Chronic exposure of interleukin-13 suppress the induction of matrix metalloproteinase-1 by tumour necrosis factor α in normal and scleroderma dermal fibroblasts through protein kinase B/Akt.

Peripheral blood mononuclear cells taken from patients with scleroderma express increased levels of interleukin (IL)-13. Moreover, the expression of matrix metalloproteinase-1 (MMP-1) from involved scleroderma skin fibroblasts is refractory to stimulation by tumour necrosis factor (TNF)-α. To elucidate the mechanism(s) involved, we examined the effect of IL-13 on TNF-α-induced MMP-1 expression in normal and scleroderma human dermal fibroblast lines and studied the involvement of serine/threonine kinase B/protein kinase B (Akt) in this response. Dermal fibroblast lines were stimulated with TNF-α in the presence of varying concentrations of IL-13. Total Akt and pAkt were quantitated using Western blot analyses. Fibroblasts were treated with or without Akt inhibitor VIII in the presence of IL-13 followed by TNF-α stimulation. MMP-1 expression was analysed by real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). Statistical analysis was performed using analysis of variance (anova) or Student's t-test. Upon TNF-α stimulation, normal dermal fibroblasts secrete more MMP-1 than systemic sclerosis (SSc) fibroblasts. This increase in MMP-1 is lost when fibroblasts are co-incubated with IL-13 and TNF-α. IL-13 induced a significant increase in levels of pAkt in dermal fibroblasts, while Akt inhibitor VIII reversed the suppressive effects of IL-13 on the response of cultured fibroblasts to TNF-α, increasing their expression of MMP-1. We show that IL-13 suppresses MMP-1 in TNF-α-stimulated normal and scleroderma dermal fibroblast. Akt inhibitor VIII is able to reverse the suppressive effect of IL-13 on MMP-1 expression and protein synthesis. Our data suggest that IL-13 regulates MMP-1 expression in response to TNF-α through an Akt-mediated pathway and may play a role in fibrotic diseases such as scleroderma.

The chemotactic attraction of human fibroblasts to a lymphocyte-derived factor.

A quantitative assay that measures fibroblast chemotaxis in vitro is described. Application of this technique has revealed that peripheral blood lymphocytes stimulated by antigen or mitogen in vitro produce a factor that is chemotactic for human dermal fibroblasts. This lymphocyte-derived chemotactic factor for fibroblasts (LDCF-F) is different from the lymphokine that is chemotactic for monocytes or macrophages. Macrophages are required for the generation of LDCF-F by T lymphocytes stimulated by phytohemagglutinin. The fibroblast chemotactic factor is heat stable (56 degrees C for 30 min), trypsin sensitive, and neuraminidase resistant. LDCF-F could function to attact connective tissue fibroblasts to sites at which cell-mediated immune reactions are occurring in vivo.

Stimulation of fibroblast chemotaxis by human recombinant tumor necrosis factor alpha (TNF-alpha) and a synthetic TNF-alpha 31-68 peptide.

Macrophages are a major source of fibrogenic factors that promote healing of injured tissue. The recruitment of fibroblasts to sites of tissue injury is a prerequisite for optimal repair of tissue damage. In the present study, human recombinant tumor necrosis factor alpha (hrTNF-alpha), a major macrophage-derived cytokine, was demonstrated to be a potent fibroblast chemoattractant, inducing migration at picomolar concentrations. Anti-hrTNF-alpha monoclonal antibody neutralized most of the fibroblast chemotactic activity generated during short-term culture of human peripheral blood monocytes stimulated with bacterial lipopolysaccharide, suggesting that TNF-alpha is a major monocyte-derived fibroblast chemoattractant. The portion of the human TNF-alpha molecule responsible for its chemotactic stimulation of fibroblasts appears to reside in residues 31-68. This region is highly conserved between TNF-alpha and lymphotoxin. This peptide is not only itself chemotactic but is also able to block the chemotactic response of fibroblasts to hrTNF-alpha and vice versa, suggesting that they each mediate fibroblast migration through similar mechanisms. These data further underscore the potential importance of TNF-alpha in modulating a variety of fibroblast functions, including chemotaxis and synthesis of collagen, glycosaminoglycans, interleukin 1 alpha (IL-1 alpha) and -beta, human histocompatibility leukocyte antigen A and B antigens, collagenase, prostaglandin E2, and IL-6.

Collagen-and collagen peptide-induced chemotaxis of human blood monocytes.

The ability of collagen and collagen-derived peptides to act as chemotactic stimuli was investigated by in vitro chemotaxis assays. Native human and chick skin collagen (type I) and alpha-chains obtained from purified chick skin collagen were each chemotactic for human peripheral blood monocytes. In addition, smaller peptides obtained either by digesting native collagen with bacterial collagenase or by degrading purified alpha-chains with cyanogen bromide or pepsin were also chemotactic for monocytes. In contrast, native collagen, alpha-chains, and smaller collagen-derived peptides were not chemotactic for human neutrophils. Since collagen is degraded at sites of tissue damage and inflammation, our findings suggest the possibility that such collagen-derived degradation products might directly serve as chemotactic stimuli for human peripheral blood monocytes in vivo.

Interleukin 1 beta propeptide is detected intracellularly and extracellularly when human monocytes are stimulated with LPS in vitro.

Human interleukin 1 beta (IL-1 beta) is synthesized as an inactive precursor that is cleaved by IL-1 converting enzyme (ICE) between Asp116 and Ala117 to form COOH-terminal mature IL-1 beta and NH2-terminal IL-1 beta propeptide. Little is known about the fate of the NH2-terminal cleavage product. In this study, human recombinant (hr)IL-1 beta propeptide (amino acids 2-116) was produced and used to prepare specific antibodies which do not recognize mature human IL-1 beta. These anti-propeptide antibodies were used for immunoprecipitation of biosynthetically labeled proteins from lipopolysaccharide-stimulated human monocytes. Analysis of immunoprecipitates by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography revealed that these antibodies recognize precursor IL-1 beta and two unique proteins: one migrating at 17.5 kD and one at 14 kD. The larger of these two proteins has a migration nearly identical to that of the recombinant IL-1 beta propeptide, and most likely represents naturally derived propeptide. The protein migrating at 14 kD may result from a second cleavage by ICE, between Asp27 and Gly28. These proteins accumulate intracellularly and extracellularly during pulse-chase experiments, and therefore represent stable products of precursor IL-1 beta cleavage.

Induction of fibroblast chemotaxis by fibronectin. Localization of the chemotactic region to a 140,000-molecular weight non-gelatin-binding fragment.

Plasma and cell-derived fibronectin are potent chemoattractants for human dermal fibroblasts in vitro. The chemotactic property of fibronectin resides in a major 140,000-mol wt non-gelatin-binding fragment of the native molecule. Human monocytes and neutrophils do not recognize fibronectin as a chemotactic stimulus. These findings suggest that fibronectin and perhaps certain fragments of fibronectin may function in vivo as a specific chemoattractant for fibroblasts and could, therefore, induce directional migration of fibroblasts to sites of tissue injury, remodeling or morphogenesis.

Stimulation of the chemotactic migration of human fibroblasts by transforming growth factor beta.

Transforming growth factor beta (TGF-beta) is a potent chemoattractant in vitro for human dermal fibroblasts. Intact disulfide and perhaps the dimeric structure of TGF-beta is essential for its ability to stimulate chemotactic migration of fibroblasts, since reduction with 2-ME results in a marked loss of its potency as a chemoattractant. Although epidermal growth factor (EGF) appears to be capable of modulating some effects of TGF-beta, it does not alter the chemotactic response of fibroblasts to TGF-beta. Specific polyvalent rabbit antibodies to homogeneously pure TGF-beta block its chemotactic activity but has no effect on the other chemoattractants tested (platelet-derived growth factor, fibronectin, and denatured type I collagen). Since TGF-beta is secreted by a variety of neoplastic and normal cells including platelets, monocytes/macrophages, and lymphocytes, it may play a critical role in vivo in embryogenesis, host response to tumors, and the repair response that follows damage to tissues by immune and nonimmune reactions.

Alterations in collagen production in mixed mononuclear leukocyte-fibroblast cultures.

The cell-cell interactions between fibroblasts and mononuclear leukocytes (MNL) which promote alterations in collagen accumulation were examined using a system of co-culture of human fibroblasts and peripheral blood MNL. The stimulation of collagen production was optimal after 48 h of co-culture and the increase in collagen correlated directly with the number of MNL added. The enhancement of collagen production was seen in both autologous and allogeneic co-cultures. Stimulation of non-collagenous protein was also noted. Co-culture supernatants contained soluble substances that were capable of stimulating collagen production, although they stimulated collagen production to a lesser degree than direct co-culture. Fractionation of these supernatants on Sephadex G-200 revealed a predominant area of stimulatory activity at 160,000 mol wt. Lesser areas of activity were noted at molecular weights of 80,000 and 25,000. Determination of the types of collagen produced by fibroblasts during co-culture with MNL showed that the ratio of type I:III collagen was decreased. These alterations in both the quantitative and qualitative accumulation of collagen mimic the changes often seen in wound healing and early inflammation suggesting that cellular interactions between fibroblasts and MNL may be important in the modulation of collagen production in normal and pathologic states.

Interleukin 1 stimulation of collagenase production by cultured fibroblasts.

Interleukin 1 is a monokine that exerts biological effects on a variety of target cells in vitro. In this report, interleukin 1 has been found to be capable of stimulating collagenase production by cultured dermal fibroblasts. The concentrations of interleukin 1 that stimulate fibroblast collagenase production are similar to those that stimulate mouse thymocyte proliferation. Analyses by high performance liquid chromatography indicate that interleukin 1, rather than a contaminating monokine, is responsible for this effect on fibroblasts. Interleukin 1, released in vivo by macrophages infiltrating sites of tissue damage or inflammation, may function to stimulate the release of collagenase by connective tissue fibroblasts.

Formation of multinucleated giant cells from human monocyte precursors. Mediation by a soluble protein from antigen-and mitogen-stimulated lymphocytes.

Multinucleated giant cells are associated with granulomas arising from immunological and nonimmunological inflammatory reactions. They are an integral part of the host immune response to chronic infectious diseases. In the present study we have demonstrated that human lymphocytes when stimulated by specific antigens of T cell mitogens produce a soluble factor that causes peripheral blood monocytes to fuse and form multinucleated giant cells in vitro. Production of the giant cell factor by antigen-stimulated peripheral blood lymphocytes correlates with the existence of cell-mediated immunity to specific antigen. Monocyte-depleted blood lymphocytes, but not purified blood monocytes, produce the giant cell factor when cultured with antigens or T cell mitogens. Gel filtration and physiochemical studies indicate that the lymphocyte-derived giant cell factor is a heat-labile protein of approximately 60,000 mol wt. These findings suggest that multinucleated giant cells in granulomas may be formed by fusion of circulating monocytes in response to the release of a 60,000-mol wt protein from antigen-stimulated T lymphocytes.

Transforming growth factor beta 1 (TGF-beta 1) induced neutrophil recruitment to synovial tissues: implications for TGF-beta-driven synovial inflammation and hyperplasia.

We have studied the consequences of introducing human recombinant transforming growth factor beta 1 (hrTGF-beta 1) into synovial tissue of the rat, to begin to better understand the significance of the fact that biologically active TGF-beta is found in human arthritic synovial effusions. Within 4-6 h after the intra-articular injection of 1 microgram of hrTGF-beta 1 into rat knee joints, extensive recruitment of polymorphonuclear leukocytes (PMNs) was observed. Cytochemistry and high resolution histological techniques were used to quantitate the influx of PMNs, which peaked 6 h post-injection. In a Boyden chamber assay, hrTGF-beta 1 at 1-10 fg/ml elicited a chemotactic response from PMNs greater in magnitude than that evoked by FMLP, establishing that TGF-beta 1 is an effective chemotactic agent for PMNs in vitro as well as in vivo. That PMNs may represent an important source of TGF-beta in inflammatory infiltrates was strongly suggested by a demonstration that stored TGF-beta 1 was secreted during phorbol myristate acetate-stimulated degranulation in vitro. Acid/ethanol extracts of human PMNs assayed by ELISA contained an average of 355 ng of TGF/beta 1 per 10(9) cells potentially available for secretion during degranulation of PMNs. [3H]Thymidine incorporation in vivo and autoradiography of tissue sections revealed that widespread cell proliferation was triggered by TGF-beta 1 injection. Synovial lining cells and cells located deep within the subsynovial connective tissue were identified as sources of at least some of the new cells that contribute to TGF-beta 1-induced hyperplasia. Our results demonstrate that TGF-beta is capable of exerting pathogenic effects on synovial tissue and that PMNs may represent a significant source of the TGF-beta present in synovial effusions.

Stimulation with type I collagen induces changes in gene expression in peripheral blood mononuclear cells from patients with diffuse cutaneous systemic sclerosis (scleroderma).

An autoantigenic role for collagen type I (CI) has been suggested previously in diffuse cutaneous systemic sclerosis (dcSSc). Whether CI is indeed capable of affecting the immune system in dcSSc is not known. Patients with early (3 years or less) or late (>3 years) dcSSc and healthy controls donated blood. Peripheral blood mononuclear cells (PBMC) were cultured with or without CI, and expression of genes known for their involvement in autoimmune and inflammatory processes was assessed using cDNA arrays; results were confirmed by real-time polymerase chain reaction and enzyme-linked immunosorbent assay for selected genes. Patients with early and late dcSSc were similarly different from healthy controls in basal gene expression. When cultured with CI, PBMC from patients with early dcSSc differed from healthy controls in expression of 34 genes, whereas PBMC from patients with late dcSSc differed from healthy controls in expression of only 29 genes. Direct comparisons of matched PBMC samples cultured with and without CI revealed differences in expression of eight genes in healthy controls, of five genes in patients with early dcSSc, and no differences in patients with late dcSSc. Thus, PBMC from patients with dcSSc respond differently than do PBMC from healthy controls when cultured with CI. Exposure to CI in culture of PBMC from patients in the early stage of dcSSc in contrast to PBMC from patients with late-stage dcSSc evokes a greater degree of activation of immune-related genes, suggesting that CI is more dominant as an autoantigen in early versus late dcSSc.

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.

Fibroblast chemotaxis induction by human recombinant interleukin-4. Identification by synthetic peptide analysis of two chemotactic domains residing in amino acid sequences 70-88 and 89-122.

Interleukin-4 is a T lymphocyte- and mast cell-derived cytokine with pleiotropic properties with biological effects on a variety of target cells including B and T lymphocytes, macrophages, hematopoietic cells, mast cells, and fibroblasts. In addition to the proliferation effect of IL-4 on fibroblasts, which has been previously described, in this report the chemotactic properties of IL-4 for fibroblasts is described. Human recombinant IL-4 induced the chemotactic migration of dermal fibroblasts in vitro in modified Boyden-type chambers at concentrations between 10(-12) and 10(-11) M. The chemotactic activity of IL-4 was neutralized by anti-human recombinant IL-4 IgG antibodies. Oligopeptides representing the complete deduced amino acid sequence of human IL-4 were synthesized by the Merrifield technique and tested for their ability to induce fibroblast chemotaxis. Two peptides representing residues 70-88 and 89-122 induced fibroblast migration. Peptide 70-88 was the more potent of the two causing chemotaxis of fibroblasts at 10(-8)-10(-6) M while peptide 89-129 induced migration at 10(-7)-10(-5) M. Although the mechanism by which IL-4 and these two peptides induce fibroblast chemotaxis is unknown, each of these three compounds were able to chemotactically desensitize fibroblasts to the chemotactic effects of the other two but not to a structurally unrelated chemotactic cytokine, transforming growth factor beta-1. These studies suggest that IL-4 might function in vivo to induce the accumulation of fibroblasts at sites of tissue injury, inflammatory and immune reactions in which T lymphocytes and mast cells participate.

Generation of a fibroblast chemotactic factor in serum by activation of complement.

When serum complement is activated by either the classical or alternative pathways, a factor with an apparent 80,000 mol wt is generated that is chemotactic for human dermal fibroblasts. The origin of this serum-derived chemotactic factor (SDCF) is not known; however, it may be a cleavage product from C5 because it is inactivated by monospecific antiserum to human C5, and it is not generated when the complement system is activated in human serum deficient in C5. SDCF is not chemotactic for human neutrophils or monocytes. Because SDCF is generated when serum complement is activated, it may function in vivo to attract connective tissue fibroblasts to sites of inflammatory reactions in which the complement system participates.

Interleukin 1 stimulates phosphatidylinositol kinase activity in human fibroblasts.

IL-1 mediates multiple cellular immune and inflammatory responses, but little is known of the intracellular biochemical mechanisms involved in IL-1 actions. We studied the effects of IL-1 on phosphatidylinositol (PtdIns) metabolism and confirmed reports indicating that IL-1 does not stimulate increased PtdIns turnover; however, we observed the accumulation of PtdIns-4-phosphate (PtdInsP) in response to IL-1. Using a fibroblast membrane preparation, we were able to detect stimulated PtdInsP accumulation within 10 s of IL-1 addition. Increased PtdInsP accumulation was due to stimulated PtdIns kinase activity, not the inhibition of PtdInsP hydrolysis by phospholipase(s). PtdIns kinase activity was magnesium dependent, increased as a function of IL-1 concentration, and specifically phosphorylated the D4 position of inositol. Stimulated PtdIns kinase activity could be detected at 10(-12) M IL-1 in fibroblast membranes, a concentration within the physiological range for IL-1 action; half-maximal activity was reached at approximately 10(-10) M IL-1. Heat denaturation of IL-1 or treatment of IL-1 with anti-IL-1 antibody abrogated the IL-1 effect. These findings demonstrate the direct, IL-1-mediated, stimulation of PtdIns kinase. IL-1-stimulated PtdIns kinase activity represents an important physiological regulatory effect by IL-1 as it could control the synthesis and/or maintenance of phosphorylated derivatives of PtdIns which comprise only a very small pool of substrates for the generation of the second messengers inositol 1,4,5-triphosphate and diacylglycerol.

Human fibroblasts synthesize elevated levels of extracellular matrix proteins in response to interleukin 4.

Interleukin 4 (also known as "B cell stimulatory factor-1"), a cytokine product of T lymphocytes and mast cells, stimulates synthesis of the extracellular matrix proteins, types I and III collagen and fibronectin, by human dermal fibroblasts in vitro. Stimulation of collagen by human recombinant (hr)IL-4 was also demonstrated in several fibroblastic synovial cell lines obtained from patients with rheumatoid arthritis and osteoarthritis. The stimulatory effect of hrIL-4 on fibroblast collagen synthesis was specifically neutralized by rabbit anti-hrIL-4 Ig. IL-4 specifically increased the steady-state levels of types I and III procollagen and fibronectin mRNAs, with no effect on cytoplasmic beta-actin mRNA. Quantitative analysis of the levels of Pro alpha 1(I) collagen transcripts in IL-4-treated fibroblast cultures was also corroborated by antisense RNA-mRNA hybridization and RNAse resistant hybrids which showed that IL-4-treated fibroblasts expressed higher levels of Pro alpha 1(I) collagen transcripts. Nuclear run-off transcription experiments indicated that IL-4 stimulated the rates of mRNA biogenesis. Based on these observations we conclude that IL-4 exerts its effect on collagen and fibronectin synthesis at the pretranslational level, resulting in synthesis of these extracellular matrix proteins. These and other data suggest that IL-4 may be a "fibrogenic cytokine" that could be important in promoting biogenesis of extracellular matrix proteins in normal wound healing and in pathological fibrosis in which mast cells and T lymphocytes play a central role.

Transforming growth factor-beta increases steady state levels of type I procollagen and fibronectin messenger RNAs posttranscriptionally in cultured human dermal fibroblasts.

Transforming growth factor-beta (TGF beta), when injected subcutaneously into newborn mice, induces a rapid fibrotic response, stimulates chemotaxis, and elevates the rates of biosynthesis of collagen and fibronectin by fibroblasts in vitro. We explored the molecular mechanisms of TGF beta-mediated stimulation of collagen and fibronectin synthesis in cultured human foreskin fibroblasts. TGF beta preferentially stimulated the synthesis of fibronectin and type I procollagen chains 3-5-fold as shown by polypeptide analysis. Concomitant elevation in the steady state levels of messenger RNAs (mRNAs) coding for type I procollagen and fibronectin also occurred but without a net increase in the rate of transcription of either of these genes. The preferential stabilization of mRNAs specifying type I procollagen and fibronectin provides a partial explanation for the mechanisms by which TGF beta enhances the synthesis of type I procollagen and fibronectin in mesenchymal cells.

Binding of chemotactic collagen-derived peptides to fibroblasts. The relationship to fibroblast chemotaxis.

We previously showed that collagen, alpha-chains, and collagen-derived peptide fragments induce chemotactic migration of human fibroblasts in vitro. We now describe biochemical and immunological evidence showing there are binding sites for collagen peptides on fibroblast membranes.By the use of (14)C-labeled alpha1(I) chain, binding to intact fibroblasts was demonstrated. The process was reversible, and time- and fibroblast concentration-dependent. Scatchard plot analyses of the data obtained for the binding of alpha1(I) suggested that there are congruent with 16 x 10(6) binding sites per fibroblast with an association constant of 1.1 x 10(7)/M for alpha1(I). Dissociation of the bound radioactivity and subsequent chromatographic analysis on agarose A-1.5 m revealed that the alpha1 was unaltered. The binding of (14)C-labeled alpha1 was inhibited by each of the CNBr peptides derived from alpha1 chain of chick skin collagen and CNBr peptide mixtures of various genetic types of collagen chains. Immunofluorescence studies with anti-alpha1 antibody showed that alpha1-treated fibroblasts exhibited strong immunofluorescence. The intensity of fluorescence was markedly diminished by prior absorption of the antibody with alpha1. The alpha1-treated cells stained with preimmune sera did not show significant fluorescence.Dose-response curves of fibroblast chemotaxis induced by alpha1 and the binding of alpha1 by fibroblasts correlate closely. Furthermore, the potency of alpha1-CNBr peptides as chemotactic agents correlates with their ability to inhibit the binding of labeled alpha1(I). These data suggest the hypothesis that collagenderived peptides cause fibroblast chemotactic migration by acting on fibroblast membranes.

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.