Soluble mediators from mononuclear cells increase the synthesis of glycosaminoglycan by dermal fibroblast cultures derived from normal subjects and progressive systemic sclerosis patients

Serum Levels of Granulocyte Macrophage Colony Stimulating Factor (GM-CSF) in a Group of Patients with Systemic Sclerosis

In this report we investigate the behaviour of the serum levels of Granulocyte Macrophage Colony Stimulating Factor (GM-CSF) in the course of Systemic Sclerosis (SS). This cytokine is produced mainly by T and NK cells, and its possible role in the pathogenesis of SS has not been previously described in the literature. Serum GM-CSF levels were assayed in 10 female patients, ageing from 35 to 70, affected by SS. These patients were not suffering from other disorders and were not being treated with steroids or immunosuppressive drug. A solid phase immunoenzymatic method was used to assess the serum levels of GM-CSF. Reference values were previously determined in a control group of 36 healthy women blood donors (19 premenopausal and 17 postmenopausal) (x̄=20.1 ±12.3 pg/ml). All the patients but one showed significantly increased serum levels of GM-CSF (x̄= 120.9 ±125.5 pg/ml). The highest levels were found in the two oldest patients, who also had the longest clinical history of SS, but a clear correlation with age, disease duration or clinical manifestations was not evident, even if the postmenopausal age group patients showed a higher mean value of GM-CSF (x̄= 148.0±144.1 pg/ml) than that found in the premenopausal age group (x̄= 57.7±1.4 pg/ml) (in contrast with the findings in the control group). The absence of other pathogenic conditions in our patients suggests that the increase in serum levels of GM-CSF might be linked to the fibroblast proliferation which is typical of SS. However, our results do not explain the role played by this factor in the fibroblastic proliferation process and an in vitro study is necessary to clarify this aspect.

Interactions between cells of the immune system and hyaluronate synthesis by human dermal fibroblasts

Mitogen- or alloantigen-activated human peripheral blood mononuclear cells (MNC) produce a soluble factor which selectively stimulates up to twenty-fold the synthesis of glycosaminoglycan (GAG) by cultured normal human fibroblasts. Confluent fibroblast monolayers were incubated with active MNC supernatants and newly synthesized GAG was measured by the incorporation of [3H]glucosamine into cetylpyridinium chloride-precipitable material. The GAG-stimulatory factor (GAG-SF) was a product of T lymphocytes. Alloreactive T cell clones obtained from the peripheral blood produced the factor after reactivation with the irradiated stimulators, and its production was dependent on HLA-DR-mediated recognition. The CD3+CD4+ clones derived from the skin-infiltrating lymphocytes in patients with early scleroderma also produced the GAG-SF upon in vitro activation with a mitogen. The GAG-SF was purified to apparent homogeneity from supernatants of concanavalin A-activated MNC by Sephadex gel filtration, ion-exchange chromatography and reverse-phase HPLC. The GAG-SF is a 67,000 Da glycoprotein with pI of 5.6. It is not mitogenic to fibroblasts and does not modulate collagen synthesis. Its purification and characterization are important, because of a possible involvement of activated lymphocytes and their products in the immunopathogenesis of human diseases characterized by fibrosis, stromal reactions and local lymphocytic infiltrates.

Differential effect of growth factors on hyaluronan synthase gene expression in fibroblasts exposed to oxidative stress

The aim of this study was to evaluate how growth factors (PDGF-BB, EGF, and TGF-1beta) modulate hyaluronan synthase (HAS) activities in normal or stressed cultured human skin fibroblasts. The effects of concomitant treatment with cytokines and FeSO4 plus ascorbate on HAS mRNA expression, protein synthesis, and hyaluronic acid (HA) concentrations were also studied. Treatment of fibroblasts with growth factors up-regulated HAS gene expression and increased HAS enzymes and HA production. PDGF-BB induced HAS mRNA expression, protein synthesis, and HA production more efficiently than EGF and TGF-1beta. EGF was less effective than TGF-1beta. In addition, TGF-1beta reduced the expression and synthesis of HAS3, while PDGF-BB and EGF had the opposite effect. Concomitant treatment with growth factors and the oxidant was able to further increase HAS mRNA expression, once again with the exception of HAS3 with TGF-1beta. HAS protein synthesis was reduced, while HA levels were unaffected in comparison to those obtained from exposure to FeSO4 plus ascorbate alone. In conclusion, although growth factors plus the oxidant synergistically induced HAS mRNA expression in part, enzyme production was not correlated with this increase. Moreover, the increase in HAS mRNA levels was not translated into a consequent rise in HA concentration.

TNF-alpha, IFN-gamma, and IL-1beta modulate hyaluronan synthase expression in human skin fibroblasts: synergistic effect by concomital treatment with FeSO4 plus ascorbate

Several reports have shown that a number of cytokines such as tumor necrosis-alpha (TNF-alpha), interferon-gamma (IFN-gamma), and interleukin-beta (IL-1beta) are capable to induce hyaluronan sinthases (HASs) mRNA expression in different cell culture types. The obvious consequence of this stimulation is a marked increment in hyaluronan (HA) production. It has been also reported that oxidative stress, by itself, may increase HA levels. The aim of this study was to evaluate how TNF-alpha, IFN-gamma,IL-1beta, and exposition to oxidative stress may modulate HAS activities in normal human skin fibroblasts. Moreover, the effects on HAS mRNA expression of the concomitant treatment with cytokines and oxidants, and the HA concentrations after treatments, were studied. TNF-alpha, IFN-gamma, and IL-1beta were added to normal or/and exposed to FeSO(4) plus ascorbate fibroblast cultures and HAS1, HAS2 and HAS3 mRNA content, by PCR-real time, was assayed 3,h later. HA levels were also evaluated after 24,h incubation. The treatment of fibroblasts with cytokines up-regulated HASs gene expression and increased HA production. IL-1beta induced HAS mRNA expression and HA production more efficiently than TNF-alpha and IFN-gamma. The exposition of the fibroblasts with the oxidant system markedly increased HAS activities while slightly HA production. The concomitant treatment of cells with the cytokines and the oxidant was able to further enhance, in a dose dependent way, with synergistic effect on HAS mRNA expression. On the contrary HA levels resulted unaffected by the concomitant treatment, and resemble those obtained with the exposure to FeSO(4) plus ascorbate only. This lack in HA production could be due to the deleterious action of free radicals on the HA synthesis.

Role of chondroitin sulfate-hyaluronan interactions in the viscoelastic properties of extracellular matrices and fluids

The purpose of this study was to investigate the role of chondroitin sulfate-hyaluronan interactions in the viscoelastic properties of tissues and fluids, using capillary and cone-on-plate viscometers. Chondroitin sulfate markedly increased the viscosity of hyaluronan solutions at a wide range of hyaluronan mass (50-1900 kDa) under physiological conditions of pH, temperature, ionic strength and glycosaminoglycan concentration (0.5-40 mg/ml), although the viscosity of the chondroitin sulfate solutions themselves was very low. In the assay using a cone-on-plate viscometer, chondroitin sulfate increased the viscosity of hyaluronan solutions at various shear rates. At low shear rates, the viscosity of a chondroitin sulfate (5 mg/ml)-hyaluronan (0.5 mg/ml) mixture was about 40% of that of an aggrecan (5 mg/ml)-hyaluronan (0.5 mg/ml) mixture, and at 2.8-fold higher concentrations, chondroitin sulfate elicited the same effect on the viscosity of hyaluronan solutions (5 mg/ml) as an aggrecan monomer. In the presence of oscillatory motion, the addition of aggrecan increased the elasticity (storage) modulus G' and the viscosity (loss) modulus G" of hyaluronan solutions and markedly decreased the loss tangent G"/G' at frequencies corresponding to normal joint movements. In contrast, chondroitin sulfate had only a marginal effect on the loss tangent G"/G', although it increased G' and G". These findings demonstrated that chondroitin sulfate, as well as aggrecan, increases the viscosity of hyaluronan solutions, although chondroitin sulfate has less effect on the elasticity of hyaluronan solutions than that of aggrecan, and suggest that chondroitin sulfate may play an important physiological role in determining the viscoelastic properties of extracellular matrices and fluids.

Human peritoneal fibroblast proliferation in 3-dimensional culture: modulation by cytokines, growth factors and peritoneal dialysis effluent

Structural and functional alterations of the peritoneal membrane are a significant problem in long-term peritoneal dialysis patients. The present study has established a 3-dimensional (3D) cell culture system to study the human peritoneal fibroblast (HPFB) and to examine its proliferative responses to cytokines and growth factors as well as dialysis effluent obtained from patients during peritoneal infection. PDGF-AB, basic FGF and IL-1 beta induced a time and dose dependent increase in 3D-HPFB proliferation. At day 9 proliferation, as assessed by MTT uptake, was increased by 2.4-, 2.3- and 1.5-fold above control by PDGF-AB (50 ng/ml), bFGF (50 ng/ml) and IL-1 beta (10 ng/ml), respectively (N = 5, P = 0.04 for all). These effects could be inhibited by co-incubation with anti-PDGF-AB antibody, anti-bFGF or IL-1ra, respectively. Exposure of 3D-HPFB to TGF-beta 1 did not result in an increase in cell proliferation. Incubation of 3D-HPFB with peritoneal macrophage (PMø) or human peritoneal mesothelial cell (HPMC) conditioned medium also resulted in a time and dose dependent increase in proliferation. At day 9, proliferation was maximally increase 1.65- and 1.92-fold by peritoneal macrophage- and mesothelial cell-conditioned medium, respectively. Cell free PDE, obtained from CAPD patients during episodes of peritonitis, induced 3D-HPFB proliferation above control values (2- to 6.5-fold increases, N = 5, P < 0.05 for all). This mitogenic potential of PDE was reduced following dilution, and with time following peritonitis there was a gradual decrease in the mitogenic effect of PDE. The proliferative potential of PDE was significantly reduced following co-incubation with IL-1ra (45.7% inhibition), anti-bFGF (34.9% inhibition) and anti PDGF-AB (27.4% inhibition). These data indicate that infected PDE causes fibroblast hyperplasia which might potentially contribute to pro-fibrotic processes during CAPD.

Successful culture and selection of cytokine gene-modified human dermal fibroblasts for the biologic therapy of patients with cancer

Human autologous dermal fibroblasts have been cultured, transduced with the interleukin-4 (IL-4) gene and used as a vaccine together with irradiated autologous tumor cells in patients with cancer participating in a phase I/II clinical trial at the University of Pittsburgh Cancer Institute. In support of this clinical trial, methods have been devised to facilitate isolation of fibroblasts from freshly harvested skin specimens, to enhance their outgrowth in large-scale cultures, and to assay cytokine (IL-4) production following transduction with the cytokine gene +/- irradiation. Fibroblasts were isolated from skin specimens by enzymatic digestion, grown in primary cultures, and transduced with a retroviral vector containing the gene for human IL-4 and the NeoR gene as a selectable marker. Following selection in G418, the irradiated, IL-4-producing fibroblasts were administered to patients in a vaccine containing irradiated autologous tumor cells. Seventy-eight specimens of human skin were processed to obtain fibroblast suspensions. Cultures of fibroblasts were established from 68 of the 78 specimens (87%). Of 33 transduced and selected fibroblast cultures, 21 produced at least 1,000 units of IL-4/24 hours per 10(6) cells, as determined by ELISA, and 17/33 or 51% were used for therapy. The primary cultures were typically maintained for up to seven or eight passages. The mean +/- SD overall time for obtaining a required number of transduced, selected cells was 53 +/- 4 days. The fibroblasts continued to produce IL-4 in culture for 3 weeks even after irradiation. Similar results have been obtained with a retroviral vector encoding IL-12. This study shows that human dermal fibroblasts can be consistently and reproducibly expanded and genetically modified to serve as a source of cytokines or other gene products for gene therapy trials.

Papulonodular mucinosis associated with systemic lupus erythematosus: possible mechanisms of increased glycosaminoglycan accumulation

BACKGROUND

The mechanism for the production of papulonodular mucinosis in patients with lupus erythematosus (LE) is not known.

OBJECTIVE

Our purpose was to determine whether fibroblasts in a patient with LE and papulonodular mucinosis produced more mucin than normal fibroblasts and whether this mucin production could be stimulated by the patient's serum.

METHODS

Skin fibroblasts from a patient with systemic LE and massive papulonodular mucin deposition, as well as normal fibroblasts, were incubated in the presence of serum from the patient or from a healthy volunteer. The production of glycosaminoglycan by fibroblasts was analyzed.

RESULTS

Fibroblasts from the patient produced more glycosaminoglycan than did normal fibroblasts. Glycosaminoglycan production was increased in all cells when incubated in the presence of the patient's serum.

CONCLUSION

Cutaneous mucin deposition in patients with papulonodular LE skin lesions is associated with increased glycosaminoglycan production by dermal fibroblasts. Our preliminary observations suggest glycosaminoglycan production by these fibroblasts appears to be stimulated by a factor, (or factors) in the patient's serum that is yet to be identified.

Cytokines in rheumatic diseases

IL-1 and related cytokines have multiple biologic activities relevant to the rheumatic diseases. In addition to mediating inflammatory and immune responses, these proteins regulate many aspects of connective tissue metabolism. The cytokines interact in complex cascades: because of this, and various technical reasons, the exact role of cytokines in the pathogenesis of rheumatic diseases remains uncertain. However, considerable experimental data suggest that the abnormal regulation of cytokines contributes to such siseases as inflammatory arthritis, systemic lupus erythematosus, scleroderma, and dermatomyositis. Animal models of these diseases have contributed to understanding the role of cytokines in pathogenesis. Furthermore, drugs useful in treating these diseases affect cytokine pathways; some cytokines, their antagonists, or related substances have been used therapeutically to treat rheumatic diseases. The therapeutic use of these agents will likely increase as knowledge about the role of cytokines in the pathogenesis of rheumatic diseases expands.

Expression of chondroitin sulfate as a unique type of proteoglycan on the cell membrane of multipotential and committed hemopoietic progenitor cells

Proteoglycans are increasingly implicated as a major factor in the regulation of hemopoiesis. They are generally synthesized by stromal cells and released to the extracellular matrix. More recently the ability of hemopoietic progenitor cells to synthesize proteoglycans has come into focus. In the present study we maintained 3 cloned factor-dependent hemopoietic progenitor cells (B6 and F-mix which are multipotential and F-2 which is bipotential) in liquid culture. The cells were pulse-labeled with 35SO4 which becomes incorporated into the glycan side-chains of proteoglycans. We then studied subcellular distribution and chemical characterization of the newly synthesized proteoglycans. All 3 cell lines synthesized chondroitin sulfate as a unique type of proteoglycan as identified by gel filtration on a Sepharose CL-4B column followed by chondroitinase ABC cleavage of its glycosaminoglycan. This single type of proteoglycan was compartmentalized into intracellular, membrane-associated and extracellular pools. Its density on the membrane appeared to be a function of the differentiation state of the cell. The functional significance of membrane-associated proteoglycan in hemopoietic progenitor cells appears to be underestimated and requires further investigation.

The glycosaminoglycan composition of the lung with acute and chronic pathology and in senescence

The content and distribution of GAGs in the anatomic structures of pathological (pneumoconiosis, pneumonia, pulmonary embolism) and senescent lungs have been measured. The total GAG content of the lung structures, except central bronchi is generally lower than normal in the pathological lungs. The GAG distribution in the pleura (DS predominant), central bronchi (C6S predominant), arteries, veins and 'total lung' is similar to the corresponding normal distribution. The other notable observations are: the concentration of HA in peripheral bronchi and alveoli is increased possibly in response to the high local concentration of coal dust; an age related GAG switch from DS in the arteries of the young to C6S in the arteries of the mature lung is confirmed; the arterial GAG content generally increases with age up to age 103 in the male; the arteries of a female smoker display the mature male pattern of GAG composition. The data suggest that gender, smoking and age, more than acute pathology, determine the GAG composition of the anatomic structures of the lung.

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.

Cytokines, fibrosis and the failure of glaucoma filtration surgery

Current therapies for the prevention of fibrosis after glaucoma filtering surgery can be effective but often produce unwanted side effects. An understanding of the cellular basis of the fibrotic reaction may lead to better treatments. Wound repair revolves around angiogenesis and the activation of fibroblasts by cytokines. These peptides, a number of which have been described, act together in intricately complicated networks to encourage fibroblast chemotaxis, proliferation and contractility, as well as to stimulate the production of glycosaminoglycans and collagen. Since interferons seem to inhibit many of these responses, they deserve further evaluation in the treatment of ocular fibrosis.

Circulating androgens in male patients suffering from systemic scleroderma

The excretion of collagen metabolites and circulating androgens was measured in ten males suffering from progressive systemic sclerosis. Significantly higher levels of sex hormone-binding globulin, total testosterone and dihydrotestosterone (DHT) (P less than 0.01), and total oestradiol (P less than 0.05), were found in patients when compared with age-matched controls. Urinary excretion of hydroxyproline in patients was found to correlate significantly with total testosterone (P = 0.035), with DHT (P = 0.005) and dehydroepiandrosterone-sulphate (DHEAS) (P = 0.034). Similarly the hydroxyproline peptide fraction was found to correlate significantly with total testosterone (P = 0.037), with DHT (P = 0.005) and with DHEAS (P = 0.008). Hydroxylysine peptide in the urine correlated significantly with free testosterone (P = 0.035) and DHT (P = 0.040). Oestrogens did not correlate with urinary excretion of collagen metabolites. These findings suggest that androgens may play a role in the pathogenesis of scleroderma in male patients.

Clinical correlations and prognosis based on hyaluronic acid serum levels in patients with progressive systemic sclerosis

The serum levels of hyaluronic acid (sHA) were measured using an affinoimmunoenzymatic assay in patients with distal (n = 16) and proximal (n = 15) progressive systemic sclerosis (PSS) and in 31 controls. The severity of PSS was evaluated using a standardized organ-involvement score. The mean sHA was significantly higher in the patients with PSS than in controls (mean +/- SD:80 +/- 43.4 micrograms/l vs. 42.3 +/- 19.1 micrograms/l, P less than 0.001). sHA was significantly higher in patients with proximal PSS than in patients with distal PSS (106.4 +/- 44.6 micrograms/l vs. 55.4 +/- 23.8 micrograms/l, P less than 0.001). A positive correlation was found between sHA and the disease score (r = 0.67, P less than 0.001). sHA was also correlated with lung diffusion capacity for carbon monoxide (r = 0.70, P less than 0.001), but only in the those patients who had abnormal lung function, and therefore presumably had lung PSS involvement. We suggest that sHA could be an indicator of the degree of systemic involvement in PSS. Its prognostic value and possible use in the follow up of patients with PSS remain to be clarified.

Altered T cell subpopulations and lymphocytes expressing natural killer cell phenotypes in patients with progressive systemic sclerosis

Scleroderma (progressive systemic sclerosis [PSS]) is known to be associated with abnormal T cell immunoregulation. In the present study, we evaluated lymphocyte phenotypes in patients with PSS and normal control subjects by flow cytometry and monoclonal antibodies for total T (CD3), T suppressor (CD8), T helper (CD4), T helper-inducer (CDw29), T suppressor-inducer (CD45R), human leukocyte antigen, DR+B (CD19), DR+T, and natural killer subsets, HNK-1 (CD57) and NKH-1 (CD56) cells. Patients with PSS compared to normal subjects had significantly lower percentages of CD3+ (p less than 0.005) and CD8+ (p less than 0.05) (similar to several patients with rheumatoid arthritis also evaluated), as well as CD45R (p less than 0.05), T+DR+ (p less than 0.05), and NKH-1 (CD56) (p less than 0.0005) cells. Patients with PSS with late-limited or generalized disease had lower percentages of CD8+, CD19, NKH-1+, and CDw29, but higher percentages of CD4+, HNK-1, and CD45R cells compared to patients with early stage disease, but these results were not statistically significant. These unique alterations in patients with PSS may prove to be useful in monitoring the stage of disease activity for therapy and further define immunologic defects.

Monocytes secrete factors regulating glycosaminoglycan synthesis in mesangial cells in vitro

The present study was conducted to determine the manner in which monocytes increase mesangial matrices, particularly glycosaminoglycans (GAGs) which interact with various other matrix components such as collagens, laminin, fibronectin and lipoproteins. A supernatant of human peripheral blood monocyte cultures activated by lipopolysaccharide (LPS) contains stimulating factors for glycosaminoglycan synthesis in rat mesangial cells (MCs). The culture supernatant in this study was concentrated and fractionated by gel chromatography and the GAG-stimulatory factor was found to have a molecular weight of 10-17 kD. This factor was shown to be present in fractions different from that of IL-1. Gel and ion-exchange chromatography studies of GAGs synthesized by MCs indicated the elution patterns of GAGs in the presence and absence of the monocyte culture supernatant to be essentially the same. Local infiltration of monocytes into the glomerulus, often seen in various types of glomerular injury, may be an important factor in the accumulation of the mesangial matrix.

Cytokine networks in the regulation of inflammation and fibrosis in the lung

To understand the processes regulating inflammation and fibrosis in the human lung, we characterized the effects of recombinant interleukin-1, tumor necrosis factor, and gamma interferon on fibroblast proliferation, collagen production, interleukin-1-alpha production, interleukin-1-beta production, and interleukin-6-production. These studies demonstrated the existence of complex cytokine networks by which inflammatory cells regulate fibroblast function and fibroblasts, in turn, feed back to regulate inflammatory cell function. They also demonstrated that, in this complex network, the effect of an individual cytokine varies with the state of activation of the target cell, the presence of other cytokines in the local microenvironment, and the ability of the target cell to produce bioactive autocoids such as prostaglandins. Aspects of this cytokine network are discussed and a testable hypothesis for granuloma and abscess formation is detailed.

Functional and phenotypic analysis of T lymphocytes cloned from the skin of patients with systemic sclerosis

Activated T lymphocytes often accumulate in the lower dermis of patients with systemic sclerosis (scleroderma) and may play a role in the development of dermal fibrosis. We propagated and cloned these cells directly from skin biopsies in four of eight cases of early, untreated systemic sclerosis with diffuse scleroderma. The cloning frequency estimates were f = 0.20 and f = 0.48 for T cells derived from the skin of two patients versus f = 0.68 and f = 0.96 for autologous blood T lymphocytes. All but one of 24 skin-derived scleroderma clones were CD4+. Clonal analyses performed with CD4+ clones from patients and normal controls showed that all but one skin-derived clones synthesized either interferon-gamma (60%), glycosaminoglycan-stimulatory factor (26%) or both (9%) when induced in vitro by a mitogen, concanavalin A, but not by autologous dermal fibroblasts. In contrast, blood-derived clones had a different functional phenotype. All skin-derived clones produced tumour necrosis factor-alpha. Our results demonstrate that T lymphocytes obtained from the skin of patients with systemic sclerosis synthesized cytokines which could modulate functions of human dermal fibroblasts.

Proteoglycan synthesis by cultured liver endothelium: the role of membrane-associated heparan sulfate in transferrin binding

Liver endothelium has been reported to possess membrane receptors for the iron-binding protein transferrin (Tf). Similarly, the core protein of proteoglycans (PG) associated with cell membrane in many cell systems can bind Tf. To find out if membrane-associated proteoglycans can explain Tf-binding ability of liver endothelium, we investigated the synthesis and distribution of proteoglycans by isolated, cultured liver capillary endothelium. Cells were isolated and cultured for 48 h in sulfate-free medium and pulse-labeled with 35SO4. The relative distribution of 35SO4-labeled macromolecules, determined in the extracellular (EC), membrane-associated (MA), and intracellular (IC) pools, was respectively 74, 15, and 10%. Membrane-associated proteoglycan (MA-PG) was further purified by ion exchange and gel chromatography. Glycosaminoglycan (GAG) chain characterization indicated about 78% chondroitin sulfate, 7% dermatan sulfate, and about 14% heparan sulfate (HS). Similar GAG chain characterization was made for PG in the EC and IC pools. Transferrin-binding ability of MA-PG was studied by affinity column chromatography, using CNBr-activated sepharose bound to transferrin. About 15% of the labeled MA-PG was specifically bound to Tf-affinity column and could be eluted by excess soluble Tf. This proportion was similar to the proportion of HS in the total membrane-associated pool. Moreover, the eluted labeled material was susceptible to pretreatment with heparitinase, confirming its HS nature. We conclude that the transport capillary endothelium of the liver can synthesize HS proteoglycans which are membrane-associated and this MA-HS pool can bind transferrin. The finding may provide a molecular basis for transferrin binding to liver endothelium and may explain the subsequent transendothelial transport of iron-transferrin complexes into the liver.

Short-term keloid treatment in vivo with human interferon alfa-2b results in a selective and persistent normalization of keloidal fibroblast collagen, glycosaminoglycan, and collagenase production in vitro

Two intralesional injections of interferon alfa-2b (1.5 million U per injection) into a progressively enlarging keloid resulted in a 41% reduction in its area. Fibroblasts cultured from the keloid before and 9 days after the initial injection were compared with fibroblasts cultured from the patient's normal skin with respect to proliferation and production of connective tissue matrix components and collagenase. There were no significant differences in the in vitro doubling times of keloidal fibroblasts before (p greater than 0.2) and after (p greater than 0.5) treatment with interferon alfa-2b, as well as of normal fibroblasts, in subconfluent cultures. Multiple passages of keloidal fibroblasts before interferon alfa-2b therapy assayed as confluent cultures produced more collagen (171%, 187%, and 204%), more glycosaminoglycans (153% and 141%), and less collagenase (26% and 31%) than the patient's own normal fibroblasts. In contrast, keloidal fibroblasts after interferon alfa-2b therapy persistently produced normal or subnormal amounts of collagen (107%, 73%, and 64%) and glycosaminoglycans (97% and 96%) and normalized levels of collagenase activity (96% and 86%). Normal amounts of fibronectin were produced by keloidal fibroblasts before and after treatment with interferon alfa-2b.

Synthesis of proteoglycans and hyaluronic acid by long-term cultures of testicular cells from immature and pubertal rats

Long-term cultures of somatic testicular cells derived from immature and pubertal rats were used to study the synthesis of proteoglycans (PG) and hyaluronic acid (HA). Labelled PG and HA in the culture medium, membrane-associated and intracellular pools were characterized by gel filtration, ion exchange chromatography and selected enzymatic and chemical treatments. Somatic cells synthesize a PG containing both heparan and chondroitin/dermatan sulfate (CS/DS) chains and a PG containing only CS/DS chains. No major qualitative changes in the type of PG were observed in cells derived from immature and pubertal animals. However, significant age-dependent differences in the cell distribution pattern of PG and HA were determined. This may have implications in the regulation of spermatogenesis.

Differential regulation of collagen, glycosaminoglycan, fibronectin, and collagenase activity production in cultured human adult dermal fibroblasts by interleukin 1-alpha and beta and tumor necrosis factor-alpha and beta

In order to clarify the role played by immunologically derived cytokines in dermal connective tissue synthesis and degradation, we investigated the effect of human recombinant (hu-r) interleukin (IL) 1-alpha and beta, hu-r tumor necrosis factor (TNF)-alpha and beta, hu-r IL 2, and hu-r granulocyte-macrophage colony-stimulating factor (GM-CSF) on the production of collagen, glycosaminoglycan, fibronectin, and collagenase activity by three lines of cultured human adult dermal fibroblasts. Our results show that 24-72 h treatment of confluent fibroblast cultures with IL 1-alpha or beta or TNF-alpha or beta causes concentration (1 to 1 X 10(4) U/ml) dependent increases in collagen, glycosaminoglycan, and collagenase activity production, but decreases in fibronectin production. In contrast, treatment with IL 2 and GM-CSF had no effect on fibroblast functions. The data show that IL 1-alpha and beta and TNF-alpha and beta differentially regulate fibroblast functions, and that increases in catabolic functions like collagenase activity production are more than tenfold greater than increases in anabolic functions like collagen production. When these results are considered along with other reports, they suggest that IL 1 and TNF may play predominately a catabolic role in situ during dermal fibrotic responses by directly inhibiting fibronectin production and indirectly causing the degradation of collagen and glycosaminoglycan by significantly increasing dermal fibroblast elaboration of collagenase and proteoglycanase activities.

Pentoxifylline inhibits normal human dermal fibroblast in vitro proliferation, collagen, glycosaminoglycan, and fibronectin production, and increases collagenase activity

Fibroblasts from normal human adult skin were cultured in vitro in the presence and absence of different concentrations of pentoxifylline or a pentoxifylline analog, A81-3138 (10(-1)-10(3) micrograms/ml). Similar concentration dependent reductions in normal proliferation of fibroblasts in fetal calf serum-driven subconfluent cultures were detected following treatment with pentoxifylline or A81-3138. Fibroblasts assayed as confluent cultures produced sub-normal amounts of collagen, glycosaminoglycans (GAGs), and fibronectin in a fashion dependent upon the concentration of pentoxifylline. In contrast, fibroblasts exposed to pentoxifylline elaborated double the collagenase activity produced by normal, untreated fibroblasts. The reduced proliferation and reduced synthetic activities were not due to a lethal toxic effect on fibroblasts by pentoxifylline and A81-3138, nor was the reduction in collagen synthesis simply due to an inability to secrete newly synthesized intracellular collagen. Unlike pentoxifylline-induced inhibition of collagen and fibronectin production, which was detected only in cultures supplemented with serum, pentoxifylline inhibits, to a similar degree, both constitutive and serum-driven production of GAGs. The addition of IL1 beta (2.5 and 10.0 U/ml) to serum-driven fibroblast cultures resulted in greater proliferation, which was inhibitable by the presence of pentoxifylline and A81-3138 as anti-fibrotic agents in certain disorders of fibrosis.

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.

Differential regulation of glycosaminoglycan, fibronectin, and collagenase production in cultured human dermal fibroblasts by interferon-alpha, -beta, and -gamma

In order to determine whether interferons (IFNs) play a universal role in terminating the fibrotic response by inhibiting other fibroblast functions in addition to growth and collagen production, we investigated the effect of human recombinant (hu-r) IFN-alpha, -beta, and -gamma on the glycosaminoglycan, fibronectin, and collagenase production of cultured human dermal fibroblasts. Our results show that short-term (48 h) treatment of confluent fibroblast cultures with hu-r-IFN-alpha 2 and hu-r-IFN-beta-ser17 causes a concentration (1 to 1 x 10(5) U/ml)-dependent inhibition of glycosaminoglycan production, has no effect on fibronectin production, and markedly increases collagenase production. In contrast, hu-r-IFN-gamma not only causes a concentration-dependent increase in collagenase production but also increases both glycosaminoglycan and fibronectin production. These results demonstrate that IFNs differently regulate fibroblast functions rather than universally inhibit all functions, and show that IFN-alpha and -beta exhibit a broader antifibrotic spectrum that IFN-gamma.

Fibroblastic subpopulations in uninjured and wounded rabbit oral mucosa

Fibroblast cultures derived from uninjured and reparative rabbit buccal mucosa were compared in terms of extracellular glycosaminoglycan (GAG) content and cellular response to interleukin-1 (IL-1). Under identical growth conditions, proliferation of both cell lines was the same. Both lines incorporated [3H]-glucosamine into GAG in cellular, pericellular, and medium fractions, with the majority of incorporated label residing in the medium. Dermatan sulfate (DS) was the predominant GAG in the medium fraction of both normal and wound fibroblast cultures; however, the two cell lines differed in the identity of the medium fraction's secondary GAG: chondroitin sulfate (CS) for normal fibroblasts and hyaluronic acid (HA) for wound-derived cells. The GAG content of the pericellular matrix for all cultures was the same regardless of the tissue of origin: heparan sulfate (HS) accompanied by a very small amount of CS. Exposure to IL-1 produced limited but highly specific effects: It was not mitogenic for either cell line but did cause a quantitative change (increase) in overall incorporation into GAG for medium and pericellular fractions for both cell lines. Further, IL-1 induced a qualitative change in GAG composition for normal mucosal fibroblastic medium fractions by causing the synthesis/release of heparan sulfate (HS) and a variant form of DS. These data support the hypothesis that different fibroblastic substrains can populate a given oral site as a function of variables such as injury and/or healing status.

Purification of a glycosaminoglycan-stimulatory lymphokine from supernatants of in vitro-activated human mononuclear cells

Glycosaminoglycans (GAGs), like collagens, are the major component of the connective tissue matrix. Fibroblasts are responsible for the production and maintenance of this matrix. Glycosaminoglycan-stimulatory factor (GAG-SF) from T lymphocytes is a lymphokine that selectively increases GAG synthesis in normal human dermal fibroblasts. Supernatants of mononuclear cells activated with a mitogen, concanavalin A, were used to purify GAG-SF to an apparent homogeneity. The GAG-SF proved to be a glycoprotein with a molecular weight of 67,000 and pI of 5.6. It was not mitogenic to fibroblasts and did not regulate collagen synthesis in confluent fibroblast cultures. The purified factor was distinct from interleukin-1 (IL-1), but it could synergize with IL-1, which was present in unpurified supernatants, in modulating the activation of fibroblasts. The purification and characterization of this lymphokine are important because it is a product of activated lymphocytes and thus may be involved in the immunopathogenesis of several human diseases characterized by the presence of lymphoid infiltrates in the target organ such as autoimmune diseases of the connective tissue, the stromal reactions in human tumors, and the fibrosis associated with chronic rejection of transplanted organs.

Reduced natural killer cell activity in patients with systemic sclerosis. Correlation with clinical disease type

Natural killer (NK) cell number and function were determined in 69 systemic sclerosis (SSc) patients (41 with diffuse cutaneous SSc, 24 with limited cutaneous SSc, and 4 with scleroderma in an overlap syndrome). The results were compared with those obtained from 5 patients with Raynaud's disease and from 27 normal controls. Natural and antibody-dependent killing was reduced in the total group of SSc patients compared with controls, but these differences were primarily attributable to patients with the diffuse form of the disease who were seen early in their illness (less than 5 years after onset). NK cell numbers were not significantly reduced in patients compared with controls, although lower numbers were observed in individuals with early diffuse disease. Other clinical parameters, such as treatment with D-penicillamine or the presence of scleroderma-specific autoantibodies, did not exert an independent effect on NK cell function. These findings suggest a possible central role for NK cells in the pathogenesis of SSc.

Heterogeneous synthetic phenotype of cloned scleroderma fibroblasts may be due to aberrant regulation in the synthesis of connective tissues

Clones of dermal fibroblasts from the skin of 4 normal subjects and 5 patients with progressive systemic sclerosis (PSS; scleroderma) were established, and their synthetic and proliferative characteristics were compared. A limiting-dilution assay was used to determine frequencies of cloning in the microcultures of dermal fibroblasts plated. The clones derived from single cells were expanded in vitro and examined (in passages C-H) for growth and synthesis of glycosaminoglycan (GAG) and collagenase-sensitive protein (CSP). The clonogenicity of PSS fibroblasts was not significantly different from that of normal fibroblasts. Normal fibroblast clones were characterized by low levels of GAG and CSP synthesis, and there was a correlation between the GAG and CSP phenotypes. In contrast, clones of PSS fibroblasts were often, but not always, high producers of GAG and CSP, but there was no correlation between the levels of GAG and CSP synthesis. It appears that scleroderma skin is composed of fibroblast clones that are unable to regulate the synthesis of connective tissue components and often synthesize large amounts of connective tissue macromolecules.

Progressive systemic sclerosis: mode of presentation, rapidly progressive disease course, and mortality based on an analysis of 91 patients

The overwhelming majority of patients with PSS present with combinations of Raynaud's phenomenon, sclerodactyly, polyarthralgias, or swelling of an extremity. However, the clinical presentation of PSS may be atypical; 14% of patients in the present series initially sought medical attention for symptoms other than Raynaud's phenomenon, tight skin, or joint pain. In the present series, only 31% of patients fulfilled the ARA criteria for PSS at the time of initial medical evaluation. Most patients manifested advanced disease by the time the criteria were fulfilled. The ARA criteria for the classification of PSS appear to have limited value with regard to making the diagnosis in an individual patient. Rapidly progressive PSS occurred in 17.6% of patients in this series and represents a particularly fulminant form of the disease whose course may not be predictable on clinical grounds at the time of initial medical evaluation or diagnosis. Patients destined to develop renal or cardiorespiratory failure usually do so in the first 3 years of disease. Close observation of PSS patients during the first 12 to 18 months may serve to identify those individuals who will undergo an accelerated disease course. Prognosis for patients with rapidly progressive PSS is poor and is associated with significantly higher mortality compared with patients with a more protracted disease course. Future therapeutic trials in PSS should be designed with the recognition that a subgroup of patients with this disorder will have a rapidly progressive disease course.

Effect of a platelet release fraction on glycosaminoglycan synthesis by cultured dermal fibroblasts from patients with progressive systemic sclerosis

Confluent cultures of dermal fibroblasts from patients with progressive systemic sclerosis (PSS) and healthy controls were investigated for the synthesis of glycosaminoglycans (GAG) in response to a platelet release fraction (PRF) obtained by treatment of pooled platelets from normal individuals with adenosine 5'-diphosphate (ADP). PRF, at concentrations of 1 to 50 micrograms protein/ml, produced a linear increase in GAG synthesis that was always greater in cultures of PSS fibroblasts than in cultures of normal fibroblasts (P less than 0.001). A partial inhibition of GAG synthesis was observed with 100 micrograms/ml of PRF. The increased GAG synthesis in cultures incubated with PRF was not due to ADP. These findings demonstrate a difference in response to PRF between PSS and normal fibroblasts and may reflect an increased responsiveness of PSS fibroblasts to platelet factors.

Systemic scleroderma. Clinical and pathophysiologic aspects

Systemic scleroderma is a generalized disease of connective tissue involving mainly the skin, the gastrointestinal tract, the lungs, the heart, and the kidneys. It can be present in different forms, of which acroscleroderma, with limited cutaneous and extracutaneous involvement, and diffuse scleroderma within a more rapid progression are most characteristic. Circulating antibodies against antinucleolar antigens are present in most patients with systemic scleroderma. They are helpful for establishing a classification and for determining the prognosis of the disease; their involvement in the pathogenesis, however, is still unclear. Alterations of the blood vessels and induction of fibroblasts by potent mediators are thought to play an important role in the early phase of scleroderma. Therefore early diagnosis is required, which then can initiate vasoactive therapy. In patients with systemic scleroderma, who also suffer from additional myositis, interstitial lung diseases, or arthritis, anti-inflammatory treatment with prednisolone and azathioprine is suggested. Development and progression of fibrosis cannot yet be influenced sufficiently. Only D-penicillamine affecting cross-linking of collagen has been widely used in scleroderma and has some beneficial effect.

Regulation of human lung fibroblast glycosaminoglycan production by recombinant interferons, tumor necrosis factor, and lymphotoxin

Mononuclear cells may be important regulators of fibroblast glycosaminoglycan (GAG) biosynthesis. However, the soluble factors mediating these effects, the importance of intercytokine interactions in this regulation and the mechanisms of these alterations remain poorly understood. We analyzed the effect of recombinant (r) tumor necrosis factor (TNF), lymphotoxin (LT), and gamma, alpha, and beta 1 interferons (INF-gamma, -alpha and -beta 1), alone and in combination, on GAG production by normal human lung fibroblasts. rTNF, rLT, and rINF-gamma each stimulated fibroblast GAG production. In addition, rIFN-gamma synergized with rTNF and rLT to further augment GAG biosynthesis. In contrast, IFN-alpha A, -alpha D, and -beta 1 neither stimulated fibroblast GAG production nor interacted with rTNF or rLT to regulate GAG biosynthesis. The effects of the stimulatory cytokines and cytokine combinations were dose dependent and were abrogated by the respective monoclonal antibodies. In addition, these cytokines did not cause an alteration in the distribution of GAG between the fibroblast cell layer and supernatant. However, the stimulation was at least partially specific for particular GAG moieties with hyaluronic acid biosynthesis being markedly augmented without a comparable increase in the production of sulfated GAGs. Fibroblast prostaglandin production did not mediate these alterations since indomethacin did not decrease the stimulatory effects of the cytokines. In contrast, protein and mRNA synthesis appeared to play a role since the stimulatory effects of the cytokines were abrogated by cyclohexamide and actinomycin D, respectively. In addition, the cytokines and cytokine combinations increased cellular hyaluronate synthetase activity in proportion to their effects on hyaluronic acid suggesting that induction of this enzyme(s) is important in this stimulatory process. These studies demonstrate that IFN-gamma, TNF, and LT are important stimulators of fibroblast GAG biosynthesis, that interactions between these cytokines may be important in this regulatory process, that these cytokines predominantly stimulate hyaluronic acid production and that this effect may be mediated by stimulation of fibroblast hyaluronate synthetase activity.

Interleukin 1 stimulates fibroblasts to synthesize granulocyte-macrophage and granulocyte colony-stimulating factors. Mechanism for the hematopoietic response to inflammation

IL-1 is a family of polypeptides which play a critical role in the inflammatory response. Characteristics of this response include an enhanced release of bone marrow neutrophils, activation of circulating and tissue-phase phagocytes, and enhanced production of neutrophils and monocytes. We have sought to understand the hematopoietic response to acute and chronic inflammatory states on a cellular and molecular level. Colony-stimulating factors (CSFs) are glycoproteins involved in the production and activation of neutrophils and monocytes in vitro and in vivo. We have found that quiescent dermal fibroblasts constitutively release granulocyte-macrophage CSF (GM-CSF), granulocyte CSF (G-CSF), and macrophage CSF in culture, and that picomolar concentrations of the inflammatory mediator IL-1 stimulate by at least fivefold the transcription and release of GM-CSF and G-CSF. These findings establish the role of IL-1 in the hematopoietic response to inflammation through the stimulation of the production and release of GM-CSF and G-CSF.

What's happened to catabolin?

Unlike other areas of research into arthritis, it is pleasing to record independent work leading to convergence of ideas instead of divergence and increasing complexity. Catabolin is now identified with interleukin-1, although there is case for the retention of the original name to describe its chondrocyte-stimulating function with subsequent matrix degradation. In 10 years, catabolin/interleukin-1 research has yielded much information about cellular interactions within the arthritic joint and has provided a probe with which the intricacies of matrix metabolism are being unravelled. In future, there are prospects of characterizing the naturally occurring inhibitors and developing new compounds which influence the actions of catabolin/IL-1 to the benefit of the patient with arthritis.

Transforming growth factor-beta: selective increase in glycosaminoglycan synthesis by cultures of fibroblasts from patients with progressive systemic sclerosis

Transforming growth factor-beta (TGF-beta) has been found in all cells examined thus far, and has been shown to play an important role in inflammation and connective tissue formation. We now report that TGF-beta, alone or in combination with epidermal growth factor (EGF), led to a preferential increase in glycosaminoglycan synthesis by cultures of dermal fibroblasts from patients with progressive systemic sclerosis (PSS) when compared with normal fibroblasts (p less than 0.001). Transforming growth factor-beta increased collagen synthesis to the same extent in both PSS and normal fibroblasts, whereas EGF had no stimulatory activity on collagen synthesis. The addition of EGF to cultures incubated with TGF-beta led to a decrease in collagen synthesis compared with the effect seen with TGF-beta alone (p less than 0.02). These studies suggest that TGF-beta may play an important role in the accumulation of connective tissue seen in PSS and that the combined action of multiple growth factors may modulate the synthetic activity of human dermal fibroblasts.

Persistence of a reduced-collagen-producing phenotype in cultured scleroderma fibroblasts after short-term exposure to interferons

Transient exposure to inflammation-associated, fibroblast-stimulatory factors appears to initiate fibrosis by inducing the persistently activated phenotypes displayed by fibroblast cultures derived from scleroderma skin and other fibrotic tissues. To determine whether one class of fibroblast-inhibitory factors, the interferons (IFNs), plays a role in terminating fibrosis by acting as persistent fibroblast deactivators, we inhibited (40-60%) the growth and collagen production of normal dermal fibroblasts and hypercollagen-producing scleroderma fibroblasts by short-term exposure to IFN-alpha, beta, or gamma. During subsequent subculture in the absence of IFNs, the growth and collagen production of normal fibroblasts and the growth of scleroderma fibroblasts increased to untreated control levels after two to three passages. In contrast, collagen production by scleroderma fibroblasts remained inhibited for at least five passages (18 cell doublings) and was not further suppressed by subsequent IFN exposure. These data suggest that IFNs may help terminate fibrosis by suppressing persistently activated fibroblast functions.

Production of a glycosaminoglycan stimulatory factor by cloned human T lymphocytes activated in vitro

Supernatants of mitogen-activated mononuclear cells contain a factor which stimulates, up to fifteen-fold, the synthesis of glycosaminoglycan (GAG) by cultured normal dermal fibroblasts. To demonstrate that the GAG stimulatory factor is a product of T lymphocytes, we cloned normal peripheral blood T lymphocytes that were activated in mixed lymphocyte culture. Selected alloreactive T cell clones were expanded in the presence of original stimulator cells and T cell growth factor. Only supernatants of the clones that were reactivated with irradiated stimulators (allogeneic peripheral blood lymphocytes of B cell lines) were capable of increasing, 3-7-fold, the GAG synthesis by dermal fibroblasts. The production of GAG stimulatory activity by alloreactive T cells was restricted by HLA-DR allorecognition. Alloactivated T cell clones produced more GAG stimulatory activity on a per cell basis than did concanavalin A-activated mononuclear cells. These results show that cloned, activated T lymphocytes are capable of releasing soluble factors that modulate GAG synthesis by normal dermal fibroblasts.

Persistence of scleroderma-like phenotype in normal fibroblasts after prolonged exposure to soluble mediators from mononuclear cells

Supernatants of mononuclear cells (MNC-SN) were shown to increase synthesis of glycosaminoglycan (GAG) by cultured normal dermal fibroblasts. Fibroblasts from the skin of patients with progressive systemic sclerosis (PSS, scleroderma) were hyporesponsive. We exposed fibroblasts outgrowing from explants of normal adult skin to MNC-SN for up to 30 generations in culture. MNC-SN were obtained by incubating normal MNC with concanavalin A. Four experimental, 4 normal control, and 3 PSS control lines were passaged by trypsinizing and splitting the cultures 1:2 every 7 days. At the third and fifth passages, portions of the experimental fibroblasts were removed from MNC-SN, then passaged in medium alone. Cell counts, assays for GAG, and electron microscopy were performed and increases in GAG after brief reexposure to MNC-SN were determined at the third, fifth, and eighth passages. In normal dermal fibroblasts, baseline GAG production, measured by 3H-glucosamine uptake, was low and increased as much as 15 times after reexposure to MNC-SN. In contrast, production was high in both experimental and PSS lines, and increases after reexposure to MNC-SN were consistently small. This PSS-like behavior persisted in experimental fibroblasts removed from MNC-SN at the third and fifth passages. Growth of experimental and scleroderma fibroblasts was slower than that of control fibroblasts. Ultrastructurally, both scleroderma and experimental dermal fibroblasts differed from normal fibroblasts by their oval cellular shape, indentations in nuclear membrane, numerous organelles and bundles of microfilaments, prominent Golgi, and intranuclear inclusions. These experiments indicate that normal adult dermal fibroblasts subjected to MNC-SN in vitro acquire a scleroderma-like phenotype that persists for many generations.