Monoclonal antibodies to the soluble human IL-6 receptor: affinity purification, ELISA, and inhibition of ligand binding

Interferons and Interferon Inhibitory Activity in Disease and Therapy

Interferon (IFN) resistance is an important factor in the pathophysiology of neoplastic disorders, certain viral infections (e.g., AIDS), and autoimmune diseases (e.g., lupus erythematosus and Wegner's granulomatosis). In addition, in some of these disorders, there is also decreased ability to produce IFNs. The capacity of viruses and neoplastic processes to interfere with the IFN system are thought to represent a “virus-against-host” or “cancer-against-host” defense mechanism. Four resistance factors have been identified: 1) release of free IFN-α/β type 1 receptors into the circulation that, at appropriate concentrations, capture and inactivate IFNs; 2) a new IFN inhibitory protein has been isolated and its chemical structure is under study; 3) prostaglandin E2, which is produced by certain tumor cells, inhibits IFN production; and 4) high levels of cAMP phosphodiesterases present, for example in certain tumor cells, reduces cAMP, an important second messenger in IFN synthesis. Studies are under way to reverse these inhibitory effects and to increase endogenous interferon production.

Interleukin-6 and interleukin-6 receptor secretion by chronic lymphatic leukaemia and normal B lymphocytes: effect of PMA and PWM

Interleukin-6 (IL-6) and soluble interleukin-6 receptor (sIL-6R) were detected in supernatants of cultures of B chronic lymphatic leukaemia (CLL) lymphocytes. Phorbol-12-myristate 13 acetate (PMA) caused a decrease in the levels of IL-6 in 14 out of 16 cultures and an increase in levels of sIL6R in all 15 cases. The effect of pokeweed mitogen (PWM) was variable and not significant. The levels of IL-6 were below the detection limit (60 pg/ml) in sera of 13 CLL patients whereas sIL-6R was detected (13 ng/ml to 97 ng/ml) in the 13 sera. IL6 was not detected in cultures of unstimulated or stimulated with PMA or PWM normal human B cells. Levels of sIL-6R were minimal in cultures of normal B lymphocytes and were increased in PMA stimulated cultures. The results are consistent with the view that B-CLL cells produce spontaneously IL-6 which could act in an autocrine fashion to cause shedding of surface IL-6R and account for the correlation found between serum levels of sIL-6R and B-CLL lymphocyte numbers. The fall in levels of IL-6 in PMA stimulated CLL cultures might express masking or degradation of IL-6 after combination with the receptor.

Test of a novel transparent floating carrier by recombinant cho cells expressing sIL6 receptor protein

We describe a carrier with some unusual properties."Cellrafts" increase yields from adherent cells in conventional static T150 flasks, by floating multilayer strips of transparent film at the oxygen-rich surface of unstirred medium. This new technique allowed microscopic inspection of cell growth inside the carriers during bulk culture. Individual carriers could be picked out for subculture of selected colonies. A novel surface treatment by hypochlorite/uv allowed recycling of used carriers. Cellrafts' open-deck structure facilitated trypsinization with90% release as viable single cells from bulk carriers. Macro size (10mm by 1 mm) enables retention in flask by a coarse sieve insert in its neck, facilitating separation of product cells or media. Residual cells in carriers regenerated repeated harvests without need for reseeding. Carriers were tested with shear-sensitive CHO clones expressing soluble human IL6 receptor (sIL6R). Control was monolayer bulk culture on trays. Floating multilayer cultures remained viable longer than monolayers, had higher cellular activity of protein expression, and were less serum dependent (resembling cells on porous carriers). Purity and anti-sIL6R binding were identical to control product. Cellrafts were also tested in a small spinner vessel, but for litre batches this proved less convenient than in T-flasks. Though yields are low compared to well established porous carrier technology (spinner or packed bed) static transparent carriers might provide transitional scaleup from normal cytogenetics laboratory culture.

The tale of soluble receptors and binding proteins: from bench to bedside

Our approach of isolating proteins from a rich source of human proteins by ligand-affinity-chromatography enabled rapid and efficient isolation of not only soluble receptors corresponding to cell-associated receptors, but also independent binding-proteins and associated enzymes. No other approach would yield the latter. During the early 80's we prepared the tools and the infrastructure that enabled the subsequent 20 years of achievements. Thus we described eight soluble receptors (R) and binding proteins (BP) for various cytokines including the IL-6R, IFN-gammaR, TNFRI, TNFRII, LDLR, IFN-alpha/betaR, IL-18BP and IL-32BP identified as Proteinase 3. The isolation of the soluble IFN-alpha/beta receptor led to the cloning of its long sought cell surface ligand binding counterpart. We have established the concept that soluble receptors and binding proteins are normal constituents of body fluids in healthy individuals and that the levels of these biomarkers are modulated in various pathological situations. Each of these proteins contributed to basic science, one of them serves as a basis for therapy and some others are in various stages of clinical development.

High circulating levels of biologically inactive IL-6/SIL-6 receptor complexes in systemic juvenile idiopathic arthritis: evidence for serum factors interfering with the binding to gp130

We previously demonstrated that high levels of IL-6/sIL-6R complexes are present in sera of patients with systemic juvenile idiopathic arthritis (s-JIA) and that the amount of IL-6 estimated in the IL-6/sIL-6R complexes is markedly higher than that measured by the B9 assay. Here, we show that two additional bioassays, employing human myeloma XG-1 cells and human hepatoma Hep3B cells, detected serum IL-6 levels similar to those measured by the B9 assay and approximately 10-fold lower than the IL-6 levels estimated to be present in the IL-6/sIL-6R complex. Using an assay for the measurement of the amount of circulating IL-6 complexed with the sIL-6R and available for binding to gp130 (gp130 binding activity), we show that the IL-6/gp130 binding activity is similar to that detected by the bioassays and again significantly lower than that estimated to be present in the IL-6/sIL-6R complex. Addition of recombinant human IL-6 (rhIL-6) to sera of patients or controls results in a markedly lower increase in the gp130 binding activity in patients than in controls. Moreover, sera from s-JIA patients inhibited in a dose dependent manner the gp130 binding activity assay. These results show that sera from patients with s-JIA contain a factor, or factors, that inhibit(s) the binding of the IL-6/sIL-6R complex to gp130. This inhibitory activity does not appear to be due to soluble gp130, C-reactive protein or autoantibodies to IL-6.

Characterization of the heparin-binding properties of IL-6

We establish, using an ELISA approach, that recombinant human and murine IL-6 bind to an immobilized heparin-BSA complex. In the case of human IL-6, this binding is displaceable by soluble heparin, IC(50) approximately 2 microg/ml, corresponding to approximately 200 nM. This binding is specific because chondroitin sulfates B and C fail to compete, whereas chondroitin sulfate A and several heparan sulfates are weak inhibitors. Of a range of chemically modified heparins examined, the strongest competitor was the 2-O:-desulfated product, but even this showed a considerably reduced IC(50) ( approximately 30 microg/ml). The epitopes of five IL-6-specific mAbs were still accessible in heparin-bound IL-6, and the dimer formed from the association of rIL-6 with its truncated soluble receptor polypeptide, srIL-6alpha, still bound to heparin. Further analysis showed that heparin competed partially and weakly with the binding of srIL-6 to IL-6; however, it competed strongly for the binding of the rIL-6/srIL-6Ralpha dimer, to soluble glycoprotein 130. In studies of the proliferation of IL-6-sensitive Ba/F3 cells expressing glycoprotein 130, we were unable to detect any effect of either the removal of cell surface heparan sulfate, or addition of soluble heparin. By contrast, heparin was able to protect IL-6 from digestion by the bacterial endoproteinase Lys-C. Overall, our findings show that IL-6 is a heparin-binding cytokine. This interaction will tend to retain IL-6 close to its sites of secretion in the tissues by binding to heparin-like glycosaminoglycans, thus favoring a paracrine mode of activity. Moreover, this binding may serve to protect the IL-6 from proteolytic degradation.

Subcutaneous administration of recombinant glycosylated interleukin 6 in patients with cancer: pharmacokinetics, pharmacodynamics and immunomodulatory effects

This is the first report of the serum profile of a glycosylated recombinant form of human IL-6 (rhIL-6) administered subcutaneously (1-10 microg/kg/day) in a phase I/II trial as a thrombopoietic agent in patients with advanced cancer. The pharmacodynamic effects of IL-6 were also examined. Detailed pharmacokinetic measurements were made in four patients. Peak concentrations at 5-8 h and a median t0.5 of ca. 5 h were similar to those previously reported for non-glycosylated IL-6. However, higher peak concentrations and apparent differences in effective dose levels to those previously reported with the non-glycosylated form were seen. Indications of an apparent attenuation in circulating IL-6 concentrations with continuing injections were seen in eight of 10 patients examined but anti-IL-6 antibody generation was seen in only two patients. Soluble interleukin 6 receptor concentrations generally decreased. No major changes in T cell subsets were seen but expression of CD25 and CD54 by T lymphocytes significantly increased, accompanied by marked increases in soluble CD25 (sIL-2R) and CD54 (sICAM-1). No consistent change in B cells, monocytes or NK cells were seen. No evidence for induction of TNF-alpha was found. This study demonstrates similar biological effects of glycosylated rhIL-6 to those reported for the non-glycosylated form but illustrates several apparent differences which are discussed further.

Decreased soluble interleukin-6 receptor in patients with acute myocardial infarction

BACKGROUND

The plasma level of interleukin-6 (IL-6), a proinflammatory cytokine, has been reported to be elevated in patients with acute myocardial infarction (AMI). In addition to a specific cell-surface IL-6 receptor, a soluble IL-6 receptor (sIL-6R) exists in plasma as an extracellular domain of glycoprotein 80. The pathophysiologic roles of IL-6 and sIL-6R in AMI are still unknown.

METHODS AND RESULTS

We measured plasma levels of IL-6 and sIL-6R in 17 patients with AMI to evaluate changes over time at 11 points in the acute phase and compared them with parameters of inflammation, myocardial injury, and atherosclerosis. IL-6 showed a triphasic increase with peaks at 3 hours (276.2 +/- 50.0 pg/mL), 2 days (153.6 +/- 35.7 pg/mL), and 5 days (180.7 +/- 52.3 pg/mL) after the onset of AMI. sIL-6R had biphasic dips at 12 hours (31.1 +/- 4.1 ng/mL) and 3 days (29.9 +/- 1.5 ng/mL) after the onset on AMI. The time-dependent changes in IL-6 paralleled those in sIL-6R from onset to 5 days. Thereafter, the changes in IL-6 and sIL-6R varied; that is, IL-6 gradually decreased from 5 days to 4 weeks, whereas sIL-6R gradually increased from 5 days to 4 weeks. Significant positive correlations were observed between the absolute increase in IL-6 and the decrease in sIL-6R and the changes in white blood cell count, erythrocyte sedimentation rate, C-reactive protein, creatine kinase, and lactic dehydrogenase. Neither IL-6 nor sIL-6R strongly correlated with parameters of coronary atherosclerosis.

CONCLUSIONS

These results demonstrate that IL-6 and sIL-6R are associated with the processes of inflammation and myocardial injury during the acute phase of AMI.

The Soluble Interleukin-6 (IL-6) Receptor/IL-6 Fusion Protein Enhances In Vitro Maintenance and Proliferation of Human CD34+CD38−/low Cells Capable of Repopulating Severe Combined Immunodeficiency Mice

In vitro maintenance and proliferation of human hematopoietic stem cells is crucial for many clinical applications. Early hematopoietic cells express low levels of FLT-3 and c-kit receptors, as well as the interleukin-6 (IL-6) receptor signal transducing element, gp130, but do not express IL-6 receptor itself. Therefore, we have attempted to maintain human cord blood or bone marrow CD34+ cells ex vivo in serum-free cultures containing stem cell factor (SCF) and FLT-3 ligand (FL) alone or together with a new recombinant molecule of soluble IL-6 receptor fused to IL-6 (IL6RIL6 chimera). The effect of IL6RIL6 chimera on the proliferation and differentiation of CD34+ cells was compared with that of each chimera component added separately. The engraftment potential of in vitro-cultured cells was determined using our recently established functional in vivo assay for primitive human severe combined immunodeficiency (SCID)-repopulating cells (SRC). We report here that IL6RIL6 chimera induced significantly higher levels of progenitors and SRC compared with SCF + FL alone or together with IL-6 and soluble IL-6 receptor. IL6RIL6 chimera prolonged in vitro maintenance of SRC for up to 14 days. Stimulation of CD34+CD38−/low enriched cells with IL6RIL6 chimera maintained the early CD34+CD38−/lowcell subpopulation, which could be detected in vitro for up to 14 days. Moreover, IL6RIL6 chimera preferentially stimulated the growth of early CD34+38−/low cells, resulting in significantly higher levels of progenitors compared with more mature CD34+38+ cells. Taken together, these findings demonstrate the importance of IL6RIL6 chimera in stimulating the proliferation of early CD34+· CD38−gp130+IL-6R−cells in vitro and extended maintenance of progenitors and SRC.

C-reactive protein: a physiological activator of interleukin 6 receptor shedding

The soluble interleukin 6 receptor (sIL-6R) circulates at elevated levels in various diseases. This suggests that inflammatory mediators control sIL-6R release. Through examination of human neutrophils, it was found that the acute phase reactant C-reactive protein (CRP) activates a threefold increase in sIL-6R production. Maximal release occurred after 30-60 min exposure to CRP (50 micrograms/ml), and was mimicked by peptides corresponding to amino acid residues 174- 185 and 201-206 of native CRP. A third peptide fragment (77-82) had no effect. Differential mRNA splicing did not account for the CRP-mediated release of sIL-6R, since this isoform was not detected in conditioned media. Furthermore, stimulation of neutrophils with CRP or with peptides 174-185 or 201-206 promoted a loss of membrane-bound IL-6R, suggesting release by proteolytic shedding. The metalloprotease inhibitor TAPI had only a marginal effect on CRP-mediated sIL-6R release, suggesting that shedding occurs via a mechanism distinct from that previously reported. It well established that IL-6 stimulates the acute phase expression of CRP. Our current findings demonstrate a novel relationship between these two mediators, since CRP may affect IL-6-mediated inflammatory events by enabling formation of the sIL-6R/IL-6 complex.

Shedding of the soluble IL-6 receptor is triggered by Ca2+ mobilization, while basal release is predominantly the product of differential mRNA splicing in THP-1 cells

The soluble IL-6 receptor (sIL-6R) is generated through either proteolytic shedding of the cognate receptor (PC-sIL-6R), or released as the product of differential mRNA splicing (DS-sIL-6R). Using monocytic THP-1 cells, we demonstrate that both mechanisms are independently regulated, and that each process contributes to sIL-6R production. Shedding of the IL-6R was activated by the Ca2+ ionophore, ionomycin, and inhibited by the TNF-alpha protease inhibitor (TAPI). In contrast, basal sIL-6R release was unaffected by Ca2+ depletion and largely insensitive to TAPI. Moreover, although IL-6R shedding was inactivated by serum starvation, non-stimulated production remained intact. Basal sIL-6R production via differential mRNA splicing was shown through the inhibitory action of brefeldin A and an enzyme-linked immunosorbent assay specific for DS-sIL-6R. Release of this isoform was unaffected by ionomycin or TAPI, indicating that Ca2+ mobilization activates PC-sIL-6R generation, but not DS-sIL-6R. The divergent control of these sIL-6R isoforms indicates that they may independently influence the inflammatory response.

Analysis of the mechanism of action of anti-human interleukin-6 and anti-human interleukin-6 receptor-neutralising monoclonal antibodies

Anti-human interleukin-6 (human IL-6) and anti-human IL-6 receptor (IL-6R)-neutralising monoclonal antibodies (mAbs) are among the most promising human IL-6-specific inhibitors and have been shown to exert short-term beneficial effects in clinical trials. Simultaneous treatment with different anti-human IL-6 or anti-human IL-6R mAbs was recently suggested to be a potent way to inhibit the action of the cytokine in vivo. Although some of these mAbs are already used, their mechanisms of action and the location of their epitopes on the surface of human IL-6 and human IL-6R are still unknown. Here, we analysed the capacity of several anti-human IL-6 and anti-human IL-6R mAbs to inhibit the interaction between human IL-6, human IL-6R, and human glycoprotein 130 (gp130). We mapped the epitopes of several of these mAbs by studying their binding to human IL-6 and human IL-6R mutant proteins. Our results show that several anti-human IL-6 and anti-human IL-6R-neutralising mAbs block the binding between human IL-6 and human IL-6R, whereas others block the binding to gp130. We provide evidence that some of the latter mAbs inhibit interaction with gp130beta1, whereas others interfere with the binding to gp130beta2. Our results suggest that residues included in the C'D' loop of human IL-6R interact with gp130beta2.

Interleukin-6: structure-function relationships

Interleukin-6 (IL-6) is a multifunctional cytokine that plays a central role in host defense due to its wide range of immune and hematopoietic activities and its potent ability to induce the acute phase response. Overexpression of IL-6 has been implicated in the pathology of a number of diseases including multiple myeloma, rheumatoid arthritis, Castleman's disease, psoriasis, and post-menopausal osteoporosis. Hence, selective antagonists of IL-6 action may offer therapeutic benefits. IL-6 is a member of the family of cytokines that includes interleukin-11, leukemia inhibitory factor, oncostatin M, cardiotrophin-1, and ciliary neurotrophic factor. Like the other members of this family, IL-6 induces growth or differentiation via a receptor-system that involves a specific receptor and the use of a shared signaling subunit, gp130. Identification of the regions of IL-6 that are involved in the interactions with the IL-6 receptor, and gp130 is an important first step in the rational manipulation of the effects of this cytokine for therapeutic benefit. In this review, we focus on the sites on IL-6 which interact with its low-affinity specific receptor, the IL-6 receptor, and the high-affinity converter gp130. A tentative model for the IL-6 hexameric receptor ligand complex is presented and discussed with respect to the mechanism of action of the other members of the IL-6 family of cytokines.

Analysis of the Human Interleukin-6/Human Interleukin-6 Receptor Binding Interface at the Amino Acid Level: Proposed Mechanism of Interaction

The interaction between interleukin-6 (IL-6) and IL-6 receptor (IL-6R) is the initial and most specific step in the IL-6 signaling pathway. Understanding its mechanism at the amino acid level is the basis for developing small IL-6–inhibiting molecules. We studied the human IL-6 (hIL-6)/hIL-6R binding interface by a combination of molecular modelling and site-directed mutagenesis. Our model suggests that the center of the interface between the two molecules consists of hydrophobic contacts predicted to account for most of the binding-free energy. These contacts can be regarded as a hydrophobic core shielded by hydrophilic residues that are also needed for recognition. Following this hypothesis, we altered in hIL-6 and hIL-6R residues predicted to reside in the contact region and to interact with each other. We studied the capacity of these mutants to form an IL-6/IL-6R complex and their ability to transduce the signal. This combined approach has led to the identification of certain residue-clusters in the binding interface and to a rational explanation of their specific interactions, suggesting therein a likely mechanism of complex formation. The results confirm the predictive model and strongly support our hypothesis. Comparison with other cytokines and their α-subunit receptors suggests that the structural location of certain binding sites are conserved.

Identification of a novel antigenic structure of the human receptor for interleukin-6 involved in the interaction with the glycoprotein 130 chain

The receptor for interleukin-6 (IL-6) is characterized by a ligand-binding glycoprotein 80 (gp80) transmembrane chain (IL-6R) which associates with a signal-transducer gp130 chain. We previously raised a series of monoclonal antibodies (mAb) recognizing different epitopes of the human IL-6R and interfering with the function of the receptor. One of them, M182, was able to diminish the proliferation of IL-6-dependent plasmacytoma cell lines although it was found unable to inhibit the binding of IL-6 to its receptor. Using an enzyme-linked immunosorbent assay for measuring the binding of IL-6 IL-6R to the gp130 chain, we showed that M182 was directed against a structure directly involved in the IL-6R gp130 interaction. M182 was able to potentiate the inhibitor effect of anti-IL-6R mAB which interfere with the binding of IL-6, leading to complete inhibition of the proliferation of IL-6-dependent cell lines. M182 was also found to synergize with inhibitory anti-IL-6 mAb. Therefore this structure appears to be an important regulatory domain of the IL-6R and a valuable target for inhibiting IL-6 signalling.

Proinflammatory cytokines and their corresponding receptor proteins in eccrine sweat glands in normal and cutaneous leishmaniasis human skin. An immunohistochemical study

Paraformaldehyde-fixed biopsy specimens of normal and chronic cutaneous leishmaniasis human skin were investigated for the presence and cellular distribution of interleukin-1 alpha, interleukin-1 beta, interleukin-6 and tumour necrosis factor-alpha and the corresponding receptors in eccrine sweat glands, using an indirect immunoperoxidase technique. There was cytoplasmic staining for all 4 cytokines as well as their receptor proteins in the clear cells of the eccrine sweat glands of both normal and inflamed skin specimens. No staining could be seen in the dark cells or the myoepithelial cells, neither in normal nor in inflamed skin. However, a difference between normal and inflamed skin was observed in the ductal system. Thus, cell layers of the dermal ducts in leishmaniasis skin were stained for all 4 cytokines, with more intense labelling in the basal cell layer of the coiled ducts, while in the normal skin, an intense staining was more evident in the inner luminal layer, with variable and less intense labelling of the basal layer. The immunolabelling for the cytokine receptors within the dermal ducts exhibited similar staining intensity in both luminal and basal cell layers, except in the case of the IL-6 receptor, which showed a moderate to intense signal in the basal cell layer but a weak staining of the luminal cell layer. Infiltrating inflammatory cells around the sweat gland apparatus in leishmaniasis skin exhibited immunoreactivities for all cytokines and their corresponding receptors.

Soluble interleukin-6 receptors in hematology patients undergoing bone marrow transplantation

Soluble interleukin-6 receptor (sIL-6R) has previously been shown to potentiate the activity of interleukin (IL)-6, which may display antitumor activity. We evaluated sIL-6R and IL-6 levels in the sera of 24 patients following transplantation (allogeneic, n=17; autologous, n=7). Five patients developed acute graft-versus-host disease (AGVHD), three had early graft rejection, and three had an early relapse following bone marrow transplantation (BMT). Soluble IL-6R levels were evaluated at day - 10, day 0, day of engraftment, and during BMT-related complications, using IL-6R-specific monoclonal antibodies (mAb) and double-sandwich ELISA. In normal controls, sIL-6R and IL-6 levels were 20+/-3 ng/ml and 0.01+/-0.005 ng/ml, respectively. Soluble IL-6R levels increased in direct correlation with engraftment in the uneventful allogeneic transplants (17.7+/-2.1 ng/ml at day 0 to 49.7+/-2.6 ng/ml at day of engraftment, n=6, P<0.05) as well as in the autologous transplants (26.8+/-2.82 at day 0 to 66.4+/-12.9 at day of engraftment, n=5, P=0.01). In contrast, IL-6 levels declined with time during the conditioning period and showed only a modest elevation following BMT. Increased levels of sIL-6R and IL-6 were found in the patients who developed AGVHD (23.8+/-4.2 and 0+/-0 ng/ml at day 0 to 79+/-6.9 and 0.26+/-0.04 ng/ml, respectively, at time of AGVHD, n=5, P=0.01). No correlation was found between the severity of AGVHD and sIL-6R levels. In the three patients with early relapse, sIL-6R levels increased from 30+/-0 ng/ml at day 0 to 90 ng/ml (P=0.05) and IL-6 levels increased from 0 to 0.16+/-0 ng/ml, respectively. The mean elevation of sIL-6R in the patients with early relapse and AGVHD was significantly higher than the mean elevation in the patients with the relatively smooth engraftment (P<0.05). Contrary to these findings, in the three patients with graft rejection, sIL-6R levels decreased while IL-6 was found to be elevated. Basic disease, conditioning regimen, type of transplant, GVHD propylaxis, and T cell depletion had no effect on sIL-6R or IL-6 levels. In summary, sIL-6R levels positively correlated with engraftment. Both sIL-6R and IL-6 levels were found to be significantly elevated in patients who developed AGVHD or early relapse following BMT. Therefore, the sIL-6R level may be used as a tool for assessing engraftment and transplant-related complications following BMT.

Cutaneous CD56+ large T-cell lymphoma associated with high serum concentration of IL-2

We report the case of a patient with a clinically aggressive large cell lymphoma (LCL) which expressed several T-lymphocyte markers and, in addition, CD56 and, to a lesser degree, CD68 antigens. A marked increase in serum concentration of interleukin (IL)-2 was found (490 and 167 pg/0.1 mL in two serum samples collected 6 months apart). This increase in IL-2 appeared unique to this lymphoma because serum concentration of IL-2 was not increased in any of the cases of various types of cutaneous lymphoproliferative disorders tested: mycosis fungoides-related cutaneous T-cell lymphoma (CTCL: 28 patients), granulomatous slack-skin syndrome (GS-SS: 1 patient), anaplastic large cell lymphoma (ALCL: 2 patients), subcutaneous gamma/delta T-cell lymphoma (gamma/delta-TCL: 1 patient), adult-type leukemia/lymphoma (ATLL: 1 patient), and lymphomatoid papulosis (LyP: 4 patients). Furthermore, the increase in IL-2 serum concentration appeared selective in this CD56+ large-cell lymphoma-bearing patient, because concentration of none of the five other cytokines tested (IL-4, IL-6, IFNgamma, GM-CSF, and TNFalpha) was increased. In contrast, soluble receptors for IL-2 and two of the other cytokines (IL-6, and TNFalpha) were markedly increased not only in this patient, but also in most patients with the other cutaneous lymphoproliferative disorders that we examined except for lymphomatoid papulosis. These data indicate that increased IL-2 serum concentration may help to diagnose a unique type of cutaneous CD56(+) large (T-) cell lymphoma and suggest that IL-2 way play a role of an autocrine growth factor for this lymphoma.

Participation of two Ser-Ser-Phe-Tyr repeats in interleukin-6 (IL-6)-binding sites of the human IL-6 receptor

The alpha-subunit of interleukin-6 (IL-6) receptor is a member of the hematopoietin receptor family. The alignment of its amino acid sequence with those of other members of this family (human somatotropin receptor/murine IL-3 receptor beta and human IL-2 receptor beta) has suggested that amino acids included in two SSFY repeats found in each of its hematopoietin receptor domains, contribute to the binding of the ligand. The involvement of these amino acids in IL-6 binding and signal transduction was studied by site-directed mutagenesis and molecular modelling. We present a computer-derived three-dimensional model of the IL-6/IL-6 receptor complex based on the structure of the human somatotropin/human somatotropin receptor complex. This model allowed the location of distinct regions important for IL-6 and gp130 binding. We show that some of the residues included in the SSFY repeats located in our IL-6 receptor model in the loops between beta-strands E and F of domain-I and B' and C', of domain-II, participate in the formation of a major IL-6-binding site. These residues are necessary for IL-6 and gp130 binding and for signal transduction. Using our IL-6 receptor mutants we mapped the epitopes of our anti-(IL-6 receptor) neutralising monoclonal antibodies to these residues. Our results demonstrate that a generic hematopoietin receptor family structural module can be used for the study of both alpha and beta receptor subunits belonging to this family.

Differential interleukin-6 (IL-6) responses of three established myeloma cell lines in the presence of soluble human IL-6 receptors

We investigated the possible influence of recombinant (r) sIL-6R on the growth of three IL-6 non-responsive or weakly IL-6 responsive long-term myeloma cell lines. The three cell lines chosen for the study (U266, L363 and Fravel) all expressed gp130 but differed in their expression of IL-6R and IL-6. mRNA analysis by northern blot and reverse transcriptase polymerase reaction showed that the cell line U266 was the only one that expressed IL-6 mRNA. Only U266 and L363 expressed IL-6R mRNA. 125I-rIL-6 binding studies and FACS analysis, using biotinylated IL-6 and antibodies directed against the IL-6R and gp130, showed corresponding results on the protein level. Addition of rsIL-6R resulted in induction of IL-6 responsiveness in L363 cells, whereas the 3H-thymidine incorporation of the cell lines U266 and Fravel was unaffected by rsIL-6R addition. In conclusion, the IL-6 unresponsive growth of several long-term myeloma cell lines in vitro can in some, but not all cases, be due to a deficiency in exogenous sIL-6R.

T cell hyperreactivity to IL-6 in chronic nonviremic HBV carriers despite normal IL-6 receptor or gp130 expression

We previously showed that T cells from chronic nonviremic HBsAg carriers activated with immobilized OKT3 MAb are hyperreactive to monocyte accessory signals, mainly to interleukin-6 (IL-6). We have further characterized this T cell hyperreactivity using phytohemagglutinin (PHA) as the primary activating signal. PHA-stimulated T cells from nonviremic patients had a significantly higher response to addition of monocytes, monocyte supernatants, and IL-6 alone or combined with IL-1 beta when compared to controls. We examined if these effects could be mediated by a differential expression of IL-6 receptor (p80) or gp130 on resting or PHA-stimulated T cells. We found that PHA, IL-6, IL-1 beta, or IL-2 induced only small changes of the dull p80 expression on T cells. In contrast, we found a significant increase of gp130 expression on PHA-activated T cells compared to unstimulated T cells, which was down-regulated by the presence of IL-6. However, no significant differences in p80 or gp130 expression were detected between patients and controls within all the culture conditions tested. Our results confirm that IL-6 is involved in the in vitro T cell hyperreactivity of nonviremic HBV carriers and indicate that this effect is not mediated by disturbances of IL-6 receptor expression.

Biological aspects of multiple myeloma

Although considerable progress has been made towards understanding many aspects of myeloma, the myeloma stem cell and the factors that drive the disease remain elusive. Recent developments in the molecular analysis of clonality have helped to confirm the presence of pre-switch B cells that are of the same clone as the myeloma plasma cells. The role of these cells in myelomagenesis has not been demonstrated, and the isotypic heterogeneity of the clonally-relevant cells suggests that the pre-switch B cells are pre-malignant progenitors of the tumour cells. Thus, the circulating clonal B cells appear to be the earliest progenitors of the mature, monoclonal plasma cells. IL-6, and possibly other cytokines, are involved in driving this process. The role of IL-6 in myeloma is complex and more involved than its proposed growth factor function. In the absence of IL-6, dependent cells become apoptotic. Increased IL-6 signalling also leads to apoptosis of myeloma cells, possibly as a result of terminal differentiation. In the presence of exogenous IL-6, the IL-6 receptor appears to be the rate-limiting factor in the pathway's activity. IL-6 may regulate the survival of myeloma cells by stimulating c-myc transcription, possibly from the P0 promoter. The high levels of c-myc transcripts and protein could regulate myeloma cell proliferation and apoptotic death by controlling p53 expression and, through it, the expression of the Rb and BAX genes. Proliferative signalling in myeloma cells is likely to be intrinsic, within the tumour cell compartment. Molecules such as CD28 and B7, both expressed by less mature myeloma cells, could represent one such self-self stimulatory mechanism, with IL-6, possibly through stimulation of c-myc expression, providing the signals for survival and differentiation.

Soluble interleukin-6 receptor strongly increases the production of acute-phase protein by hepatoma cells but exerts minimal changes on human primary hepatocytes

Interleukin-6 (IL-6) interacts with a system of receptors, which include a 80-kDa IL-6-binding subunit (IL-6R) and a transducing element (gp130). The soluble form of IL-6R (sIL-6R) can bind its ligand and induce cellular responses by association with gp130, thus acting as an IL-6 agonist. We and others have previously shown that the responsiveness to IL-6 is different in hepatoma and human primary hepatocytes. We therefore compared the effects of sIL-6R on the two types of cells, and on the B9 hybridoma, another IL-6-sensitive cell line. Human primary hepatocytes, hepatoma cells PLC/PRF/5, and B9 cells were incubated with different concentrations of IL-6, sIL-6-R, or both. The hepatocyte culture supernatants were tested for their content of acute-phase proteins (APP). The proliferation of B9 cells was assessed by a colorimetric method. Results showed that sIL-6R alone markedly increased the production of APP by hepatoma cells in a dose-dependent manner, but affects only minimally primary hepatocytes and the proliferation of B9 cells. The combinations of IL-6R and its ligand enhanced the effects of Il-6 alone in both PLC/PRF/5 and B9 cells, but had no effect on primary hepatocytes. An immunohistochemical study indicated that the cell-surface expression of IL-6R was dramatically lower in hepatoma cells than in primary hepatocytes. In conclusion, our results show that the expression of IL-6R is low in the hepatoma cell PLC/PRF/5 when compared with primary hepatocytes and that this difference can, at least partly, explain their deficient responsiveness to IL-6. On the other hand, it appears that IL-6R expression by primary hepatocytes is sufficient and that circulating sIL-6R is unlikely to play a significant role in the modulation of IL6 effects.

Soluble tumor necrosis factor receptors and soluble interleukin-6 receptor in fetal and maternal sera, coelomic and amniotic fluids in normal and pre-eclamptic pregnancies

The aim of this study was (a) to measure soluble tumor necrosis factor receptors (sTNF-Rs) and soluble interleukin-6 receptor (sIL-6-R) in coelomic and amniotic fluids, cord and maternal sera in pregnancy and labor, (b) to examine whether the changes in concentrations of biologically active TNF and IL-6 are related to changes in their soluble receptors, and (c) to determine if levels of soluble receptors in pre-eclamptic disorders differ from normal pregnancies at delivery. Materials collected from 206 women during pregnancy and at delivery were analyzed for soluble receptors by enzyme-linked immunosorbent assay (ELISA). All receptors were present in higher concentrations in coelomic than in the corresponding amniotic fluid. Concentrations increased in amniotic fluid from first to second trimester. The level of sIL-6-R then remained unchanged to term, but there was a decrease in the sTNF-Rs which might account for the simultaneous appearance of bioactive TNF. Labor did not affect the concentration of any receptor in amniotic fluid. In maternal serum, sTNF-Rs increased with gestational age and labor in parallel with IL-6. The origin and physiological importance of these soluble receptors are still unknown. In pre-eclamptic disorders p55 sTNF-R was elevated in maternal serum before initiation of labor compared to normal pregnancy.

Serum soluble interleukin 6 (IL-6) receptor and IL-6/soluble IL-6 receptor complex in systemic juvenile rheumatoid arthritis

By using a sandwich ELISA, soluble human IL-6 receptor (sIL-6 R) levels were measured in the sera of 20 healthy children and of 25 patients with systemic juvenile rheumatoid arthritis (JRA). In patients with systemic JRA, serum sIL-6 R levels (114.6 +/- 37.7 ng/ml) were significantly lower (P < 0.01) than those of healthy children (161.2 +/- 45.5 ng/ml). Serum sIL-6 R levels were negatively correlated (r = -0.610, P < 0.001) with serum IL-6 levels measured with the B9 cells. The serum IL-6/sIL-6 R complex was detected using an ELISA based on a monoclonal antibody to IL-6 for capture and on a monoclonal antibody to human sIL-6 R for detection. Healthy controls had little, if any, detectable serum IL-6/sIL-6 R complex (OD 0.024 +/- 0.027), while the majority of patients with systemic JRA presented measurable serum IL-6/sIL-6 R complex (OD 0.492 +/- 0.546). IL-6 levels estimated in the circulating IL-6/sIL-6 R complexes were in the range of nanograms per milliliter and approximately 20-fold higher than those measured by the B9 cells. Since serum C-reactive protein concentrations were much more correlated with serum levels of IL-6/sIL-6 R complexes (r = 0.713, r2 = 0.51, P < 0.0001) than with the serum IL-6 levels measured with the B9 cells (r = 0.435, r2 = 0.19, P = 0.05), the large quantities of serum IL-6 present in IL-6/sIL-6 R complexes appear to be biologically relevant in vivo, at least as far as the induction by IL-6 of acute phase protein production.

Immunoassay for functional human soluble interleukin-6 receptor in plasma based on ligand/receptor interactions

Soluble forms of most cytokine receptors, able to bind effectively to their respective ligands, have now been described. A soluble interleukin-6-binding molecule derived from the gp80 component of the multichain IL-6 receptor can be detected in biological fluids, and can act as an agonist of IL-6 activity. The clinical significance of the soluble receptor levels still remains to be explored. We took advantage of the characterization of an anti-IL-6 monoclonal antibody and of an anti-IL-6R monoclonal antibody that both bound to IL-6/IL-6R complexes to design an immunometric assay for the measurement of soluble IL-6R complexed to IL-6. This reaction scheme was designated as ELIA (enzyme-ligand immunoassay). When exogeneous IL-6 was added in excess to an sIL-6R containing sample, all sIL-6R was present in a complexed form. Thus, the reaction scheme could also be used to determine total sIL-6R concentrations. A recombinant sIL-6R standard was prepared from the supernatant of murine thymoma cells transfected with a gene coding for an extracellular portion of the IL-6 receptor. The assay permitted the precise and reproducible measurement of sIL-6R in serum or plasma. This approach is of general relevance for the determination of soluble cytokine receptors in biological fluids, provided that adequate anti-cytokine and anti-receptor antibodies are available.

A monoclonal anti-human IL-6 receptor antibody inhibits the proliferation of human myeloma cells

A monoclonal antibody (UV4) against the human IL-6 receptor (hIL-6R) was generated by immunizing BALB/c mice with both a human myeloma cell line (U266) and a murine cell line (M12.4/R) transfected with the hIL-6R cDNA. Flow cytometric analysis demonstrated that UV 4 stains the hIL-6R+ cell lines U266 and U937, but not the hIL-6R- cell lines Daudi and K562. Competitive inhibition assays demonstrated that preincubation of U266 cells with UV4 inhibited the binding of a phycoerythrin (PE)-IL-6 conjugate to the hIL-6R and also inhibited the proliferative activity of IL-6 on the IL-6-dependent human myeloma cell lines ILKM2 and ILKM3. In contrast, UV4 did not interfere with the proliferation of the hIL-6R- Burkitt's lymphoma cell line, Daudi. Direct sandwich radioimmunoassays further confirmed that the UV4 bound to the same molecule as the goat anti-hIL-6R antibody. These results suggest that both UV4 and human IL-6 bind to the same or adjacent epitopes on the hIL-6R. This monoclonal antibody should facilitate studies of the structure-function relationship of IL-6R and may be useful for the treatment of IL-6-dependent diseases such as multiple myeloma.

Increased and highly stable levels of functional soluble interleukin-6 receptor in sera of patients with monoclonal gammopathy

Soluble human interleukin-6 receptor (sIL-6R) was measured in the serum of 30 healthy individuals, 32 individuals with monoclonal gammopathy of undetermined significance (MGUS), 20 patients with early multiple myeloma (MM) and 54 patients with overt MM. The serum activity recognized by an immunoradiometric assay was determined to be sIL-6R, because of its binding capacity to IL-6 and its molecular mass of 55 kDa. All sera of healthy individuals contained sIL-6R (mean value: 89 ng/ml, range 17-300 ng/ml). Serum sIL-6R levels were increased by 51% in patients with MGUS (mean value: 135 ng/ml, p < 0.005), by 44% in patients with early myeloma (mean value: 128 ng/ml, p < 0.001) and by 116% in patients with overt MM (mean value: 193 ng/ml, p < 0.001). In patients with MM, a complete lack of correlation (p > 0.7) was found between serum sIL-6R levels and other previously recognized prognostic factors in this disease, particularly serum IL-6 levels and those factors related to tumor cell mass. The independence of serum sIL-6R levels on tumor cell mass was directly demonstrated by studying four patients with MM treated with autologous bone marrow transplantation for periods of between 320 and 760 days. These levels were found to be remarkably stable and constant, independent of whether patients relapsed or achieved complete remission. Finally, physiological concentrations of sIL-6R were found to increase by tenfold the sensitivity of human myeloma cell lines to IL-6. These observations suggest a high control of the sIL-6R level in vivo, and, possibly, an important functional role of this circulating protein in patients with monoclonal gammopathies.

Soluble interferon-alpha receptor molecules are present in body fluids

Soluble forms of the interferon-alpha receptor (sIFN-alpha R) were identified in human serum and urine by Western blotting with monoclonal antibodies (MAb) directed against IFN-alpha R, and by immunoprecipitation (Iptn) of a covalently cross-linked complex of IFN-alpha R and [125I]IFN-alpha with anti IFN-alpha MAb. Elevated levels of sIFN-alpha R were found in sera of hairy cell leukemia patients. The soluble receptor from serum migrated as a 55 kDa protein in SDS-PAGE, and, as expected, the cross-linked product migrated as a 75 kDa protein. The soluble receptor from urine was found to be a protein of mol. wt. 45 kDa and its cross-linked complex migrated as a 65 kDa protein. The calculated mol. wt. of the entire extracellular domain of the IFN-alpha R prior to post-translational modifications is 47,000. Since there are 12 potential glycosylation points in this extracellular domain, its actual mol. wt. may be as high as 70,000 Da. It is therefore concluded that sIFN-alpha R molecules, corresponding to truncated forms of the extracellular domain of the cell surface IFN-alpha R, are present in human serum and in normal human urine.

Live Borrelia burgdorferi preferentially activate interleukin-1 beta gene expression and protein synthesis over the interleukin-1 receptor antagonist

Lyme arthritis is one of the few forms of chronic arthritis in which the cause is known with certainty. Because cytokines are thought to contribute to the pathogenesis of chronic arthritis, we investigated the effect of the Lyme disease spirochete, Borrelia burgdorferi, on the gene expression and synthesis of IL-1 beta and the IL-1 receptor antagonist (IL-1ra) in human peripheral blood mononuclear cells. Live B. burgdorferi induced fivefold more IL-1 beta than IL-1 alpha and sevenfold more IL-1 beta than IL-1ra; LPS or sonicated B. burgdorferi induced similar amounts of all three cytokines. This preferential induction of IL-1 beta was most dramatic in response to a low passage, virulent preparation of B. burgdorferi vs. three high passage avirulent strains. No difference in induction of IL-1ra was seen between these strains. The marked induction of IL-1 beta was partially diminished by heat-treatment and abrogated by sonication; IL-1ra was not affected. This suggested that a membrane component(s) accounted for the preferential induction of IL-1 beta. However, recombinant outer surface protein beta induced little IL-1 beta. By 4 h after stimulation, B. burgdorferi induced sixfold more IL-1 beta protein than LPS. In contrast to LPS-induced IL-1 beta mRNA which reached maximal accumulation after 3 h, B. burgdorferi-induced IL-1 beta mRNA showed biphasic elevations at 3 and 18 h. B. burgdorferi-induced IL-1ra mRNA peaked at 12 h, whereas LPS-induced IL-1ra mRNA peaked at 9 h. IL-1 beta synthesis increased in response to increasing numbers of spirochetes, whereas IL-1ra synthesis did not. The preferential induction by B. burgdorferi of IL-1 beta over IL-1ra is an example of excess agonist over antagonist synthesis induced by a microbial pathogen, and may contribute to the destructive lesion of Lyme arthritis.

Association of recombinant soluble IL-6-signal transducer, gp130, with a complex of IL 6 and soluble IL-6 receptor, and establishment of an ELISA for soluble gp130

IL-6 mediates its pleiotropic functions through two membrane proteins, a ligand-binding molecule (IL-6 receptor, IL-6R) and a non-ligand-binding signal transducer (gp130). Starting with a previously isolated cDNA clone encoding human gp130, recombinant soluble gp130 (sgp130) lacking the transmembrane and cytoplasmic regions was expressed in COS7 cells or CHO cells. sgp130 could associate with a complex of IL-6 and soluble IL-6R (sIL-6R), also lacking transmembrane and cytoplasmic regions. This indicated that extracellular region of gp130 was responsible for the association with IL-6R which was occupied by IL-6. An enzyme-linked immunosorbent assay (ELISA) for the quantitation of sgp130 was established, which was based on the interaction of sgp130 with the complex of IL-6 and sIL-6R and could detect sgp130 as low as 1 ng/ml.