Recombinant interferon-gamma inhibits the mitogenic effect of platelet-derived growth factor at a level distal to the growth factor receptor

Investigational Approaches to Pulmonary Hypertension

Pulmonary vascular disease (PVD) revolves around a series of switches in the smooth muscle cell (SMC) phenotype. Differentiation of SMC from precursor cells causes muscularization of normally non-muscular peripheral arteries; hypertrophy and hyperplasia of existing SMC and increased connective tissue protein synthesis cause thickening of the wall, and migration of SMC into the subendothelial space is the basis of intimal proliferation. To uncover the pathophysiologic mechanisms of these changes, we have used a variety of animal models and cell culture systems. From rats in which hypertensive PVD was induced by exposure to chronic hypoxia or following injection of the pyrrolizidine alkaloid, monocrotaline, we have identified increased pulmonary artery (PA) elastolytic activity which occurs early and which accompanies progressive rather than reversible PVD. Inhibition of elastolytic activity prevents or reduces PVD. We are cloning the gene for this new enzyme to study its regulation in PVD. To address the mechanism of SMC proliferation under conditions of high PA pressure and flow, we cultured endothelial cells on Polyvinylchloride membranes and pulsated them at high pressure. This caused reduced synthesis of heparan sulfate. The resulting decrease binding of fibroblast growth factor would lessen its mitogenic effect and modulate SMC proliferation in response to other growth factors from platelets or serum. To study SMC migration, we cultured endothelial and SMC from the ductus arteriosus (a fetal vessel which spontaneously develops intimal proliferation in late gestation). The migratory SMC phenotype is a function of increased production of fibronectin governed by a translational control mechanism, and increased endothelial hyaluronan regulated by transforming growth factor β. SMC migration is also related to impaired assembly of elastin, the result of a chondroitin sulfate-induced decrease in elastin binding proteins and the production of a novel ‘defunct’ 52 kD tropoelastin.

Understanding the final stages of wound contraction

Much research has been undertaken to improve our understanding of the processes of wound contraction. This article, the second in a two-part series, focuses on granulation tissue modulation.

Interferon gamma up-regulates a novel protein in vascular smooth muscle cells

PURPOSE

By means of the technique of messenger RNA (mRNA) differential display, we previously isolated a partial DNA clone found to be down-regulated at the polytetrafluoroethylene (PTFE) hyperplastic arterial anastomosis compared with the normal artery. The partial DNA gene sequence was found to be homologous with interferon gamma up-regulated protein (IGUP) first found in human psoriatic keratinocytes. We cloned the entire IGUP gene from human vascular smooth muscle cells (VSMCs) to determine its regulation by gamma interferon (gamma-IFN) and other cytokines in cultured human VSMCs.

METHODS

By means of polymerase chain reaction, the IGUP gene was amplified from a QUICK-Clone complementary DNA human aorta kit using 5' and 3' oligonucleotide primers to the known IGUP sequence. Immunohistocytochemistry studies compared normal artery and distal anastomotic IH. Human VSMCs were stimulated with 1000 U/mL of gamma-IFN, 5 ng/mL of platelet-derived growth factor BB (PDGF-BB), 3. 2 ng/mL basic fibroblast growth factor, 3.3 ng/mL transforming growth factor beta(TGF-beta), 10 ng/mL of vascular endothelial growth factor, and 10% fetal bovine serum (FBS) for zero, 24, 48 and 72 hours. Western blot analysis of lysates of the stimulated VSMCs was performed to determine up-regulation of IGUP.

RESULTS

DNA sequencing confirmed the cloning of the entire coding region of the IGUP gene with 100% homology to the known IGUP DNA sequence. There was strong expression of IGUP in quiescent VSMCs and marked reduction of expression of IGUP in proliferating smooth muscle cells. gamma-IFN was the only cytokine, of the cytokines evaluated, to up-regulate production of IGUP in VSMCs.

CONCLUSION

IGUP is a novel protein in VSMCs found to be down-regulated in areas of anastomotic IH, as compared with a normal artery. We have now shown IGUP to be up-regulated only by gamma-IFN in human VSMCs. IGUP may, therefore, be the intermediary for the known gamma-IFN inhibition of human VSMC proliferation.

Reversible inhibitory effects of interferon-gamma and tumour necrosis factor-alpha on oligodendroglial lineage cell proliferation and differentiation in vitro

We have investigated the effects of the two prominent inflammatory cytokines, interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha), on oligodendroglial lineage cell development and survival. Purified oligodendrocytes and oligodendrocyte precursors obtained from neonatal rat brain primary cultures were subcultured in a defined, serum-free medium and exposed to IFN-gamma (1-100 U/ml, TNF-alpha (25-100 ng/ml) or both (100 U/ml and 50 ng/ml respectively) from day 1 to day 3 or from day 3 to day 6. While cell survival was not affected in any of the conditions tested, IFN-gamma dose-dependently inhibited [3H]thymidine or bromodeoxyuridine incorporation (by up to 50%) and the reduction of the tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT; by up to 33%). TNF-alpha synergized with IFN-gamma, but was ineffective by itself. Moreover, IFN-gamma totally antagonized the induction by basic fibroblast growth factor and platelet-derived growth factor of the proliferation of the oligodendroglial lineage cell population under study. IFN-gamma also blocked the differentiation of oligodendrocyte precursors, as evidenced by cell morphology, immunostaining for early and late differentiation markers (galactocerebroside and myelin basic protein respectively) and activity of ceramide galactosyl transferase. Again, the effect of IFN-gamma was potentiated by TNF-alpha, which was ineffective when tested alone. The inhibitory activity of IFN-gamma was rapidly reversible: 3 days after removal of the cytokine, administered from day 1 to day 3, complete recovery of cll proliferation and differentiation could be documented. The cytokine-induced arrest in the expression of differentiation antigens was accompanied by perturbations in the expression of the corresponding mRNAs, revealed by a semiquantitative reverse transcription-polymerase chain reaction method. In particular, the message for myelin basic protein (and, in the case of treatment from days 3 to 6, also that for myelin associated glycoprotein) was decreased in cultures exposed to IFN-gamma, and further depressed in cultures treated with IFN-gamma and TNF-alpha, while TNF-alpha alone was ineffective. The above observations may help explain the role of IFN-gamma and TNF-alpha in the pathogenesis of inflammatory demyelinating diseases, in which increases in the levels of these substances have been described. In particular, in the case of multiple sclerosis, our results may bear on the problem of defective remyelination and are consistent with the frequent relapsing-remitting course of the disease.

Interferon alfa and gamma inhibit proliferation and collagen synthesis of human Ito cells in culture

During the course of ongoing liver fibrogenesis, Ito cells acquire myofibroblastic features, proliferate, and synthesize increased amounts of extracellular matrix components. Interferon (IFN) alfa and IFN gamma have been shown to elicit antiproliferative and/or antifibrogenic effects in various cell cultures of mesenchymal origin. The aim of this study was to investigate the effects of IFN-alpha and IFN-gamma on cultured human myofibroblastic Ito cells (MFBIC) proliferation and collagen synthesis and secretion. Serum-stimulated incorporation of [3H]-thymidine into DNA of MFBIC was dose-dependently decreased by both cytokines. IFN-alpha (10(4) U/mL) and IFN-gamma (10(3) U/mL) decreased DNA synthesis by 69% and 66%, respectively. Inhibition of cell proliferation was confirmed by cell counting. Similar results were observed when cell growth was stimulated with platelet-derived growth factor (PDGF-BB, PDGF-AA) or transforming growth factor (TGF)-beta 1. Collagen secretion per cell was inhibited by both cytokines, as assessed by [3H]-hydroxyproline incorporation. After a 6-day treatment, IFN-gamma showed a greater potency than IFN-alpha in inhibiting secretion of newly synthetized collagen (41% and 4% of control in the presence of 10(2) U/mL of IFN-gamma and 10(4) U/mL of IFN-alpha, respectively). Both IFN-alpha and IFN-gamma concurrently decreased steady-state expression of type I and type III procollagen messenger RNAs (mRNAs) in quiescent MFBIC. Viability assays ruled out cytotoxic effects of the two molecules. Finally, both IFNs decreased smooth muscle alpha-actin (SM alpha-actin) expression, whether assayed by immunoblotting or by Northern blot analysis. We conclude that IFN-alpha and IFN-gamma inhibit proliferation as well as collagen synthesis in human MFBIC.

Modulation of experimental mesangial proliferative nephritis by interferon-gamma

The observation that interferon-gamma (IFN-gamma) inhibits cell proliferation and collagen synthesis of a variety of cell types in culture has suggested that IFN-gamma may be useful in the treatment of fibroproliferative diseases. We administered recombinant IFN-gamma subcutaneously (10(5) U/kg/day for 3 days) to rats, beginning one day after the induction of mesangial proliferative nephritis with anti-Thy 1 antibody. IFN-gamma reduced glomerular (primarily mesangial) cell proliferation by 44% at days 2 and 4 compared to vehicle injected control rats with anti-Thy 1 nephritis (that is, proliferating cells that excluded the macrophage marker, ED-1, P < 0.001). Despite the inhibition of mesangial cell proliferation, IFN-gamma did not reduce the overall extracellular matrix deposition (by silver stain) or deposition of type IV collagen or laminin (by immunostaining) at 4 or 7 days, and glomerular type IV collagen and laminin mRNA levels were increased (1.4 and 1.7-fold) at 4 days relative to controls. The inability of IFN-gamma treatment to reduce mesangial matrix expansion may relate to the fact that IFN-gamma treated rats had a twofold increase in glomerular macrophages (that is, ED-1 positive cells, P < 0.001 at 2 and 4 days) with an increase in oxidant producing cells (day 2, P < 0.05) and a 1.6-fold increase in glomerular TGF-beta mRNA expression (4 days). This suggests that the effect of IFN-gamma to inhibit mesangial cell proliferation in glomerulonephritis may be offset by the ability of IFN-gamma to increase glomerular macrophages and TGF-beta expression. These data also show that IFN-gamma can partly dissociate the mesangial proliferative response from the extracellular matrix expansion in glomerulonephritis.

Increased mitogenic activity of scleroderma serum: inhibitory effect of human recombinant interferon-gamma

OBJECTIVES

To investigate the role of platelet activation in the development of systemic sclerosis and the role of interferon-gamma (IFN gamma) in the inhibition of mitogenic activity induced by whole blood serum of patients with systemic sclerosis.

METHODS

The mitogenic activity of whole blood serum in the absence or presence of different concentrations of IFN gamma (a potent inhibitor of induced collagen synthesis in dermal fibroblasts) and platelet-poor plasma derived serum were tested on human dermal fibroblasts by measuring incorporation of [3H]thymidine. Platelet activation was determined by quantification of plasma beta-thromboglobulin (beta-TG) using a beta-TG radioimmunoassay kit.

RESULTS

The mitogenic activity was significantly increased in whole blood serum and in platelet-poor plasma derived serum of the patients compared with controls. In contrast, no significant increase in beta-TG concentration was observed in scleroderma platelet-poor plasma compared with control. Recombinant human IFN gamma had a greater inhibitory effect on the mitogenic activity induced by whole blood serum of patients than on that produced with control sera, at any concentration of IFN gamma tested.

CONCLUSIONS

Our results suggest that mitogenic activity observed in the plasma of sclerodermic patients could originate from cells other than platelets and could be involved in the development of fibrosis. The potent inhibitory effect of IFN gamma on this proliferative activity may account for the beneficial effect of this cytokine in the treatment of progressive systemic sclerosis.

Interleukin-1 beta and interferon gamma interact with fibroblast growth factor-2 in the control of neuroblastoma cell proliferation and differentiation

Based on our previous observations that neuroblastoma (NB) cells express fibroblast growth factor-2 (FGF-2; basic FGF) and respond to it [Janet T. et al. (submitted); Wewetzer K. et al. (1993) J. Neurosci. Res. 36, 209-215), we attempted to find to what extent selected cytokines [interleukin (IL)-1 beta and interferon gamma (IFN gamma)] may modulate FGF-mediated proliferative activity and differentiation. The NB cell lines IMR-32, SH-SY5Y, GIMEN and LAN-1 and colorimetric assays were used for the determination of cell numbers. IL-1 beta (and several other ILs, including IL-1 alpha, -2, -3, and 6) per se did not affect proliferation of any cell line studied. IFN gamma inhibited growth of GIMEN and LAN-1 cells, but was uneffective on IMR-32 and SH-SY5Y cells. FGF-2 was antimitogenic for GIMEN cells. IFN gamma reversed and IL-1 beta enhanced this antimitogenic effect of FGF-2. FGF-2 per se did not affect LAN-1 cells and did not modulate the growth inhibitory actions of IFN gamma on these cells. FGF-2 induced proliferation of IMR-32 and SH-SY5Y cells. This effect was not modulated by IFN gamma or IL-1 beta. These results suggest a heterogeneous response pattern of human NB cell lines towards the cytokines studied and complex interactions of FGF-2, IL-1 beta and IFN gamma.

Immunohistochemical study of 30 cases of cyclosporin A-induced gingival overgrowth

Immunohistochemical techniques were used to study the presence of cyclosporin A (CsA) and leukocyte subsets in 30 gingival biopsies of renal transplant subjects with gingival overgrowth (GO). Statistical analysis revealed significant differences in the total number of inflammatory cells determined by monoclonal antibody CD45, the monocyte/macrophage (CD68) subset, the plasmatic cells (EMA), and the total of T-lymphocytes (CD3) (P < 0.001, Student t test) between the treated subjects and the healthy control group. Differences were found in the helper/inducer T lymphocytes CD4 (P < 0.001 Student t test) and cytotoxic/suppressor T lymphocyte (CD8) (P < 0.01, Student t test) subsets between both groups. The CD4/CD8 ratio was greater in the transplant subjects than in the control group (1.82 +/- 0.16 versus 1.35 +/- 0.05 respectively) (P < 0.05 Student t test). There was no significant difference in the populations CD16+, CD57+, and CD20+. The CD45+ CD4+, and CD68+ cells increased in number along with the degree of GO. The number of epithelial cells/mm2 which displayed a deposit of CsA increased in accordance with the degree of GO (P < 0.05, Kruskal-Wallis's test). Likewise, the intraepithelial deposit of CsA in the GO region was found to be related to the inflammatory infiltrate CD4+, CD8+, and CD68+ (r = 0.7432; r = 0.7346; r = 0.77005, respectively). Our findings suggest that the intraepithelial deposit of CsA and the inflammatory infiltrate play a predominantly pathogenic role and are both related to the degree of GO.

Interferon-gamma inhibits DNA synthesis and insulin-like growth factor-II expression in human neuroblastoma cells

Interferon-gamma (IFN-gamma) is known to be an antiproliferative, differentiating agent in many cell types, including neuroblastoma. In this study, we determined the effects of IFN-gamma on cellular growth and expression of insulin-like growth factor II (IGF-II) and IGF receptors in the human neuroblastoma cell line SH-SY5Y. Incubation of SH-SY5Y cells in IFN-gamma (20-100 U/ml) induced the formation of long neuritic processes. IFN-gamma treatment also induced decreases in [3H]TdR incorporation, as well as serum-dependent changes in cell number. Treatment with IFN-gamma reduced cell number 33% in the presence of serum but had no effect on cell number in the absence of serum. IGF-II mRNA content was 60% inhibited by IFN-gamma, and was not serum dependent. The concentration of immunoreactive IGF-II in SH-SY5Y conditioned medium was also reduced in the presence of IFN-gamma, to less than half of control levels. In contrast, type I IGF receptor mRNA content was increased more than three-fold after treatment with IFN-gamma and serum. Co-incubation in IFN-gamma (20-100 U/ml) and IGF-II (3-10 nM) prevented the inhibitory effects of IFN-gamma on [3H]TdR incorporation in serum-free media. Our results suggest that IFN-gamma may inhibit DNA synthesis and cell growth by interfering with an IGF-II/type I IGF receptor autocrine growth or survival mechanism.

A glycosylation-deficient endothelial cell mutant with modified responses to transforming growth factor-beta and other growth inhibitory cytokines: evidence for multiple growth inhibitory signal transduction pathways

An endothelial cell line (M40) resistant to growth inhibition by transforming growth factor-beta type 1 (TGF beta 1) was isolated by chemical mutagenesis and growth in the presence of TGF beta 1. Like normal endothelial cells, this mutant is characterized by high expression of type II TGF beta receptor and low expression of type I TGF beta receptor. However, the mutant cells display a type II TGF beta receptor of reduced molecular weight as a result of a general defect in N-glycosylation of proteins. The alteration does not impair TGF beta 1 binding to cell surface receptors or the ability of TGF beta 1 to induce fibronectin or plasminogen activator inhibitor-type I production. M40 cells were also resistant to growth inhibition by tumor necrosis factor alpha (TNF alpha) and interleukin-1 alpha (IL-1 alpha) but were inhibited by interferon-gamma (IFN gamma) and heparin. These results imply that TGF beta 1, TNF alpha, and IL-1 alpha act through signal transducing pathways that are separate from pathways for IFN gamma and heparin. Basic fibroblast growth factor was still mitogenic for M40, further suggesting that TGF beta 1, TNF alpha, and IL-1 alpha act by direct inhibition of cell growth rather than by interfering with growth stimulatory pathways.

Mitogenic activity of interferon gamma on growth-arrested human vascular smooth muscle cells

Interferon gamma (IFN-gamma) is a multifunctional lymphokine secreted by activated T lymphocytes, which are found in atherosclerotic lesions. IFN-gamma has been reported to suppress the proliferation of vascular smooth muscle cells (SMCs). However, as we report in this paper, IFN-gamma is mitogenic for vascular SMCs under certain circumstances. Recombinant human IFN-gamma (1-100 units/ml), in a dose-dependent fashion, stimulated cell multiplication and [3H]thymidine and 5-bromo-2'-deoxyuridine incorporation into DNA by cultured arterial SMCs that had been growth arrested by culturing in 1% plasma-derived serum for 5 days. IFN-gamma also accentuated the mitogenic activity of platelet-derived growth factor (PDGF)-BB. A time-course study revealed that there was a time lag of 4-6 hours between the G1-->S transition of quiescent SMCs stimulated by IFN-gamma and that of SMCs stimulated by PDGF-BB. A synergistic effect of IFN-gamma on the mitogenicity of PDGF became apparent after a similar time lag, suggesting that the IFN-gamma-related mitogenicity is mediated by a substance(s) secreted by IFN-gamma-treated SMCs. In fact, conditioned medium of IFN-gamma-treated SMCs was mitogenic for SMCs. Mitogenic activity in the conditioned medium was also detected by an assay using Swiss 3T3 cells, which originate from mice and, therefore, are not responsive to human IFN-gamma. The production of the mitogenic factor was blocked by anti-IFN-gamma antibody. Mitogenicity of the conditioned medium was not eliminated by addition of neutralizing antibody against PDGF, indicating that any autocrine growth factor(s) secreted by IFN-gamma-treated SMCs was not PDGF.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha-smooth muscle actin is expressed in a subpopulation of cultured and cloned fibroblasts and is modulated by gamma-interferon

Clinical and experimental investigations have shown that, during wound healing and fibrocontractive diseases, fibroblasts acquire, more or less permanently according to the situation, morphological and biochemical features of smooth muscle (SM) cells including the expression of alpha-SM actin. Primary and passaged cultures of rat and human fibroblasts contain a subpopulation of cells expressing alpha-SM actin. These cells could derive from SM cells and/or pericytes present in the tissue from which cultures have been produced or represent bona fide fibroblasts. We have investigated the presence of alpha-SM actin in fibroblast cultures, clones, and subclones. In all cases the fibroblastic populations studied showed a proportion of alpha-SM actin expressing cells. Even after cloning, we never obtained populations negative for alpha-SM actin. We conclude that alpha-SM actin expression in fibroblastic cultures is not due to contaminant cells but is a feature of fibroblasts themselves. Our results support the view that fibroblastic cells are a heterogeneous population. It has been previously shown that gamma-interferon (gamma-IFN) decreases alpha-SM actin expression in SM cells. In rat and human fibroblasts, gamma-IFN decreases alpha-SM actin protein and mRNA expression as well as proliferation. The properties of this cytokine make it a good candidate for exerting an anti-fibrotic activity in vivo.

Biochemical events accompanying macrophage activation and the inhibition of colony-stimulating factor-1-induced macrophage proliferation by tumor necrosis factor-alpha, interferon-gamma, and lipopolysaccharide

Agents that can arrest cellular proliferation are now providing insights into mechanisms of growth factor action and how this action may be controlled. It is shown here that the macrophage activating agents tumor necrosis factor-alpha (TNF alpha), interferon-gamma (IFN gamma), and lipopolysaccharide (LPS) can maximally inhibit colony stimulating factor-1 (CSF-1)-induced, murine bone marrow-derived macrophage (BMM) DNA synthesis even when added 8-12 h after the growth factor, a period coinciding with the G1/S-phase border of the BMM cell cycle. This inhibition was independent of autocrine PGE2 production or increased cAMP levels. In order to compare the mode of action of these agents, their effects on a number of other BMM responses in the absence or presence of CSF-1 were examined. All three agents stimulated BMM protein synthesis; TNF alpha and LPS, but not IFN gamma, stimulated BMM Na+/H+ exchange and Na+,K(+)-ATPase activities, as well as c-fos mRNA levels. IFN gamma did not inhibit the CSF-1-induced Na+,K(+)-ATPase activity. TNF alpha and LPS inhibited both CSF-1-stimulated urokinase-type plasminogen activator (u-PA) mRNA levels and u-PA activity in BMM, whereas IFN gamma lowered only the u-PA activity. In contrast, LPS and IFN gamma, but not TNF alpha, inhibited CSF-1-induced BMM c-myc mRNA levels, the lack of effect of TNF alpha dissociating the inhibition of DNA synthesis and decreased c-myc mRNA expression for this cytokine. These results indicate that certain biochemical responses are common to both growth factors and inhibitors of BMM DNA synthesis and that TNF alpha, IFN gamma, and LPS, even though they all have a common action in suppressing DNA synthesis, activate multiple signaling pathways in BMM, only some of which overlap or converge.

Effect of gamma-interferon on collagen synthesis by normal and fibrotic human lung fibroblasts

Increased lung collagen and increased collagen synthesis by lung fibroblasts is well recognized in pulmonary fibrosis. gamma-Interferon has been shown to inhibit collagen synthesis by fibroblasts. To understand its effect on lung fibroblasts we compared how this lymphokine affects the growth and collagen synthesis of normal and fibrotic human lung fibroblasts. The results showed that gamma-IFN inhibited DNA synthesis in all fibroblast strains examined. Both collagen production and type 1 mRNA levels were reduced in three normal and two fibrotic cell strains exposed to gamma-IFN, while they were not affected in one strain from fibrotic lung. Even though an occasional cell was unaffected by the gamma-IFN, collagen mRNA level was reduced in most cells and it remained reduced for 48 h after removing the gamma-IFN. These results show that gamma-IFN inhibits the growth of fibroblast cultures derived from normal and fibrotic human lungs and suppresses collagen synthesis in most of these cells.

Tumor necrosis factor stimulates DNA synthesis of mouse hepatocytes in primary culture and is suppressed by transforming growth factor beta and interleukin 6

In a previous study, we revealed that tumor necrosis factor (TNF) was secreted in mouse liver at an early phase of liver regeneration after partial hepatectomy. Here, we investigated direct actions of TNF on the in vitro DNA synthesis of adult mouse hepatocytes in primary culture. TNF enhanced both 3H-TdR uptake and the number of 3H-TdR-labeled nuclei of hepatocytes. Their time courses were similar to those by epidermal growth factor (EGF) with about a 15 h lag period and a peak period of 24-48 h. This action of TNF was abrogated by DNA polymerase alpha inhibitor, aphidicolin and blocked specifically by anti-TNF antibody. The actions of rmTNF and rhTNF were not distinguishable; ED50 was about 7.5U/ml (5ng/ml) and 30U/ml (20ng/ml) for maximal response (about 2-fold or more of control). Other inflammatory monokines showed differential effects on in vitro DNA synthesis of hepatocyte. Neither type of interleukin 1 affected hepatocyte DNA synthesis in the range examined (up to 50 ng/ml). IL-6 markedly inhibited the hepatocyte DNA synthesis stimulated by TNF and EGF. The action of TNF was completely suppressed by transforming growth factor beta, which is known as a potent inhibitor of hepatocyte growth. Interferon gamma also blocked this TNF action when added simultaneously. These results indicate that the activation of tissue macrophages and local secretion of TNF in liver after partial hepatectomy is of physiological importance in liver regeneration, in part by a direct stimulation of hepatocyte DNA synthesis. Cytokines induced by TNF may also participate in the later termination of liver regeneration.

T lymphocytes inhibit the vascular response to injury

The proliferation of vascular smooth muscle cells is controlled by specific growth factors and cytokines acting in paracrine networks. Macrophage products such as the platelet-derived growth factor and interleukin 1 promote smooth muscle proliferation and are released in the arterial wall during atherosclerosis and repair processes. T lymphocytes are also present in vascular tissue, but their role in vascular growth control in vivo has been unclear. We now demonstrate that rats in which T lymphocytes have been eliminated by a monoclonal antibody develop larger proliferative arterial lesions after balloon-catheter injury. Larger lesions also develop in athymic rnu/rnu rats that lack T lymphocytes, when compared with rnu/+ littermates with normal T-cell levels. Finally, injection of the lymphokine interferon gamma inhibits smooth muscle proliferation and results in smaller lesions compared with controls injected with buffer alone. These results indicate that T lymphocytes modulate smooth muscle proliferation during vascular repair. We propose that T lymphocytes may play an important, immunologically nonspecific role in tissue repair processes.

Differential control of mesangial cell proliferation by interferon-gamma

Rat mesangial cells were shown to be sensitive to recombinant interferon-gamma (IFN-gamma). IFN-gamma reduced thymidine uptake by these cells and inhibited cell proliferation. Incubation of the cells with 1000 U/ml IFN-gamma decreased thymidine uptake by up to 64% and cell numbers were decreased by 17%. The effects of IFN-gamma were dose and time dependent and were partially reversible by the anti-IFN-gamma monoclonal antibody DB-1. This lymphokine did not reduce incorporation of RNA and protein precursors however. Measurements of 3H-uridine and 3H-leucine incorporation indicated significant increases in RNA and protein synthesis (37% and 45%, respectively) on a per cell basis. The mitogenic effects of IL-1 and platelet-derived growth factor (PDGF) were also susceptible to IFN-gamma-mediated inhibition but the mitogenic response to epidermal growth factor (EGF) was much less sensitive. We conclude that while IFN-gamma may act to modulate the mitogenic signals provided by some factors such as IL-1 and PDGF, the response to EGF appears to be unaffected.

Recombinant interferon-gamma inhibits the growth of IL-6-dependent human multiple myeloma cell lines in vitro

Recombinant human IFN-gamma (100-1000 U/ml) inhibited the IL-6-induced growth of 2 human IL-6-dependent multiple myeloma (MM) cell lines U-1958 and U-266-1970 in vitro. In contrast, the U-1996 line, independent of IL-6 for maintenance at a slow growth rate but responding to IL-6 by increased proliferation, and the IL-6-independent U-266-1984 were refractory to the anti-proliferative effect of IFN-gamma. The effect of IFN-gamma in the sensitive MM cell lines was cytostatic in U-266-1970, and cytostatic and cytotoxic in U-1958. Northern blot analysis revealed that the growth inhibition of the IL-6-dependent MM cell line U-1958 was not due to down-regulation of IL-6 receptor mRNA expression and that the differential sensitivity to IFN-gamma was not due to differences in IFN-gamma receptor expression. The growth inhibition was not a consequence of an IFN-gamma-induced terminal differentiation as flow cytometric analyses demonstrated an arrest in all phases of the cell cycle. IFN-alpha inhibited the growth in 3 of the 4 cell lines tested. The results thus suggest that the particular MM phenotype, which includes IL-6 dependency for survival and growth, may also be characterized by IFN-gamma sensitivity. Furthermore, the study demonstrates that MM cell lines are not simultaneously sensitive to IFN-gamma and alpha, indicating that the mechanisms of action of the two types of IFN are distinct.

Fibrogenic cytokines: the role of immune mediators in the development of scar tissue

A variety of diseases that are characterized by fibrosis share common features including the proliferation of fibroblasts and the deposition of extracellular matrix. Fibrosis often begins as an inflammatory reaction with leukocyte infiltration followed by the elaboration of cytokines. Here, Elizabeth J. Kovacs argues that the aberrant production of these mediators sustains the connective tissue accumulation that results in permanent alteration in tissue structure and function.

Transforming growth factor-beta and gamma-interferon have dual effects on growth of peripheral glia

The influence of transforming growth factor-beta (TGF-beta) and gamma-interferon on DNA synthesis in Schwann cells and enteric glia in culture has been studied. TGF-beta stimulated the DNA synthesis of short-term (less than 2 weeks in culture) Schwann cells, whereas gamma-interferon was ineffective. The stimulatory effect of TGF-beta was additive to the stimulation of DNA synthesis due to axonal membrane fragments. In contrast to their effect on short-term Schwann cells, both TGF-beta and gamma-interferon inhibited DNA synthesis in enteric glial cells and in long-term (over 3 months in culture) Schwann cells. When short-term Schwann cells were stimulated to divide by axolemma or glial growth factor, gamma-interferon did not inhibit this enhanced DNA synthesis although it suppressed DNA synthesis induced by cAMP analogues. These results raise the possibility that TGF-beta and gamma-interferon might have a role in controlling glial proliferation during development and/or regeneration of the peripheral nervous system.

Interferon gamma inhibits both proliferation and expression of differentiation-specific alpha-smooth muscle actin in arterial smooth muscle cells

Differentiation of muscle cells is characterized morphologically by the acquisition of contractile filaments and characteristic shape changes, and on the molecular level by induction of the expression of several genes, including those for the muscle-specific alpha-actin isoforms. IFN-gamma is an inhibitor of proliferation for several cells, including vascular smooth muscle, and is also an inducer of differentiated properties for several hematopoietic cells. We have therefore investigated whether IFN-gamma affects the expression of alpha-smooth muscle actin in cultured arterial smooth muscle cells. Cells exposed to IFN-gamma show a reduction of alpha-smooth muscle actin-containing stress fibers, as detected by immunofluorescence. The effect was observed in all phases of the cell cycle, and was caused by a reduction of the synthesis of alpha-smooth muscle actin protein as revealed by two-dimensional electrophoretic analysis of actin isoforms. RNA hybridization using a cRNA probe that hybridizes to all actin mRNAs showed that IFN-gamma-treated cells have a reduced content of the 1.7-kb mRNA that codes for alpha-smooth muscle actin, and to a lesser extent, also of the 2.1-kb mRNA encoding the beta and gamma-cytoplasmic actins. The reduction of alpha-smooth muscle actin mRNA was confirmed using an alpha-smooth muscle actin-specific cRNA probe. The reduction of alpha-smooth muscle actin mRNA occurs within 12 h, and is dependent on protein synthesis, since cycloheximide treatment reversed the effect. The inhibition of this mRNA species was dose dependent, and detectable by RNA hybridization at a dose of 50 U/ml IFN-gamma. These results suggest that the differentiation of arterial smooth muscle cells is not necessarily coupled to an inhibition of cellular proliferation. Instead, IFN-gamma may regulate the expression of several genes that control both proliferation and expression of differentiation markers.