Localization of PDGF-B protein in macrophages in all phases of atherogenesis

Immunological control mechanisms in plaque formation

Atherosclerosis is characterized by cholesterol accumulation, inflammation, and fibrous tissue formation. We have analyzed inflammatory components of atherosclerotic plaques and obtained evidence for T lymphocyte activation and cytokine secretion. A molecular genetical characterization of T cell clones obtained from atherosclerotic lesions revealed that the cells are heterogeneous with regard to antigen receptor gene organization. This indicates that they are derived from several progenitors and respond to different antigenic epitopes. The latter are not yet known, and it is also unclear to what extent the lymphocytic infiltrate in plaques represent a local immune response. Vascular effects of cytokines produced by plaque macrophages and lymphocytes were studied in cell culture and animal experiments. It was found that the T cell cytokine, interferon-gamma, inhibits cholesterol accumulation and foam cell formation by down-regulating the scavenger receptor on macrophages. It also inhibits smooth muscle proliferation in culture and the formation of arterial restenosis after angioplasty in experimental animals. Together, these studies emphasize the importance of vascular-immune interactions in the pathogenesis of atherosclerosis.

Interleukin 6 gene transcripts are expressed in human atherosclerotic lesions

Factors controlling the proliferation of vascular smooth muscle cells (SMC) are thought to be key elements in the progression of atherosclerosis. We have previously shown that interleukin 6 (IL-6) stimulates the growth of SMC in vitro and that IL-6 gene transcripts are expressed in atherosclerotic lesions of genetically hyperlipidemic rabbits. To understand the involvement of IL-6 in the development of human atherosclerosis, we investigated IL-6 mRNA expression in atherosclerotic arteries from patients undergoing surgical vascularization, utilizing reverse transcription polymerase chain reaction (RT-PCR) and in situ hybridization analyses. In RT-PCR analysis, the atherosclerotic arteries showed 10- to 40-fold levels of IL-6 mRNA expression over the non-atherosclerotic artery. In in situ hybridization analysis, IL-6 gene transcripts were observed in the thickened intimal layer of atherosclerotic lesions. These results strongly suggest the involvement of IL-6 in the development of human atherosclerosis.

Intraglomerular expressions of IL-1 alpha and platelet-derived growth factor (PDGF-B) mRNA in experimental immune complex-mediated glomerulonephritis

Both PDGF and IL-1 play important roles as autocrine growth factors for cultured mesangial cells, and may be closely associated with the progression of glomerulonephritis. In this study we investigated intraglomerular expressions of PDGF-B and IL-1 alpha mRNA in mice with bovine serum albumin (BSA) nephritis, a model of immune complex-mediated glomerulonephritis, using the reverse transcription-polymerase chain reaction (RT-PCR) method. We also quantified intraglomerular PDGF-B mRNA by the competitive PCR and studied the correlation between the level of intraglomerular PDGF-B mRNA expression and the degree of observed glomerular injury. While expression of neither PDGF-B nor IL-1 alpha mRNA was detected in glomeruli from control mice, both were strongly expressed in glomeruli from mice with BSA nephritis. IL-1 alpha mRNA in glomeruli showed low accumulation in mice with mild glomerular injury, and was increased in mice with moderate glomerular injury. In contrast, high intraglomerular expression of PDGF-B mRNA occurred in all mice with mild glomerular injury and continued throughout the course of the disease. We observed no correlation between the level of PDGF-B mRNA expression and the histologic grade of renal damage. These results suggest that PDGF and IL-1 have different growth properties, and PDGF might play a role as a competence factor rather than a progression factor in the pathogenesis of immune complex-mediated glomerulonephritis.

Probucol reduces the cellularity of aortic intimal thickening at anastomotic regions adjacent to prosthetic grafts in cholesterol-fed rabbits

Intimal hyperplasia is a persistent problem after implantation of prosthetic grafts. Although the mechanisms underlying this hyperplastic response are unknown, it has been proposed that such responses may be due to chronic vascular injury similar to that of atherogenesis. Thus, the role of oxidation was explored using the potent antioxidant drug probucol. Adult New Zealand White rabbits fed a modestly (0.25%) cholesterol-enriched diet had a polytetrafluoroethylene prosthetic graft placed into the lower aorta. After the grafting procedure, a group of 11 rabbits was placed on the cholesterol-enriched diet supplemented with 1% wt/wt probucol while a control group of 10 rabbits was placed on the cholesterol-enriched diet alone. The rabbits were maintained for a further 10 weeks before histological examination of the area surrounding the graft. Although administration of probucol did not significantly alter the dimensions of lesions at the anastomotic sites, the drug promoted striking histological changes in the surrounding tissue. Both groups of rabbits had a similar intimal hyperplastic response of the aortic tissue surrounding the graft. The vascular lesions present in the perigraft region of the control group consisted of a normal-appearing media but a thickened intima. The thickened intima contained numerous smooth muscle cells in a network of extracellular matrix. Regions in the neointima that were rich in smooth muscle cells exhibited modest staining for proliferating cell nuclear antigen. A few macrophages were present in the control group as determined by immunostaining with the monoclonal antibody RAM-11. In contrast, administration of probucol led to a marked reduction in the presence of RAM-11-staining macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of hypercholesterolemia on initial and chronic phases of rat nephrotoxic serum nephritis: development of focal segmental glomerulosclerosis, analogous to atherosclerosis

The effects of hypercholesterolemia on both the initial and chronic phases of rat nephrotoxic serum (NTS) nephritis have been investigated. Injury during the initial phase of NTS nephritis in hypercholesterolemic rats maintained on a cholesterol-supplemented diet (Group 2) was characterized by segmentally accentuated accumulations of vacuolated cells with lipid droplets (foam cells) in the glomeruli, while the kidneys of rats fed a standard diet (Group 1) revealed only mild intracapillary cell proliferation. Immunoelectron microscopy showed that the foam cells observed in Group 2 rats were largely derived from macrophages. The glomerular macrophage number, defined by the number of ED1-positive cells per glomerulus, was significantly higher in Group 2 than in Group 1 animals at days 5-6 (3.4 +/- 1.4 in Group 1 against 6.3 +/- 1.0 in Group 2; p < 0.01) as well as at days 21-28 (5.5 +/- 2.6 in Group 1 against 10.9 +/- 2.8 in Group 2; p < 0.01). In contrast, the numbers of OX19-positive T-lymphocytes and OX33-positive B-lymphocytes were similar in both groups. In the chronic phase of NTS nephritis at week 20, semiquantitative evaluation of the glomerular lesions disclosed more severe focal segmental glomerulosclerosis (FSGS) in Group 2 compared with Group 1 animals (glomerular injury score: 14 +/- 10 in Group 1 against 73 +/- 17 in Group 2; p < 0.01). Accumulations of lipid and foam cells were invariably seen in the sclerotic foci of Group 2 animals. The results indicate that hypercholesterolemia played an important role in the accelerated development of FSGS in rat NTS nephritis.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of follistatin, an activin-binding protein, in vascular smooth muscle cells and arteriosclerotic lesions

Activin-A has a mitogenic effect on vascular smooth muscle cells (SMCs) and is produced by monocyte/macrophage lineage cells. Here, we studied the expression of follistatin, an activin-binding protein, in both A10 cells, a rat aortic SMC line, and vascular SMCs derived from adult rat aorta. Follistatin mRNA was detected in these cells by Northern blot analysis. Ligand blot and immunoblot analyses demonstrated that follistatin was produced in the conditioned medium at a higher level by A10 cells than by SMCs. Furthermore, immunostaining and in situ hybridization of the arteriosclerotic lesions showed that follistatin was highly expressed in the diseased artery, where abnormal proliferation of SMCs occurred. We suggest that follistatin is produced by vascular SMCs and is involved in the course of atherogenesis.

Expression of intercellular adhesion molecule-1 on rat vascular smooth muscle cells by pro-inflammatory cytokines

Infiltration of mononuclear cells is an early pathological finding in human and experimental atherosclerosis. However, the cellular and molecular basis for cell infiltration is incompletely understood. While the intercellular adhesion molecule-1 (ICAM-1) is expressed on endothelial cells and promotes the adhesion of mononuclear cells, there is little information on the expression of ICAM-1 on vascular smooth muscle cells (SMC). In this study, we investigated the expression of ICAM-1 on cultured rat SMC and its regulation by pro-inflammatory cytokines, interleukin 1 alpha (IL-1 alpha), interleukin 6 (IL-6) and monocyte chemoattractant protein 1 (MCP-1). In immunohistochemical staining, ICAM-1 molecules were constitutively expressed on the surface of SMC. In flow cytometric and ELISA analyses, ICAM-1 molecule expression on SMC was significantly upregulated by IL-1 alpha and MCP-1, but not by IL-6, in a dose-dependent manner. The effects of IL-1 alpha and MCP-1 were observed as early as 4 h. In Northern blot analysis, ICAM-1 mRNA was slightly detectable in unstimulated SMC, but its expression was clearly observed following exposure to IL-1 alpha or MCP-1. These results suggest that ICAM-1 on SMC, as well as on endothelial cells, could participate in the focal accumulation of mononuclear cells in human atherosclerotic lesions.

Platelet-derived growth factor AB heterodimer interchain interactions influence secretion as well as receptor binding and activation

Platelet-derived growth factor (PDGF) is a disulfide-linked dimer comprised of two related polypeptide chains. To investigate the effects of an inactivating lesion introduced into one chain of the nascent PDGF dimer, approaches were developed to optimize synthesis, assembly, secretion, and purification of heterodimers between normal PDGF A and wild-type or mutant PDGF B. PDGF AB heterodimers were released into culture fluids less efficiently than PDGF AA, but to a greater degree than the cell-associated PDGF BB. These results suggest that interactions between two chains influence PDGF secretion. Analysis of heterodimers between PDGF A and disabled PDGF B mutants on cells that express either alpha or beta PDGFRs demonstrated that the impaired biologic activity of the mutant PDGF B chain was ameliorated with respect to binding and triggering of alpha PDGFRs. In cells that expressed both receptor types, heterodimers of mutant PDGF B and wild-type PDGF A gained substantially in their ability to recruit and trigger alpha, but not beta, PDGFRs. Partial rescue of impaired PDGF B mutant chain function by dimer formation with a wild-type PDGF A chain implies that interchain interactions markedly affect PDGFR binding and activation.

Regulation of human aortic endothelial cell-derived mesenchymal growth factors by allogeneic lymphocytes in vitro. A potential mechanism for cardiac allograft vasculopathy

Cardiac allograft vasculopathy is thought to be triggered by an alloreactive response to the donor coronary vasculature, resulting in smooth muscle cell proliferation and ultimate occlusion of the donor coronary arteries. To determine whether allogeneic lymphocytes are capable of regulating endothelial-derived smooth muscle cell (SMC) growth factors, human aortic endothelial cells (HAECs) were exposed to allogeneic lymphocytes. The HAEC-lymphocyte co-cultures were assessed for (a) lymphocyte proliferation in response to the allogeneic HAECs; (b) release of soluble factors that stimulate human aortic SMC proliferation; and (c) alteration of HAEC mRNA levels for a panel of known SMC growth factors. Co-culture conditioned medium increased SMC proliferation, compared to medium conditioned by HAECs alone. HAECs exposed to allogeneic lymphocytes increased their expression of mRNA for basic fibroblast growth factor, transforming growth factors alpha and beta, and platelet derived growth factor A and B chains. These results demonstrate that allogeneic lymphocytes are capable of inducing HAECs to increase mRNA levels for several mesenchymal growth factors and to release bioactive products capable of stimulating SMC cell proliferation in vitro. Additionally, the data support the hypothesis that alloreactive lymphocytes can stimulate allogeneic donor endothelial cells to produce growth factors that may contribute to the intimal thickening seen in cardiac allograft vasculopathy.

Porcine vascular smooth muscle cells immortalized with SV40 ori-defective DNA: characteristics of cell growth and collagen synthesis

A cell line derived from medial smooth muscle cells (SMC) was established from the porcine coronary artery by transfection with ori-defective simian virus 40 plasmid DNA (SV40 DNA). The characteristics of transfected cells (SV40-SMC) such as cell growth, collagen and non-collagen syntheses were investigated. SV40-SMC expressed SV40 large T antigen, c-myc and c-myb encoded proteins in the nuclei. SV40-SMC demonstrated a 'hills and valleys'-like arrangement in overconfluence and actin filaments upon immunofluorescent staining. Under electron microscopic observation, SV40-SMC had larger amounts of synthetic organelles and smaller amounts of filament bundles than those of SMC. SV40-SMC demonstrated three times higher growth activity and 4.4 times greater cellular density than SMC. Smooth muscle cells did not grow in media containing 5% plasma derived serum (PDS) instead of normal serum, whereas SV40-SMC proliferated in this medium. SV40-SMC did not grow in soft agar gel, while HeLa S3 cells, a cell line of human cervical carcinoma, formed colonies in this gel. By immunofluorescent (IF) staining, collagen phenotypes I, III, IV and V were detected in both SV40-SMC and SMC. However, protein synthesis including collagen and non-collagen was higher in SV40-SMC than in the control sample. It was concluded that SV40-SMC were a continuous cell line for vascular SMC regarding morphological characteristics, and demonstrated a higher growth activity, with increased collagen and non-collagen syntheses. This cell line is useful for the investigation of atherogenesis in relation to a proliferation of SMC and an accumulation of extracellular matrices in vascular intima.

Platelet-derived growth factor and transforming growth factor-beta 1 differentially affect the synthesis of biglycan and decorin by monkey arterial smooth muscle cells

Platelet-derived growth factor (PDGF) and transforming growth factor-beta 1 (TGF-beta 1), two growth-regulatory peptides with opposite effects on arterial smooth muscle cell (ASMC) proliferation, were examined for their influence on the synthesis of two small chondroitin sulfate/dermatan sulfate proteoglycans (CS/DS PGs) called biglycan and decorin. Quiescent ASMCs treated with either PDGF or TGF-beta 1 for 24 hours increased [35S]sulfate incorporation into biglycan 3.3- and 2.9-fold, respectively, whereas the incorporation of [35S]sulfate into decorin was not significantly affected. Treatment with TGF-beta 1 but not PDGF more than doubled the steady-state level of messenger RNA (mRNA) transcripts hybridizing to a complementary DNA (cDNA) encoding biglycan. Both growth factors had little or no effect on steady-state levels of mRNA transcripts hybridizing to a decorin cDNA. Incorporation of [35S]sulfate into biglycan glycosaminoglycan (GAG) was maximal by 12 to 18 hours after either PDGF or TGF-beta 1 addition. Both PDGF and TGF-beta 1 increased the molecular sizes of biglycan and decorin. This increase was a result of the synthesis of longer GAG chains substituted on the core proteins of both PGs. PDGF but not TGF-beta 1 led to an increase of more than twofold in the ratio of 6'- to 4'-sulfated disaccharides in these newly synthesized GAG chains. These results indicate that PDGF and TGF-beta 1 have specific but different effects on the synthesis of small CS/DS PGs by monkey ASMCs in culture.

Regional expression of the platelet-derived growth factor and its receptors in a primate graft model of vessel wall assembly

Healing baboon polytetrafluoroethylene grafts express PDGF mRNA in the neointima. Perfusates of graft segments also contain PDGF-like mitogenic activity. To extend these findings, we studied the expression and regional distribution of the PDGF protein isoforms and their receptors in this prosthetic graft model. By immunohistochemistry, as well as ELISA and Western blot analysis of tissue extracts, both PDGF-A and PDGF-B were identified in macrophages within the interstices of the synthetic material. In contrast, the neointima contained predominantly PDGF-A localized to the endothelial surface and the immediate subjacent smooth muscle cell layers. Tissue extracts of neointima and graft material were mitogenic for baboon aortic smooth muscle cells in culture; nearly all of this proliferative activity was blocked by a neutralizing anti-PDGF antibody. PDGF receptor beta-subunit mRNA and protein were easily detectable in the neointima and graft material. PDGF receptor alpha-subunit mRNA was also observed in the graft matrix and at lower levels in the neointima. This pattern of ligand and receptor expression further implicates locally produced PDGF as a regulator of neointimal smooth muscle cell growth in this model. The coexpression of ligand and receptor in the macrophage-rich matrix also suggests that PDGF may participate in the foreign body response.

Recruitment and dynamics of leukocytes in the formation of arterial intimal thickening--a comparative study with normo- and hypercholesterolemic rabbits

Leukocyte involvement in intimal thickening was investigated as a function of time and diet. Fibromuscular or foam cell-rich thickings were induced by electrical stimulation (ES) of carotid arteries in rabbits either on a normal or a high (1%) cholesterol diet. Under both dietary conditions granulocytes (predominantly neutrophils), monocytes and lymphocytes migrated through and accumulated beneath a continuous, yet structurally altered endothelium already after 1 day of ES. This preceded the occurrence of smooth muscle cells (SMCs) in the intima. Under normocholesterolemia, leukocyte attachment to the endothelium decreased with continued ES, which coincided with the re-establishment of a normal endothelial cell pattern. Neutrophils ceased to invade the stimulated intima and disappeared from the lesion after 14 days. The proportion of mononuclear leukocytes was also reduced in the thickened intima, finally amounting to 5.5 +/- 5.9% in the 4-week-old fibromuscular lesion where SMCs prevailed. Hypercholesterolemia did not affect neutrophil involvement in response to ES. However, it provoked lipid deposition first in macrophages, then in SMCs and resulted in elevated amounts of mononuclear leukocytes both within the foam cell-rich thickening and in association with the overlying endothelium. These data indicate adaptive behavior of leukocytic infiltration in the development of fibromuscular thickening, and a shift to a chronic inflammatory response under additional hypercholesterolemia.

Tissue localization of beta receptors for platelet-derived growth factor and platelet-derived growth factor B chain during wound repair in humans

The expression and localization of PDGF beta receptors and PDGF-AB/BB in human healing wounds was evaluated by immunohistochemical techniques and in situ hybridization. Expression of PDGF beta receptor protein and PDGF-AB/BB were analyzed in wound margin biopsies using the PDGFR-B2 and PDGF 007 antibodies. PDGF beta receptor expression was minor in normal skin. An increased expression of PDGF beta receptor protein was prominent in vessels in the proliferating tissue zone in wounds as early as 1 d after surgery and was apparent < or = 4 wk after surgery. There was also a concordant increase in PDGF beta receptor mRNA detected by in situ hybridization. PDGF-AB/BB was present in healing wounds as well as in normal skin. In normal skin, expression of PDGF-AB/BB was confined to peripheral nerve fibers and to solitary cells of the epidermis and of the superficial dermis. In wounds, infiltrating mononuclear cells also stained for PDGF-AB/BB. To identify cell types expressing PDGF AB/BB and PDGF beta receptors, respectively, we performed double immunofluorescence stainings. PDGF beta receptors were expressed by vascular smooth muscle cells and cells in capillary walls; the receptor protein could not be detected in neurofilament containing structures, T lymphocytes, or CD68 expressing macrophages. PDGF-AB/BB colocalized with neurofilaments, it was present in Langerhans cells of the epidermis and in HLA-DR positive cells located in the epidermal/dermal junction area. Of the macrophages infiltrating the wound, 43 +/- 18% stained positively for PDGF AB/BB. Since PDGF-AB/BB and PDGF beta receptors are expressed in the healing wound, two essential prerequisites for a role of PDGF in wound healing are fulfilled.

Probucol inhibits mononuclear cell adhesion to vascular endothelium in the cholesterol-fed rabbit

Mononuclear cells, isolated from the blood of hyperlipidaemic patients, are hyper-reactive and possess an increased propensity to adhere to vascular endothelial cells. Hyperlipidaemia is also associated with a dysfunctional endothelium, to which mononuclear cells stick with greater avidity. In order to assess the importance of lipid peroxidation and free-radical generation in these processes, we have investigated the effects of probucol on mononuclear cell adhesion to vascular endothelial cells in vivo and in vitro in the cholesterol-fed rabbit. New Zealand White rabbits were fed either: (i) control chow (n = 15), (ii) 2% cholesterol (n = 11), or (iii) 2% cholesterol with 1% probucol (n = 11). Mononuclear cell adherence to endothelium in the common carotid artery was assessed 5 weeks after the start of the experimental diet using the Hoechst 33342 staining technique. The 2% cholesterol diet caused a more than 6-fold increase in mean mononuclear cell adherence (P < 0.001). Concurrent probucol therapy abrogated the effects of cholesterol feeding, and in animals in this group, in vivo mononuclear cell adherence did not differ significantly from control animals. In vivo mononuclear cell adherence was directly related to serum cholesterol levels (r = 0.68, P < 0.0001) and inversely related to serum probucol concentrations (r = -0.63, P < 0.002). Concurrent probucol therapy also reduced the in vitro binding of mononuclear cells, isolated from hypercholesterolaemic animals, to endothelial cell monolayers (P < 0.01). These data suggest that the increased binding of mononuclear cells to vascular endothelium of cholesterol-fed rabbits may be a free radical mediated process that is inhibited by antioxidants.

Regulation of endothelial adhesion molecules by ligands binding to the scavenger receptor

Monocyte adherence to the endothelium, their penetration to the subendothelial space and excessive lipid accumulation (foam cell formation) are the initial events in atherogenesis. Scavenger receptors have been reported to play an important role in foam cell formation, since modified low density lipoproteins can be taken up via scavenger receptors in a non-down-regulated fashion. In this study we demonstrate that stimulation of scavenger receptors in endothelial cells induces the expression of endothelial adhesion molecules. Polyinosinic acid (poly I), a known scavenger receptor ligand, significantly induced the expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-selectin on human umbilical vein endothelial cells when compared with polycytidylic acid (poly C), a structurally related compound to poly I, which does not bind to the scavenger receptor. The effect of scavenger receptor ligands on the endothelial cell line EA hy. 926 was also tested. Poly I up-regulated ICAM-1 expression also on EA hy. 926 cells, while it had no effect on IL-1 beta or tumour necrosis factor-alpha (TNF-alpha) production on the same cell line. Poly I-induced ICAM-1 expression on EA hy. 926 cells could be inhibited by H7, a protein kinase C inhibitor, while HA 1004, a preferential protein kinase A inhibitor, had no effect on ICAM-1 expression. The role of protein kinase C in scavenger receptor-mediated adhesion molecule upregulation was confirmed by the ability of poly I to directly activate protein kinase C, when measured with 3H-phorbol dibutyrate binding to EA hy. 926 cells, while poly C again was ineffective.

The pathogenesis of atherosclerosis: a perspective for the 1990s

Atherosclerosis, the principal cause of heart attack, stroke and gangrene of the extremities, is responsible for 50% of all mortality in the USA, Europe and Japan. The lesions result from an excessive, inflammatory-fibroproliferative response to various forms of insult to the endothelium and smooth muscle of the artery wall. A large number of growth factors, cytokines and vasoregulatory molecules participate in this process. Our ability to control the expression of genes encoding these molecules and to target specific cell types provides opportunities to develop new diagnostic and therapeutic agents to induce the regression of the lesions and, possibly, to prevent their formation.

Cell proliferation in human arteriovenous fistulas used for hemodialysis

The long-term patency of arteriovenous (AV) fistulas created for hemodialysis of renal-failure patients is usually measured in months, particularly when polytetrafluoroethylene (PTFE) material is interposed between the artery and vein. This is due to the rapid development of intimal hyperplastic lesions in the anastomosis region of the PTFE graft material with the vein. We studied the proliferative patterns in seven human AV fistulas removed at the time of fistula revision. Cell proliferation was determined by using an antibody to the proliferating cell nuclear antigen (PCNA), and specific cell types were identified by immunochemical reagents for smooth muscle cells, monocytes/macrophages, monocytes, lymphocytes, and endothelial cells. All venous segments exhibited a markedly hyperplastic intima. Vascularization of the intima and media by capillary-sized vessels was found. The main intimal cellular component was smooth muscle. Macrophages were usually seen around microvessels, and many also populated the perigraft region of the adventitia. In contrast to human atherosclerotic lesions, high rates of cell proliferation were observed in these fistulas. PCNA indices (percentage of cells that were PCNA positive [mean +/- SD]) were as follows: intima 17.7 +/- 11.3%, media 24 +/- 11.2%, and adventitia 20 +/- 11.6%. However, the distribution of PCNA-positive cells was not uniform. Instead, the PCNA index in microvessel-containing intimal fields was five to six times that of avascular fields (28.9 +/- 10.6% versus 4.9 +/- 4.5%, respectively, p < 0.001). Double immunolabeling revealed a large proportion of PCNA-positive microvascular endothelial cells and surrounding pericyte-like smooth muscle cells, as well as smooth muscle cells without visual connection to either microvessels or the lumen.(ABSTRACT TRUNCATED AT 250 WORDS)

Antioxidant treatment inhibits the development of intimal thickening after balloon injury of the aorta in hypercholesterolemic rabbits

The effect of the antioxidant butylated hydroxytoluene (BHT) on the accumulation of intimal smooth muscle cells (SMC) and development of intimal thickening after balloon catheter injury of the aorta were studied in rabbits with dietary-induced hyperlipidemia. Two sets of New Zealand White rabbits (eight rabbits in each group) were fed either 0.25% cholesterol or 0.25% cholesterol/1% BHT for a total of 6 wk. Serum lipid levels did not differ between the two groups. 3 wk after the start of the study, a balloon injury of the aorta was performed, after which the rabbits were kept on their respective diets for another 3 wk. After this period of time, the rabbits were killed and their aortas were investigated. The BHT-treated rabbits had only one fourth of the intimal thickness (P < 0.0001) and half the number of SMC/mm intima (P < 0.001), as compared to the rabbits fed only cholesterol. There was also a lower number of macrophages in the BHT-treated group. T lymphocytes were present in the intima of cholesterol-fed rabbits, whereas no such cells could be identified in the BHT-fed animals. There were significantly lower levels of autooxidation products of cholesterol (7-oxocholesterol, cholesterol-5,6-epoxide, and 7 beta-hydroxycholesterol) in the aortas of BHT-treated rabbits, P < 0.001. In conclusion, the antioxidant BHT effectively inhibited the accumulation of intimal SMC and the development of intimal thickening of the aorta in hypercholesterolemic rabbits after a balloon catheter-induced injury. These results indicate that antioxidants may modify intimal response to injury.

Recombinant platelet-derived growth factor B gene expression in porcine arteries induce intimal hyperplasia in vivo

Platelet-derived growth factor (PDGF) B chain induces cell proliferation in vitro and is associated with arterial lesions that cause cardiovascular disease. However, it has been difficult to document the biological response to PDGF B gene expression in arteries in vivo. To determine the biologic effects of this growth factor in vivo, we have introduced an eukaryotic expression vector plasmid encoding recombinant PDGF B by direct gene transfer into porcine iliofemoral arteries using DNA liposome complexes. The presence of PDGF B plasmid DNA and expression of recombinant mRNA were confirmed by polymerase chain reaction analysis, and recombinant PDGF protein was demonstrated by immunohistochemistry. Intimal thickening was observed in porcine arteries 21 days following transfection with the recombinant PDGF B gene compared with arteries transduced with a control gene, E. coli beta-galactosidase. An eightfold increase in intimal to medial ratio was present in PDGF B gene transfected arteries compared with control transfected arteries (P = 0.001). This study suggests that expression of a recombinant PDGF B gene in vivo can play a role in the induction of intimal hyperplasia, which can lead to cardiovascular diseases.

Evidence for involvement of phospholipase C-gamma 2 in signal transduction of platelet-derived growth factor in vascular smooth-muscle cells

In order to examine the mechanisms underlying smooth-muscle cell proliferation, we investigated effect of platelet-derived growth factor (PDGF) dimers on proliferation of rabbit vascular smooth-muscle cells (VSMCs) and also involvement of phospholipase C (PLC) isoforms in the signal transduction. PDGF-BB and -AB, but not -AA, stimulated cell proliferation and intracellular production of inositol trisphosphate. Northern and Western analyses demonstrated that VSMCs mainly expressed PLC-gamma 2 and PLC-delta 1 among four PLC isoforms tested. A number of cellular proteins, including PLC-gamma 2, but not PLC-delta 1, were phosphorylated on a tyrosine residue by the stimulation of either PDGF-BB or -AB. These results suggest a functional association of PDGF receptor and PLC-gamma 2 that might be responsible for PDGF-dependent VSMC growth. In addition, the expression of PLC-gamma 2 was extremely low in the primary VSMC cultures and was induced during further cultivation of the primary cultures, indicating that an acquisition of PDGF-signal-transducing components, including PLC-gamma 2, may be an important step for proliferation of smooth-muscle cells.

Effects of doxazosin on atherosclerosis in cholesterol-fed rabbits

Doxazosin was administered to rabbits fed diets enriched in cholesterol and peanut oil for 7.5 or 12 weeks, in 2 separate experiments. Doxazosin suppressed the accumulation of cholesterol and formation of atherosclerotic plaques in the aortas of treated rabbits and prevented a diet-induced increase in aortic collagen and wall mass. Doxazosin was more effective in the thoracic and abdominal segments of the aorta than in the aortic arch. Pharmacokinetic analysis indicated that treated rabbits were exposed to concentrations of doxazosin, integrated over 24 h, which were consistent with the therapeutic range of doxazosin measured in patients treated for hypertension. Doxazosin did not alter serum levels of cholesterol or triglycerides, nor were there any consistent effects on glucose, free fatty acid or ketone levels. Hypotheses of the mechanism of action of doxazosin are discussed, including the possible involvement of alpha 1-adrenergic receptors in recruitment of smooth muscle cells by subintimal macrophages and nonadrenergic mechanisms of inhibition of lipid infiltration.

Ultrastructural evidence of cell-mediated endothelial cell injury in cardiac transplant-related accelerated arteriosclerosis

Accelerated arteriosclerosis secondary to chronic allograft rejection is a major long-term complication of heart transplantation. Accelerated arteriosclerosis has been associated with an endothelialitis, and the majority of the involved inflammatory cells are T lymphocytes and macrophages. Coronary arteries from six heart allograft recipients with transplant-related arteriosclerosis were examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Four hearts were explants from heart transplant recipients with severe accelerated arteriosclerosis who were undergoing retransplantation, and two were obtained from autopsied recipients. The patients ranged in age from 6 to 60 years (mean, 44 years). The graft survival for these six hearts ranged from 1.4 to 5.6 years (mean, 4.3 years). Lymphocytes, macrophages, and smooth muscle cells were identified by TEM in the intimas of all the vessels examined. The lymphocytes were often in contact with macrophages or in close proximity to injured endothelial cells. Areas of endothelial injury were characterized by vacuolization of endothelial cells and partial denudation of the endothelium with fibrin deposition. SEM also revealed endothelial cell injury with disorganization of the endothelium and gaps between endothelial cells. Leukocytes and platelets were often noted in these gaps. These findings suggest that accelerated arteriosclerosis in heart transplant recipients is associated with an accumulation of macrophages, lymphocytes, and smooth muscle cells in the intima as well as with lymphocyte-directed endothelial injury.

Cytokine regulation of granulocyte-macrophage colony stimulating factor and macrophage colony-stimulating factor production in human arterial smooth muscle cells

Smooth muscle cells (SMC) are the major cell type found in the walls of large blood vessels and appear to participate in local immune and inflammatory reactions, as well as in certain vascular diseases. We tested whether human arterial SMC can produce in vitro the colony stimulating factors (CSFs), granulocyte macrophage-CSF (GM-CSF) and macrophage CSF (M-CSF). Untreated internal mammary artery and aortic SMC produced no detectable GM-CSF but constitutively made M-CSF, measured by ELISA and radioimmunoassay, respectively. Interleukin-1 (IL-1) and, to a lesser extent, tumor necrosis factor alpha (TNF alpha) stimulated GM-CSF formation within 3 h; mRNA levels also increased particularly in the presence of the protein synthesis inhibitor, cycloheximide. IL-1, TNF alpha and, in addition, interferon-gamma (IFN-gamma) raised the M-CSF levels within 6 h; cycloheximide potentiated the effects of IL-1 and TNF alpha on mRNA levels. These results suggest that cytokine-stimulated human arterial SMC may be a source of the M-CSF found in atherosclerotic lesions. Since monocytes/macrophages can be activated by GM-CSF and M-CSF, while GM-CSF can also affect granulocyte function, SMC may participate in inflammatory reactions and vascular diseases by releasing these cytokines.

Neointimal macrophages colocalize with extracellular matrix gene expression in human atherosclerotic pulmonary arteries

Vascular remodeling in adult atherosclerotic pulmonary arteries is characterized by discrete areas of neointimal extracellular matrix gene expression, suggesting regulation by local factors. Though the factors responsible for inducing matrix gene expression in atherosclerotic lesions are largely unknown, several observations suggest macrophages may be a focal source of those factors. Immunohistochemistry confirmed the presence of macrophages in the neointima of atherosclerotic elastic pulmonary arteries from patients with unexplained pulmonary hypertension. Areas of neointima containing dense clusters of macrophages were separated by sparsely populated areas. Foamy macrophages resided more deeply within the neointima than nonfoamy macrophages, which were found more often subjacent to the endothelium or within the lumenal one-third of the neointima. Combined immunohistochemistry-in situ hybridization indicated neointimal fibronectin and type I procollagen gene expression was intimately associated only with nonfoamy neointimal macrophages. These observations suggest that: (a) nonfoamy neointimal macrophages participate in the local regulation of extracellular matrix gene expression in atherosclerotic pulmonary arteries; (b) foamy macrophages, which are not associated with matrix gene expression, have undergone modulation of their secretory phenotype.

Manidipine affects rPDGF-BB-induced gene transcription of low-density lipoprotein receptors and 3-hydroxy-3-methylglutaryl coenzyme A reductase in human mesangial cells

The effects of manidipine, a newly developed Ca2+ channel blocker, on recombinant platelet-derived growth factor BB (rPDGF-BB)-induced transcription of the low-density lipoprotein receptor and the 3-hydroxy-3-methylglutaryl coenzyme A reductase genes in human mesangial cells are reported. The transcription of the rPDGF-BB-induced gene of the low-density lipoprotein receptor was enhanced and maintained over a longer period, whereas the transcription of the 3-hydroxy-3-methylglutaryl reductase gene was blocked by manidipine at nanomolar concentrations. The results suggest that aside from the ability to block manidipine's potential-operated Ca2+ channels, manidipine also affects gene transcription of relevant proteins involved in the regulation of cholesterol metabolism at concentrations close to those efficacious for clinical therapies. This may further explain the antiinflammatory and organ-protective activities of the compound.

Oncostatin M is a mitogen for rabbit vascular smooth muscle cells

The growth regulatory protein oncostatin M was initially discovered in macrophage-conditioned medium. We investigated the effects of oncostatin M on cultured rabbit aorta smooth muscle cells (SMCs) and found that the peptide stimulated an increase in the incorporation of [3H]thymidine into DNA. The magnitude of the stimulation was dependent on oncostatin M concentration and SMC confluency. In subconfluent cultures, 1-2 nM stimulated 4- to 5-fold increases in DNA synthesis after 20 hr. Other structurally related cytokines (granulocyte colony-stimulating factor, leukemia inhibitory factor, interleukin 6, ciliary neurotrophic factor) did not affect SMC DNA synthesis. After 5 or 8 days, oncostatin M caused a doubling in SMC number and also induced a transformed phenotype. The combination of oncostatin M and platelet-derived growth factor for 8 days resulted in a 4-fold increase in cell number, approximately the same increase in cell number as induced by the addition of 10% fetal calf serum. Further investigation suggested that the mitogenic effect of oncostatin M was in part due to tyrosine kinase activation. Within 1-2 min, the factor increased phosphotyrosine levels of several SMC proteins. In addition, detectable increases in diacylglycerol levels occurred within 2-5 min, reached 50% above control by 30 min, and remained elevated through 45 min of incubation with oncostatin M. SMC inositol phosphate levels were also elevated within 2 min and then returned to near control values by 20 min. Within 30 min, oncostatin M induced expression of the immediate-early gene EGR-1. These data indicate that oncostatin M may be an important, naturally occurring mitogen for vascular SMCs.

Smooth muscle cells and the pathogenesis of the lesions of atherosclerosis

In this review we have tried to identify the characteristic features of SMCs in developing lesions of atherosclerosis and the extracellular factors that may be involved in regulating these altered features. Though the list seems long and complex there is probably a great deal of interplay among the different regulatory mechanisms. The function and activities of SMCs in the artery are dependent on the milieu created by the surrounding cells and the components of the extracellular matrix. In the normal, uninjured media of the artery, SMC phenotype and function seem to be in large part determined by the extracellular matrix in which they are embedded and by diffusible factors, in particular from endothelial cells. Endothelial cell injury, infiltration of monocytes and lymphocytes, and ultimately, thrombosis and platelet release, as seen in developing lesions of atherosclerosis, dramatically alter the balance of growth-regulatory and vasoactive factors present in the local environment. These extracellular factors (table and figure) can alter both SMC phenotype, and thus responsiveness, and SMC migration, proliferation, and synthesis of the extracellular matrix. A better understanding of how specific factors mediate these responses, should make it possible to determine the ways in which the SMC response can be modulated. Though growth regulatory molecules seem to be key to this process, the challenge for the future is to understand their regulation in the environment of the artery wall and the interplay between growth-regulatory molecules, extracellular matrix, and vasoactive agents.

Constitutive and inducible expression of PDGF in the human basophilic cell line, KU 812

The human basophilic cell line KU 812, that also has some mast cell characteristics, was found to express the PDGF-A gene and secrete PDGF-A like activity. After treatment with IL-6+ TNF-alpha, the PDGF-A mRNA expression increased as did cytoplasmic immunostaining with anti-PDGF antibodies. Secretion of PDGF-A was visualized by immunoprecipitation. An augmentation of non-secreted PDGF-like activity after IL-6+ TNF-alpha treatment was not accompanied by induction of the long splice variant of the PDGF-A-chain mRNA. Treatment with TPA caused an increase in PDGF-A expression and in addition, an induction of PDGF-B transcripts were seen. Staining of cytospin preparations with anti-PDGF antibodies visualized a substantial increase in immunostaining of the TPA treated cells and both intracellular and secreted PDGF-AA-like activity was substantially increased as compared to untreated control cultures. There was a concomitant induction of exon 6 specific mRNA, corresponding to a cellular retention signal after TPA treatment. Our results show that PDGF can be produced by a cell line of the basophilic/mast cell lineage, i.e. cells involved in allergic disorders and inflammation.

Altered protein secretion and extracellular matrix deposition is associated with the proliferative phenotype induced by allylamine in aortic smooth muscle cells

Repeated cycles of allylamine-induced aortic injury in vivo modulate the proliferative potential of smooth muscle cells (SMCs) during serial propagation in vitro. This modulation may be partly mediated by disturbances in polyphosphoinositide metabolism which afford allylamine-treated cells a growth advantage over control cells [Cox, Murphy and Ramos (1990) Exp. Mol. Pathol. 53, 52-63]. The present studies were conducted to further evaluate the mechanisms which mediate the enhanced proliferative potential of allylamine cells. Cellular growth and/or [3H]thymidine incorporation into DNA were evaluated in control and allylamine cells seeded on plastic culture dishes or glass coverslips in the presence of 0.1, 1 or 10% fetal bovine serum (FBS). On either substrate, incubation in 0.1% FBS for 48 h inhibited DNA synthesis in cultures of both cell types, but the inhibitory response was more pronounced in allylamine cells. Subsequent challenge with 10% FBS increased thymidine incorporation to a greater extent in allylamine cells. Interestingly, enhanced DNA synthesis of allylamine cells was associated with increased cell numbers only when seeded on a glass surface. The enhanced growth rate on glass was not due to increased plating efficiency since comparable attachment rates were observed for both cell types. Reseeding of control cells on glass substrates pre-coated by allylamine cells afforded control cells a growth advantage comparable with that observed for allylamine cultures. Conditioned media from growth-arrested, as well as cycling cultures, of allylamine cells stimulated DNA synthesis in cultures of either cell type to a greater extent than conditioned media from control counterparts. In addition, the responsiveness of allylamine cells to secreted products was enhanced relative to that of control cells. Metabolic labelling studies revealed that the synthesis and/or secretion of 52, 46, 33 and 28 kDa proteins was enhanced in allylamine cultures relative to controls, and that the expression of two proteins of 30 and 31 kDa only occurred in allylamine cultures. We conclude that the enhanced growth response of allylamine cells is associated with both altered protein secretion and differential extracellular matrix deposition.

Secretion of epidermal growth factor-like molecular species by lung parenchymal macrophages: induction by interferon-gamma

A population of cells enriched for pulmonary interstitial macrophages was obtained by differential adherence of lung parenchymal cells released by dissociation with trypsin. These cells secreted a molecule or molecules that bound to epidermal growth factor (EGF) receptors expressed on pulmonary fibroblasts. Secretion was reproducibly stimulated by exposure of the macrophages to interferon-gamma. Binding to EGF receptors could be blocked by a polyclonal antibody to EGF. It could also be partially blocked by incubation with heparin, suggesting that at least a component of the activity might be due to a member of the heparin-binding subgroup of the EGF family of growth factors. Because pulmonary fibrosis is consistently associated with inflammatory accumulation of activated T-lymphocytes, induction by interferon-gamma of growth factor secretion by macrophages could have pathogenetic importance. We speculate that similar cellular interactions may play a role in the progression of other chronic inflammatory lesions to fibrosis.

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)

Free radical-mediated platelet activation by hemoglobin released from red blood cells

It is known that the rate of thrombus formation depends on interaction between platelets and erythrocytes, but the mechanism of this process has remained obscure. We here show that nanomolar levels of hemoglobin released from damaged red blood cells can induce platelet aggregation. The molecular mechanism is not receptor-based, but involves oxidation of oxyhemoglobin by platelet-derived hydrogen peroxide, with subsequent generation of a small unknown free radical species, detected by ESR spectroscopy. Methemoglobin and carbon monoxide-treated hemoglobin are unable to cause platelet activation or radical formation. The aggregation of platelets induced by hemoglobin is completely blocked by catalase or radical scavengers. These findings indicate a role for a novel extracellular free radical second messenger in the activation of platelets.

Human aortic endothelial cells express the type I but not the type II receptor for interleukin-1 (IL-1)

Endothelial cells (EC) are very responsive to the proinflammatory cytokine interleukin-1 (IL-1). EC are induced by IL-1 to secrete chemotactic factors and to increase expression of cell surface adhesion molecules leading to increased leukocyte adhesion. Activated EC further contribute to the inflammatory response by secreting additional cytokines. IL-1 interacts with EC through high-affinity cell-surface receptors. However, the low number of receptors present on EC has made characterization difficult. Further, recent evidence has suggested diversity in the responses of EC from different regions of the vascular system. Interested in the effect of IL-1 on early atherosclerotic lesion formation, we have characterized the IL-1 receptors on human aortic endothelial cells (HAEC). Using a direct binding assay, we found that HAEC have 1,000-3,000 IL-1 receptors per cell and bind IL-1 alpha with a Kd of 3.5 x 10(-10) M. We found that a monoclonal antibody specific for the type I receptor completely blocks IL-1 alpha binding. The blocking antibody also completely inhibits the IL-1 induced increase in intracellular adhesion molecule 1 (ICAM-1) expression by HAEC. Using solution hybridization and ribonuclease protection with an antisense probe, a sensitive method for detection of low abundance mRNA species we found that HAEC as well as human umbilical vein EC (HUVEC) have significant levels of mRNA for the type I IL-1 receptor. To test whether HAEC might also contain transcripts for the type II IL-1 receptor, we compared levels of mRNAs by polymerase chain reaction (PCR) amplification of cDNAs reverse-transcribed from total RNA. We found only transcripts for the type I receptor and not the type II receptor in HAEC. Based on this data, we conclude that aortic endothelial cells respond to IL-1 through the type I receptor.

Probucol inhibits neointimal thickening and macrophage accumulation after balloon injury in the cholesterol-fed rabbit

Restenosis is a frequent long-term complication after balloon angioplasty. Although smooth muscle cells form the major constituent of the occluding lesion, macrophage-derived foam cells are usually also present in high abundance. The latter have the potential to accelerate the rate of reocclusion because they elaborate many potent cytokines and growth factors, which may act to either recruit cells into the neointima or cause neointimal cell proliferation. Macrophage-derived foam-cell formation depends upon the uptake of modified low density lipoprotein via a scavenger receptor-mediated pathway. Foam-cell formation is accompanied by the release of smooth muscle cell mitogens and chemoattractants. We have examined the effects of probucol, a lipid-soluble antioxidant, in the balloon-catheterized carotid artery of the cholesterol-fed rabbit to evaluate the importance of oxidative processes in restenosis. After 5 weeks, serum cholesterol levels were 32% lower (P < 0.05) in rabbits fed 1% probucol with 2% cholesterol, compared with those receiving cholesterol alone. Probucol inhibited neointimal macrophage accumulation by 68% (P < 0.001), reduced absolute intimal size by 51% (P < 0.05), and reduced the intima/media thickness ratio by 51%. These inhibitory effects were directly related to serum probucol concentrations and appeared to be unrelated to probucol's hypocholesterolemic activity. These data suggest that reactive oxygen species may be involved in the intimal response to injury and that antioxidants, such as probucol, may be therapeutically useful as inhibitors of restenosis.

Association between high levels of growth factors in plasma and progression of coronary atherosclerosis

Although intimal proliferation of smooth muscle cells (SMC) is recognized as one of the key mechanisms in the development of atherosclerosis, our knowledge of the role of circulating growth factors for SMC in this process is limited. In the present study the plasma levels of platelet-derived growth factor (PDGF), beta-thromboglobulin (beta-TG), platelet factor 4 (PF 4) and total growth factor activity were determined in a group of 30 young postinfarction patients who had participated in an angiographic study of mechanisms associated with progression of coronary atherosclerosis. Significant correlations were found between the total growth factor activity in plasma and progression (r = 0.42, P < 0.05), as well as severity (r = 0.52, P < 0.01), of global coronary atherosclerosis. Attempts to identify the nature of the total growth factor activity indicated that less than 20% could be attributed to PDGF, the major serum mitogen for SMC. PDGF levels determined by radioimmunoassay were not related to progression or severity of global coronary atherosclerosis, but showed a significant association with the number and severity of distinct stenoses (r = 0.40, P < 0.05). Due to the retrospective design of this study, it is not possible to conclude whether there is a causal relationship between circulating growth factors and development of coronary atherosclerosis.

Interferon-gamma suppresses PDGF production from THP-1 cells and blood monocyte-derived macrophages

Involvement of the immunological mechanisms in atherogenesis has recently been suggested by immunohistological detection of macrophages and T lymphocytes in atherosclerotic lesions. In the present study, we have investigated the regulatory effect of interferon-gamma (IFN-gamma), a cytokine secreted by activated T cells, on the production and secretion of platelet-derived growth factor (PDGF) from macrophages in culture. The human monocytic leukemia cell line, THP-1, was treated with phorbol 12-myristate 13-acetate (PMA) for 24 h to induce macrophage differentiation and PDGF production, and then various doses of recombinant human IFN-gamma (0-1000 I.U./ml) were added to the culture. After 48 h, the conditioned medium and the cells were harvested and analyzed for PDGF production. PDGF-dependent mitogenic activity in the conditioned medium, estimated by neutralization of mitogenic activity with anti-PDGF antibody, was suppressed by IFN-gamma treatment. Radioimmunoassays for PDGF also revealed a decrease in both PDGF-AA and -BB in the conditioned medium with IFN-gamma treatment, whereas neither total cell DNA as an indication of cell number nor overall protein synthesis based on [3H]leucine incorporation were decreased. Northern analysis of total RNA extracted from the cells demonstrated that IFN-gamma suppressed the level of PDGF mRNA. Analysis of mRNA degradation in the presence of actinomycin D demonstrated that the decrease in PDGF mRNA was not due to enhanced degradation of mRNA. A similar inhibitory effect of IFN-gamma on PDGF mRNA levels was also found in monocyte-derived macrophages cultured in the presence of granulocyte-macrophage colony stimulating factor. These results suggest that IFN-gamma modulates production and secretion of PDGF from macrophages and that the functions of macrophages in atherogenesis may be regulated by the cellular interactions between T cells and macrophages through the action of cytokines such as IFN-gamma.