Cytokines and soluble receptors of the interleukin-1 family in Schnitzler syndrome.

OBJECTIVES: Schnitzler syndrome (SchS) is an autoinflammatory disorder characterized by chronic urticaria, fever, and monoclonal gammopathy. The success of interleukin-1 (IL-1) blocking therapies suggests a crucial role for IL-1 in disease induction. The aim of this study is to perform a comprehensive analysis of IL-1 family cytokines and soluble receptors in a group of SchS patients. METHOD: Three patients fulfilling the criteria for the diagnosis of SchS were recruited; 80 blood donors formed the control group. IL-1 family cytokines (IL-1α, IL-1ß, IL-33, IL-18), soluble receptors (sIL-1R1, sIL-1R2, sIL-1R3, sIL-1R4), and antagonists [IL-1Ra, IL-18 binding protein (IL-18BP)] were measured by a multiarray enzyme-linked immunosorbent assay. Free IL-18 was calculated as the amount of IL-18 not inhibited by IL-18BP. Cytokine levels were compared by the Mann-Whitney test. RESULTS: IL-18 and free IL-18 were increased in patients compared with controls (p = 0.005 and p = 0.0082, respectively), while IL-18BP levels were not different. IL-1α, IL-1ß, and IL-33 were undetectable in both patients and controls. The soluble receptors sIL-1R1, sIL-1R2, and ST2/sIL-1R4, and the IL-1 antagonist IL-1Ra were all within normal ranges; sIL-1R3 was significantly lower in patients than in controls (p = 0.039). CONCLUSIONS: The data indicate that SchS is characterized by increased circulating levels of free IL-18, possibly leading to a higher activation of innate/inflammatory effector cells. At variance with other inflammatory diseases, the lack of increase in sIL-1R1 and sIL-1R2 and the decreased levels of sIL-R3 imply a failure in the counterbalancing mechanism aimed at inhibiting excessive IL-1ß in tissues.

Neuroinflammation in Parkinson's patients and MPTP-treated mice is not restricted to the nigrostriatal system: microgliosis and differential expression of interleukin-1 receptors in the olfactory bulb.

Neuroinflammation may play a role in the pathogenesis of Parkinson's disease (PD). The present study questioned whether this neuroinflammatory response differs between the olfactory bulb, as an early affected region and the nigrostriatal system. Indeed, increased microgliosis was shown in post-mortem olfactory bulb of PD patients. Also in olfactory bulb of MPTP-treated mice, microgliosis and increased expression of IL-1alpha, IL-1beta and IL-1ra mRNA was observed early after treatment. These observations implicate that neuroinflammation is not restricted to the nigrostriatal system. MPTP-induced microgliosis in striatum and olfactory bulb was reduced in IL-1alpha/beta knockout mice, indicating that IL-1 affects microglia activation. Importantly, MPTP induced differential regulation of IL-1 receptors. mRNA levels of IL-1RI and, to a lesser extent, IL-1RII were increased in striatum. Interestingly, in the olfactory bulb only IL-1RII mRNA was enhanced. We suggest that differential regulation of IL-1 signaling can serve as an important mechanism to modulate neuroinflammatory activity after MPTP treatment and possibly during PD.

The interleukin 1 receptor family.

Interleukin-1 is a key inflammatory cytokine that mediates its effects through a type I receptor and a receptor accessory protein. These two molecules are members of a wider family of proteins that have in common the presence of immunoglobulin domains in the extracellular region of the protein and a TIR domain in the cytoplasmic region. The nature of this family of proteins and their signal transduction pathway is discussed in this review.

Identification and characterization of two members of a novel class of the interleukin-1 receptor (IL-1R) family. Delineation of a new class of IL-1R-related proteins based on signaling.

Two novel members of the interleukin-1 receptor (IL-1R) family, identified by homology searches of human genomic sequence data bases, are described. The genes have been named according to their structural features: TIGIRR-1 (three immunoglobulin domain-containing IL-1 receptor-related) and TIGIRR-2. TIGIRR-2 has recently been identified as causing mental retardation when mutated (Carrie, A., Jun, L., Bienvenu, T., Vinet, M. C., McDonell, N., Couvert, P., Zemni, R., Cardona, A., Van Buggenhout, G., Frints, S., Hamel, B., Moraine, C., Ropers, H. H., Strom, T., Howell, G. R., Whittaker, A., Ross, M. T., Kahn, A., Fryns, J. P., Beldjord, C., Marynen, P., and Chelly, J. (1999) Nat. Genet. 23, 25-31) and called IL1RAPL, a name we will also use henceforth. Neither receptor alone was able to mediate transcriptional activation of NF-kappaB in response to IL-1alpha, IL-1beta, or IL-18. In order to begin to elucidate the function of these and other orphan IL-1R family members, we have developed a functional assay utilizing a panel of chimeric receptors containing the extracellular and transmembrane domains of either type I IL-1R or IL-1R accessory protein (AcP) coupled to the cytoplasmic domains of all family members. Coexpression of each IL-1R chimera with each AcP chimera and an NF-kappaB-responsive reporter demonstrated that the cytoplasmic domains could be classified as IL-1R-like, AcP-like, or neither. Any IL-1R-like cytoplasmic domain could cooperate with any AcP-like cytoplasmic domain. The TIGIRR-1 and IL1RAPL cytoplasmic domains, however, were unable to signal as either IL-1R-like or AcP-like components, suggesting that they function as a new class of receptors within this family.

The rat intraovarian interleukin (IL)-1 system: cellular localization, cyclic variation and hormonal regulation of IL-1beta and of the type I and type II IL-1 receptors.

An increasing body of evidence supports the possibility that intraovarian interleukin (IL)-1 plays an intermediary role in the periovulatory cascade. To gain further insight into the intraovarian IL-1 hypothesis, we studied the cellular localization cyclic variation and hormonal regulation of IL-1beta, as well as of the type I and type II IL-1 receptors (IL-1R) in immature rats. In situ hybridization localized IL-1beta and type I IL-1R transcripts to the granulosa cell compartment, the innermost layers of the theca interna and to the oocyte of the untreated immature ovary. Molecular probing of whole ovarian material in the course of a simulated estrous cycle revealed a progressive preovulatory increase in IL-1beta and type I IL-1R transcripts to an in vivo peak at the time of ovulation (3.0- and 2.5-fold increases over untreated controls; P < 0.05). Comparable efforts to localize and probe for type II IL-IR transcripts failed to elicit a detectable signal. The basal in vitro expression pattern of IL-1beta and type II IL-1R transcripts by whole ovarian dispersates revealed an early (4 h) spontaneous increase to a peak (2.1- and 5.8-fold increases over time 0: P < 0.05) followed by a gradual decline to a 48 h nadir. Treatment of whole ovarian dispersates with the IL-1 receptor antagonist (IL-1RA) or with IL-1beta failed to alter the initial (4 h) burst of IL-1beta or of type II IL-1R expression thereby suggesting IL-1-independence. Treatment with hCG proved equally ineffective. However, longer-term treatment of whole ovarian dispersates with IL-1beta produced a significant secondary increase (5.9-fold over time 0; P < 0.05) in IL-1beta (but not type II IL-1R) transcripts by 48 h. This IL-1 effect was completely blocked by co-treatment with IL-1RA thereby suggesting mediation via a specific IL-1 receptor. Qualitatively comparable but quantitatively reduced results obtained for isolated granulosa cells. The basal in vitro expression pattern of type I IL-1R transcripts by whole ovarian dispersates revealed a progressive spontaneous increase (3.1-fold increase overall) over the 48 h culture. Treatment with IL-1beta produced a significant (P < 0.05) increase (5-fold) in type I IL-1R transcripts by 48 h, an effect which was completely blocked by co-treatment with IL-1RA. Taken together, these observations: (1) localize IL-1beta and its type I receptor to granulosa cells, the innermost layers of the theca interna and to the oocyte; (2) confirm their periovulatory in vivo expression pattern; (3) document their expression by untreated cultured whole ovarian dispersates; and (4) demonstrate their in vitro responsiveness to receptor-mediated/IL-1-driven autocrine amplification. The type II IL-1R was undetectable in vivo, its in vitro expression pattern proving IL-1- and hCG-independent. The periovulatory expression pattern of IL-1beta and its receptor (type I) is compatible with the notion that the intraovarian IL-1 system may play an intermediary role in the ovulatory process.

Residual bodies and IL-1alpha stimulate expression of mRNA for IL-1alpha and IL-1 receptor type I in cultured rat Sertoli cells.

The cytokine interleukin (IL)-1alpha may be produced both by Sertoli cells and immature male germ cells from rat and is thought to play a role in autocrine and/or paracrine regulation of the spermatogenesis. The localization of IL-1 receptors in seminiferous tubules is unknown. In this study we found a constitutive expression of IL-1 receptor type I (IL-I RI) mRNA in cultured Sertoli cells and peritubular cells from rat, whereas no such transcripts were observed in immature germ cells (pachytene spermatocytes and round spermatids). An autostimulation of IL-1alpha mRNA synthesis has previously been described in other cell types. Stimulation of Sertoli cells with recombinant IL-1alpha for 0-7 h resulted in a rapid increase in both IL-1alpha and IL-1 RI mRNA. When Sertoli cells were cultured with residual bodies for 0-48 h, mRNA levels for both IL-1alpha and IL-1 RI were increased in a biphasic manner. We suggest that phagocytosis of residual bodies triggers an autocrine IL-1alpha loop in Sertoli cells where both IL-1alpha and one of its receptors are stimulated.

Increased soluble interleukin-1 type II receptor concentrations in postoperative patients and in patients with sepsis syndrome.

Plasma interleukin-1 (IL-1) activity is modulated in part through the simultaneous appearance of several inhibitors of IL-1 action, including interleukin-1 receptor antagonist (IL-1ra) and the soluble IL-1 type II receptor (IL-1RII). However, little is known concerning the plasma appearance of these inhibitors in patients following operative trauma or those with sepsis syndrome. In the present report, plasma IL-1beta, IL-1ra, and soluble IL-1RI and IL-1RII concentrations were evaluated in 118 patients with sepsis syndrome or after elective operative trauma. Plasma concentrations of IL-1ra increased significantly following elective operative repair of thoraco-abdominal and abdominal aortic aneurysms, and after bowel resection for inflammatory bowel disease, but did not increase after laparoscopic cholecystectomy. Plasma IL-1ra levels were also elevated in patients with sepsis syndrome. In contrast, soluble IL-1RII levels were only increased in patients after operative repair of thoraco-abdominal aortic aneurysms and in sepsis syndrome, whereas concentrations were unaffected by the other more modest surgical procedures. Plasma IL-1RI concentrations decreased in all postoperative patients in the first 24 hours after surgery. We conclude that both plasma IL-1ra and soluble IL-1RII concentrations often increase in sepsis and following some operative trauma. Less severe operative trauma increases the plasma concentration of only IL-1ra, whereas both IL-1ra and soluble IL-1RII are increased in patients with sepsis syndrome or following thoraco-abdominal aneurysm repair.

The effect of cytokine stimulation on IL-1 receptor mRNA expression by intestinal epithelial cells.

Interleukin-1 (IL-1) can induce intestinal epithelial cells (IEC) to produce several cytokines and acute phase proteins, suggesting that IEC may be important in a cytokine network at the intestinal mucosa to amplify the effects of IL-1 during an inflammatory response. However, little is known about the type of IL-1 receptor expressed by IEC and the effect of cytokines on the expression of these receptors. In this study, the expression by IEC of IL-1 receptor Type I (IL-1RI) and type II (IL-1RII) mRNA was examined by reverse transcriptase polymerase chain reaction. Both isolated rat IEC and the rat IEC-6 intestinal epithelial cell line were found to express mRNA for IL-1RI but not IL-1RII. Stimulation of the IEC-6 cells with IL-1beta or TNF-alpha down-regulated the expression of mRNA for IL-1RI at 24 hr, yet transforming growth factor-beta1 was found to have no effect. These results suggest a possible mechanism to limit the effect of IL-1 on IEC function during the mucosal inflammatory response by down-regulating the expression of the Type I IL-1 receptor.

Reactive oxygen intermediates cause rapid release of the interleukin-1 decoy receptor from human myelomonocytic cells.

Free radicals play an important role in inflammation. We found that reactive oxygen intermediates (ROI) inhibit interleukin-1beta (IL-1beta) binding on human myelomonocytes. Production of superoxide anion (O2-) by Xanthine (X) and Xanthine-Oxidase (XO) or NADPH caused a reduction (48% +/- 15% in 25 experiments) in the IL-1beta binding of polymorphonuclear cells (PMN) and monocytes that was inhibited by superoxide dismutase (SOD). Hydrogen peroxide (H2O2) was only active on monocytes and this effect was prevented by catalase. O2(-)-induced loss of IL-1beta binding on PMN reached half maximum at 5 minutes and peaked after 30 minutes. The reduction of IL-1beta binding was due to reduction of IL-1beta receptors (R) on PMN surface without any change in affinity. ROI-induced reduction of surface IL-1R was not caused by receptor internalization, but rather by the release of a soluble form (45 kD) of the type II decoy R. The action of ROI on IL-1 binding was selective because major histocompatibility complex class I, CD18 and CD16 were unaffected. The O2(-)-induced release of IL-1 decoy R was not affected by protein synthesis inhibitors, but was partially blocked by protease inhibitors. Release of the IL-1 type II decoy R might represent one mechanism by which ROI antagonize and limit the proinflammatory effects of IL-1.

Biologic basis for interleukin-1 in disease.

To understand the role of the proinflammatory cytokine interleukin-1 (IL-1) in disease, investigators have studied how production of the different members of the IL-1 family is controlled, the various biologic 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-1Beta, IL-1Beta converting enzyme, and IL-1R type I have also been studied. Humans have been injected with IL-1 (either IL-1alpha or IL-1beta) for enhancing bone marrow recovery and for cancer treatment. The IL-1-specific receptor antagonist (IL-1Ra) has also been tested in clinical trials. The topics discussed in this review include production and activities of IL-1 and IL-1Ra molecules, the effects of IL-1 on gene expression, functions of cell-bound and soluble IL-1 receptors, the importance of the IL-1R accessory protein, newly discovered signal transduction pathways, naturally occurring cytokines limiting IL-1 production or activity, the effects of blocking cyclooxygenase and nitric oxide, and the outcomes of IL-1 and IL-1 Ra in human trials. Special attention is paid to IL-1beta converting enzyme and programmed cell death. The roles of IL-1 in hematopoiesis, leukemia, atherosclerosis, and growth of solid tumors are also discussed. This is a lengthy review, with 586 citations chosen to illustrate specific areas of interest rather than a compendium of references. At the end of each section, a short commentary summarizes what the author considers established or controversial topics linking the biology of IL-1 to mechanisms of disease.

Human synovial fibroblasts coexpress IL-1 receptor type I and type II mRNA. The increased level of the IL-1 receptor in osteoarthritic cells is related to an increased level of the type I receptor.

BACKGROUND: Cytokines, in particular IL-1, are believed to be responsible for mediating cartilage degradation in osteoarthritis (OA). To investigate the role of the IL-1 system in this disease, we studied in normal and OA human synovial fibroblasts the nature, the number, and the level of expression of the IL-1 receptor (IL-1R) and through which receptor the biologic stimulation of these cells by IL-1 is mediated. EXPERIMENTAL DESIGN: We determined the IL-1R level by radioligand assay, the type of IL-1R with the use of specific antibodies and by the reverse transcriptase-PCR (RT-PCR), and the mRNA level of the type I IL-1R by slot blot analysis. Biologic activity was measured on the synovial fibroblasts via IL-1 binding and prostaglandin E2 production. RESULTS: Binding data revealed the presence of a single class of high affinity IL-1R in both normal (kD, 21 +/- 4.5 pM) and OA (kD, 23 +/- 5.0 pM) human synovial fibroblasts. The number of receptors was significantly higher (p < 0.004) in OA synovial fibroblasts (2534 +/- 187 sites/cell) than in normal cells (1310 +/- 96 sites/cell). This increase was transient; OA synovial fibroblasts in second and third passages had a normal level of IL-1R. Analysis of the mRNA species by RT-PCR revealed that both type I and type II IL-1R are coexpressed in normal and OA synovial fibroblasts; the type I mRNA was the most predominant in all samples. No difference in the relative amount of type I IL-1R mRNA level was found between normal and OA cells. A blocking Ab against the type I IL-1R completely inhibited, in both normal and OA cells, the receptor binding and IL-1 beta stimulated PGE2 production, whereas the treatment with anti-type II IL-1R was ineffective. CONCLUSIONS: These results indicate that the type I IL-1R is up-regulated in OA synovial fibroblasts and is responsible for mediating the biologic activation of these cells by IL-1. This phenomenon is probably secondary to an abnormality in the post-transcriptional regulation of the type I IL-1R. Although type II IL-1R is also expressed, its translation seems to be inoperative, or this receptor is already shed.

Inducible expression of type 2 IL-1 receptors by cultured human keratinocytes. Implications for IL-1-mediated processes in epidermis.

Two species of cell surface receptor for IL-1 (IL-1R) have been characterized. Only one of these, the type 1 IL-1R, transduces a signal after ligand binding. Whereas mRNA for the nonsignal transducing type 2 IL-1R seems to have a broad tissue distribution, functional type 2 IL-1R has been carefully studied only in leukocytes and related cell lines. Because normal human keratinocytes, which are IL-1 alpha-producing epithelial cells, inducibly express large numbers of IL-1R, we have studied their putative type 1 and type 2 IL-1R at the level of RNA, protein, and biologic function. At the level of function, gene expression of the IL-1-inducible cytokine granulocyte-macrophage-CSF by keratinocytes was mediated entirely by low numbers of type 1 IL-1R, although type 2 IL-1R were more numerous on both resting and activated keratinocytes. Type I IL-1R mRNA was detected only at very low levels, whereas a marked induction of type 2 IL-1R mRNA was readily observed in activated keratinocytes. A sensitive and specific ELISA demonstrated shed type 2 IL-1R in the conditioned medium of IFN-gamma or PMA-activated keratinocytes. Keratinocyte type 2 IL-1R bound IL-1 alpha with higher affinity (Kd approximately 3 x 10(-9) M) than type 2 IL-1R on leukocytes; however, the intracellular epithelial form of the IL-1R antagonist was bound 100-fold less avidly. These findings demonstrate that a normal nontransformed epithelial cell may express large numbers of the nonsignal transducing type 2 IL-1R that binds IL-1 with high affinity and can be shed into the pericellular environment. This receptor may function as an IL-1 antagonist in autocrine, juxtacrine, and paracrine cutaneous pathways.

Expression of type I and type II interleukin-1 receptors in mouse brain.

Although binding sites for IL-1 have been identified in the mouse brain, it is still unknown whether these binding sites correspond to the type I or type II IL-1 receptor. Quantitative autoradiography was used to confirm the presence of specific binding sites for radiolabelled recombinant human IL-1 alpha (125I-HuIL-1 alpha) in the brain of DBA/2 mice. IL-1 binding was highest in the dentate gyrus, consisting of a single class of high affinity binding sites with a Kd of 0.1 nM and a Bmax of 57 fmol/mg protein. A similar Kd of 0.2 nM was obtained using isolated membranes from the whole hippocampus, although the number of binding sites was lower (2 fmol/mg protein). Affinity cross-linking of 125I-Hu-IL-1 alpha to hippocampal membranes revealed the existence of two types of IL-1 receptor proteins, consistent with the sizes of the type I (85 kD) and type II (60 kD) IL-1 receptor. Oligonucleotide probes were then synthesized and used in RT-PCR followed by Southern blotting to show that the whole brain expresses transcripts for both the type I and type II IL-1 receptors. The murine neuroblastoma cell line, C1300, expresses type I rather than type II IL-1 receptor mRNA. The type I receptor protein can be identified by flow cytometry on the membrane of the C1300 neuronal cell line using indirect immunofluorescence with a rat anti-mouse type I IL-1 receptor MoAb. These data show that mouse brain expresses both type I and type II IL-1 receptor mRNA and proteins and offer further support to the idea that type I IL-1 receptors are synthesized and expressed by neurons.

Gene regulation of interleukin-1 beta, interleukin-1 receptor type I, and plasminogen activator inhibitor-1 and -2 in human granulosa-luteal cells.

OBJECTIVE: To investigate the regulation of messenger ribonucleic acid (mRNA) levels of interleukin-1 beta (IL-1 beta), interleukin-1 (IL-1) receptor type 1, and plasminogen activator (PA) inhibitor-1 and -2 in cumulus cells, granulosa-luteal cells, and macrophage-depleted granulosa-luteal cells obtained from human preovulatory follicles. DESIGN: Prospective longitudinal study. SETTING, PATIENTS: Patients undergoing assisted reproductive technologies (ART) in the Department of Gynecology and Obstetrics, Stanford University, Stanford, California. INTERVENTIONS: Cumulus cells and granulosa-luteal cells were collected by ultrasound-guided transvaginal aspiration at the time of ART. MAIN OUTCOME MEASURES: Northern blot analysis of mRNA levels of IL-1 beta, IL-1 receptor type 1, PA inhibitor-1 and -2 in cumulus cells, granulosa-luteal cells and macrophage-depleted granulosa-luteal cells, and indirect immunocytochemical analysis of the IL-1 system and macrophages in granulosa-luteal cell preparations were performed. RESULTS: Interleukin-1 beta mRNA levels in uncultured cumulus cells were less than those of uncultured granulosa-luteal cells with no differences in IL-1 receptor type 1 mRNA levels between these two cell types. Granulosa-luteal cell IL-1 receptor type 1 mRNA levels were expressed constitutively throughout 24 hours of culture with no effect by hCG, whereas IL-1 beta mRNA levels increased within 6 hours, and then remained elevated for 24 hours with no effect by hCG. Interleukin-1 beta significantly increased granulosa-luteal cell mRNA levels of IL-1 beta (over twofold), IL-1 receptor type 1 (over twofold), PA inhibitor-1 (approximately 1.4-fold), and PA inhibitor-2 (approximately 1.6-fold). In contrast, IL-1 beta had no effect on IL-1 beta and IL-1 receptor type 1 mRNA levels in macrophage-depleted granulosa-luteal cells. Granulosa-luteal cells, not macrophages, account for the majority of the immunocytochemical staining for IL-1 beta and IL-1 receptor type 1 in follicular aspirates. CONCLUSIONS: These studies suggest that the IL-1 system is regulated in human granulosa-luteal cells during the periovulatory period. Furthermore, the augmentation of PA inhibitor-1 and -2 mRNA levels by IL-1 beta suggests a potential role for IL-1 beta in remodeling of the human ovary during the periovulatory period.

Importance of brain IL-1 type II receptors in fever and thermogenesis in the rat.

Interleukin-1 (IL-1) acts centrally to induce fever and thermogenesis in rodents. The central actions of IL-1 alpha and IL-1 beta apparently involve different mechanisms, and the effects of IL-1 beta are not consistent with interaction with a type I (IL-1RI) 80-kDa receptor. In the present study the involvement of the type II IL-1 receptor (IL-1RII) was tested in the rat by examining the effects of central injection of a monoclonal antibody (ALVA-42), which blocks the IL-1RII. Pretreatment of rats with ALVA-42 (6 micrograms icv) inhibited the thermogenic and pyrogenic responses to intracerebroventricular injection of 5 ng (but not 50 ng) of IL-1 beta in conscious rats but did not significantly modify responses to IL-1 alpha. ALVA-42 also failed to modify the responses to peripherally administered IL-1 beta (1 microgram) but significantly attenuated the pyrogenic and thermogenic responses to peripheral (125 micrograms) or central (1 microgram) injection of endotoxin. These data indicate that IL-1RII mediates the central effects of a low dose of IL-1 beta, but not IL-1 alpha, on fever and thermogenesis in the rat. They also imply that responses to endotoxin are due, at least in part, to the activation of IL-1RII by IL-1 beta released within the brain and that effects of peripherally injected IL-1 beta involve different mechanisms, probably associated with IL-1RI.

Interleukin-1 type II receptor: a decoy target for IL-1 that is regulated by IL-4.

Interleukin-1 (IL-1) interacts with cells through two types of binding molecules, IL-1 type I receptor (IL-1R I) and IL-1R II. The function of IL-1R II is unknown. In studies using monoclonal antibodies, IL-1 prolonged the in vitro survival of polymorphonuclear cells (PMN) through IL-1R I, and IL-4 antagonized the action of IL-1 by inducing expression and release of IL-1R II. Dexamethasone also induced expression and release of the IL-1R II in PMN. These results, together with the effect of antibodies to IL-1R on IL-1-induced production of cytokines in monocytes, indicate that IL-1 acts on myelomonocytic cells through IL-1R I and that IL-1R II inhibits IL-1 activity by acting as a decoy target for IL-1. The existence of multiple pathways of regulation emphasizes the need for tight control of IL-1 action.

An mRNA homologous to interleukin-1 receptor type I is expressed in cultured rat sympathetic ganglia.

Interleukin-1 (IL-1) induces substance P (SP) gene expression in cultured rat superior cervical ganglion (SCG) explants. In order to study the molecular mechanism of this action of IL-1, the presence of an interleukin-1 receptor (IL-1R) activity and the identity of an mRNA homologous to known IL-1R sequence was determined in SCG. The SP increase is blocked by recombinant IL-1 receptor antagonist protein, so IL-1 must be interacting with a specific receptor. We have cloned cDNA homologous to IL-1R type I from rat SCG using a reverse transcription-polymerase chain reaction (RT-PCR). The resulting cDNA sequence is strongly homologous with mouse and human IL-1R cDNA of the T cell and fibroblast type (type I; encoding an 80-kDa protein). mRNA specific for IL-1R can be readily detected in intact SCG by quantitative RT-PCR and S1 hybridization. However, the level of IL-1R mRNA increases 3-6-fold by 2 days in culture. This increase is independent of the presence of dexamethasone, IL-1 beta or IL-1 receptor antagonist protein ligands. The increase of IL-1R following explantation, a model of nerve injury, may provide a mechanism linking inflammatory signalling to neuronal phenotypic changes.

Independent binding of interleukin-1 alpha and interleukin-1 beta to type I and type II interleukin-1 receptors.

Interleukin (IL)-1 refers to a group of three polypeptide hormones with a wide range of cellular targets. Two types of IL-1 receptor have been identified and characterized by cDNA cloning. Both human type I and type II IL-1 receptors contain extracellular domains of approximately 310 residues and a single membrane-spanning region. The type I receptor contains a cytoplasmic domain of 213 residues. The cytoplasmic region of the type II receptor is 29 residues in length. It has been found recently that a number of cells express both forms of receptor. By analogy with other cytokine receptor systems, the two IL-1 receptors might be expected to form a heterodimeric complex, the type II receptor being an alpha-chain-like structure, functioning only to bind ligand, and associating with the type I receptor (a beta-chain-like structure) which would transduce signals. In this report we show that this is not the case, but rather that IL-1, when complexed to type II receptor, cannot bind type I receptors, and vice versa. These data show that the complex patterns often observed for IL-1 binding to cells cannot be accounted for by the same type of mechanism that underlies the behavior of, for example, the IL-2 system.

Human aortic endothelial cells express the type I but not the type II receptor for interleukin-1 (IL-1).

Endothelial cells (EC) are very responsive to the proinflammatory cytokine interleukin-1 (IL-1). EC are induced by IL-1 to secrete chemotactic factors and to increase expression of cell surface adhesion molecules leading to increased leukocyte adhesion. Activated EC further contribute to the inflammatory response by secreting additional cytokines. IL-1 interacts with EC through high-affinity cell-surface receptors. However, the low number of receptors present on EC has made characterization difficult. Further, recent evidence has suggested diversity in the responses of EC from different regions of the vascular system. Interested in the effect of IL-1 on early atherosclerotic lesion formation, we have characterized the IL-1 receptors on human aortic endothelial cells (HAEC). Using a direct binding assay, we found that HAEC have 1,000-3,000 IL-1 receptors per cell and bind IL-1 alpha with a Kd of 3.5 x 10(-10) M. We found that a monoclonal antibody specific for the type I receptor completely blocks IL-1 alpha binding. The blocking antibody also completely inhibits the IL-1 induced increase in intracellular adhesion molecule 1 (ICAM-1) expression by HAEC. Using solution hybridization and ribonuclease protection with an antisense probe, a sensitive method for detection of low abundance mRNA species we found that HAEC as well as human umbilical vein EC (HUVEC) have significant levels of mRNA for the type I IL-1 receptor. To test whether HAEC might also contain transcripts for the type II IL-1 receptor, we compared levels of mRNAs by polymerase chain reaction (PCR) amplification of cDNAs reverse-transcribed from total RNA. We found only transcripts for the type I receptor and not the type II receptor in HAEC. Based on this data, we conclude that aortic endothelial cells respond to IL-1 through the type I receptor.