and 50 ng/ml primed the cells for enhanced generation of oxygen radicals following stimulation with the chemotactic peptide f-Met-Leu-Phe or the phorbol ester PMA. The enhancement of the oxidative burst response occurred both at the level of superoxide anion generation, an early step in the activation pathway, and at the level of the hydrogen peroxide-myeloperoxidase mediated response, a later step in the oxidative burst pathway. The priming ability was abolished by heat treatment of rIL-6 at 100 degrees C but not at 70 degrees C. Stimulation of B cell growth and immunoglobulin production combined with enhancement of oxidative burst response of phagocytic cells by IL-6 provide an effective mechanism of fighting against invading micro-organisms.