Serum levels of IL-6 type cytokines and soluble IL-6 receptors in active B-cell chronic lymphocytic leukemia and in cladribine induced remission

We have investigated the serum concentrations of interleukin-6 (IL-6) and two IL-6 family cytokines-oncostatin M (OSM) and leukemia inhibitory factor (LIF)-in 63 patients with B-cell chronic lymphocytic leukemia (B-CLL) and 17 healthy controls using the enzyme-linked immunosorbent assay (ELISA) method. Simultaneously, we measured the serum levels of the soluble forms of two subunits of the IL-6 receptor complex-ligand binding glycoprotein 80 (sIL-6R) and glycoprotein 130 (sgp130). The cytokines and receptors were evaluated in 25 untreated patients and 38 patients treated with cladribine (2-CdA), as well as in 17 healthy controls. We have correlated the serum levels of these proteins with Rai's clinical stage of the disease, the response to 2-CdA treatment and some hematological parameters. We have also evaluated the correlation of the IL-6 serum level with the concentration of OSM and IL-6 soluble receptors. IL-6 was measurable in 62/63 (98.4%), OSM in 20/25 (80%) of untreated and 14/38 (37.8%) of the treated patients. sIL-6R and sgp130 were detectable in all 63 patients and LIF in none of the CLL patients. IL-6 serum level in untreated patients was not significantly different as compared to its concentration in the control group (P>0.05). However, in the patients treated with 2-CdA the IL-6 level was significantly lower (P<0.02), and the lowest concentration was found in the patients with complete remission (CR; median 1.4pg/ml; P<0.02). The concentration of sIL-6R was significantly higher in untreated (median 61.8 ng/ml) and treated (median 50.1 ng/ml) CLL patients when compared to normal persons (median 41.2 ng/ml; P=0.04; P<0.001, respectively). There was no difference between the sIL-6R levels in the patients with CR and the healthy controls. In non-responders sIL-6R concentration was the highest and similar to its level in the untreated patients. OSM level was higher in the untreated patients (median 1.8pg/ml) than in the normal controls (median 0.0pg/ml; P<0.001) and in the CR patients (median 0.0pg/ml; P<0.03). The serum concentration of sgp130 was similar in the untreated (median 480 pg/ml) and treated (median 470 pg/ml) patients, as well as in the healthy persons (median 420 pg/ml; P>0.05). We have found significant positive correlation between the levels of sIL-6R and the lymphocytes count in CLL patients (p=0.423; P<0.001). In addition, sIL-6R and OSM serum concentrations correlated also with CLL Rai stage. In conclusion, the serum level of IL-6, OSM and sIL-6R, but not LIF and sgp130, are useful indicators of CLL activity.     

A synthetic corticosteroid,dexamethasone regulates generation of soluble form of interleukin-6 receptor of human lymphocytes,in vitro

In contrast to most of the soluble cytokine receptor antagonists properties, the soluble IL-6 receptor (sIL-6R) occurring in various body fluids of healthy persons and patients with various diseases is an agonist. The enhancing effect is due to its ability to form complex with IL-6 and to bind to gp130 making constitutively IL-6 receptor negative cells responsive for IL-6. The generation as well as the functional role of soluble IL-6 receptor is poorly understood. Earlier, we found that the sIL-6R levels in sera of patients with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) were higher than those of the control group measured by ELISA sandwich technology. In the present study we detected different levels of sIL-6R in the supernatants of lymphocyte cultures of healthy persons and patients with RA as well as SLE. Moreover, we found, that in vitro dexamethasone treatment stimulated generation of sIL-6R in both healthy persons and in active SLE, while it strongly suppressed production of sIL-6R in both RA groups. At mRNA level, we found that in SLE both the IL-6R mRNA encoding the membrane spanning and alternatively spliced (soluble) variants increased. Surprisingly, the strong decrease of sIL6R protein in RA was not found at mRNA level.     

Purification and characterization of soluble human IL-6 receptor expressed in CHO cells

An immunosorbent assay system to detect genetically engineered IL-6 receptor (IL-6R) was established, whereby soluble IL-6 receptor (sIL-6R) was detected in the culture medium when sIL-6R cDNA was transfected into COS1 cells. A stably transformed Chinese hamster ovary (CHO) cell line constitutively expressing sIL-6R has been established. The recombinant sIL-6R was purified to homogeneity by sequential filtration and chromatography of the culture medium. The recombinant sIL-6R augmented the sensitivity of M1 cells to IL-6 in growth inhibition assay in a dose-dependent manner. Furthermore, a radioisotope immunosorbent assay (RIA) utilizing recombinant sIL-6R was established which could detect IL-6 in a quantity as low as 10 ng/ml.     

Quantitative analysis of serum IL-6 and its correlation with increased levels of serum IL-2R in HIV-induced diseases

We have devised a luminescence sandwich ELISA for the quantification of IL-6 in both sera and cell culture supernatants, which had a detection limit of 100 fg/ml of test sample. By using the luminescence sandwich-ELISA, low but measurable levels of IL-6 (9.5 pg/ml on average) were found in the sera from normal individuals. The serum levels of IL-6 were elevated in HIV-seropositive asymptomatic carriers (55.5 pg/ml on average), and the IL-6 levels were correlated with the degree of HIV-induced disease progression (AIDS-related complex 106.8 pg/ml on average and (AIDS 283 pg/ml). IL-6 immunoreactivity in the sera of AIDS patients eluted at a 25,000 m.w. major peak, which was biologically active and heat-stable, and a 500,000 m.w. minor peak in size-exclusion HPLC. Interestingly, a significant correlation was observed between the serum IL-6 levels and soluble IL-2R levels. In vitro, HIV infection of PHA-activated PBMC led to enhanced release of IL-6 into the culture supernatants. Moreover, soluble IL-2R release was markedly increased by adding exogenous IL-6, whereas it was decreased by adding the neutralizing anti-IL-6 mAb to the cultures. These results demonstrate that increased IL-6 levels are significantly associated with sIL-2R levels, and suggest a cause of the increased levels of this receptor in patients with HIV infection. Furthermore, both serum IL-6 and serum IL-2R levels in HIV infection reflect the stage of the HIV-induced disease.     

Soluble IL-2 receptor as an agent of serum-mediated suppression in human visceral leishmaniasis

In visceral leishmaniasis (VL), patient's lymphocytes are not activated by leishmania Ag stimulation, and their sera exhibit a potent nonspecific suppressive effect on the responses of normal lymphocytes. Sera were obtained from 33 VL patients, eight patients with subclinical VL, and from 27 normal volunteers. Only sera from VL patients markedly reduced Con A-induced lymphocyte proliferative responses, as well as IL-2 or IFN-gamma production by normal lymphocytes. Addition of exogenous human rIL-2 to cultures containing VL patient sera partially reversed the normal lymphocyte proliferative capacity and restored IFN-gamma production. This phenomenon was consistent with the presence of greatly elevated levels of soluble IL-2R (sIL-2R) in VL patients' sera (4299 +/- 2351 U/ml), well above those of normal sera (180 +/- 94 U/ml), or of sera from patients with subclinical leishmania infection without immunosuppression (1002 +/- 281 U/ml). Furthermore, the removal of sIL-2R reduced VL serum suppressive activity as evaluated by effects on IL-2 and on IFN-gamma production. These data suggest the participation of high levels of sIL-2R in the serum-mediated suppression in VL.     

Relationship between circulating interleukin-10 (IL-10) with interleukin-6 (IL-6) type cytokines (IL-6, interleukin-11 (IL-11), oncostatin M (OSM)) and soluble interleukin-6 (IL-6) receptor (sIL-6R) in patients with multiple myeloma

We investigated the serum concentration of the interleukin-10 (IL-10), along with cytokines of interleukin-6 (IL-6) family (IL-6, IL-11 and oncostatin M - OSM), as well as soluble receptor for IL-6 (sIL-6R), in 121 patients with multiple myeloma (MM) and 28 healthy subjects. We studied the interactions between IL-10 and other cytokines, and the receptor. The correlation between IL-10 and some clinical and laboratory parameters associated with the disease activity were also analysed. The IL-10 was detectable in all patients with multiple myeloma and in all controls. The IL-10 concentration was significantly increased in myeloma patients compared with healthy persons (mean - 7.09 and 2.1 pg/ml, respectively) (p = 0.008). The level of IL-10 correlated positively with the advanced stage of disease estimated according to the Salmon and Durie classification (I versus III stage - p = 0.03). Higher values of IL-10 were found in patients with the light chain disease, hypercalcaemia, and correlated with the elevated concentrations of C-reactive protein (CRP). IL-6 was detected in 117 of the 121 patients and in all controls. The concentration of IL-6 was statistically increased in MM patients compared with control group (mean - 16.06 and 4.49 pg/ml, respectively) (p = 0.01). We found a positive correlation between IL-10 and IL-6 serum levels in MM patients. The relationship, expressed as Spearman's rank sum coefficient (rho = 0.249, p = 0.006) was significant. IL-11 was detected in 26 of the 121 MM patients and in 3 of the 28 healthy subjects at the mean concentration of 1.2 and 0.6 pg/ml respectively (p > 0.05). OSM was at detectable levels in 51 of the 121 patients and in only 4 of the 28 controls (mean - 3.84 and 0.1 pg/ml, p = 0. 002). The correlation between IL-10 and IL-11 levels in MM patients was not significant, but there was a strong statistical correlation between IL-10 and OSM concentrations (rho= 0.327, p = 0.0002). The serum concentration of sIL-6R was measurable in all patients and all controls (mean - 66.00 and 39.57 ng/ml respectively), but the difference between these groups was not significant. We found significant, positive correlation between the levels of IL-10 and sIL-6R (rho= 0.233, p = 0.01). In conclusion, we state that the serum concentrations of IL-10, IL-6, OSM and sIL-6R in MM patients may be a useful markers for the evaluation of the disease activity.     

人IL-6 /sIL-6R 结合分子模型的建立及在药物筛选中的应用

目的：建立人IL-6 /sIL-6R 结合的分子模型,用于筛选IL-6 /sIL-6R的抑制剂。方法：将人IL-6基因克隆至原核表达载体pET28a（+）中表达IL-6蛋白,western blot及人IL-6检测试剂盒分析鉴定表达蛋白。同法将人sIL-6R在pET15b载体中表达,纯化并用western blot检测目的蛋白。依据ELISA原理建立IL-6 /sIL-6R 结合的分子模型,并通过改变IL-6、sIL-6R及IL-6 antibody的浓度来优化该模型,用于IL-6 /sIL-6R拮抗药物的筛选。结果：人IL-6可在载体PET28a（+）中高效表达,且经western blot鉴定正确,人IL-6检测试剂盒检测显示具有较高的免疫活性。sIL-6R在PET15b中表达,western blot鉴定正确。通过对IL-6 /sIL-6R结合的分子模型的优化,得到其最佳条件为：IL-6R 1?g/well, IL-6 500ng/well, IL-6 antibody 1?g/well。应用该模型筛选发现有些化合物可显著抑制IL-6与其受体的结合。结论：成功构建IL-6 /sIL-6R结合的分子模型,为高通量筛选IL-6拮抗剂提供平台。     

Effects of IL-6 and its soluble receptor on proteoglycan synthesis and NO release by human articular chondrocytes: comparison with IL-1. Modulation by dexamethasone.

Contradictory results have been reported on the effects and role of IL-6 on proteoglycan (PG) synthesis. Having shown recently that in vitro IL-6 depends on the presence of soluble IL-6 receptor alpha (sIL-6Ralpha) to fully exert its effects on chondrocytes, we conducted the present study to analyse the effects of IL-6 on PG synthesis by human articular chondrocytes in the presence of sIL-6Ralpha. PG synthesis was quantified by specific ELISA using a monoclonal antibody (MAB) raised against the keratan sulphate region of PG as a capture antibody, and a MAB to the acid binding region as a detector. It proved specific for PG from primary (differentiated) chondrocytes. In the absence of sIL-6Ralpha, IL-6 had a slight inhibitory effect on PG synthesis by articular chondrocytes. sIL-6Ralpha alone also had slight but consistent inhibitory effects. When adding sIL-6Ralpha at concentrations of 50 ng/ml corresponding to levels found in synovial fluid, the effects of IL-6 increased consistently. However, even at optimal concentrations (30-100 ng/ml of IL-6sR per 100 ng/ml of IL-6), maximal inhibition (48%) did not equal the degree of inhibition achieved by IL-1 at 1 ng/ml (66%). Similar effects, although slightly weaker, were observed on osteoarthritic cells. Dexamethasone, over a wide range of concentrations, markedly enhanced proteoglycan synthesis and completely reversed the downregulatory effects of IL-1 and IL-6 + sIL-6Ralpha. The effects of IL-1 were partially inhibited by an anti-IL-6 antibody. Finally, unlike IL-1, IL-6 + sIL-6Ralpha only weakly stimulated nitric oxide (NO) synthesis. In conclusion, sIL-6Ralpha potentiates the inhibitory effect of IL-6 on PG synthesis by articular chondrocytes, but the overall effect of IL-6 + IL-6sR is moderate compared to the effects of IL-1.     

Cerebrospinal fluid and serum protein levels of tumour necrosis factor-alpha (TNF-alpha) interleukin-6 (IL-6) and soluble interleukin-6 receptor (sIL-6R gp80) in multiple sclerosis patients

The aim of this study was to evaluate soluble proteins of tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and IL-6 receptor subunit gp80 (sIL-6R gp80), as markers of multiple sclerosis (MS). Paired cerebrospinal fluid (CSF) and serum samples of 20 MS patients and 15 controls suffering from non-inflammatory neurological diseases have been assayed retrospectively using monoclonal antibodies-based ELISAs. While TNF-alpha could not be detected in CSF, it was measurable in 20% of total sera. Interleukin-6 was measurable in 5% of total CSF and in 10% of total sera only. However, soluble IL-6R gp80 protein subunit was readily measurable, showing sera concentration (pg/mL) about 34 times higher and specific content (pg/mg total protein) around five times lower than those in paired CSF, similarly for both group of patients. No significant difference of sIL-6R gp80 level, which could be disease-, gender- or age-related, and no correlation of CSF sIL-6R gp80 content with that of paired serum or with routine clinical data for CSF, have been observed. We have concluded that soluble proteins of TNF-alpha, IL-6 and sIL-6R gp80 assayed by monoclonal antibodies-based ELISAs could not serve as markers of the MS activity.     

A soluble form of IL-13 receptor alpha 1 promotes IgG2a and IgG2b production by murine germinal center B cells.

A functional IL-13R involves at least two cell surface proteins, the IL-13R alpha 1 and IL-4R alpha. Using a soluble form of the murine IL-13R alpha 1 (sIL-13R), we reveal several novel features of this system. The sIL-13R promotes proliferation and augmentation of Ag-specific IgM, IgG2a, and IgG2b production by murine germinal center (GC) B cells in vitro. These effects were enhanced by CD40 signaling and were not inhibited by an anti-IL4R alpha mAb, a result suggesting other ligands. In GC cell cultures, sIL-13R also promoted IL-6 production, and interestingly, sIL-13R-induced IgG2a and IgG2b augmentation was absent in GC cells isolated from IL-6-deficient mice. Furthermore, the effects of the sIL-13R molecule were inhibited in the presence of an anti-IL-13 mAb, and preincubation of GC cells with IL-13 enhanced the sIL-13R-mediated effects. When sIL-13R was injected into mice, it served as an adjuvant-promoting production to varying degrees of IgM and IgG isotypes. We thus propose that IL-13R alpha 1 is a molecule involved in B cell differentiation, using a mechanism that may involve regulation of IL-6-responsive elements. Taken together, our data reveal previously unknown activities as well as suggest that the ligand for the sIL-13R might be a component of the IL-13R complex or a counterstructure yet to be defined.     

Soluble interleukin-18 receptor complex is a novel biomarker in rheumatoid arthritis

Introduction

There has been no report in the literature of a soluble form of interleukin (IL)-18 receptor α (IL-18Rα). In this study, we evaluated the levels and characteristics of soluble IL-18Rα (sIL-18Rα) in the sera of patients with rheumatoid arthritis (RA) and compared these results to control populations.

Methods

The sIL-18Rα complex was isolated from pooled human blood serum using an anti-IL-18Rα monoclonal antibody affinity column. The purified sIL-18Rα was then examined using Western blot analysis and used in experiments to evaluate the effects on an IL-18-responsive natural killer (NK) human cell line, NK0. An enzyme-linked immunosorbent assay was developed, and sera from 145 patients with RA, 6 patients with adult-onset Still's disease, 31 patients with osteoarthritis (OA), 39 patients with systemic lupus erythematosus (SLE) and 67 controls were tested, along with levels of immunoglobulin M, rheumatoid factor, anticyclic citrullinated peptide antibody, IL-18, IL-13 and interferon (IFN)-γ. Area under the receiver operating characteristic curve (ROC-AUC) analysis was used to evaluate the diagnostic utility of the sIL-18Rα complex.

Results

The isolated sIL-18Rα complex can be associated with IL-18 and the soluble form of the IL-18Rβ chain. The sIL-18Rα complex bound to the surface to the NK0 cell line, antagonized the stimulatory effects of IL-18 and IL-2 on the NK0 cell line and inhibited IFN-γ production by the cells. The serum levels of sIL-18Rα complex in RA (186.0 ± 33.5 ng/mL, n = 145) and adult-onset Still's disease (98.2 ± 8.9 ng/mL, n = 6) were significantly (P < 0.001) higher than those in the healthy controls (52.3 ± 8.5 ng/mL, n = 67), OA (38.6 ± 5.4 ng/mL, n = 31), SLE (44.6 ± 3.2 ng/mL, n = 39). The serum level of sIL-18Rα complex was not significantly different between RA and adult-onset Still's disease patients. The serum levels of IL-18, IL-13 and IFN-γ in the RA patients were significantly (P < 0.01) higher than in OA and SLE patients as well as healthy controls. ROC-AUC analysis of the serum concentration of sIL-18Rα indicated that it was significantly diagnostic of RA. Moreover, a tumor necrosis factor inhibitor, etanercept, significantly (P < 0.0001) decreased levels of sIL-18Rα in the sera of 29 RA patients 6 months after treatment.

Conclusions

The sIL-18Rα complex could be a potentially useful biomarker for the diagnosis of RA.     

Context-dependent IL-6 potentiation of interferon- gamma-induced IL-12 secretion and CD40 expression in murine microglia

Interleukin-6 (IL-6) is produced by neurons, astrocytes, and microglia, and elevated levels of IL-6 within the CNS have been documented in multiple neurological disorders including Alzheimer's disease, stroke, epilepsy, attention deficit disorder, cerebral palsy, and multiple sclerosis. Here, we sought to understand how IL-6 regulates microglial signal transduction and their immune properties. Using highly enriched cultures of neonatal murine microglia we show that IL-6 alone has direct effects on microglia as it activates STAT3 and extracellular signal-regulated kinase pathways in a time- and dose-dependent fashion and it enhances interferon-gamma (IFNγ)-stimulated IL-12 secretion. However, other immune properties were only weakly modulated by IL-6 when administered without the soluble IL-6 receptor (sIL-6R). For instance, IFNγ-induced expression of the co-stimulatory molecule, CD40 was dependent on sIL-6R administration. IL-6 with or without sIL-6R did not affect major histocompatability complex class II expression. In granulocyte–macrophage colony-stimulating factor (GMCSF)-induced dendritic cell-like microglia, IL-6/sIL-6R and IFNγ stimulated an even greater increase in CD40 expression compared with primary microglia. Altogether, our results demonstrate that microglial responses to IL-6 are not simple in that the effects of IL-6 are context-dependent. In particular, the presence or absence of sIL-6R, IFNγ or GMCSF will alter the type and amplitude of their response.     

Serum concentrations of sIL-2R, IL-6, TGF-beta1, neopterin, and zinc in chronic hepatitis C patients treated with interferon-alpha

T lymphocytes and immunoregulatory cytokines play an important role in the host response to hepatitis C virus (HCV) infection. Zinc is required for a wide spectrum of immune functions, including T-cell activity. To determine the clinical significance of the cytokines sIL-2R, IL-6, TGF-beta1, neopterin, and of zinc in chronic heptatitis C virus (HCV) infection, we investigated their concentrations in the serum of 16 patients with chronic HCV infection before, during and at the end of therapy with interferon (IFN) alpha (Roferon A), and after 6 months follow-up. Elevated concentrations of sIL-2R, IL-6, TGF-beta1, and neopterin were found in the serum of all patients prior to therapy, as compared to healthy controls. sIL-2R patterns differed in responders and non-responders. While the mean concentration of sIL-2R (335.75 pg/ml) before therapy was about 40% higher in complete responders (n=4) than in controls (272.20 pg/ml), the mean concentration in non-responders (n=6) was 4-fold higher than in controls (1153.33 pg/ml). During therapy, sIL-2R levels in responders decreased by about 40%. Mean IL-6 concentrations in both complete and partial responders (n=6) decreased continuously during treatment, while mean concentrations in non-responders decreased for only a short time, and increased again after cessation of therapy. Mean levels of TGF-beta1 behaved similarly to those of IL-6. Only negligible differences in mean neopterin levels were found between responders and non-responders over the entire observation time. The mean serum zinc concentrations slightly decreased in all 3 patient groups, the greatest reduction occurring in 3 of the 4 responders. The present findings underscore the importance of the immune system in the pathogenesis of chronic HCV infection. Serum sIL-2R levels may be used as a serological marker of outcome following IFN-alpha treatment.     

The Soluble Interleukin-6 Receptor Is a Mediator of Hematopoietic and Skeletal Actions of Parathyroid Hormone

Both PTH and IL-6 signaling play pivotal roles in hematopoiesis and skeletal biology, but their interdependence is unclear. The purpose of this study was to evaluate the effect of IL-6 and soluble IL-6 receptor (sIL-6R) on hematopoietic and skeletal actions of PTH. In the bone microenvironment, PTH stimulated sIL-6R protein levels in primary osteoblast cultures in vitro and bone marrow in vivo in both IL-6^+/+ and IL-6^−/− mice. PTH-mediated hematopoietic cell expansion was attenuated in IL-6^−/− compared with IL-6^+/+ bone marrow, whereas sIL-6R treatment amplified PTH actions in IL-6^−/− earlier than IL-6^+/+ marrow cultures. Blocking sIL-6R signaling with sgp130 (soluble glycoprotein 130 receptor) inhibited PTH-dependent hematopoietic cell expansion in IL-6^−/− marrow. In the skeletal system, although intermittent PTH administration to IL-6^+/+ and IL-6^−/− mice resulted in similar anabolic actions, blocking sIL-6R significantly attenuated PTH anabolic actions. sIL-6R showed no direct effects on osteoblast proliferation or differentiation in vitro; however, it up-regulated myeloid cell expansion and production of the mesenchymal stem cell recruiting agent, TGF-β1 in the bone marrow microenvironment. Collectively, sIL-6R demonstrated orphan function and mediated PTH anabolic actions in bone in association with support of myeloid lineage cells in the hematopoietic system.     

Interleukin 6 and 8 levels in plasma and fibroblast cultures in psoriasis

Fibroblasts have been implicated in psoriatic inflammatory processes. The aim of the study was to evaluate soluble interleukin 2 receptor (sIL-2R), interleukin 6 (IL-6), and interleukin 8 (IL-8) plasma levels in psoriatic patients and IL-6 and IL-8 levels in fibroblast culture supernatants. Cytokines levels in plasma and supernatants were measured by ELISA. Plasma sIL-2R, IL-6, and IL-8 levels were higher before the treatment in comparison to healthy controls (P < 0.001) and decreased after treatment. Fibroblasts from healthy controls, psoriatic lesional skin, and noninvolved psoriatic skin, when stimulated with tumor necrosis factor alpha, released considerable amounts of IL-6 and IL-8. No significant difference between healthy controls and psoriatic fibroblasts was observed. Monitoring plasma sIL-2R levels could be employed as a reliable method of psoriasis activity. IL-8 and IL-6 plasma levels seem to reflect psoriasis activity, and treatment response, respectively. Fibroblasts are not a major source of increased IL-6 and IL-8 production in psoriasis.     

Human soluble IL-6 receptor: its detection and enhanced release by HIV infection.

By using a fluorescence sandwich ELISA for the quantification of soluble human IL-6R, normal human PBMC were found to be induced to release IL-6R into culture supernatant by stimulation with PHA. Furthermore, certain promonocyte cell lines and human T-cell leukemia virus I (HTLV-I)-positive cell lines produced sIL-6R into culture supernatants constitutively. However, this was not found with HTLV-I negative T cell lines and Burkitt's B cell line. In addition, generation of supernatant IL-6R of the promonocyte cell line was significantly increased 27-fold after PMA treatment and sevenfold after infection with HIV. The released IL-6R molecules were characterized as an apparent m.w. of 50 to 55 kDa by both size-exclusion HPLC and immunoprecipitation of the soluble protein with IL-6R-specific mAb followed by SDS-PAGE analysis. Furthermore, increased levels of serum IL-6R were detected in blood donors seropositive for HIV. Moreover, the released IL-6R could bind efficiently to purified rIL-6 on solid phase and suppressed the proliferative responses of PBMC. These results suggest that the release of soluble IL-6R might be linked to regulatory functions of immune responses induced by IL-6 stimulation during normal and human retrovirus-infected cell growth and differentiation.     

Interleukine-6 (IL-6) synthesis and gp130 expression by human pericardium.

Growing evidence shows that cytokines of the IL-6 family play an important regulatory role in heart physiology such as inducing cardiomyocyte hypertrophy. The purpose of this study was to see if IL-6 and its soluble receptors (sIL-6R and sgp130) could be detected in pericardial fluids, and to see if they are produced by the pericardium. We report that human pericardial fluid from patients with coronary pathologies contained IL-6, sIL-6R, and sgp130. However, the levels present in sera and pericardial fluid did not correlate, which suggests local production. This observation was confirmed by in vitro studies demonstrating massive IL-6 production by cultured pericardial samples, which could be strongly inhibited by methylprednisolone. RT-PCR studies revealed that IL-6 was weakly expressed in fresh tissues and strongly induced after culture. In situ hybridisation and immunohistochemical analysis showed that IL-6 and gp130 were mainly present in mesothelial cells. sIL-6R and sgp130 were also produced by pericardium in vitro, and their synthesis was upregulated by methylprednisolone. Taken together, these results demonstrate that IL-6 is present in pericardial fluid and that its presence could be due to synthesis by pericardial tissue. In vitro studies suggest that IL-6 production by this tissue could be strongly induced and regulated. A potential paracrine role of these factors in cardiomyocyte functions in normal or pathological conditions is discussed.     

Expression of interleukin 2 and the interleukin 2 receptor in aging rats

Lymphocytes of aged animals exhibit a marked decrease in proliferative capacity in response to mitogen stimulation when compared to those of younger animals. In humans and mice the decreased proliferation is due at least in part (i) to the inability of lymphocytes to synthesize sufficient interleukin 2 (IL-2) and (ii) to decreased expression of IL-2 receptors (IL-2R) on the surface of aged lymphocytes. We compared proliferative abilities, IL-2 production, and IL-2R expression in splenocyte cultures of 4- to 5- and 22- to 24-month-old Fischer 344 rats stimulated with either concanavalin A (Con A) or A23187 and phorbol myristate acetate (PMA). Proliferation was significantly decreased in aged lymphocytes (30-50%) with both treatment protocols. However, unlike mice and humans we observed no difference in IL-2 activity, IL-2 mRNA levels, or IL-2R cell surface expression of lymphocytes from young and aged rats stimulated with either Con A or A23187 and PMA. These results indicate that factors other than decreased expression of IL-2 and IL-2R are responsible for the diminished proliferative capacity of aged rat lymphocytes following mitogen stimulation.     

Soluble interleukin-6 receptor alpha inhibits the cytokine-Induced fractalkine/CX3CL1 expression in human vascular endothelial cells in culture

Soluble form of IL-6 receptor alpha (sIL-6R) is known to serve as an agonist, without exogenous IL-6, on endothelial cells which do not express IL-6R but have only IL-6 receptor beta chain, gp130. We investigated the effect of sIL-6R on fractalkine expression in human umbilical vein endothelial cells (HUVECs) in culture. sIL-6R markedly inhibited HUVEC fractalkine/CX3CL1 expression induced by interleukin (IL)-1alpha, tumor necrosis factor (TNF)-alpha, or interferon (IFN)-gamma. IL-1alpha-induced fractalkine expression was inhibited by sIL-6R in time- and concentration-dependent manners. The experiment using actinomycin D indicated that sIL-6R lowered the stability of fractalkine mRNA. The inhibitory effect of sIL-6R was reversed by anti-gp130 neutralizing antibody. sIL-6R inhibited adhesion of mononuclear cells (MNCs) to HUVEC monolayers stimulated with IFN-gamma, but it did not inhibit the adhesion to monolayers stimulated with IL-1alpha. MNC chemotactic activity of conditioned medium of HUVEC stimulated with IL-1alpha or IFN-gamma was inhibited by co-treatment with sIL-6R. sIL-6R may play a regulatory role in immune responses by modulating the interaction between leukocytes and the vascular endothelium.