Stimulation of rheumatoid synovial cell collagenase and prostaglandin production by partially purified lymphocyte-activating factor (interleukin 1)

Effects of interleukin-1 on fibroblast extracellular matrix, using a 3-dimensional culture system

This study describes the alterations induced by Interleukin-1 alpha and -beta (IL-1 alpha and IL-1 beta) on fibroblast-synthesized extracellular matrix. Fibroblasts were grown between pieces of dentin or in collagen-coated Terasaki wells for 3 or 6-9 weeks to create 3-dimensional cell-containing matrices constituted primarily of proteoglycans and collagens, respectively. Following incubation with IL-1 alpha or IL-1 beta (10(-9) M) at 37 degrees C for 24 or 72 hr, samples were prepared for light and electron microscopy. Both IL-1 alpha and IL-1 beta induced collapse of the extracellular matrix by 72 hr, as manifested by a decrease of the cross-sectional area and an increased density of the matrices. Three-week matrices were reduced 26% and 45% by using IL-1 alpha and IL-1 beta, respectively. Comparable values obtained by using 6-week matrices were 14% and 30%. Cells within the matrix, normally stellate in shape with numerous extended processes, attained a more rounded or spindle shape with few and reduced processes and showed apparent alterations at cell matrix attachment sites and rearrangement of the cytoskeleton. Elongated cells at the top of the matrix appeared more compressed. The alterations were more pronounced in cultures incubated with IL-beta than with IL-1 alpha. Immunocytochemistry of extracellular matrix components revealed a decrease in staining intensity of chondroitin and dermatan sulfate in the 3-week matrix following IL-1 beta incubation. There was also a decrease in collagen type 1 staining of 9-week matrices treated with IL-1 alpha or IL-1 beta. These studies show that IL-1 has an effect on fibroblast-synthesized extracellular matrix and indicate that the effects of IL-1 alpha and IL-1 beta may differ. The resulting collapse of the matrix appears at least in part to be due to changes in proteoglycans and collagens.

Gingival fibroblasts degrade type I collagen films when stimulated with tumor necrosis factor and interleukin 1: evidence that breakdown is mediated by metalloproteinases

We previously suggested that periodontal pathogens might mediate connective tissue degradation in periodontal diseases through the ability of antigens from their cell walls to stimulate cytokine production by circulating mononuclear cells. Such cytokines would then induce metalloproteinase (MP) synthesis by resident gingival cells and thus initiate matrix degradation. In the present investigation human gingival fibroblasts (HGFs) were grown on [14C]-labelled type I collagen films and stimulated with either tumor necrosis factor (TNF) or interleukin-1 (IL-1) for 48 h. Collagenolysis occurred in a dose-dependent manner; the optimal dose for human rTNF alpha was 100 ng/ml and for rIL-1 alpha and rIL-1 beta, 1 ng/ml. Collagen degradation was accompanied by increased synthesis and release of the MPs collagenase, gelatinase and stromelysin, and there was a reduction in free TIMP (tissue inhibitor of metalloproteinases): collagenase and stromelysin were detected in both active and latent forms. Cytokine-stimulated collagenolysis was abolished by the addition of exogenous human rTIMP (5 units/ml). We also measured collagenase and TIMP by ELISAs which recognize all forms of collagenase (latent, active or complexed) and TIMP (free or complexed). These showed that while collagenase activity (0.6-1.2 microgram/ml) correlated with lysis, total TIMP levels remained unchanged at approximately 0.2 microgram/ml. These results demonstrate important roles for MPs and TIMP in regulating type I collagen degradation by HGFs, and support the hypothesis that connective tissue destruction during inflammatory diseases may be initiated, at least in part, by TNF and IL-1.

Inflammatory cytokines induce synthesis and secretion of gro protein and a neutrophil chemotactic factor but not beta 2-microglobulin in human synovial cells and fibroblasts

Exposure of human synovial cells and fibroblasts in monolayer culture to interleukin 1 results in prominent secretion of proteins with Mr values of 6000 and 7000. By N-terminal sequence analysis, the Mr-6000 protein is identified as the protein encoded by a recently described gro mRNA. The Mr-7000 protein is identical to a neutrophil chemotactic factor released from monocytes. Stimulation of normal human fibroblasts with tumour necrosis factor alpha also results in expression and secretion of these two proteins. In addition to these cytokine-induced proteins, we have identified beta 2-microglobulin as an Mr-8000 protein constitutively secreted by synovial cells.

The effects of methotrexate on the production and activity of interleukin-1

To explore the possibility that the mechanism of action of methotrexate (MTX) in rheumatoid arthritis (RA) is related to modulation of interleukin-1 (IL-1), the effects of MTX on IL-1 production and activity were evaluated. Human peripheral blood mononuclear cells and murine peritoneal and splenic cells were stimulated by lipopolysaccharide to produce IL-1. No inhibition of IL-1 synthesis or secretion caused by MTX treatment could be demonstrated either in vitro or in vivo, in patients with RA or in mice treated with MTX. We did show, however, that MTX had an inhibitory effect on IL-1 activity in 2 assays that demonstrate 2 different functions of IL-1. In a 2-step assay using LBRM-33-1A5 (1A5) and CTLD cells, MTX inhibited the secretion of IL-2 by 1A5 lymphoma cells in response to phytohemagglutinin and IL-1. In an assay using D10.G4.1 (D10) cells, MTX inhibited IL-1-induced proliferation of the D10 T cell clone. No effect of the drug on IL-2 activity was observed. The results demonstrate that MTX is capable of inhibiting some IL-1 activities without affecting IL-1 production or secretion. We propose that the inhibition of IL-1 activity or IL-1-dependent events may be one of the mechanisms of action of MTX in RA.

Independent effects of interleukin-1 on proteoglycan breakdown, proteoglycan synthesis, and prostaglandin E2 release from cartilage in organ culture

Exposure of bovine nasal cartilage in culture to interleukin-1 (IL-1) leads to a time- and concentration-dependent stimulation of proteoglycan breakdown and prostaglandin E2 (PGE2) release, and to inhibition of proteoglycan synthesis. The threshold levels of IL-1 required for initiating these effects were different, and IL-1 was 10 times more potent in inhibiting synthesis than in stimulating breakdown of proteoglycan. Kinetic studies indicated that the effects on proteoglycan metabolism occurred earlier (16-24 hours) than those for PGE2 release (48 hours). Selective effects were observed with inhibitors. Nonsteroidal antiinflammatory drugs blocked PGE2 production in response to IL-1, but had no effect on proteoglycan metabolism, and the antiarthritic drugs that blocked IL-1-stimulated breakdown augmented the inhibition of proteoglycan synthesis. We suggest that the effects of IL-1 on proteoglycan breakdown, proteoglycan synthesis, and PGE2 release are mediated by independent post-receptor mechanisms.

Stimulation of interleukin 6-like B-cell differentiation factor production in human adherent synovial cells by recombinant interleukin 1

Abnormal production of immunoglobulin in the joint space is frequently observed in patients with rheumatoid arthritis (RA). We have previously demonstrated that adherent synovial cells (ASC) from patients with RA are involved in B-cell differentiation by their spontaneous production of B-cell differentiation factor (BCDF). The regulation of the production of this factor, however, has not yet been described. We investigated the effects of recombinant interleukin 1 alpha and beta (rIL-1 alpha and rIL-1 beta) on the production of BCDF in ASC. Increased production of BCDF was observed with increased rIL-1 concentration. Production of BCDF was detected 3 h after exposure of ASC to rIL-1 and increased throughout a 48-h culture. This BCDF, assayed on SKW6-CL4 cells, was found to share a common active site with interleukin 6. The effect of rIL-1 was almost neutralized by anti-IL-1 antibody and the addition of polymyxin B did not diminish the effect of rIL-1, indicating that rIL-1 itself stimulates ASC in vitro. These results suggest that IL-1 may play a regulatory role in the production of BCDF in synovial tissue.

Human recombinant interleukin-1 alpha increases biosynthesis of collagenase and hyaluronic acid in cultured human chorionic cells

The influence of human recombinant interleukin-1 alpha (hrIL-1) on biosynthesis of collagenase and glycosaminoglycans was investigated with fibroblast-like cells of human chorionic membrane. hrIL-1 stimulated cells to produce procollagenase in a dose-dependent manner. Furthermore, it similarly accelerated both biosynthesis and secretion of hyaluronic acid in chorionic cells, but did not modulate the biosynthesis of sulfated glycosaminoglycans. Therefore, the relative concentration of hyaluronic acid vs total glycosaminoglycans increased significantly. These results are connected with the decrease in tensile strength observed in ruptured fetal membranes. Thus, it is proposed that IL-1 from effused leukocytes in fetal membranes plays an important role in connective tissue metabolism, especially in premature rupture of membranes with chorioamnionitis.

Regulation of expression of the cell adhesion receptors, integrins, by recombinant human interleukin-1 beta in human osteosarcoma cells: inhibition of cell proliferation and stimulation of alkaline phosphatase activity

Recombinant human interleukin-1 beta, a mediator of osteoblastic cell function, was found to regulate the expression of the cell adhesion receptors, integrins, on human osteosarcoma cells. Interleukin-1 beta (IL-1 beta) at picomolar concentrations, specifically elevated approximately six- to tenfold the expression of the beta 1 subunit and its associated alpha subunits, but not the related vitronectin receptor, within 20 hours. Integrin beta 1 messenger RNA levels were elevated within 6 hours and peaked to tenfold higher levels after 20 hours exposure to IL-1 beta in two human osteosarcoma cell lines. The increase in the cell-surface beta 1 integrins resulted in a stronger binding of the IL-1 beta-treated cells to fibronectin. Cell growth was also inhibited by IL-1 beta, cell morphology was altered, and IL-1 beta-treated cells expressed an approximately two- to threefold higher alkaline phosphatase. This increase in alkaline phosphatase activity was found to be independent of the inhibition of cell proliferation. These data indicate that the beta 1 integrin family of cell surface receptors is a target for regulation by IL-1 beta, which also regulates cell proliferation and the expression of the osteoblastic phenotype in human osteosarcoma cells.

Induction of interleukin-1 receptors on chondrocytes by fibroblast growth factor: a possible mechanism for modulation of interleukin-1 activity

Interleukin-1 is a polypeptide factor with profound effects on several cell types, such as chondrocytes, fibroblasts, and T-cells. The ability of interleukin-1 to induce the synthesis of matrix-degradative enzymes, as well as prostaglandin E2, suggests a pivotal role for this mediator in chronic inflammation. Previous studies have shown that the effect of human monocyte interleukin-1 on the synthesis of collagenase and neutral proteases by chondrocytes was enhanced by basic fibroblast growth factor. Using recombinant human interleukin-1B, we have examined whether the potentiation of interleukin-1 effects by fibroblast growth factor is related to changes in the number or affinity of interleukin-1 receptors. Our studies confirm that rabbit articular chondrocytes in culture contain a single class of high-affinity receptors for interleukin-1 with a Ka of 0.9-1.1 x 10(-13) M-1. While the untreated chondrocytes contain approximately 1,620 receptors per cell, fibroblast growth factor-treated cells exhibit a higher number of receptors (approximately 2,960 per cell) with no apparent change in the affinity. The increase in receptor number can be abolished by inhibitors of lysosomal function, indicating a requirement for intracellular processing of the fibroblast growth factor. Our results suggest that the potentiation of interleukin-1 catabolic effects by fibroblast growth factor may be related to its ability to induce additional interleukin-1 receptors on the chondrocyte cell surface.

Recombinant human interleukin 1 alpha is cytotoxic for and increases surface expression of HLA-A,B,C antigens of a human hepatoma cell line, PLC/PRF/5

Our study was undertaken to determine whether human recombinant interleukin 1 alpha (rIL 1 alpha) has any effect on the proliferation and expression of HLA-A,B,C antigens of human liver cell lines. The addition of rIL 1 alpha reduced the cell number of the human hepatoma cell line, PLC/PRF/5. This effect was determined to be cytotoxic, but not growth inhibitory, rIL 1 alpha did not change the number of Chang cell or SK-Hep-1 at a concentration as, high as 25,000 U/ml. rIL 1 alpha enhanced the expression of HLA-A,B,C antigens on PLC/PRF/5, but had no effect on Change cell or SK-Hep-1. Receptor binding studies showed that 125I-rIL 1 alpha bound to PLC/PRF/5 in a specific and saturable manner, but did not bind to Chang cell or SK-Hep-1. Scatchard plot analysis of the binding to PLC/PRF/5 revealed a single type of high affinity binding site with an apparent dissociation constant of approximately 5 x 10(-5) M and the presence of approximately 150 binding sites per cell. These findings suggest that IL 1 alpha may play a role in host defense against some hepatomas as cytotoxic factor and may be an enhancer of expression of HLA-A,B,C antigens on tumor cells.

Immunohistochemical detection and immunochemical analysis of type II collagen degradation in human normal, rheumatoid, and osteoarthritic articular cartilages and in explants of bovine articular cartilage cultured with interleukin 1

Articular cartilage destruction and loss of function in arthritic diseases involves proteolytic degradation of the connective tissue matrix. We have investigated the degradation of cartilage collagen by developing immunochemical methods that permit the identification and analysis of type II collagen degradation in situ. Previously, a technique to specifically identify type II collagen degradation in situ in articular cartilage did not exist. These methods utilize a polyclonal antiserum (R181) that specifically reacts with unwound alpha-chains and CNBr-derived peptides, alpha 1(II)CB11 and alpha 1(II)CB8, of human and bovine type II collagens. The experimental approach is based on the fact that when fibrillar collagens are cleaved the helical collagen molecule unwinds, exposing hidden epitopes. Here we demonstrate the use of R181 in studying type II collagen degradation in bovine articular cartilage that has been cultured with or without IL-1 and in human normal, rheumatoid, and osteoarthritic articular cartilages. Compared to cartilages either freshly isolated or cultured without IL-1, bovine cartilage cultured with IL-1 for 3-5 d showed an increase in both pericellular and intercellular immunohistochemical staining. Extracts of these cartilages contained type II collagen alpha chains that were increased in amount after culture with IL-1 for 11 d. In addition, culture with IL-1 resulted in the appearance of alpha chain fragments of lower molecular weight. All human arthritic tissues examined showed areas of pronounced pericellular and territorial staining for collagen degradation as compared with non-diseased tissues, indicating that chondrocytes are responsible in part for this degradation as compared with non-diseased tissues. In most cases rheumatoid cartilage was stained most intensely at the articular surface and in the deep and mid-zones, whereas osteoarthritic cartilage usually stained more in the superficial and mid-zones, but less intensely. Distinct patterns of sites of collagen degradation reflect differences in collagen destruction in these diseases, suggesting possible different sources of chondrocyte activation. These experiments demonstrate the application of immunological methods to detect collagen degradation and demonstrate an increase of collagen degradation in human arthritides and in IL-1-treated viable bovine cartilage.

Stimulation of glycosaminoglycan synthesis in cultured human dermal fibroblasts by interleukin 1. Induction of hyaluronic acid synthesis by natural and recombinant interleukin 1s and synthetic interleukin 1 beta peptide 163-171

Hyaluronic acid (HA) is believed to play a critical role in wound healing and in morphogenesis. Factors controlling the production of HA by fibroblasts in normal and pathological states are not completely understood. In this report we have observed that natural human interleukin (IL-1)1 beta and human recombinant (hrIL)-1 alpha and beta are potent stimulators of HA production by fibroblasts in vitro. Hyaluronic acid is the major species of glycosaminoglycan (GAG) stimulated by IL-1 in fibroblasts. PGE2 does not appear to be involved directly in this IL-1 effect on fibroblasts, but stimulation of HA production by IL-1 is dependent on protein synthesis. The synthetic human IL-1 beta peptide 163-171 (Val-Gln-Gly-Glu-Glu-Ser-Asn-Asp-Lys), which has been previously shown to stimulate thymocyte proliferation but not fibroblast PGE2 production, is also able to stimulate fibroblast HA production. The synthesis and secretion of IL-1 by mononuclear phagocytes at sites of inflammation and immune reactions in vivo could potentially serve as a signal for fibroblasts to synthesize HA, which in turn could serve to facilitate and modulate reparative and immune processes by virtue of its ability to alter cell-cell, cell matrix, and cell-membrane receptor interactions.

Inhibition of collagen synthesis by interleukin-1 in three-dimensional collagen lattice cultures of fibroblasts

Interleukin-1 (Il-1) was added to collagen lattice cultures of human skin fibroblasts. No cell division was induced, the ability of fibroblasts to contract the lattices was decreased and a dose-related inhibition of collagen synthesis without effect on non-collagen proteins was found. Indomethacin had no influence on these effects.

Differential stimulation of collagenase and chemotactic activity in fibroblasts derived from rat wound repair tissue and human skin by growth factors

Epidermal growth factor and cartilage-derived basic fibroblast growth factor (EGF and CD-bFGF) are mitogens shown to increase the rate of wound repair in animal models. In addition to being a mitogen for granulation tissue, CD-bFGF stimulates the recruitment of cells to the wound site. CD-bFGF and a closely-related chondrosarcoma-derived fibroblast growth factor stimulated chemotaxis of granulation tissue cells in vitro, each factor having a maximum activity at a concentration of 55 pM. Epidermal growth factor was also a potent chemoattractant for rat granulation tissue fibroblasts; however, maximum activity was obtained at 1.7 nM. Cells from all stages of wound repair were chemotactically responsive to these factors, but there was some attenuation of the response to bFGF in cells derived from fully-organized day 28 granulation tissue. Collagenase-catalyzed restructuring of collagen, an additional significant feature of wound repair, is probably critical to cell movement in an extracellular matrix. Cells derived from organizing (6-day old) sponge granulation tissue secreted latent collagenase constitutively in vitro. In the presence of serum, the production of collagenase was stimulated three-four fold by 1.8 nM bFGF derived either from cartilage or chondrosarcoma. When serum was present, as at a wound site, collagenase production was not enhanced by the addition of EGF. Cells from fully organized, day 21 sponge granulation tissue did not secrete latent collagenase constitutively and could not be stimulated to do so by the addition of EGF, bFGF, or phorbol ester. Human skin fibroblast collagenase production was also stimulated by bFGF and was refractory to EGF. While both classes of growth factor have the ability to promote wound healing, the varying responses they elicit in cell populations from the wound site emphasize the different pathways of cellular activation.

Induction of articular cartilage degradation by recombinant interleukin 1 alpha and 1 beta

The purpose of this study was to compare the effects of human recombinant interleukin 1, alpha and beta, on articular cartilage. The effects of rIL-1 alpha and rIL-1 beta on proteoglycan degradation and synthesis following treatment of bovine articular cartilage in serum-free organ culture were quantified. Purified human IL-1 and both rIL-1 alpha and rIL-1 beta induced a two-fold or greater increase in glycosaminoglycan (GAG) release from cultured articular cartilage. Levels or rIL-1 alpha as low as 15 pM induced increased proteoglycan degradation whereas identical levels of rIL-1 beta did not. Killing of the cartilage cells abolished induced GAG release by all forms of IL-1. Analysis of proteoglycan size following IL-1 treatment showed limited degradation of material released into the culture medium or remaining within cartilage. Both forms of recombinant IL-1 inhibited GAG synthesis when continually present in the culture medium. Actinomycin D and cycloheximide inhibited IL-1 dependent cartilage destruction whereas indomethacin did not.

Interleukin 1 suppresses expression of cartilage-specific types II and IX collagens and increases types I and III collagens in human chondrocytes

In inflammatory diseases such as rheumatoid arthritis, functions of chondrocytes including synthesis of matrix proteins and proteinases are altered through interactions with cells of the infiltrating pannus. One of the major secreted products of mononuclear inflammatory cells is IL-1. In this study we found that recombinant human IL-1 beta suppressed synthesis of cartilage-specific type II collagen by cultured human costal chondrocytes associated with decreased steady state levels of alpha 1 (II) and alpha 1(IX) procollagen mRNAs. In contrast, IL-1 increased synthesis of types I and III collagens and levels of alpha 1(I), alpha 2(I), and alpha 1(III) procollagen mRNAs, as we described previously using human articular chondrocytes and synovial fibroblasts. This stimulatory effect of IL-1 was observed only when IL-1-stimulated PGE2 synthesis was blocked by the cyclooxygenase inhibitor indomethacin. The suppression of type II collagen mRNA levels by IL-1 alone was not due to IL-1-stimulated PGE2, since addition of indomethacin did not reverse, but actually potentiated, this inhibition. Continuous exposure of freshly isolated chondrocytes from day 2 of culture to approximately half-maximal concentrations of IL-1 (2.5 pM) completely suppressed levels of type II collagen mRNA and increased levels of types I and III collagen mRNAs, thereby reversing the ratio of alpha 1(II)/alpha 1(I) procollagen mRNAs from greater than 6.0 to less than 1.0 by day 7. IL-1, therefore, can modify, at a pretranslational level, the relative amounts of the different types of collagen synthesized in cartilage and thereby could be responsible for the inappropriate repair of cartilage matrix in inflammatory conditions.

Bone-resorbing agents promote and interferon-gamma inhibits bone cell collagenase production

Parathyroid hormone, prostaglandin E2, 1 alpha,25-dihydroxyvitamin D3, interleukin-1, tumor necrosis factor alpha, and epidermal growth factor, all known stimulators of bone resorption, markedly enhanced collagenase secretion by rat fetus osteoblastlike cells in primary culture as judged by enzyme-linked immunosorbent assay. Untreated cells contained no immunostainable or extractable collagenase. Collagenase was detected in the treated cells and media only after 1-3 h of treatment, and there was no increment in collagenase activity when cells were treated in the presence of actinomycin D or cycloheximide. Cells secreted collagenase in a latent form and also elaborated collagenase inhibitor; chromatographic separation of collagenase from collagenase inhibitor and subsequent activation of the collagenase with trypsin yielded the active species in stimulated but not in unstimulated cells. The ability of individual prostanoids, among seven tested, to promote collagenase production correlated positively with their reported capacity to promote bone resorption. Interferon-gamma (IFN-gamma), a known resorption inhibitor, blocked the increment in collagenase production caused by all agents tested. These results indicate a close linkage between stimulation of bone resorption and collagenase production by osteoblastlike cells. Various resorption stimulators, including some not previously tested for effects on collagenase, augment the de novo synthesis and secretion of collagenase and act by an IFN-gamma-inhibitable mechanism.

Cyclic AMP--an intracellular second messenger for interleukin 1

We demonstrated that interleukin 1 (IL-1), a potent peptide mediator in immune and inflammatory responses, stimulates the synthesis of cAMP in a variety of IL-1-responsive cell targets. We also showed that cAMP analogs and cAMP-inducing agents can replace IL-1 in the induction of interleukin 2 receptors on lymphocytes as well as in phytohemagglutinin-induced murine thymocyte proliferation. By use of IL-1 and the cAMP-inducer, forskolin, a direct correlation between the induced level of cAMP and the degree of lymphocyte interleukin 2 receptor expression or thymocyte proliferation was established. Our results indicate that cAMP may be an important intracellular second messenger for IL-1.

The biochemical and histological effects of artificial ligament wear particles: in vitro and in vivo studies

Growing evidence suggests that biochemical mechanisms play a role in the pathogenesis of arthritis. Cartilaginous wear particles have been shown to induce destructive enzymes and cytokines. To assess the biocompatibility of artificial ACL replacements, the effects of wear particles from the following ligaments were analyzed biochemically and histologically: GORETEX, Stryker Dacron Ligament Prosthesis, Versigraft carbon, Kennedy LAD, Xenograft, Leeds-Keio, and human patellar tendon allograft. Ligaments were frozen and ground to produce wear particles similar to those seen clinically and were added to lapine synovial cell cultures. The resulting conditioned medium was analyzed for collagenase, gelatinase, and chondrocyte activating factor (CAF) production. All of the ligaments induced significantly elevated enzyme and CAF production by the synoviocytes, with Xenograft and carbon inducing significantly higher enzyme levels than those of the other five ligaments. Five milligrams of wear particles were injected into the knees of 4 kg to 5 kg rabbits that were analyzed histologically after 14 weeks. Wear particles accumulated in the periarticular synovial folds and induced modest to severe macrophage infiltration in the synovium. A hypothetical model explaining the role of artificial ligament wear particles in the pathogenesis of arthritis is presented.

Correlation of plasma interleukin 1 levels with disease activity in rheumatoid arthritis

The mean plasma level of interleukin 1 beta (IL-1 beta), measured by immunoassay, was significantly higher in 51 patients with rheumatoid arthritis (RA) than in 21 healthy controls of similar age. Further, in the RA group, plasma IL-1 beta correlated positively with Ritchie joint index, pain score, and erythrocyte sedimentation rate and correlated negatively with haemoglobin concentration. In individual patients with active disease who had serial measurements, plasma IL-1 beta also correlated with clinical disease activity. These results support the idea that IL-1 beta has a central role in the pathogenesis of RA.

Effect of interleukin 1 beta on osteoblastic clone MC3T3-E1 cells

The effect of recombinant interleukin 1 Beta (IL-1(beta)) was investigated on osteoblastic cell line MC3T3-E1 cloned from mouse calvaria. IL-1(beta) stimulated cell proliferation which increased cell number and caused dose-related stimulation of DNA synthesis, with a maximal effect at a concentration of 12.5 U/ml; suppressed alkaline phosphatase activity and collagen synthesis maximally at 0.5 and 62.5 U/ml, respectively; and increased the amount of free [3H] hydroxyproline in the cultures, but the amount was quite low. Prostaglandin E2 synthesis was also stimulated dose dependently by the presence of IL-1(beta), with a maximal increase at 2.5 U/ml, at which concentration the prostaglandin E2 level in the medium was 1.61 +/- 0.10 ng/ml. The increased prostaglandin E2 synthesis did not affect either the IL-1(beta)-mediated change in DNA or collagen synthesis or alkaline phosphatase activity. These results extend the possibility that IL-1(beta) is to act as a regulator of bone formation.

Tumor necrosis factor inhibits collagen and fibronectin synthesis in human dermal fibroblasts

Tumor necrosis factor (TNF) caused inhibition of collagen production by confluent cultures of human dermal fibroblasts in a dose-dependent manner. Concomitant increase of prostaglandin E2 release was observed as a result of TNF-induced cell activation. However, a blockade of the cyclooxygenase pathway of arachidonate metabolism by indomethacin did not abrogate the inhibitory effect of TNF on collagen synthesis, suggesting that this effect could be independent of prostaglandin metabolism. Gel electrophoresis of the newly synthesized macromolecules from the culture media showed that both type I and type III collagens as well as fibronectin were affected by the inhibition. Electrophoresis of cell layer-associated proteins demonstrated that the reduction in amounts of collagen and fibronectin in the medium did not result from an intracellular accumulation of these macromolecules. Production of procollagens was reduced in parallel to that of collagens, suggesting that the effect of TNF is exerted before the processing steps of procollagens. These results clearly show that TNF could play a role in modulation of matrix deposition by fibroblasts during inflammatory processes.

Identification of a high-affinity receptor for interleukin 1 alpha and interleukin 1 beta on cultured human rheumatoid synovial cells

In this report the binding of recombinant human interleukins 1 alpha and 1 beta (rIL-1 alpha and rIL-1 beta) to primary cultures of human rheumatoid synovial cells is measured and compared to the concentrations of these mediators required for stimulation of PGE2 production by these same cells. The average concentration of IL-1 alpha required for half-maximal stimulation of PGE2 was 4.6 +/- 1.5 pM (+/- SEM) (n = 6), whereas for IL-1 beta half-maximal stimulation was observed at a concentration of 1.3 +/- 0.24 pM (n = 6). Both direct and competitive binding experiments were performed. In direct binding experiments, IL-1 alpha bound with a Kd of 66 pM (n = 1), while IL-1 beta bound with a Kd of 4 pM (n = 2). In competitive binding experiments, IL-1 alpha inhibited binding of 125I-IL-1 alpha with a Ki of 33-36 pM (n = 2) and binding of 125I-IL-1 beta with a Ki of 51-63 pM (n = 2). IL-1 beta inhibited binding of 125I-IL-1 alpha with a Ki of 2-3 pM (n = 2) and binding of 125I-IL-1 beta with a Ki of 7 pM (n = 2). The binding data were best fit by a model specifying a single class of receptors with homogeneous affinity for either IL-1 alpha or IL-1 beta and with an abundance of 3,000-14,000 sites per cell. Autoradiography showed that the vast majority of the synoviocytes within the cultures possessed IL-1 receptors. Comparison of biological response curves with the binding curves indicates that the observed receptors exhibit sufficiently high affinity to mediate the response of human synoviocytes to low picomolar concentrations of IL-1 alpha and IL-1 beta.

The effect of calcium channel blockers and calmodulin inhibitors on the macrophage factor-stimulated synthesis of collagenase by rabbit chondrocytes

Macrophages and monocytes secrete a factor(s) which can stimulate the synthesis of collagenase in synovial cells and in chondrocytes. Incubation of rabbit chondrocytes with macrophage conditioned medium (MCM) and with the calcium channel blockers, nifedipine, verapamil or diltiazem (up to 200 microM) had no effect on collagenase synthesis. However, TMB-8 (8-[N,N-diethylamino]-octyl 3,4,5-trimethoxybenzoate hydrochloride), an inhibitor of internal calcium movement, did inhibit the process with an IC50 of approximately 130 microM. The calmodulin antagonists, trifluoperazine, chlorpromazine and calmidazolium (R-24571) were effective inhibitors of the process with IC50's of 40 microM, 18 microM and 3.5 microM, respectively. Collagenase activity itself was not affected by these agents. The data suggests that calmodulin and/or internal calcium movement may play a role in the macrophage factor-stimulated synthesis of collagenase in rabbit chondrocytes.

Macromolecular osteolytic factor synthesised by squamous carcinoma cell lines from the head and neck in vitro is interleukin 1

Three human cell lines derived from oro-pharyngeal squamous cell carcinomas of the head were investigated for bone-resorbing activity in vitro. Culture media from all three spontaneously produced a non-dialysable osteolytic factor with activity in three in vitro assays for interleukin 1 (IL1), viz. the lymphocyte activating factor (LAF) assay, stimulation of collagenase synthesis by articular chondrocytes, and stimulation of prostaglandin E2 synthesis by fibroblasts. Addition of anti-human IL1 antibody to the culture media abolished all the bone-resorbing activity. Fractionation of the cell culture media by high performance liquid chromatography (HPLC) showed a single peak of activity in the chondrocyte assay with an apparent mol.wt of 15-17,000. This co-eluted with activity in a preparation of IL1 from rat peritoneal macrophage cultures. These results indicate that IL1 is responsible for the prostaglandin-independent bone resorbing activity synthesised by these cells in vitro, and may contribute to the bone destruction associated with the tumour.

Aminobisphosphonate inhibition of interleukin-1-induced bone resorption in mouse calvariae

Interleukin-1 (IL-1) is probably an important lymphokine mediator of inflammation and bone resorption. IL-1 derived from mononuclear cells, a melanoma cell line (MM96 cells), and recombinant human IL-1 (rHuIL-1 beta) increased in vitro bone resorption, as measured by the release of 45Ca from cultured mouse calvariae. The 50% maximum active resorption was observed with 0.125 ng/ml or approximately 10(-11) M rHuIL-1 beta. The resorptive action of IL-1 was not entirely dependent on prostaglandin mediation, since its effect was evident when prostaglandin synthesis was inhibited in the cultures by indomethacin. IL-1-induced resorption has been shown to be inhibited by 10(-5) M 3-amino-1-hydroxypropylidene-1-1-bisphosphonate (APD). This inhibition was partially reversed by increasing doses of IL-1. In vitro toxicity studies showed that at concentrations of 10(-4) M, APD inhibited the growth of cultured MM96, murine myelomonocytic P388D1, and rat osteosarcoma UMR 106 cells, but not other mast and lymphoid cell lines. These in vitro observations may have relevance to the use of APD in bone and joint diseases in which inflammation and bone resorption are prominent.

Recombinant interleukin-1 stimulates prostaglandin E2 production by osteoblastic cells: synergy with parathyroid hormone

Recombinant mouse IL-1 (Interleukin-1) has been shown to be capable of stimulating prostaglandin E2 (PGE2) production by isolated rat osteoblastic cells in a dose-dependent manner. The rapidity of the effect (1 hour) and the potency of IL-1 (5 x 10(-12) M) in producing this effect suggest that IL-1 may exert some of its effects on bone via PGE2. Parathyroid hormone (PTH) appears to have a strong synergistic effect with IL-1. These data further substantiate the role of IL-1 in bone physiology.

Interleukin-1 alpha modulates collagen gene expression in cultured synovial cells

The effects of porcine interleukin-1 (IL-1) alpha on collagen production were studied in cultured human rheumatoid synovial cells. Addition of 0.05-5 ng of IL-1/ml into the cultures resulted in a dose-dependent decreased rate of collagen released into the medium over 24 h. To determine whether this inhibition was due to secondary action of prostaglandin E2 (PGE2) secreted in response to IL-1, cultures were incubated in presence of various inhibitors of arachidonate metabolism. Depending on the cell strains, these inhibitors were able to suppress or diminish the effect of IL-1, suggesting that PGE2 is involved in the mechanism. Depression of collagen production caused by IL-1 mainly affected type I collagen and therefore led to a change in the type I/type III collagen ratio in the extracellular medium. Steady-state levels of mRNA for types I and III procollagens were estimated by dot-blot hybridization and compared with the amounts of respective collagens produced in the same cultures. IL-1 generally increased procollagen type I mRNA, but to a variable extent, as did indomethacin (Indo). Depending on the cell strain, the combination of indo and IL-1 could elevate the mRNA level of type I procollagen compared with Indo alone. These results did not correlate with the production rate of collagen in the medium, which was diminished by exposure to IL-1. The level of mRNA for collagen type III was not greatly changed by incubation with IL-1, and a better correlation was generally observed with the amount of type III collagen found in the medium. These data suggest that an additional control mechanism at translational or post-translational level must exist, counterbalancing the stimulatory effect of IL-1 on collagen mRNA transcription. It is likely that IL-1 could modulate the production of collagen in synovial cells by an interplay of different mechanisms, some of them limiting the effect of primary elevation of the steady-state mRNA level.

Human recombinant interleukin-1 regulates cellular mRNA levels of dermatan sulphate proteoglycan core protein

Human skin fibroblasts were exposed to various concentrations (from 0.01 to 5.0 units/ml) of human recombinant interleukin-1 alpha and interleukin-1 beta (IL-1 alpha and IL-1 beta). Both IL-1 alpha and IL-1 beta were found to increase dermatan-sulphate-proteoglycan (DSPG) core-protein mRNA levels. Maximal increase (3.0-fold) was seen at 48 h after addition of 1 unit of IL-1 beta/ml. In spite of the elevated DSPG-core-protein mRNA only a slight increase (from 10 to 18%) could be seen in the production of DSPG to cell-culture medium. No changes in the molecular mass of DSPG could be detected.

Augmented interleukin-1 production and HLA-DR expression in the synovium of rheumatoid arthritis patients. Possible involvement in joint destruction

Potent interleukin-1 (IL-1) activity was detected in culture supernatants from synovium, obtained by arthroscopy, from rheumatoid arthritis (RA) patients but not from non-RA patients. Production of IL-1 by RA synovium correlated well with findings of inflammation on arthroscopy and HLA-DR expression in immunohistochemical staining. Furthermore, there was a positive correlation between IL-1 production from RA synovium and joint changes detected on roentgenograms. These findings strongly suggest that IL-1 might play an important role in the joint destruction in RA.

Osteoclast activating factor is now interleukin-1 beta: historical perspective and biological implications

Interleukin-1 (IL-1) represents a family of polypeptides with widespread immunological and non-immunological activity. Recent studies show that osteoclast activating factor (OAF) is homologous to IL-1B. In this review, the biological properties, cell sources and actions of IL-1 are discussed. The numerous biological effects of IL-1 on various host systems suggest that elevated levels of the mediator may be an indicator of a pathological process. Since the IL-1 family plays an important role as a key mediator of the inflammatory, immunological and bone resorptive responses it is of considerable concern to dentists.

The role of tumor necrosis factor and interleukin 1 in the immunoinflammatory response

Monocytes and tissue macrophages produce at least two groups of protein mediators of inflammation, interleukin 1 (IL-1) and tumor necrosis factor (TNF). Recent studies have emphasized that TNF and IL-1 modulate the inflammatory function of endothelial cells, leukocytes, and fibroblasts. Although these cytokines share a number of biologic properties, they have quite distinct gene and protein structures. It is our purpose to focus on the role of these mediators in inflammation.

Macrophage-derived cytokines amplify immune complex-triggered O2-. responses by rat alveolar macrophages

Interleukin-1 (IL-1) and tumor necrosis factor (TNF) are monocyte macrophage-derived hormonelike regulatory proteins that participate in many physiologic and pathophysiologic processes. Several proinflammatory activities have been attributed to these cytokines, but their importance in anatomically compartmentalized inflammatory processes is unclear. The current in vitro studies have been designed to examine modulatory influences of these cytokines on O2-. responses of rat phagocytes implicated as effector cells in immune complex mediated lung injury. Purified human IL-1, recombinant human TNF (rTNF), and culture supernatant from zymosan-activated alveolar macrophages significantly amplified O2-. responses of immune complex-stimulated alveolar macrophages but did not enhance the responses of neutrophils. Equivalent concentrations of IL-1, rTNF, and alveolar macrophage culture supernatant had no direct stimulatory effect on alveolar macrophages as measured by O2-. production. Culture media from unstimulated alveolar macrophages exerted negligible effects on O2-. generation by immune complex-activated alveolar macrophages. These data indicate that O2- responses of immune complex alveolar macrophages can be enhanced by the presence of IL-1, TNF, or media from activated macrophages. It is possible that macrophage products may greatly amplify tissue injury through the enhancement of oxygen radical production.

Direct evidence for granuloma-inducing activity of interleukin-1. Induction of experimental pulmonary granuloma formation in mice by interleukin-1-coupled beads

Pulmonary granulomas were induced in BALB/c mice by the intratracheal injection of Sephadex G-50 and latex beads. Very large granulomas developed around Sephadex G-50 beads. Minimal inflammation was produced in mice given latex beads. Aqueous extracts prepared from pulmonary granuloma lesions induced in mice by Sephadex G-50 beads contained high levels of interleukin-1 (IL-1) activity but not interleukin-2 (IL-2) activity. IL-1 activity in the extracts correlated with granuloma size. In a subsequent step, large granulomas were induced by the intratracheal injection of Sepharose 4B beads coupled to fractions of the extracts containing IL-1 activity (ie, granuloma-derived IL-1) prepared from Sephadex G-50-induced granulomatous lungs. In addition, large granulomas were induced by the intratracheal injection of recombinant IL-1-coated Sepharose 4B beads. In contrast, very small granulomas were seen when IL-2-coated or plain Sepharose 4B beads were injected into mice. These results indicate that IL-1 participates in the induction and/or expression of granulomas.

Recombinant human granulocyte-macrophage colony-stimulating factor induces secretion of autoinhibitory monokines by U-937 cells

Colony-stimulating factors are required for survival proliferation, differentiation and functional activation of granulocytes, macrophages and their precursor cells. In the present report, however, we demonstrate antiproliferative activity of recombinant human (rh) granulocyte-macrophage colony-stimulating factor (GM-CSF) on monoblast cell line U-937 and provide evidence for the involvement of tumor necrosis factor alpha TNF-alpha and interleukin 1 beta (IL 1 beta) in its growth inhibitory action. GM-CSF (but not granulocyte CSF, G-CSF or macrophage CSF, M-CSF) suppressed DNA synthesis and self renewal of U-937 cells. Similarly, medium conditioned by U-937 cells in response to GM-CSF (GM-CSF U-937-CM) was able to reduce clonogenicity and [3H]thymidine uptake by U-937 cells. Since neutralization of GM-CSF present in GM-CSF U-937-CM by monoclonal antibody to GM-CSF did not abrogate the autoinhibitory activity present in GM-CSF U-937-CM, we considered the possibility that other soluble molecules are released by U-937 cells upon GM-CSF stimulation. Neutralization by antibodies to IL 1 beta and TNF-alpha suggested that both monokines could be the antiproliferative principle operating in GM-CSF U-937-CM. Moreover, employing IL 1 beta-specific enzyme-linked immunosorbent assay, TNF-alpha specific radioimmunoassay, Northern analysis using a cloned TNF-alpha-specific cDNA and an oligonucleotide probe for IL 1 beta, we demonstrate GM-CSF-inducible IL 1 beta and TNF-alpha gene expression by U-937 cells at the mRNA and protein level. Although M-CSF expression was induced under similar conditions, M-CSF failed to inhibit growth of U-937 cells.

Modulation of fibroblast functions by interleukin 1: increased steady-state accumulation of type I procollagen messenger RNAs and stimulation of other functions but not chemotaxis by human recombinant interleukin 1 alpha and beta

Interleukin-1 (IL-1) is synthesized by and released from macrophages in response to a variety of stimuli and appears to play an essential role in virtually all inflammatory conditions. In tissues of mesenchymal origin (e.g., cartilage, muscle, bone, and soft connective tissue) IL-1 induces changes characteristic of both destructive as well as reparative phenomena. Previous studies with natural IL-1 of varying degrees of purity have suggested that it is capable of modulating a number of biological activities of fibroblasts. We have compared the effects of purified human recombinant (hr) IL-1 alpha and beta on several fibroblast functions. The parameters studied include cell proliferation, chemotaxis, and production of collagen, collagenase, tissue inhibitor of metalloproteinase (TIMP), and prostaglandin (PG) E2. We observed that hrIL-1s stimulate the synthesis and accumulation of type I procollagen chains. Intracellular degradation of collagen is not altered by the hrIL-1s. Both IL-1s were observed to increase the steady-state levels of pro alpha 1(I) and pro alpha 2(I) mRNAs, indicating that they exert control of type I procollagen gene expression at the pretranslational level. We found that both hrIL-1 alpha and beta stimulate synthesis of TIMP, collagenase, PGE2, and growth of fibroblasts in vitro but are not chemotactic for fibroblasts. Although hrIl-1 alpha and beta both are able to stimulate production of PGE2 by fibroblasts, inhibition of prostaglandin synthesis by indomethacin has no measurable effect on the ability of the IL-1s to stimulate cell growth or production of collagen and collagenase. Each of the IL-1s stimulated proliferation and collagen production by fibroblasts to a similar degree, however hrIL-1 beta was found to be less potent than hrIL-1 alpha in stimulating PGE2 production. These observations support the notion that IL-1 alpha and beta may both modulate the degradation of collagen at sites of tissue injury by virtue of their ability to stimulate collagenase and PGE2 production by fibroblasts. Furthermore, IL-1 alpha and beta might also direct reparative functions of fibroblasts by stimulating their proliferation and synthesis of collagen and TIMP.

Response of epidermolysis bullosa fibroblasts to factors derived from macrophages and polymorphonuclear leukocytes in terms of collagenase production

In order to investigate the role of inflammatory cells in altering the collagenase production by epidermolysis bullosa (EB) fibroblasts, macrophage and polymorphonuclear leukocyte (PMN) factors obtained from mouse peritoneal fluids were added to the fibroblast culture system, and collagenase activity was assayed after a 48-h incubation. Data obtained here revealed that the response of collagenase production by fibroblasts was quite different, depending on the type of EB. Namely, EB dystrophica recessiva (EBDR) (n = 2) fibroblasts produced significant amounts of collagenase in the range of 5.07 (U/ml) to 6.04 in response to macrophage-conditioned medium, macrophage lysate, and PMN lysate, compared with 0.13 in the absence of these. On the other hand, EB dystrophica dominans (EBDD) (n = 1) fibroblasts showed little or no overt increase in enzyme production in the presence of macrophage lysate and PMN lysate, which resulted in a moderate increase to 3.82 in response to macrophage-conditioned medium. Furthermore, EB simplex (EBS) (n = 1) fibroblasts produced collagenase up to 3.84 in response to these three factors. These factors can be inactivated by treating with trypsin, pronase, and phenylglyoxal. Our data clearly indicated that, in the comparisons of EBDD and EBS fibroblasts, EBDR fibroblasts showed quite high response to factors derived from macrophages and PMNs in terms of collagenase production. This fact may raise a clue that accounts for the high levels of tissue collagenase activity, which plays a potentially major role in blister formation in EBDR.

Dissection of the mechanisms of immune injury in rheumatoid arthritis, using total lymphoid irradiation

Eleven patients with intractable rheumatoid arthritis were treated with total lymphoid irradiation. After radiotherapy, there was a marked decrease in the number and function of peripheral blood helper/inducer (Leu-3+) T lymphocytes, in the spontaneous secretion of interleukin-1 by synovial biopsy specimens, and in the activity of the joint disease. In contrast, levels of IgM, IgA, and IgG rheumatoid factors and C3 concentrations in blood and synovial fluid samples did not change significantly after therapy with total lymphoid irradiation.

Degradative pathways in cultured synovial fibroblasts: selective effects of pulsed electromagnetic fields

A cell culture model for studying the cytokine-mediated degradation of connective tissue was exposed to clinically applied, low-frequency pulsed electromagnetic fields (PEMF), and levels of collagenolytic activity, two lysosomal hydrolases, and prostaglandin E2 were measured. PEMFs reduced the release of two lysosomal enzymes by cultured rabbit synovial fibroblasts but did not affect their response to mononuclear-cell-conditioned medium. PEMF did not alter levels of cytokine activity produced by a mixed mononuclear cell population, nor did they affect the cytokine-mediated release of collagenase or prostaglandin E2 by synovial fibroblasts. The relevance of these findings to the clinical application of PEMF to soft- and hard-tissue injuries is discussed.

Effect of purified human interleukin-1 on cartilage degradation

The effects of highly purified human monocyte-derived interleukin-1 (IL-1) on bovine nasal cartilage breakdown were investigated. Cartilage degradation was determined by quantifying the fraction of total proteoglycan released from cartilage during 8 days of culture. The response appeared to be chondrocyte-dependent, for IL-1 stimulated proteoglycan (PG) release from living but not from dead (frozen-thawed) cartilage. IL-1 action on living cartilage was heat labile and concentration dependent, with significant effect at 5 U/ml and maximal effect at 10-20 U/ml. Kinetic studies showed significant stimulation of PG release by 3 days of incubation with 10 U/ml IL-1. Studies in which IL-1 was removed on day 1 or day 4 showed that the cartilage-degrading effect of this monokine was reversible. Although IL-1 caused little change in the Sepharose CL-2B chromatographic profile of released PGs using an associative elution buffer, a significant shift to lower mol wt was observed under dissociative conditions. To probe the mechanism of IL-1 action, cartilage samples were incubated with IL-1 in the presence of the protein synthesis inhibitor, cycloheximide, or the lysosomal membrane-stabilizing steroid, hydrocortisone. Cycloheximide at 5-10 micrograms/ml completely blocked IL-1-induced breakdown. One the other hand, 3 x 10(-7) M hydrocortisone had little or no effect on IL-1 action. IL-1 was also shown to stimulate the degradation of human articular cartilage.

The MRL-lpr/lpr mouse. A model for the study of rheumatoid arthritis

Autoimmune MRL-lpr/lpr mice develop a spontaneous destructive arthropathy sharing some features with rheumatoid arthritis including synovial cell proliferation, pannus formation, rheumatoid nodule-like lesions and circulating rheumatoid factors. Rheumatoid factors elaborated by MRL-lpr/lpr mice exhibit binding characteristics similar to those found in the sera of patients with rheumatoid arthritis; however, these autoantibodies do not appear to be essential for the induction of arthritis in MRL-lpr/lpr mice. Molecular studies, indicating that VH genes from several VH families are capable of encoding these rheumatoid factors, argue against the existence of unique "autoantibody genes" in the germline of MRL-lpr/lpr mice. Although the mechanisms underlying cartilage injury in MRL-lpr/lpr mice have not been elucidated, available evidence suggests that invading synovial cells play an important role. Delineation of the cellular and molecular mechanisms responsible for articular destruction in MRL-lpr/lpr mice may provide important insights concerning the pathogenesis of rheumatoid arthritis.

Prostaglandin concentrations in amniotic fluid of women with intra-amniotic infection and preterm labor

This study was undertaken to examine the effects of intrauterine infection and preterm labor on the amniotic fluid concentrations of prostaglandins in women with premature rupture of the membranes. Amniotic fluid was obtained from four groups of patients with premature rupture of the membranes: group 1, patients without labor or infection; group 2, patients with labor but without infection; group 3, patients with an intra-amniotic infection but without labor; group 4, patients with both infection and labor. Prostaglandins E2 and F2a were measured by radioimmunoassays. Preterm labor, in the absence of infection, was not associated with significant increases in amniotic fluid concentrations of prostaglandins. Women with preterm labor and intra-amniotic infections had higher amniotic fluid concentrations of prostaglandins than women with preterm labor in the absence of infection or women with intra-amniotic infection in the absence of labor. These observations are compatible with the participation of prostaglandins in the mechanisms of onset of preterm labor associated with intra-amniotic infection.

Interleukin I and the glomerular mesangium. II. Monokine stimulation of mesangial cell prostanoid secretion

Monocytic (MC) infiltration is a prominent feature of many forms of immune-mediated glomerulonephritis. Through the release of interleukin-1, (IL-1), monocyte/macrophages have been shown to induce the proliferation of mesangial cells and to stimulate the secretion of a glomerular basement membrane-degrading neutral proteinase. In addition, mesangial cells release a cytokine that expresses many of the biologic properties of monocyte IL-1, including stimulation of mesangial cell proliferation. Because many of the actions of IL-1 are mediated by the induction of prostanoid prostaglandin (PG) synthesis, the authors determined the effects of purified macrophage and mesangial IL-1 on the secretion of prostaglandin E (PGE), prostacyclin, and thromboxane. The results indicated that cycling MCs release primarily PGE in response to purified IL-1. The local release by either monocytes or mesangial cells of IL-1 during glomerular inflammation, with subsequent mesangial cell generation of vasodilatory PGE, may be responsible in part for the alterations in the glomerular microcirculation observed in these disorders.