Detection and characterization of high affinity plasma membrane receptors for human interleukin 1

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.

Interleukin 1 signaling occurs exclusively via the type I receptor

Two receptors for the proinflammatory cytokine interleukin 1 (IL-1) have been cloned and characterized biochemically. While it has been well established that the type I (80-kDa) IL-1 receptor can mediate responses to IL-1, the function of the type II (60-kDa) IL-1 receptor has been unknown. In this manuscript we describe experiments designed to ask whether the type II receptor is capable of delivering a biological signal. We have examined two types of experimental situation: responses to IL-1 in cells which express predominantly the type II receptor, and responses to IL-1 which have been suggested previously in the literature to be mediated by type II receptors. In both situations we find that the responses instead are mediated via type I receptors. A blocking antibody against the type II receptor never inhibits, and in fact sometimes enhances, the responses. We conclude that a very small number of type I receptors is sufficient to mediate all of the actions of IL-1 which we have examined here and that the function of the type II receptor may not be to transduce signals.

Mathematical modeling of T-cell proliferation

A mathematical model of the T-lymphocyte proliferation process (in vivo and in vitro) is presented. This model takes into account cell-cycle progression and the regulation by lymphokines (lymphocyte activating factor interleukin 1 and T-cell growth factor interleukin 2). Using data on the generalized picture of the short-term course of viral hepatitis B, the parameter estimation procedure is carried out. The possibility of immunocorrection (by means of injection of a pharmacologic dose of IL-2) during the immune response to viral hepatitis B with T-lymphocyte deficiency is shown.

Synergistic antiproliferative effects of interleukin-1 alpha and doxorubicin against the human ovarian carcinoma cell line (NIH:OVCAR-3)

Interleukin-1 alpha (IL-1 alpha) exerts antiproliferative effects on a human ovarian carcinoma cell line, NIH:OVCAR-3, which is resistant to clinically relevant concentrations of doxorubicin (DOX) and other chemotherapeutic agents. This action of IL-1 alpha depends on the presence of type I (80 kDa) receptors, although no quantitative relationship has been established between receptor occupancy and inhibition of cell growth. When NIH:OVCAR-3 cells were exposed to IL-1 alpha and DOX in combination, a mutual potentiation of the antiproliferative effects of the two agents was observed. This synergistic effect was not due to IL-1 receptor expression up-regulation by DOX, and receptor-dependent internalization of the cytokine was also unaffected. The involvement of IL-1 receptors is supported by the observation that synergism between the two agents was diminished (but not abolished) in the presence of a specific IL-1 receptor antagonist at concentrations blocking more than 75% of IL-1 alpha binding. DOX was found to significantly increase IL-1 alpha accumulation by NIH:OVCAR-3 cells after long-term (48 hr) exposure to the cytokine at 37 degrees, which might be due to increased nonspecific fluid phase uptake or to interference with cytokine degradation and/or release processes. The potent synergy of IL-1 alpha and DOX against ovarian carcinoma cells in vitro suggests that this drug combination may be effective against this disease in the clinic.

IL-1-induced murine osteoblast IL-6 production is mediated by the type 1 IL-1 receptor and is increased by 1,25 dihydroxyvitamin D3

IL-1-induced osteoblast IL-6 production represents one possible mechanism by which IL-1 augments bone resorption. In this report, we show that the murine osteoblastic cell line (MC3T3-E1) expresses type 1 IL-1 receptors based on 125I-HrIL1 alpha binding, blocked by type 1 IL-1R antibodies (35F5), and analysis of MC3T3 RNA by reverse transcription (RT)-DNA amplification and Northern analysis. MC3T3 cells do not express detectable type 2 IL-1R mRNA by RT-DNA amplification. IL-1 induces (IL-1 ED50, 0.1 pM) IL-6 production through the type 1 IL-1R as 35F5 antibodies block IL-1-stimulated IL-6 production. Vitamin D3 increases IL-1R expression dose- and metabolite-dependently, with 1,25-(OH)2D3 having the greatest potency, and also enhances IL-1's capacity to stimulate IL-6 production at low IL-1 levels. Both IL-1 and 1,25-(OH)2D3 induce type 1 IL-1R and not type 2 IL-1R upregulation based on ligand binding and RT-DNA amplification. Increased IL-1R expression requires a 5-7-h treatment and is protein/RNA synthesis dependent. These observations imply that IL-1-induced IL-6 production in osteoblasts is mediated by type 1 IL-1Rs and that increased IL-1R expression could play a role in mediating IL-1-induced skeletal responses.

Lack of effect of interleukins 1 alpha and 1 beta, during in vitro perifusion, on anterior pituitary release of adrenocorticotropic hormone and beta endorphin in the male rat

It has been demonstrated that interleukin 1 (IL1) injection provokes a great variety of biological effects, notably an activation of the corticotropic axis, increasing plasma adrenocorticotropic hormone (ACTH) and corticosterone. However, the primary site of action of IL1 is still controversial. In the present study, we first verified the in vivo capability of human interleukins 1 alpha (hIL1 alpha) and 1 beta (hIL1 beta) to release ACTH and beta endorphin (beta EP) in the normal male rat, before investigating, through an anterior pituitary (AP) perifusion system, the hIL1 alpha and hIL1 beta effects on basal and corticotropin-releasing factor (CRF)-induced ACTH and beta EP secretions. This system enabled the examination of a dynamic profile of hormones secretion, avoiding the possibility of feedback mechanisms, as is the case with the use of regular but very often longtime incubations. The results showed that in a perifusion system, with a short duration treatment (below 2 hr) compatible with the kinetics of action observed in vivo, basal and CRF-induced ACTH and beta EP release were not modified in the presence of a broad range of concentrations (from 10(-12) to 10(-9) M) of hIL1 alpha or hIL1 beta. Taken together, these results clearly show that in an in vitro situation close to physiological conditions, the primary site of action of hIL1 alpha and hIL1 beta on ACTH and beta EP release is not located at the AP level in the male rat.

Characterization and identification of interleukin-1 receptors on bovine fibroblasts

Interleukin-1 (IL-1), a pro-inflammatory cytokine, initiates its many biological effects by first binding to cell-surface receptors. Prior to this study, there were no published reports addressing the nature of the bovine IL-1 receptor. In this study, we characterized and identified cell-surface IL-1 receptors on bovine fibroblasts. Direct binding studies using [125I]-labeled bovine IL-1 beta demonstrated that bovine fibroblasts had approximately 130 high affinity and 2,500 low affinity binding sites (Kd = 4.9 x 10(-11) M and 3.7 x 10(-9) M, respectively). Competitive binding studies using unlabeled recombinant bovine IL-1 beta, IL-2, IFN-alpha, and bovine insulin demonstrated that only unlabeled bovine IL-1 beta competitively blocked fibroblast binding of [125I]-labeled bovine IL-1 beta. Affinity cross-linking of [125I]-labeled IL-1 beta to fibroblasts demonstrated that IL-1 receptors on bovine fibroblasts have an apparent M(r) of 71.5 kD. This report provides the first characterization and identification of IL-1 receptors on bovine fibroblasts.

Interleukin-1 binding sites on astrocytes

Interleukin-1 has been shown to have regulatory effects on glial cell functions. In this study, we examined the capacity of astroglial cells to specifically bind recombinant iodinated human interleukin-1 alpha. This was performed in mouse brain by both in situ and in vitro autoradiography, on areas of gliosis and on astrocytes and microglia primary and secondary cultures respectively. Specific binding was shown in the brain sections over areas of glial proliferation, and in addition, quantitative autoradiography was performed. Analysis of competition experiments by autoradiography led to EC50 values of 5 x 10(-11) M for human interleukin-1 alpha and approximately 10(-9) M for the interleukin-1 receptor antagonist. In cultures, iodinated human interleukin-1 alpha bound specifically to astrocytes but was unable to bind to microglial cells. Competition binding experiments in astrocyte cultures led to EC50 values of 8 x 10(-11) M and 1 x 10(-10) M for human interleukin-1 alpha and mouse interleukin-1 beta respectively, and an EC50 higher than 10(-9) M for the antagonist. The presence of interleukin-1 receptors on astroglial cells provides biochemical support for the various effects of interleukin-1 in the central nervous system, particularly those concerning the formation of scar tissue, possibly by astroglia proliferation after brain injury.

Heterogeneity of type-II interleukin-1 receptors. Heterogeneity of B-cell interleukin-1 binding created by dimerization of type-II interleukin-1 receptors

The binding of IL-1 alpha and IL-1 beta to two human lymphoblastoid B-cell lines, Raji and RPMI 1788, was compared with binding to the murine T-cell line, EL4. Dramatic differences in IL-1 binding were observed. Both human B-cell lines bound much less IL-1 alpha than IL-1 beta, expressed 5-10 times more receptors per cell for IL-1 beta than did the EL4 cell line, and demonstrated a large difference in the ability of IL-1 alpha to compete with IL-1 beta for binding. The B-cell lines demonstrated a low number of high-affinity IL-1 alpha receptors and a large number of IL-1 alpha receptors with a much lower affinity. Inhibition studies demonstrated that only IL-1 beta could compete for the binding of radiolabeled IL-1 beta to the B-cell IL-1R. Furthermore, SDS-PAGE analyses of lysates of the B-cell lines that had been affinity cross-linked with 125I-IL-1 alpha revealed two bands corresponding to IL-1R structures of 60 and 110 kD. These results coupled with a nonequilibrium binding study suggested a dimerization of a common type-II IL-1R polypeptide, the dimer being responsible for the high-affinity IL-1 alpha-binding site of the B-cell lines.

Activation of the sphingomyelin signaling pathway in intact EL4 cells and in a cell-free system by IL-1 beta

The mechanism of interleukin-1 (IL-1) signaling is unknown. Tumor necrosis factor-alpha uses a signal transduction pathway that involves sphingomyelin hydrolysis to ceramide and stimulation of a ceramide-activated protein kinase. In intact EL4 thymoma cells, IL-1 beta similarly stimulated a rapid decrease of sphingomyelin and an elevation of ceramide, and enhanced ceramide-activated protein kinase activity. This cascade was also activated by IL-1 beta in a cell-free system, demonstrating tight coupling to the receptor. Exogenous sphingomyelinase, but not phospholipases A2, C, or D, in combination with phorbol ester replaced IL-1 beta to stimulate IL-2 secretion. Thus, IL-1 beta signals through the sphingomyelin pathway.

Function of peritoneal exudate cells after abdominal surgery

Peritoneal macrophages and polymorphonuclear neutrophils are key cells in the repair of postoperative injury. Increased numbers of macrophages migrate into the peritoneal cavity after operation and the function of these cells changes over the postoperative interval. Macrophage activities, such as respiratory burst, arachidonic acid metabolism, monokine secretion, and plasminogen activator inhibitory activity, are elevated by peritoneal operation. However, the secretion of plasminogen activator activity is decreased after operation. The kinetics with which each of these functions changes varies with the parameter examined, indicating a complex regulation of the differentiation of leukocytes after operation. In addition, the activity of postoperative macrophages can be modulated in vitro by exposure to cytokines and conditioned media from polymorphonuclear neutrophils and macrophages. Thus, cell-cell interactions and factors secreted within the peritoneal cavity may regulate the contribution of postoperative leukocytes to peritoneal repair after operation.

Cytokine regulation of the interleukin-1 receptor antagonist protein in U937 cells

A naturally occurring receptor-level antagonist of interleukin-1 (IRAP or IL-1 ra) has recently been cloned. To determine what stimuli might regulate this inhibitor, cytokines were tested for their effects on the steady-state level of IRAP mRNA in phorbol ester-differentiated U937 cells. The cytokines tested fell into one of three groups: (a) inducers: granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-4, (b) weak inducers (< 2-fold stimulation): [IL-1 alpha, IL-1 beta, and transforming growth factor-beta (TGF-beta)] and (c) cytokines with no effect: (IL-2, platelet-derived growth factor, acidic fibroblast growth factor, basic fibroblast growth factor, epidermal growth factor, granulocyte colony-stimulating factor, IL-3, IL-5, IL-6, interferon-gamma, multi-colony stimulating factor, tumor necrosis factor-alpha and IRAP itself. One hundred U/ml of either GM-CSF or IL-4 was the dose inducing peak IRAP mRNA expression; that peak expression occurred 12 h after addition of cytokine. GM-CSF induced a 34 +/- 15-fold increase in IRAP mRNA, and IL-4 induced a 15 +/- 6-fold increase. In the same RNA samples, GM-CSF increased IL-1 beta mRNA 5.9 +/- 1.7-fold, but IL-4 decreased IL-1 beta mRNA to half that of control levels (0.45 +/- 0.17). Thus, a single stimulus (IL-4) decreased the expression of an agonist (IL-1) while it increased the expression of an antagonist (IRAP). When U937 cells were treated with both IL-4 and GM-CSF, the level of IRAP mRNA induced was additive, suggesting that the cytokines acted differently to increase IRAP mRNA levels. The level of IL-1 mRNA in cells treated with both IL-4 and GM-CSF was intermediate. Dexamethasone and cycloheximide inhibited all mRNA increases and did not reverse IL-4-induced decreases in IL-1 mRNA. These studies have identified two cytokines which induce IRAP in the monocytic cells studied, and have partially characterized the differential regulation of IL-1 and its antagonist, IRAP.

Interleukin-1 beta and IgG subclass concentrations in gingival crevicular fluid from patients with adult periodontitis

Interleukin-1 beta (IL-1 beta) and the four IgG subclasses were measured in gingival crevicular fluid (GCF) at 35 sites in 19 patients with adult periodontitis. Serum concentrations of the IgG subclasses were assayed in 16 patients. IL-1 beta was detected in GCF at 88.6% of sites at concentrations ranging from 12.38-420.90 pg/microliters (mean 138.35 +/- 112.61 pg/microliters). IgG1 was detected at 81.2% sites, IgG2 at 93.6%, IgG3 at 71% and IgG4 at 71%. Absolute concentrations in GCF were: IgG1--2.419 g/l +/- (SD) 3.389; IgG2--2.945 +/- 6.434; IgG3--0.118 +/- 0.144; IgG4 0.864 +/- 1.336. There were no significant correlations between IL-1 beta concentrations, GCF volume or the clinical status of the sample site. IL-1 beta was not correlated with any of the IgG subclasses. The absolute concentrations of all subclasses in GCF were significantly negatively correlated with GCF volume and positively correlated with the Bleeding Index. Only IgG4 was significantly negatively correlated with the probeable crevice depth index. The concentration of each IgG subclass was positively correlated with the other three IgG subclasses. Subclass concentrations in GCF, relative to serum concentrations, were not correlated with GCF volume or clinical status. Relative concentrations of IgG1, IgG2 and IgG3 showed significant positive correlation with each absolute concentration of the other subclasses but IgG4 did not show this relation. It was concluded that IL-1 beta is not related to clinical measurements of inflammation or previous attachment loss. The data suggest that IgG in GCF is largely derived from plasma but that some IgG4 may be locally synthesized.

Evidence that MAP (mitogen-activated protein) kinase activation may be a necessary but not sufficient signal for a restricted subset of responses in IL-1-treated epidermoid cells

We have investigated the activation of mitogen-activated protein kinase (MAP-kinase) in KB human epidermoid carcinoma cells treated with interleukin 1 (IL-1). MAP-kinase activity was transient; the time required for activity to reach a maximal level was dependent upon the dose of IL-1, ranging from 15 minutes to 45 minutes. The level of kinase induction correlated well with dose-response curves for two characteristic IL-1-induced responses, PGE2 and IL-6 production. MAP-kinase activity returned to basal levels within 2 hours regardless of the amount of IL-1 added to the system. Exposure of KB cells to free IL-1 was accordingly restricted to periods of 2 hours or less, by replacing IL-1 with an excess of IL-1 receptor antagonist. Even after 2 hours exposure, the ability of IL-1 to induce IL-6 or PGE2 was still IL-1ra-inhibitable by more than 80%, suggesting that events downstream of, or parallel to MAP-kinase activation, requiring the continual formation of new IL-1 receptor complexes, are needed to fully elicit these responses. Two general serine/threonine kinase inhibitors, K252a and quercetin, were found to strongly inhibit MAP kinase in vivo with ED50s of c. 100 nM and 30 microM, respectively. At these concentrations, both compounds effectively inhibited IL-1-driven PGE2 and IL-6 induction without affecting general protein synthesis or secretion. Other non-selective kinase inhibitors had less effect on MAP-kinase activation or IL-1-induced biological responses. The transient activation of MAP-kinase induction correlated strikingly with activation of the transcription factor NF-kappa B. IL-1-induced NF-kappa B activation was, however, relatively insensitive to inhibition by K252a or quercetin. We suggest that MAP-kinase is likely to be a necessary, but not sufficient, intermediate in some (IL-6, PGE2 induction) but not all (NF-kappa B activation) IL-1 responses in these cells.

Expression and biological activity of interleukin-1 receptors in mouse gamma/delta thymocytes during ontogeny

We have recently shown that the response of mouse thymocytes to interleukin (IL)-1 + IL-2 was maximal at birth and that the responding cells displayed a CD4-CD8- T cell receptor (TcR) gamma/delta + phenotype. Unexpectedly, despite their high proportion of gamma/delta + cells, fetal thymocyte populations responded only weakly to IL-1 + IL-2. In this report, we demonstrate that the discrepancy between the day 17.5 fetal and newborn sensitivities to the combined action of IL-1 and IL-2 is a consequence of the different patterns of high-affinity IL-1 receptor (IL-1R) expression displayed by these two cell subsets. Actually, high- and low-affinity IL-1R are found in TcR gamma/delta + newborn cells and, in contrast, only low-affinity IL-1R are detectable in day 17.5 fetal cells. Our binding and functional studies strongly support the hypothesis that high-affinity IL-1R on the one hand, and low-affinity ones on the other hand, are involved in the response to IL-1 + IL-2 of newborn and day 17.5 fetal thymocytes, respectively. In addition, the high-affinity IL-1R appear to be far more efficient than the low-affinity receptors in promoting IL-2 responsiveness of thymocytes.

The therapeutic potential of interleukin-1 and tumor necrosis factor on hematopoietic stem cells

Dose intensity is emerging as a crucial determinant of success in cytotoxic cancer therapy; however, myelosuppression presents as one of the major complications encountered with increased dose intensity. Therefore, investigators are looking at the use of cytokine administration in combination with cytotoxic therapy to overcome this problem. Interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF-alpha) have been shown to be beneficial in protecting the hematopoietic system from radiation and chemotherapy. In this report, we give an overview of studies using IL-1 and TNF-alpha as protective agents and discuss possible mechanisms involved in their protective action. Mice pretreated with IL-1 and/or TNF-alpha were shown to be protected from the lethal effects of radiation and it has been suggested that the mechanism for this protection may be through the production of the antioxidant enzyme manganese superoxide dismutase. Similarly, aldehyde dehydrogenase, an enzyme important in the metabolic pathway of cyclophosphamide compounds, has been implicated as being important in the protection of hematopoietic cells from 4-hydroperoxycyclophosphamide. While IL-1 and TNF-alpha stimulate both of these enzymes, other mechanisms are probably also operative for other forms of chemotherapy, i.e. IL-1 and TNF-alpha were shown to protect hematopoietic progenitors from phenylketophosphamide, a cyclophosphamide derivative that is not metabolized by the enzyme aldehyde dehydrogenase. Furthermore, malignant as well as normal cells may possess receptors for these cytokines; therefore, IL-1 and TNF-alpha will have to be selective in their protection. They must be capable of protecting normal hematopoietic cells while rendering malignant cells susceptible to the toxic actions of the chemotherapy.(ABSTRACT TRUNCATED AT 250 WORDS)

A soluble receptor for interleukin-1 beta encoded by vaccinia virus: a novel mechanism of virus modulation of the host response to infection

Vaccinia virus gene B15R is shown to encode an abundant, secretory glycoprotein that functions as a soluble interleukin-1 (IL-1) receptor. This IL-1 receptor has novel specificity since, in contrast with cellular counterparts, it binds only IL-1 beta and not IL-1 alpha or the natural competitor IL-1 receptor antagonist. The vaccinia IL-1 beta receptor is secreted when expressed in a baculovirus system and competitively inhibited binding of IL-1 beta to the natural receptor on T cells. Deletion of B15R from vaccinia virus accelerated the appearance of symptoms of illness and mortality in intranasally infected mice, suggesting that the blockade of IL-1 beta by vaccinia virus can diminish the systemic acute phase response to infection and modulate the severity of the disease. The IL-1 beta binding activity is present in other orthopoxviruses.

Tumor necrosis factor and interleukin 1 inhibit parathyroid hormone-responsive adenylate cyclase in clonal osteoblast-like cells by down-regulating parathyroid hormone receptors

The effects of the monokines tumor necrosis factor alpha (TNF) and interleukin 1 (IL 1) on parathyroid hormone (PTH)-responsive adenylate cyclase were examined in clonal rat osteosarcoma cells (UMR-106) with the osteoblast phenotype. Recombinant TNF and IL 1 incubated with UMR-106 cells for 48 hr each produced concentration-dependent inhibition of PTH-sensitive adenylate cyclase, with maximal inhibition of PTH response (40% for TNF, 24% for IL 1) occurring at 10(-8) M of either monokine. Both monokines also decreased adenylate cyclase stimulation by the tumor-derived PTH-related protein (PTHrP). In contrast, TNF and IL 1 had little or no inhibitory effect on receptor-mediated stimulation of adenylate cyclase by isoproterenol and nonreceptor-mediated enzyme activation by cholera toxin and forskolin; both monokines increased prostaglandin E2 stimulation of adenylate cyclase. Binding of the radioiodinated agonist mono-[125I]-[Nle8,18, Tyr34]bPTH-(1-34)NH2 to UMR-106 cells in the presence of increasing concentrations of unlabeled [Nle8,18, Tyr34]bPTH-(1-34)NH2 revealed a decline in PTH receptor density (Bmax) without change in receptor binding affinity (dissociation constant, Kd) after treatment with TNF or IL 1. Pertussis toxin increased PTH-sensitive adenylate cyclase activity but did not attenuate monokine-induced inhibition of PTH response. In time course studies, brief (1 hr) exposure of cells to TNF or IL 1 during early culture was sufficient to decrease PTH response but only after exposed cells were subsequently allowed to grow for prolonged periods. Inhibition of PTH response by monokines was blocked by cycloheximide. The results indicate that TNF and IL 1 impair responsiveness to PTH (and PTHrP) by a time- and protein synthesis-dependent down-regulation of PTH receptors linked to adenylate cyclase.

Muscle protein breakdown during endotoxemia in rats and after treatment with interleukin-1 receptor antagonist (IL-1ra)

The purpose of this study was to examine the effect of endotoxemia on muscle protein degradation and to test the hypothesis that muscle proteolysis during endotoxemia is regulated by interleukin-1 (IL-1). Both total and myofibrillar protein breakdown rates in incubated extensor digitorum longus muscles were increased after the subcutaneous injection of 0.1 or 1.0 mg/kg endotoxin in rats. The endotoxin-induced increase in muscle protein breakdown was blunted by IL-1 receptor antagonist, administered intraperitoneally at a total dose of 45 or 105 mg/kg. Results suggest that endotoxemia in rats gives rise to sepsislike changes in muscle protein breakdown. Increased muscle protein breakdown during endotoxemia may be regulated, at least in part, by IL-1.

Detection of cytokine receptors by high-sensitivity immunofluorescence/flow cytometry

Cytokines have profound effects on cells, and act through receptors which need only be at low concentrations (around 100 copies per cell) to transmit activation signals. The detection of such low concentrations is possible using monoclonal antibodies and fluorescence/flow cytometry, but only by using specialized techniques. The best results so far have been obtained using biotinylated second antibody followed by phycoerythrin-streptavidin, and batches of these reagents have to be carefully selected. Analysis of the fluorescence is best done using 546 nm excitation from a mercury arc lamp, but 512 nm excitation from an argon-ion laser can also be used. With appropriate alignment, instruments with 488 nm fixed-wavelength lasers can give sensitivity almost as good as the 546 nm system. Working at high sensitivity, background levels also increase, particularly for B lymphocytes. Background staining can be reduced to acceptable levels by blocking the two major mechanisms for non-specific binding. Applications of these methods to the detection of cytokine receptors on normal and malignant cells are reviewed.

Multiple amino acid substitutions suggest a structural basis for the separation of biological activity and receptor binding in a mutant interleukin-1 beta protein

Receptor binding and biological activity properties of human interleukin-1 beta can be dissociated by mutating a single amino acid, arginine 127, to glycine (IL-1 beta R----G) [Gehrke et al. (1990) J. Biol. Chem. 265, 5922-5925]. The mechanism underlying the reduced biological activity has been examined by replacing arginine 127 with several other amino acids, followed by determination of biological activity using a T-helper cell proliferation assay. Mutant IL-1 beta proteins containing lysine, glutamic acid, tryptophan, or alanine in place of arginine 127 maintain biological activity. These data strongly suggest that IL-1 beta biological activity is not directly dependent upon the specific properties of charge, hydrophobicity/hydrophilicity, or side-chain group presented by the residue at position 127. Molecular modeling analyses indicate that the structural integrity of the antiparallel beta-strand 1/12 pair is disturbed in the glycine 127 mutant protein. Collapse of beta-strand 1 into a hydrated space between strands 1, 2, and 4 could structurally alter a cleft in IL-1 beta that contains a cluster of highly conserved amino acids, including a key aspartic acid residue [Ju et al. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 2658-2662]. Mutagenesis data and the differential activities of the IL-1 beta R----G and IL-1 receptor antagonist proteins in stimulating early and late gene expression [Conca et al. (1991) J. Biol. Chem. 266, 16265-16268] suggest that multiple receptor-ligand contacts, exclusive of those required for receptor binding, are required for the stimulation of full IL-1 biological activity.

Native cytokine antagonists

Cytokines orchestrate the complex homeostasis of cells and tissues by acting in both an autocrine and paracrine fashion. The processes responsible for regulation of cytokines is not well understood. This chapter has summarized what is known about antagonism and inhibition of the action of cytokines. Several concepts have emerged from work in this area. At least two cytokines (IL-1 alpha and IL-1 beta) have an endogenous receptor antagonist, the IL-1 receptor antagonist. This is the first example of one endogenous molecule directly blocking the binding of another molecule to its receptor: most forms of regulation occur through independent receptors. Several cytokines, including TNF, IFN-gamma, IL-2 and IL-4, are inhibited by soluble receptors. Several cytokines, including IL-10, TGF-beta and MDF, act to inhibit other cytokines. It is likely that these inhibitors will be found to have pleiotropic actions in vivo. Finally, we describe antibody inhibition of cytokines. Detailed studies will be required to understand the complex interplay of the aforementioned cytokine inhibitors and the processes they regulate.

Increased interleukin 1 receptor, type I, at messenger RNA and protein level in skin fibroblasts from patients with systemic sclerosis

Summary. To elucidate the mechanisms of the fibrosis in systemic sclerosis (SSc) through the action of a cytokine, interleukin 1 (IL-1), we studied the specific biologic and biochemical features of interleukin 1 receptor (IL-1R) as expressed on the surfaces of fibroblast cells in cultures from 3 SSc patients and 3 normal donors. 125I-IL-1 beta binding assays revealed a high density of IL-1R on the cell surfaces of SSc fibroblasts as compared to those of normal subjects. We also found an enhanced expression of IL-1R messenger RNA (mRNA) in SSc fibroblasts, using Northern blot or slot blot analysis. These findings indicate that the expression of IL-1R on SSc fibroblasts were spontaneously induced at the transcriptional level. It is suggested that SSc fibroblasts are more sensitive to IL-1, and that the signal transduction of IL-1 through IL-1R may be eventually involved in the fibrosis of SSc.

Interleukin-1 up-regulates transcription of its own receptor in a human fibroblast cell line TIG-1: role of endogenous PGE2 and cAMP

The regulation of interleukin-1 receptor (IL-1R) mRNA expression by IL-1 in a human lung fibroblast cell line (TIG-1) was investigated. After 2 h of stimulation with human recombinant IL-1 alpha or IL-1 beta, the levels of T cell/fibroblast-type IL-1R mRNA increased, and the elevation was sustained for at least 72 h. IL-1 also stimulated synthesis of prostaglandin E2 (PGE2) and secondary cAMP accumulation. Exogenously added PGE2 increased the levels of both IL-1R mRNA and intracellular cAMP. Forskolin, cholera toxin and 8-Bromo adenosine (8-Br-cAMP) all increased IL-1R mRNA levels. Indomethacin blocked IL-1 stimulation of IL-1R mRNA expression, PGE2 production and cAMP. 125I-labeled IL-1 alpha-binding studies showed that this cell line expresses 2.6 x 10(4) IL-1R per cell with a Kd of 5.1 x 10(-10) M. After treatment of the cells with IL-1, the level of IL-1R increased over that of control cells. PGE2 also increased IL-1R without alteration in its affinity. Cross-linking experiments indicate that this cell line expresses the 80-kDa receptor molecule before and after treatment with PGE2; the molecular mass corresponds to the T cell/fibroblast type I IL-1R. These results indicate that IL-1 does not directly stimulate expression of IL-1R mRNA or cell surface IL-1R, but only indirectly by stimulation of endogenous PGE2.

The interleukin-1 receptor in normal and osteoarthritic human articular chondrocytes. Identification as the type I receptor and analysis of binding kinetics and biologic function

OBJECTIVE

To identify and investigate the kinetic binding properties of interleukin-1 receptors (IL-1R), and examine the abilities of the 2 IL-1 isoforms to stimulate metalloprotease synthesis, in normal and osteoarthritic (OA) chondrocytes.

METHODS

Receptor affinity and density were determined using radioligand binding experiments and flow cytometry. Immunocytochemical analysis and affinity cross-linking studies were performed for characterization of IL-1R.

RESULTS

While no difference in receptor affinity between normal and OA chondrocytes was noted in binding studies (Kd approximately 30 pM), a 2-fold increase in receptor density was found in OA chondrocytes as compared with normal chondrocytes (mean 4,069 sites/cell versus 2,315 sites/cell). Flow cytometry experiments also showed a significant increase in receptor density in OA cells, as well as an enhancement in the percentage of positive cells in diseased cartilage compared with normal. Binding data for both IL-1 isoforms revealed a single class of binding sites and receptor specificity. Factors such as IL-2, interferon-gamma, tumor necrosis factor alpha, and bovine insulin did not compete with IL-1 beta. By covalent ligand cross-linking and electrophoretic analysis, only type I IL-1R, a protein of 80 kd, was detected on chondrocytes. By immunocytochemical analysis, IL-1R was identified at the cell membrane level, in both normal and OA chondrocytes. The presence of nuclear staining was also observed, but only in OA chondrocytes. Recombinant human IL-1 (alpha and beta) induced the secretion of stromelysin and collagenase in a dose-dependent manner. The IL-1 concentration required for half-maximal metalloprotease stimulation was 3-4 times lower in OA chondrocytes than in normal cells.

CONCLUSION

These results indicate that OA chondrocytes have a higher sensitivity to the stimulation of metalloprotease synthesis by IL-1 than do normal cells. This could be related to the increased levels of IL-1R expressed in the OA cells. The implications of these findings with regard to the possible roles of IL-1 and IL-1R in the pathogenesis of OA are discussed.

Psoriatic skin reveals the in vivo presence of an epidermal IL-1 inhibitor

Production of inhibitor(s) of IL-1 activity can be induced in keratinocytes by exposure to UVB. We describe in this study the characterization of an endogenous constitutively expressed IL-1 inhibitor which is present in extracts of human psoriatic epidermal keratome biopsies. Size-fractionated extracts of normal human epidermis did not reveal IL-1 inhibitory factor(s) activity in normal epidermis. Psoriatic epidermal extracts, however, contained virtually no IL-1 bioactivity and inhibited the activity of recombinant human IL-1 beta. This IL-1 inhibitor has a molecular weight of approximately 30 kDa and a pI of 5.3, as revealed by fast protein liquid chromatography size fractionation and chromatofocusing of psoriatic epidermal extracts. IL-1 inhibitory activity was not blocked by neutralizing anti-TGF beta monoclonal antibody. It did not have any inhibitory effect upon normal cellular proliferation but could block the IL-1 induction of IL-2 production by LBRM.33 cells as late as 4 h after exposure of LBRM.33 cells to IL-1. Thus, in vivo human psoriatic epidermis expresses an IL-1 inhibitor that specifically inhibits IL-1 activity but which appears distinct from previously described UV-induced epidermal IL-1 inhibitory activity or TGF beta.

Characterization of IL-1 inhibitory factor released from human alveolar macrophages as IL-1 receptor antagonist

IL-1 possesses pleiotropic properties on various cells and its activity may be stringently regulated in several ways. We have previously reported that both IL-1 and its inhibitory factor are concomitantly released from alveolar macrophages in both healthy subjects and patients with chronic inflammatory lung diseases. An increase in IL-1 activities and a decrease in inhibitory activities are characteristics found in both healthy smokers and patients with interstitial lung diseases. In this study, we further examined the biological properties of IL-1 inhibitory factor. The inhibitor exhibited a dose-dependent specific inhibition of an augmentation by IL-1 of PHA-induced murine thymocyte proliferation, while no inhibition of the augmentation by IL-2, IL-4, IL-6, or tumour necrosis factor (TNF) was found. 125I-labelled IL-1 alpha binding on PHA-stimulated murine thymocytes revealed two types of IL-1 binding sites, 44 sites/cell with a Kd of 2.7 x 10(-10) M and 230 sites/cell with a Kd of 2.5 x 10(-9) M. Alveolar macrophage culture supernatants blocked the binding of labelled IL-1 to the IL-1 receptor in a dose-dependent fashion. Scatchard plot analysis revealed that the inhibitory factor in the supernatants blocked the binding competitively. These results indicate that alveolar macrophages produce a specific IL-1 inhibitory factor, functioning as an IL-1 receptor antagonist.

Contrasting effects of the protein kinase C inhibitor staurosporine on the interleukin-1 and phorbol ester activation pathways in the EL4-6.1 thymoma cell line

EL 4-6.1 cells, variants of the murine EL4 thymoma cell line, can be activated by interleukin 1 (IL-1) or phorbol 12-myristate-13-acetate (PMA), or PMA+IL-1 to secrete interleukin 2 (IL-2) and interleukin 4 (IL-4) and to express the IL-2 receptor (IL-2R). To compare the different activation pathways, we examined the effects of staurosporine (STAR) and 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), two protein kinase C (PKC) inhibitors, on the induction of interleukin secretion and IL-2R expression in these cells. We report here that nanomolar concentrations of STAR strongly potentiated (20- to 30-fold) the production of IL-2 or IL-4, when EL 4-6.1 cells were induced by IL-1 alpha (or IL-1 beta) alone. By contrast, at identical concentrations, STAR dose-dependently inhibited the production of IL-2 and IL-4 resulting from PMA or PMA+IL-1 cell treatment. STAR also negatively affected the expression of IL-2R, which was dependent on PMA-sensitive PKC with either IL-1, PMA, or PMA+IL-1 stimulation. The changes in interleukin production and IL-2R expression in EL 4-6.1 activated cells were correlated with changes at the mRNA level measured by quantitative polymerase chain reaction (PCR). This finding suggests a pretranslational effect of the drug. At micromolar concentrations, H7 showed the same effects as STAR, but only increased IL-1-triggered interleukin secretions twofold. We observed that the action of PKC inhibitors did not result from modification of IL-1 receptor (IL-1R) expression in EL 4-6.1 cells. Thus, our data show that PKC inhibitors clearly distinguish between IL-1 and PMA stimulatory pathways. In addition, they suggest that the IL-1 stimulatory pathway involves PKC(s) [or other undefined kinase(s)] which regulate this pathway and differ from PKC(s) activated by PMA.

Regulation of interleukin-1 receptors on AtT-20 mouse pituitary tumour cells

To study the cellular mechanisms of interleukin-1 (IL-1) in the pituitary corticotroph, we studied the properties of IL-1 receptors on a mouse pituitary ACTH-producing cell line, AtT-20. Scatchard plot analysis revealed a single type of receptor with a Kd (dissociation constant) of 93 pM, and 482 binding sites/cell. [125I]IL-1 alpha binding competed with IL-1 alpha and IL-1 beta in an equimolar fashion. A 24 h pre-incubation with either CRH, epinephrine or nor-epinephrine increased the [125I]IL-1 alpha binding sites in the AtT-20 cells and conversely, a similar pre-incubation with either dexamethasone or tumour necrosis factor-alpha (TNF alpha) decreased them without affecting the affinity of the receptors in either case.

Differential effect of interleukin 1 on naive and memory CD4+ T cells

Freshly derived murine CD4+ T cells are divided into naive and memory cells based on the expression of CD45 isoforms. Cross-linking the T cell receptor CD3 complex either by plastic-bound anti-CD3 antibodies or the antibody presented on non-lymphoid Fc gamma receptor type II-positive Chinese hamster ovary cells in absence of competent antigen-presenting cells fails to activate naive cells to either secrete cytokines or to proliferate. In contrast, memory cells secrete their characteristic cytokines [interleukin (IL) 2, IL4, and interferon-gamma] and show significant proliferation to this stimulus. IL 1 however, is required for their optimal clonal expansion. Differential expression of IL 1 receptor mRNA in memory cells also correlate with their responsiveness to IL 1. Thus, these data reveal a basic difference in the requirements for activation of naive and memory CD4+ T cells.

Differential binding of IL-3 and GM-CSF to human monocytes

Human monocytes respond to IL-3 and GM-CSF with a similar range of functional activities, and at similar cytokine concentrations. We have recently shown, however, that the rate of monocyte activation is greater in response to GM-CSF than to IL-3. In order to understand the basis of this phenomenon we investigated the interaction of IL-3 and GM-CSF with their surface receptors by means of kinetic binding experiments. 125I-GM-CSF showed very rapid association to monocytes at 37 degrees C, with a half-time of only 40 sec. The pattern of binding with this ligand was complex, with a decline in overall cell-associated radioactivity after 2 min of incubation. In contrast, 125I-IL-3 showed slower association, with a half-time at 37 degrees C of 2.5 min. The different rates of association correlated well with the different rates of cell activation induced by the two cytokines. On the other hand, rates of internalisation were similar for the two cytokines, with half-times of 14-15 min. Competition binding experiments performed under high affinity conditions showed that IL-3 and GM-CSF cross-competed for binding on the surface of monocytes. In contrast, under low affinity conditions IL-3 did not compete for 125I-GM-CSF binding while GM-CSF was a strong competitor of 125I-IL-3 binding. In quantitative inhibition experiments GM-CSF showed inhibitory effects on low affinity 125I-IL-3 binding at lower concentrations than those needed with unlabelled IL-3. It is suggested that current models of IL-3/GM-CSF receptor interactions need to be revised in order to accommodate the unique pattern of competition on human monocytes presented here.

Increased expression of the interleukin 1 receptor on blood neutrophils of humans with the sepsis syndrome

Because of the potential importance of interleukin 1 (IL-1) in modulating inflammation and the observations that human blood neutrophils (PMN) express IL-1 receptors (IL-1R) and synthesize IL-1 alpha and IL-1 beta, we studied the IL-1R on blood PMN from a group of patients with the sepsis syndrome. We report a marked enhancement in the sites per cell of IL-1R expressed on sepsis-PMN of 25 consecutively studied patients compared to 20 controls (patient mean = 9,329 +/- 2,212 SE; control mean = 716 +/- 42 SE, respectively). There was no demonstrable difference in the Kd of IL-1R on sepsis-PMN (approximately 1 nM) as determined by saturation curves of 125I-IL-1 alpha binding and the IL-1R on sepsis-PMN had an apparent Mr approximately 68,000, a value like that of normal PMN. Cytofluorographic analysis indicated that the sepsis-PMN phenotype is a single homogeneous population with respect to IL-1R expression. In contrast, expression of the membrane complement receptor CR3 is not increased on sepsis-PMN. Similar increases in expression of IL-1R were not observed in various other inflammatory processes, including acute disseminated inflammation and organ failure not caused by infection, acute infection without organ failure, and immunopathologies such as active systemic lupus erythematosus and rheumatoid arthritis. Enhanced expression of IL-1R was not related simply to the state of myeloid stimulation. Increased expression of IL-1R on normal PMN was induced in vitro by incubating cells with recombinant human granulocyte-macrophage/colony-stimulating factor for 18 h and this response was inhibited by cycloheximide, suggesting the possibility that de novo synthesis of IL-1R might occur in PMN during the sepsis syndrome.

The structure of murine interleukin-1 beta at 2.8 A resolution

The three-dimensional structure of recombinant murine interleukin-1 beta has been solved by X-ray crystallographic techniques to 2.8 A resolution and refined to a crystallographic R factor of 0.192. Although murine interleukin-1 beta crystallizes in the same space group as human interleukin-1 beta with almost identical unit cell dimensions, the packing of the molecules is quite different. The murine interleukin-1 beta structure was solved by molecular replacement using the refined structure of human interleukin-1 beta as trial structure, and found to be related to the human structure by a nearly perfect twofold rotation about the crystallographic y-axis and a 14 degrees rotation about the z-axis, with no translation. The folding of murine interleukin-1 beta is similar to that found for the human variant, consisting of 12 beta strands wrapped around a core of hydrophobic side chains in a tetrahedron-like fashion. Significant differences with respect to the human structure are seen at the N terminus and in 4 of the 11 loops connecting the 12 beta strands.

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.

Modulation of interleukin-1-induced alterations in cartilage proteoglycan metabolism by activation of protein kinase C

Interleukin-1 (IL-1) stimulates proteoglycan degradation and prostaglandin E2 (PGE2) release and inhibits proteoglycan synthesis by cartilage in organ culture. Addition of the protein kinase C (PKC) activator, mezerein, resulted in the concentration-dependent inhibition of IL-1 activity on proteoglycan metabolism. Similar effects were seen with other compounds which stimulated PKC, such as teleocidin B4 and phorbol dibutyrate (PDBu), but not with a phorbol analog that is inactive in stimulating PKC. Simultaneous addition of the PKC antagonist, staurosporine, blocked the mezerein-induced inhibition of IL-1 activity on both proteoglycan degradation and synthesis in a concentration-related manner. In contrast to its inhibition of the effect of IL-1 on proteoglycan metabolism, mezerein did not block the release of PGE2 by cartilage in response to IL-1 but caused a synergistic stimulation of PGE2 release. Importantly, in cultures made deficient in PKC by prolonged incubation with PDBu, the effects of this PKC agonist on proteoglycan breakdown and PGE2 were blocked, while stimulation by IL-1 persisted. These data indicate that the effects of IL-1 on proteoglycan metabolism and prostaglandin production are mediated by an intracellular signal distinct from PKC and suggest that activation of PKC in chondrocytes may play a role in modulating the action of IL-1 on proteoglycan metabolism.

Interleukin-1 binds to specific receptors on human bronchial epithelial cells and upregulates granulocyte/macrophage colony-stimulating factor synthesis and release

Cultured human bronchial epithelial cells constitutively produce granulocyte/macrophage colony-stimulating factor (GM-CSF). An upregulation of the synthesis and release of GM-CSF from those cells might contribute to the persistence of infiltration and local activation of inflammatory cells in some inflammatory diseases of the airways, such as asthma. Increased levels of immunoreactive and biologically active interleukin-1 (IL-1) have been identified in the airway secretions of asthmatic patients, together with an increase in GM-CSF contents. As IL-1 is known to upregulate GM-CSF production in many cell populations, in this study we investigated the ability of IL-1 to bind to specific receptors on bronchial epithelial cells and promote GM-CSF synthesis and release. Bronchial epithelial cells possessed specific single-class surface receptors for recombinant IL-1. The addition of exogenous IL-1 led to a dose-dependent increase in the accumulation of GM-CSF mRNA and release of immunoreactive GM-CSF to the culture medium. Release of IL-1 in the bronchial mucosa during allergic and nonallergic responses may lead to enhanced GM-CSF synthesis and release by epithelial cells, thus promoting airway inflammation.

Cytokine receptors

The molecular characterization of cytokine receptors has progressed rapidly over the past 5 years as a result of availability of radiolabeled cytokines, as well as the identification or creation of cell lines that express significant numbers of receptors at the cell surface. This explosion in research effort has led to establishment of multiple cytokine-receptor gene families and the realization that inhibition of cytokine function at the level of ligand-receptor interaction may be an important area for therapeutic drug development.

Characterization of the human IL-5 receptors on eosinophils

Interleukin 5 (IL-5) receptors on the cell surface of human eosinophils and other hematopoietic cells were characterized using radiolabeled recombinant IL-5. The binding of 35S-labeled murine IL-5 to eosinophils from normal human peripheral blood was rapid and saturable within a 30-min incubation at both 4 and 37 degrees C. The binding of 35S-labeled murine IL-5 to eosinophils was inhibited by an excess of unlabeled murine and human IL-5 or by an anti-murine IL-5 monoclonal antibody (NC17) but not by other human cytokines. Scatchard plot analysis revealed that human eosinophils have a single class of high affinity receptor (Kd 170-330 pM; number of binding sites: 260-380/cell). IL-5 receptors on eosinophils from four patients with eosinophilia displayed similar characteristics. Affinity cross-linking experiments resulted in the identification of human IL-5 receptor on eosinophils with a molecular mass of 55-60 kDa. Among the various cells besides eosinophils and cell lines that we could test, a subline of HL-60 (YY-1 cells) was found to display a significant number of IL-5 receptor. These results suggest that IL-5 may act on limited types of cells in the human system.

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.

Interleukin 1 beta induces rapid phosphorylation and redistribution of talin: a possible mechanism for modulation of fibroblast focal adhesion

The majority of interleukin 1 (IL-1) receptors in human fibroblasts has been shown to be localized at focal adhesions. This study describes rapid alterations caused by IL-1 beta/IL-1-receptor interaction at these sites. Fibroblast monolayers, incubated with IL-1 beta and prepared for electron microscopy, showed successive loss of cell-substratum contact and fewer and less-pronounced processes. Immunocytochemistry revealed loss and redistribution of the talin staining initially observed after 5-15 min of IL-1 beta incubation. Similarly, the cytoskeleton showed a decrease in staining and a disorganization starting from 15 to 30 min after IL-1 addition, whereas extracellular fibronectin appeared largely unaffected. Prelabeling with [32P]phosphate showed a 2- to 3-fold increase in the level of talin phosphorylation, peaking at 15 min. Phospho amino acid analyses revealed a higher level of serine and threonine phosphorylation. The data suggest that the action of IL-1 beta on fibroblasts may be partially mediated by direct phosphorylation of talin via activation of a protein serine/threonine kinase, leading to changes in transmembrane linkage proteins and the cytoskeleton. Such alterations at focal adhesions may provide a mechanism by which IL-1 can rapidly modulate cell-matrix interactions during inflammation and wound healing.