Studies on IL-1 receptors on D10S T-helper cells: demonstration of two molecularly and antigenically distinct IL-1 binding proteins

[Ischemic cardiopathy: inflammation markers and the cardiovascular risk]

In recent years it has been established that inflammation is a key mechanism in the pathogenesis of atherosclerosis and in coronary artery disease progression. Inflammation is a host response to a wide variety of tissue injuries. A persistent or continually repeated insult will lead to chronic inflammation which may result in tissue destruction and/or loss of normal organ function. Atherosclerosis and other pathologies involving inflammation are associated with increased levels of cytokines, which in turn raise acute-phase proteins levels in blood (acute inflammation markers, i.e. fibrinogen and C-reactive protein). It has been shown recently that concentrations of these proteins are higher in individuals at increased risk of developing cardiac events in the years to come. This is true both in apparently healthy men and women and in ischaemic heart disease patients. CRP is currently the inflammatory marker which appears to have captured the investigators' attention around the globe. In this report we review the current data on the relationship between atherosclerosis and inflammation, with special attention to cytokines and acute phase reactants. The use of acute phase reactants as prognostic risk markers in ischaemic heart disease is also discussed.

Interleukin-1, interleukin-1 receptors and interleukin-1 receptor antagonist

IL-1 (IL-1 alpha or IL-1 beta) is the prototypic "multifunctional" cytokine. Unlike the lymphocyte and colony stimulating growth factors, IL-1 affects nearly every cell type, and often in concert with other cytokines or small mediator molecules. Although some lymphocyte and colony stimulating growth factors may be therapeutically useful, IL-1 is a highly inflammatory cytokine and the margin between clinical benefit and unacceptable toxicity in humans is exceedingly narrow. In contrast, agents that reduce the production and/or activity of IL-1 are likely to have an impact on clinical medicine. In support of this concept, there is growing evidence that the production and activity of IL-1, particularly IL-1 beta, are tightly regulated events as if nature has placed specific "road blocks" to reduce the response to IL-1 during disease. In addition to controlling gene expression, synthesis and secretion, this regulation extends to surface receptors, soluble receptors and a receptor antagonist. Investigators have studied how production of the different members of the IL-1 family is controlled, the various biological activities of IL-1, the distinct and various functions of the IL-1 receptor (IL-1R) family and the complexity of intracellular signaling. Mice deficient in IL-1 beta, IL-1 beta converting enzyme (ICE) and IL-1R type I have also been studied. Humans have been injected with IL-1 (either IL-1 alpha or IL-1 beta) for enhancing bone marrow recovery and for cancer treatment. The IL-1 specific receptor antagonist (IL-1Ra) has also been tested in clinical trials.

Antibodies to Domains II and III of the IL-1 Receptor Accessory Protein Inhibit IL-1β Activity But Not Binding: Regulation of IL-1 Responses Is Via Type I Receptor, Not the Accessory Protein

The IL-1R accessory protein (IL-1RAcP) plays a role in IL-1R signaling by forming a complex with IL-1RI bound to the IL-1 ligand. We identified four hydrophilic peptide regions of the extracellular IL-1RAcP that may be available for complex formation (peptide 1, 71–83 domain I; peptide 2, 204–211 domain II; peptide 3, 282–292 domain III; and peptide 4, 304–314 domain III). These peptides were synthesized, coupled to keyhole limpet hemocyanin, and used to produce rabbit antisera. Each affinity-purified antiserum showed specificity for the respective peptide without cross-reactivity. Anti-peptide 2, 3, and 4 recognized surface expression of IL-1RAcP on the Th2 D10S cells by FACS and inhibited IL-1-driven proliferation. Anti-peptide 4 recognized intact IL-1RAcP and soluble IL-1RAcP. Anti-IL-1RAcP-peptide 4, which targets the terminal segment of domain III, inhibited 80% of IL-1β-driven proliferation of D10S cells. However, these IL-1RAcP Abs had no effect on the activity of human or mouse IL-1α. Whereas IL-1β down-regulated IL-1RI surface expression (p < 0.05), there was no change in the surface expression of IL-1RAcP. Moreover, murine IL-10 increased surface expression of IL-1RI, but did not affect expression of IL-1RAcP or the proliferation of D10S cells. Steady state levels of mRNA for IL-1RAcP and IL-1RI in D10S cells showed a similar pattern to that of surface expression of the respective receptors. We conclude that 1) blocking IL-1RAcP inhibits IL-1 signaling in D10S cells, 2) domains-II and III may be involved in complex formation with IL-1RI, 3) IL-1RAcP is not regulated as is IL-1RI in the same cells, and 4) IL-1 responsiveness is dependent on the expression of IL-1RI, not IL-1RAcP.

Interleukin-1 receptor mRNA expression in activated bovine leukocytes in vitro

Interleukin-1 (IL-1) is a key player in inflammation and the immune response. To better understand the complex interactions of IL-1 and its receptors in inflammation, we need to investigate how type I and type II IL-1 receptors (IL-1RI and IL-1RII) are regulated by cytokines and other mediators. Using semiquantitative reverse transcriptase PCR and Northern analysis, we examined the regulation of IL-1RI and IL-1RII mRNA levels in bovine polymorphonuclear leukocytes (PMNs) (i.e., neutrophils) and peripheral blood mononuclear cells (PBMCs) in vitro. IL-1RI mRNA levels were up-regulated in PBMCs by recombinant bovine IL-1beta (rBoIL-1beta), recombinant bovine granulocyte-macrophage colony-stimulating factor (rBoGM-CSF), rBoIL-4, recombinant bovine gamma interferon (rBoIFN-gamma), and dexamethasone. IL-1RI mRNA was increased in bovine PMNs exposed to rBoGM-CSF, rBoIL-4, and dexamethasone but was down-regulated by rBoIL-1beta and rBoIFN-gamma. IL-1RII mRNA was increased in bovine PBMCs and PMNs after exposure to rBoIL-1beta, rBoGM-CSF, rBoIL-4, and dexamethasone. In contrast, rBoIFN-gamma down-regulated the expression of bovine IL-1RII mRNA in PBMCs. These findings suggest that the expression of bovine IL-1RI and IL-1RII mRNAs is regulated differently by certain soluble stimuli (e.g., IFN-gamma) in PMNs and PBMCs.

Human monocyte/macrophage response to cobalt-chromium corrosion products and titanium particles in patients with total joint replacements

The responses of human peripheral blood monocytes of 10 normal volunteers and 14 patients with total hip replacements to particles of commercially pure titanium and chromium orthophosphate (a corrosion product from cobalt-chromium alloy implants) were studied. In addition, these phagocytosable particles were added to cultured mononuclear cells isolated from the interfacial membrane of 14 patients with failed implants. Peripheral blood monocytes from patients who had had a total hip replacement produced significantly higher levels of interleukin-1 (both interleukin-1 alpha and interleukin-1 beta) and prostaglandin E2 following particulate stimulation than those from normal volunteers. Supernatants from both titanium and chromium orthophosphate-stimulated peripheral blood monocytes from the volunteers and patients with total hip replacement induced bone resorption (assayed in organ cultures of newborn mouse calvariae) and the proliferation of human fibroblasts. The levels of bone resorption were significantly higher (p < 0.05) in patients with implants than in normal volunteers. There were no significant differences in the responses of cells between patients with focal osteolysis and those without osteolysis. Interfacial membrane mononuclear cells also produced high levels of interleukin-1 alpha, interleukin-1 beta, and prostaglandin E2 and expressed bone resorptive activities following stimulation with either titanium or chromium orthophosphate. More importantly, interfacial membrane mononuclear cells "spontaneously" produced high levels of prostaglandin E2 that were comparable with the response of peripheral blood monocytes stimulated with particulate wear debris. The clinical relevance of this study is 2-fold. First, mononuclear cells from patients with total hip replacement were some-how "sensitized" to metal particles in comparison with mononuclear cells from individuals without an implant. Second, the chromium orthophosphate corrosion product was a potent macrophage/monocyte activator and may contribute to macrophage-mediated osteolysis and aseptic loosening.

An antibody to a 17 amino acid synthetic peptide of the type I interleukin-1 receptor preferentially blocks interleukin-1 beta binding

On the basis of their relative hydropathy and alpha-helical structure, we prepared antibodies to four synthetic peptides with amino acid sequences homolgous to four hydrophilic, extracellular regions of the murine 80 kDa type I interleukin-1 receptor (IL-1RI). Antibodies to each of the four peptides recognized their specific immunogen. Human [125I]-IL-1 alpha or -beta was crosslinked to murine EL4 and D10S cells. Antiserum to peptide 150-166 precipitated the IL-1/IL-1R complex, whereas antibodies to peptide 66-84, 190-200, or 266-285 did not. Antibody to peptide 150-166 did not precipitate the type II IL-1R. Anti-IL-1RI150-166 blocked 71% of the binding of radiolabeled human IL-1 beta to EL4 cells and 50% of the binding to D10S cells. Using affinity-purified anti-IL-1RI150-166, we compared the ability of this antibody to inhibit the binding of murine or human IL-1 alpha to that of murine or human IL-1 beta. At a concentration of 20 ng/ml, affinity-purified anti-IL-1RI150-166 blocked 50% binding of murine IL-1 beta. At 1 microgram/ml, 90% blockage was observed. In contrast, no significant blockade of IL-1 alpha binding was observed at concentrations as high as 3 micrograms/ml of anti-IL-1RI150-166. The selective blockade of IL-1 beta forms was not due to differences in the affinities of these ligands for receptors on these cells. The antibody also blocked the binding of human IL-1 beta but not human IL-1 alpha to EL4 cells. The biologic activity of murine IL-1 beta but not IL-1 alpha on EL4 cells was also inhibited by this antibody. These data suggest (1) that antibody to a specific epitope on the extracellular domain interferes with the binding of IL-1 beta but not IL-1 alpha, (2) the differential inhibition of binding of IL-1 beta but not IL-1 alpha by anti-IL-1RI150-166 also blocks biologic activity, and (3) IL-1 alpha and IL-1 beta may transduce different signals by binding to separate loci on the IL-1RI.

Interleukin-1 and its inhibitors: implications for disease biology and therapy

IL-1 alpha and IL-1 beta are polypeptide hormones that exhibit a broad spectrum of beneficial and harmful biologic activities. Clinical trials designed to benefit from its stimulatory effects on human hematopoiesis and from its role in improving host defenses, are being currently conducted. Other in vivo studies, using IL-1 inhibitors with an attempts to block the detrimental effects of IL-1, are underway. Because of the multifunctional effects of IL-1 in human physiology and its pathogenetic role in several diseases, the capability to control the effects of IL-1 may prove to be a useful tool in medical practice.

Bone resorption activity of particulate-stimulated macrophages

Particulate wear debris from bone cement or prosthetic components can stimulate macrophages to cause bone resorption in a dose-dependent manner. This bone resorption activity of particulate-stimulated macrophages is associated with increased levels of both prostaglandin E2 (PGE2) and interleukin-1 (IL-1). In this study we compared the effect of particulate size, concentration, and composition on the secretion of IL-1 and PGE2 by peritoneal macrophages and on the bone-resorbing activity of conditioned medium (CM) harvested from particulate-challenged macrophages. Particulates (titanium, Ti; polymethylmethacrylate, PMMA; and polystyrene, PS) only with phagocytosable size stimulated peritoneal macrophages to secrete IL-1 and PGE2 in a dose- and time-dependent manner. Ti particles (1-3 microns) exhibited significantly enhanced bone-resorbing activity measured as 45Ca release. The maximum bone-resorbing response was observed at a concentration of 0.1% Ti (approximately 10-15 Ti particulates per cell), which also corresponded with the highest IL-1 levels measured in particulate-challenged CM. This was measured using either conditioned media from Ti-stimulated macrophages or in cocultures of calvarial bone and macrophages in the presence of Ti. Exogenous PGE2 and recombinant human IL-1 could significantly increase the 45Ca release; indomethacin (IM) significantly reduced both the spontaneous calcium efflux and active 45Ca release from in vivo labeled calvarial bones. However, IM and/or anti-IL-1 antibodies could suppress only partly the macrophage-mediated bone resorption, indicating that, in a macrophage-bone coculture system, factors other than PGE2 and IL-1 also may regulate particulate-induced bone resorption, probably involving multiple cell types.

Comparison of IL-1 alpha effectiveness in activating murine pre-B and T cell lines

Interleukin-1 (IL-1) is a potent agent that induces a wide range of biological effects. The action of IL-1 is mediated by surface IL-1 receptors (IL-1R). Two types of IL-1 receptors have been identified in lymphocytes. In this study we examined activity of IL-1 alpha in two murine lymphocyte lines that express different types of IL-1 receptors. The T lymphoid cell line EL-4 6.1 C10 expresses type I IL-1R that mediates IL-1 alpha-induced IL-2 gene expression and secretion of IL-2. The pre-B lymphoid cell line 70Z/3 was previously shown to express type II IL-1R and responds to IL-1 alpha by expressing immunoglobulin kappa light chain mRNA and increased levels of surface IgM. We found that IL-1 alpha was as potent in inducing IgM expression in 70Z/3 cells as it was in inducing IL-2 secretion in EL-4 6.1 C10 cells. Likewise, the IL-1 alpha concentration sufficient to trigger kappa light chain gene expression in 70Z/3 cells was similar to the concentration of IL-1 alpha sufficient to trigger IL-2 gene expression in EL-4 6.1 C10. In both cell lines, IL-1 alpha activated NF-kappa B-like DNA-binding activity but in EL-4 6.1 C10 cells the IL-1 alpha concentration sufficient to induce NF-kappa B response was 1000-fold lower than in 70Z/3 cells. Monoclonal antibody, mAb M15, to the type I IL-1R blocked IL-1-induced responses in EL-4 6.1 C10 cells. Surprisingly mAb M15 also blocked IL-1 action in 70Z/3 cells, even though these cells predominantly express type II IL-1R. 15% of the total IL-1 binding sites in 70Z/3 cells were recognized by mAb M15. Human IL-1 receptor antagonist (IL-1ra), which binds to the natural murine type I but not the type II IL-1R, blocked IL-1 alpha responses in EL-4 6.1 C10 and 70Z/3 cells. Although at low levels, Northern blot analysis confirmed that 70Z/3 cells express low levels of type I IL-1R mRNA. Taken together, these results suggest that type I IL-1R are expressed and transduce IL-1 signals in both 70Z/3 and El-4 6.1 C10 cells.

Coexpression of type I and type II IL-1 receptors in the murine T helper 2 cell line D10N

IL-1 receptor heterogeneity in murine lymphocytes was investigated by cross-linking to [125I]IL-1 alpha and competition with IL-1 receptor antagonist, and the molecular identity of the IL-1 receptors was identified with PCR using primers specific for type I and type II IL-1 receptors. The thymoma cell line E14 6.1 exhibits exclusively the 80 kDa receptors which proved to be the type I receptor according to PCR analysis. In the pre-B cell line 70Z/3, predominantly a 60 kDa type II receptor but also a trace of type I receptor can be identified by PCR. The Th2 cell line D10N expresses both types of IL-1 receptors in equivalent amounts according to cross-linking experiments and PCR. The proliferative response of D10N cells to IL-1 is inhibited by IL-1 ra which according to cross-linking affects the binding to the type I receptor only. It is concluded that coexpression of both types of IL-1 receptors might be a characteristic of murine Th2 cells and that their growth-dependence on IL-1 is mediated by the type I receptor.

1,25-Dihydroxyvitamin D3 increases type 1 interleukin-1 receptor expression in a murine T cell line

The biologically active metabolite of vitamin D3, 1,25 (OH)2 D3, exerts important immunoregulatory effects in addition to being a central mediator of calcium/phosphate metabolism. Utilizing an interleukin 1 responsive murine T cell line and 125I-interleukin 1 alpha, we show that 1,25 (OH)2 D3 (5,50 nM) enhanced 125I-interleukin 1 alpha binding up to almost 2-fold over control. This 1,25 (OH)2 D3 effect occurred in a dose-dependent manner and was detectable after 24 h but not before 7 h of culture. Scatchard analysis of 125I-interleukin 1 alpha binding data demonstrated that 1,25 (OH)2 D3 enhanced interleukin 1 receptor number without a significant change in affinity. The biologically less potent metabolite of vitamin D3, 25 (OH) D3, also augmented 125I-interleukin 1 alpha binding but at steroid levels 2-3 log orders greater than 1,25 (OH)2 D3. This observation, combined with the presence of high-affinity 3H-1,25 (OH)2 D3 receptors (88 sites/cell, K = 0.45 nM) in cytosolic extracts, strongly suggests that the nuclear vitamin D receptor mediates this steroid's effect on interleukin 1 receptor expression. Based on the capacity of an anti-type 1 interleukin 1 receptor monoclonal antibody (35F5) to block 1,25 (OH)2 D3-enhanced 125I-interleukin 1 alpha binding, we conclude that this steroid augments type 1 interleukin 1 receptor expression. When combined with interleukin 1, a cytokine that also impacts MD10 interleukin 1 receptor expression, 1,25 (OH)2 D3 enhanced interleukin 1 receptor expression. Northern blots hybridized with a 32P-type 1 interleukin 1 receptor cDNA probe show that 1,25 (OH)2 D3 enhanced type 1 interleukin 1 receptor steady state mRNA levels. Functionally, 1,25 (OH)2 D3 pretreatment augmented the MD10 proliferative response to suboptimal levels of interleukin 1 (< 100 fM interleukin 1 alpha). These findings further support 1,25 (OH)2 D3's role as an immunoregulatory molecule and provides a possible mechanism by which this steroid could potentiate certain immune activities.

Identification and purification of a receptor on macrophages for the dengue virus-induced suppressor cytokine

Dengue type 2 virus (DV)-induced suppressor cytokine (SF) binds to macrophages to transmit the suppressor signal to recruit the second subpopulation of suppressor T cells. The present study was undertaken to identify and purify the receptor for SF (SF-R) on macrophages. The binding of 125I-SF to macrophages was saturable and reversible. Scatchard analysis showed the presence of both high (54,000/cell) and low (1.78 x 10(6)/cell) affinity receptor sites. The binding of 125I-SF to macrophages was inhibited by pretreatment of macrophages with anti-SF antiserum but not by a heterologous antiserum. Normal mouse peritoneal macrophage membrane was solubilized with Triton-X-100 and the components separated by low pressure liquid chromatography (LPLC) to purify SF-R. The presence of SF binding moiety (SF-R) was screened at each step of purification. The purified SF-R resolved into two bands of 45-50 kD mol. wt on SDS-PAGE. 125I-SF+SF-R complex run on SDS-PAGE showed a single band at about 55-60 kD mol. wt by autoradiography. Anti-SF-R antiserum reacted with SF-R in a Western blot test; the reaction was abolished by pretreatment of the blots with proteinase K, but not by pretreatment with periodic acid. SF-R was composed of two polypeptide chains (alpha and beta) which were obtained in pure form by high performance liquid chromatography (HPLC) of dithiothreitol- and iodoacetamide-treated SF-R. Only the beta chain bound SF.

Nuclear internalisation and DNA binding activities of interleukin-1, interleukin-1 receptor and interleukin-1/receptor complexes

This paper presents evidence to suggest that interleukin-1 alpha as a complex with its receptor is able to express DNA binding activity. Both the interleukin-1/receptor complex and the interleukin-1 receptor appear to be able to bind to DNA, however interleukin-1 on its own showed no binding activity. Interleukin-1 was found to be internalised into the nuclei of all cells examined (EL4, MEL, HL-60, K562, THP-1 and Jurkat cells). The data suggest the possible modulation of genes by interaction of interleukin-1/receptor complexes with DNA structures.

Interleukin 4 (IL) 4 up-regulates gene and surface IL 1 receptor type I in murine T helper type 2 cells

The T cell-derived cytokine interleukin (IL) 4 is known to increase the proliferative response of T cells stimulated with IL 1. IL 4 is also an autocrine growth factor for type II T helper cells (Th2) cells. In the present studies, we examined the effect of murine recombinant IL 4 on the expression of the IL 1 receptor type I (IL 1RtI) in murine Th2 cell lines at the mRNA and surface level. Using a specific anti-murine IL 1RtI monoclonal antibody and flow microfluorometry, we found that IL 4 increased the surface expression of IL 1RtI in a dose-dependent manner. In D10S cells, a subline of the Th2 cell line D10.G4.1, 50-500 pg/ml IL 4 up-regulated the receptor 1.8- to 3.2-fold (p less than 0.05). This up-regulation was also seen at the mRNA level. The effect was not due to increased stability of the mRNA, since IL 4 did not modify the half-life of IL 1RtI mRNA. IL 4 also up-regulated IL 1RtI on CDC25 cells, another Th2 cell line. However, we did not observe an effect of IL 4 on gene expression of IL 1RtI in BALB/c 3T3 fibroblasts. IL 2 and IL 4 showed an additive effect in up-regulating IL 1RtI and D10S cells. These studies indicate that IL 4 up-regulates IL 1RtI in murine Th2 cells by increasing gene expression for IL 1RtI without affecting mRNA stability. Thus, IL 4 production by Th2 cells may amplify the immune response via up-regulation of IL 1RtI.

Enhancement of growth of virulent strains of Escherichia coli by interleukin-1

Interleukin-1 (IL-1) is a polypeptide cytokine that mediates many physiological responses to infection and inflammation and is a growth factor for certain mammalian cells. Virulent and avirulent clinical isolates of Escherichia coli were grown in culture media in the presence of human IL-1. IL-1 beta, but not tumor necrosis factor or IL-4, enhanced the growth of virulent, but not avirulent, E. coli. This enhancement was blocked by the IL-1 receptor antagonist (IL-1ra). Radiolabeled IL-1 bound to virulent but not avirulent E. coli in a specific and saturable fashion; IL-1ra inhibited this binding. Thus, human IL-1 may recognize a functional IL-1-like receptor structure on virulent E. coli and may be a virulence factor for bacterial pathogenicity.

A novel IL-1 receptor, cloned from B cells by mammalian expression, is expressed in many cell types

cDNA clones corresponding to an Mr approximately 80,000 receptor (type I receptor) for interleukin-1 (IL-1) have been isolated previously by mammalian expression. Here, we report the use of an improved expression cloning method to isolate human and murine cDNA clones encoding a second type (Mr approximately 60,000) of IL-1 receptor (type II receptor). The mature type II IL-1 receptor consists of (i) a ligand binding portion comprised of three immunoglobulin-like domains; (ii) a single transmembrane region; and (iii) a short cytoplasmic domain of 29 amino acids. This last contrasts with the approximately 215 amino acid cytoplasmic domain of the type I receptor, and suggests that the two IL-1 receptors may interact with different signal transduction pathways. The type II receptor is expressed in a number of different tissues, including both B and T lymphocytes, and can be induced in several cell types by treatment with phorbol ester. Both IL-1 receptors appear to be well conserved in evolution, and map to the same chromosomal location. Like the type I receptor, the human type II IL-1 receptor can bind all three forms of IL-1 (IL-1 alpha, IL-1 beta and IL-1ra). Vaccinia virus contains an open reading frame bearing strong resemblance to the type II IL-1 receptor.

Interaction of recombinant monocyte-derived interleukin 1 receptor antagonist with rheumatoid synovial cells

Interleukin 1 receptor antagonist (IL-1ra) is a newly described cytokine that is produced by human monocytes cultured on adherent immunoglobulin G (IgG). These studies have characterized the binding of IL-1ra to receptors on human rheumatoid synovial cells in comparison to binding of IL-1 alpha. The human synovial cells bound 35S-IL-1ra with a Kd of 213 pM and a Ki of 134 pM. 125I-IL-1 alpha bound to the synovial cells with similar values, showing a Kd of 205 pM and a Ki of 58 pM. Cross-inhibition studies were performed to examine whether IL-1ra and IL-1 alpha interacted with the same receptors and in an identical fashion. At the highest concentrations of inhibitory proteins, the binding of each ligand was inhibited 100% by the same or opposite ligand. This result indicated that IL-1ra and IL-1 alpha bound to the same receptors and not to overlapping subsets of receptors. In addition, the binding of 35S-IL-1ra was inhibited in an identical fashion by equimolar amounts of IL-1ra or IL-1 alpha. However, twofold or greater amounts of IL-1ra in comparison to IL-1 alpha were required to offer comparable inhibition of binding of 125I-IL-1 alpha. These results suggest that IL-1ra and IL-1 alpha bind with equal avidity to IL-1 receptors but may not bind identically. Additional experiments are necessary to establish whether these two ligands may bind to different regions of the extracellular portion of the IL-1 receptor.

Interleukin-1 receptors on human thyroid cells and on the rat thyroid cell line FRTL-5

Cellular binding of interleukin-1 (IL-1) was tested on monolayers of human thyrocytes in secondary culture, on long-term cultures of human thyrocytes, and on the rat thyroid cell line FRTL-5. The human thyrocytes in secondary culture showed specific binding of human 125I-rIL-1 alpha. Scatchard plots of data obtained at 4 degrees C indicated the presence of a single population of receptors with a Kd of 30 to 170 pM and 2,000 to 6,000 receptors per cell. Incubation at room temperature resulted in internalization of the receptor-ligand complex. Parallel experiments were performed with the IL-1 receptor-positive murine T-cell lines EL-4 and NOB-1. The IL-1 receptors on these cells had Kd values one fifth to one tenth those on human thyroid cells in secondary culture. Both rIL-1 alpha and rIL-1 beta inhibited 125I-rIL-1 alpha binding to human thyrocytes and the murine T cells. In contrast to the cells in secondary culture, there was no specific binding of 125I-rIL-1 alpha to long-term cultivated human thyroid cells or to the FRTL-5 cells. We concluded that recently described differences in the response to IL-1 of different thyroid cell culture systems are most likely caused by differences in expression of IL-1 receptors.

Modification of biological responses to interleukin-1 by agents that perturb signal transduction pathways

In this study we have examined the effect of agents known to perturb certain signal transduction pathways on the biological responses of target cells to stimulation with interleukin-1 (IL-1). In the murine thymoma cell line EL4, IL-1 stimulation results in the secretion of interleukin-2 (IL-2), which was subsequently measured by proliferation of an IL-2-dependent cell line. Agents that elevated intracellular cAMP blocked or partially blocked IL-1 induction of IL-2 secretion, whereas agents that activated protein kinase C (PKC) resulted in a synergistic enhancement. Both pertussis and cholera toxins also inhibited IL-1-induced IL-2 secretion, although probably by acting at different levels. IL-1 simulation of human and murine fibroblasts resulted in release of prostaglandin E2. This response was inhibitable by pertussis toxin but not by cholera toxin, whereas co-stimulation of the fibroblasts with IL-1 and phorbol ester resulted in a synergistic response. Murine fibroblasts could also be stimulated to proliferate by IL-1, and this response was also inhibitable by pertussis toxin. These findings are consistent with coupling of the IL-1 receptor to a signalling pathway via a pertussis toxin substrate.

Interleukin 1 responsiveness and receptor expression by murine TH1 and TH2 clones

Murine Th1 and Th2 T cell lines differ in their responses to interleukin 1 (IL 1). Therefore, we examined two T-cell lines, D10.G4.1 (Th2) and MTg12B (Th1) in an attempt to correlate IL 1 receptor (IL 1R) expression with their IL 1 responsiveness. D10.G4.1 cells, which respond to IL 1, expressed two forms of the IL 1R, with molecular masses of approximately 80 kDa and approximately 60 kDa. In contrast, MTg12B cells failed to respond to IL 1 and only expressed the approximately 60 kDa receptor form. This suggests that the approximately 80 kDa receptor is essential for signaling. Expression of both IL 1R forms on D10.G4.1 cells could be inhibited by the anti-IL 4 antibody, 11B11. Antigen presentation reversibly upregulated both forms of the IL 1R, whereas stimulation with concanavalin A (ConA) and anti-CD3 only upregulated the approximately 60 kDa moiety. Upregulation of the approximately 80-kDa IL 1R by repeated antigenic stimulation resulted in a marked increase in sensitivity of D10.G4.1 cells to IL 1.