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Cardiovascular Research 1998 37(1):216-224; doi:10.1016/S0008-6363(97)00224-1
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Copyright © 1998, European Society of Cardiology

Human monocyte-endothelial cell interaction induces platelet-derived growth factor expression

Hiroshi Funayamaa, Uichi Ikedaa,*, Masafumi Takahashia, Youichi Sakatab, Sei-Ichi Kitagawac, Yu-Ichi Takahashid, Jun-Ichi Masuyamae, Yusuke Furukawac, Yasusada Miurac, Shogo Kanoe, Michio Matsudab and Kazuyuki Shimadaa

aDepartment of Cardiology, Jichi Medical School, Minamikawachi-machi, Tochigi 329-04, Japan
bDepartment of Thrombosis and Hemostasis, Jichi Medical School, Tochigi, Japan
cDepartment of Hematology, Jichi Medical School, Tochigi, Japan
dDepartment of Clinical and Laboratory Medicine, Tohoku University School of Medicine, Miyagi, Japan
eDepartment of Clinical Immunology, Jichi Medical School, Tochigi, Japan

* Corresponding author. Tel. +81-285-44-2111; Ext. 3556; Fax +81-285-44-5317; E-mail: uikeda@jichi.ac.jp

Received 12 May 1997; accepted 12 August 1997


   Abstract
Top
 Abstract
1 Introduction
 2 Methods
 3 Results
 4 Discussion
 References
 
Objective: The purpose of this study was to investigate whether the synthesis of platelet-derived growth factor (PDGF), a major mitogen and chemoattractant for vascular smooth muscle cells, was induced by the direct cell-to-cell interaction between human monocytes and umbilical vein endothelial cells (ECs). Methods: PDGF protein and mRNA expression were determined by cellular ELISA, immunohistochemical and Northern blot analyses. Results: Coculture of monocytes and ECs secreted a large amount of PDGF into the supernatant, whereas culture of ECs or monocytes alone induced low levels of PDGF production. In Northern blot analysis, substantial amounts of PDGF-A and -B mRNA were induced by coculture of monocytes with ECs. Immunohistochemistry revealed that PDGF-B chain protein was detectable in both ECs and monocytes. PDGF production by ECs induced by conditioned medium of the coculture was significantly inhibited by Abs against interleukin-1β (IL-1β) and tumor necrosis factor-{alpha} (TNF{alpha}). Conclusions: These results indicate that the direct cell-to-cell interaction between human monocytes and ECs induces PDGF synthesis in both types of cells, suggesting that PDGF produced locally by monocyte-EC adhesive interaction plays an important role in the pathogenesis of atherosclerosis by promoting the migration and accumulation of vascular smooth muscle cells.

KEYWORDS Atherosclerosis; Adhesion; Interleukin; Tumor necrosis factor


   1 Introduction
Top
 Abstract
 1 Introduction
2 Methods
 3 Results
 4 Discussion
 References
 
Platelet-derived growth factor (PDGF) is a major mitogen and chemoattractant for vascular smooth muscle cells [1, 2]. Two different PDGF chains termed A and B encoded by different genes have been identified leading to three different PDGF isoforms, the AA and BB homodimers and the AB heterodimer [3, 4]. Although vascular smooth muscle cells secrete the AA-dimer exclusively, endothelial cells secrete a mixture of PDGF-AA, -BB, and -AB [5]. PDGF has been hypothesized to be responsible for intimal proliferation in atherosclerosis, and this hypothesis originated from the observations that platelets contain a mitogen for smooth muscle cells and that platelets accumulate and release their granules at the site of endothelial denudation [6, 7]. The source of PDGF was presumed to be external to the vessel wall, in the from of blood borne platelets. However, in hypertension or hyperlipidemia, smooth muscle cell proliferation occurs without endothelial denudation and platelet aggregation [8]. PDGF is also synthesized and secreted by various cell types such as endothelial cells (ECs) [9–11], macrophages [12–14], smooth muscle cells [15]and fibroblasts [16]at least in vitro. Since the above cell types are present in human atherosclerotic plaques, the PDGF hypothesis of atherogenesis has been modified to include the possible production of PDGF within the developing human intima [17]. Indeed the presence of local PDGF in the atheroma is supported by recent studies showing that PDGF-B mRNA can be detected by Northern blots of human carotid plaques removed at surgery [18]. Similarly, in situ hybridization and immunocytochemistry of human atherosclerotic lesions have demonstrated localization of PDGF-A and -B mRNA in mesenchymal cells and ECs [19], and PDGF-B protein in macrophages [20].

Monocyte adhesion to the vascular endothelium and subendothelial migration are an early crucial event in the development of atherosclerosis [21–24]. This adhesion is mediated by specific adhesion molecules expressed on monocyte and EC surfaces [25, 26], and may play an important role in several biological functions, such as cytokine and gene induction [27–30]. However, little is known about whether cell-to-cell interaction of monocytes and ECs is able to induce the synthesis of PDGF. In the present study, we demonstrate that direct adhesion of monocytes to ECs induces PDGF synthesis in both types of cells.


   2 Methods
Top
 Abstract
 1 Introduction
 2 Methods
3 Results
 4 Discussion
 References
 
2.1 Reagents
PDGF enzyme-linked immunosorbent assay (ELISA) kit was purchased from Amersham International plc (Bucks, England). IL-1{alpha}, IL-1β, and TNF{alpha} ELISA kits were obtained from Otsuka Pharmaceutical Co., Ltd. (Tokushima, Japan). Monoclonal mouse anti-human PDGF-B was provided by Mochida Pharmaceutical Co., Ltd. (Tokyo, Japan). Human PDGF-A and -B cDNA probes were provided by Dr. I. Nagaoka (Juntendo University School of Medicine, Tokyo, Japan). A solution of type I collagen, extracted from porcine skin (Cellmatrix I-A), was purchased from Nitta Gelatin Co. (Osaka, Japan). Fetal bovine serum (FBS) and endothelial cell growth supplement (ECGS) were purchased from Equitech-Bio., Inc. (Ingram, Texas) and Collaborative Research (Bedford, MA), respectively. Bovine serum albumin (BSA) and insulin-transferrin sodium selenite media supplement were obtained from Sigma Chemical Co. (St. Louis, MO). N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES), gelatin, ethylenediamine tetraacetic acid (EDTA), and paraformaldehyde were obtained from Wako Pure Chemical Industries Ltd. (Osaka). Collagenase was obtained from Worthington Biochemical Co. (Freehold, NJ). Porcine heparin was purchased from Nakarai Chemical Co. (Osaka). Medium 199 (M-199), RPMI1640 and glutamine were obtained from ICN Biomedical Inc. (Costa Mesa, CA). Biotinylated rabbit anti-mouse IgG and streptavidin reagent (Histofin) were purchased from Dako Japan Co., Ltd. (Kyoto, Japan) and Nichirei Co. (Tokyo), respectively. Polyclonal Abs against IL-1{alpha}, IL-1β, TNF{alpha}, and IL-1 receptor antagonist (IL-1ra) were purchased from Pepro Tech Inc. (Rocky Hill, NJ). Monoclonal Ab (mAb) against E-selectin (BBIG–E4) was purchased from R&D Systems (Minneapolis, MN) [31]. MAbs against CD18 (7E4) and intercellular adhesion molecule-1 (ICAM-1; 84H10) were purchased from Immunotech (Westbrook, ME) [32, 33]. MAbs against very late antigen-4 (VLA-4: CD49d; P4G9) and vascular cell adhesion molecule-1 (VCAM-1; HAE-2Z) were purchased from Telios (San Diego, CA) and Genzyme (Cambridge, MA), respectively [34]. Collagen type I, soluble fibronectin, and laminin were purchased from Chemicon (Temecula, CA).

2.2 Human EC culture
ECs were harvested from human umbilical cord veins treated with 0.1% collagenase as described elsewhere [35], and grown on 5% gelatin-precoated 60 mm culture dishes in M-199, containing 20% heat-inactivated FBS, 1% penicillin/streptomycin (PS) solution, glutamine (2 mmol/l), HEPES (15 mmol/l), heparin (100 µg/ml), and ECGS (60 µg/ml) (EC medium). Cells between passages 2 and 4 were used.

2.3 Isolation of human monocytes
Mononuclear cells were prepared from heparinized venous blood of healthy adult donors as described previously [36, 37], using dextran sedimentation, centrifugation with Ficoll-Conray, and hypotonic lysis of contaminated erythrocytes. Monocytes were further purified from mononuclear cells by centrifugal elutriation with a Hitachi SRR6Y elutriation rotor (Hitachi Ltd, Tokyo) [37]. Mononuclear cell fractions contained 15% to 25% monocytes, 75% to 85% lymphocytes, and less than 1% neutrophils. Monocyte fractions contained more than 85–95% monocytes as determined by Wright-Giemsa staining of cytospin preparations. All of the fractions were resuspended in M-199 supplemented with 0.5% BSA, insulin (10 µg/ml), transferrin (10 µg/ml), 1% PS solution and 2 mmol/l glutamine (assay medium) as described previously [38].

2.4 Coculture and separate coculture of monocytes and ECs
EC monolayers cultured on gelatin-coated 48-multiwell plates (Corning; Cambridge, MA) in 200 µl EC medium were washed twice with assay medium. Monocytes were directly added to EC monolayers in 200 µl assay medium, incubated at 37°C in a 5% CO2 humidified incubator for the required periods, and the media were collected, centrifuged (10 min, 1500 g) to remove cell debris and stored at –70°C.

To determine whether the monocyte-EC-induced increase in PDGF production was mediated by cell-to-cell contact or by soluble factors produced by those cells, inner wells (cell culture insert, catalogue No. 3495, Falcon) were used to divide each well of a 24-well multiwell plates into two compartments [30]. ECs were cultured on the gelatin-coated lower compartment, grown to confluence (1.2x105 cells), washed twice with assay medium, and incubated in 850 µl of assay medium. Monocyte suspensions containing 1.2x105 cells in 150 µl of assay medium were added to the upper compartment of the inner well. After 18 h of incubation at 37°C, the media were collected and stored at –70°C.

2.5 ELISA determination of PDGF
PDGF concentrations in conditioned medium were determined by ELISA according to the manufacture's instructions. This PDGF assay kit cross-reacts with human PDGF-AB (100%), PDGF-AA (10%), and PDGF-BB (2%). The lower level of the detection for PDGF-AB was 8.4 pg/ml.

2.6 Northern blot analysis
Total RNA was prepared by the guanidine isothiocyanate-cesium chloride method. Equal amounts of total RNA (20 µg) were size-fractionated by electrophoresis on denaturing 1.0% agarose/formaldehyde gels and transferred to nylon membranes (Hybond N+, Amersham). Hybridizations were performed with excess of Formula -deoxycytidine-5'-triphosphate (dCTP)-labeled human PDGF-A and -B cDNA probes (specific activity>1x108 cpm/µg DNA) at 65°C for 24 h. The PDGF-A probe consisted of a 1.3 kb EcoRI/EcoRI restriction fragment [39]. The PDGF-B probe consisted of a 0.9 kb EcoRI/BamHI restriction fragment [39]. At the end of hybridization, the filters were washed twice in 0.2xSSC at 60°C (1xSSC contains 0.15 mol/l NaCl, 0.015 mol/l sodium citrate, pH 7.0), then exposed to Kodak XAR-5 film overnight at –70°C with one intensifying screen.

2.7 Immunohistochemistry
Monocytes (1.5x105 cells) or IL-1β (25 U/ml) were added to the confluent EC layers on coverslips in eight-well culture plates (Lab-Tek chamber slide; Nunc, IN). After incubation at 37°C for 18 h, the ECs were rinsed with serum-free M-199 and fixed with 4% paraformaldehyde in PBS for 10 min at room temperature. Prior to staining, the slides were again fixed for 20 min in 0.3% H2O2 in methanol and rinsed in 0.1% Triton X-100/PBS, and nonspecific binding sites were blocked with mouse IgG. The slides were rinsed in 0.1% Triton X-100/PBS followed by the addition of PDGF-B Ab (5 µg/ml). After incubation at 4°C for 12 h, the slides were rinsed again in PBS, overlaid with biotinylated mouse anti-sheep IgG, incubated for 60 min at 37°C, and rinsed in PBS. The slides were treated with streptavidin reagent (Histofin) for 30 min at room temperature, rinsed in PBS, overlaid with a solution of 0.05% 3,3,'-diaminobenzidine tetrahydrochloride in 0.05 mol/l Tris-HCl buffer (pH 7.6) and 0.01% H2O2 for 5 min at room temperature to allow color development, and rinsed with distilled water. Mayer's hematoxylin was used as a counterstain.

2.8 Statistical analysis
Data are expressed as means±SE of three samples, which represented at least three separate experiments. Differences were analyzed by one-way ANOVA combined with Scheffe's test, and values of P<0.05 were considered to be statistically significant.


   3 Results
Top
 Abstract
 1 Introduction
 2 Methods
 3 Results
4 Discussion
 References
 
3.1 Production of PDGF by coculture of monocytes with ECs
We first examined the induction of PDGF synthesis by coculture of monocytes with ECs at the protein level. Coculture of monocytes (6.0x104 cells) with ECs (6.0x104 cells) induced the secretion of a large amount of PDGF into culture supernatants in a time-dependent manner (Fig. 1). A lesser amount of PDGF was secreted into culture supernatants from ECs or monocytes alone.


Figure 1
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  		Fig. 1 Production of PDGF upon coculture of monocytes with ECs. ECs (6.0x104 cells) were cocultured with monocytes (Mo; 6.0x104 cells) for the indicated periods. PDGF concentration in the supernatant was measured by an ELISA method. Open circles; ECs alone, closed circles; coculture of monocytes with ECs, open squares; monocytes alone. Values represent means±SE of three samples.

 
Fig. 2 shows PDGF secretion upon coculture of monocytes with ECs, in which different numbers of monocytes were added to a constant number of ECs. Significant secretion of PDGF was detected at a monocyte/EC numerical ratio of 0.5. The secretion of PDGF was further increased by increasing the number of added monocytes up to a ratio of 5.


Figure 2
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  		Fig. 2 Effects of increasing number of monocytes on PDGF production upon coculture of monocytes with ECs. Different numbers of monocytes (0.3–6.0x105 cells) were added to a constant number of ECs (6.0x104 cells). The numerical ratios of monocytes/ECs were 0, 0.05, 0.5, 1, 5 and 10. After coculture for 18 h, PDGF concentration in the supernatant was measured by an ELISA method. Values represent means±SE of three samples. *p<.05 compared with ECs without monocytes.

 
3.2 PDGF production upon separate coculture
We then analyzed the possible mechanism underlying the expression of PDGF induced by coculture of monocytes with ECs. To determine whether PDGF production by the coculture is mediated by direct cell-to-cell contact, we performed a separate coculture assay using an inner well system that physically separated monocytes on the upper compartment from the underlying EC layer on the lower compartment while allowing free diffusion of soluble mediators. As shown in Fig. 3, PDGF secretion into the lower compartment by coculture of monocytes with ECs was substantially greater than that induced by separate coculture of monocytes with ECs, suggesting that direct adhesion between monocytes and ECs is essential for PDGF production.


Figure 3
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  		Fig. 3 Production of PDGF upon coculture and separate coculture of monocytes with ECs. Confluent ECs (1.2x105 cells) cultured on the lower compartment of the inner well system were coincubated for 18 h with monocytes (1.2x105 cells) added to the upper or lower compartment. PDGF concentration in the lower compartment was measured by an ELISA method. ECs; ECs alone were in the lower compartment, Coculture; ECs and monocytes were in the lower compartment, Separate coculture; ECs were in the lower compartment and monocytes were in the upper compartment, Mo; monocytes alone were in the upper compartment. Values represent means±SE of three samples. *p<.0001.

 
3.3 Induction of PDGF mRNA expression by coculture of monocytes with ECs
The PDGF ELISA kit used in the present experiments detected mainly PDGF-AB, which is a heterodimer of PDGF-A and -B. We then examined the expression of PDGF-A and -B mRNA by coculture of monocytes with ECs. As shown in Fig. 4, unstimulated ECs expressed low levels of PDGF-A and -B mRNA, while coculture of monocytes with ECs induced substantial amounts of their accumulation at 6–12 h.


Figure 4
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  		Fig. 4 Time course of induction of PDGF-A and PDGF-B mRNA expression upon coculture of monocytes with ECs. ECs (1.2x106 cells) were cocultured with monocytes (1.2x106 cells) for 0, 2, 6 and 12 h. 20 µg of total RNA was size-fractionated by electrophoresis and transferred to nylon membranes. Membranes were directly visualized by UV transillumination and then hybridized with Figure 4-labeled human PDGF-A and -B cDNA probes.

 
3.4 Immunohistochemical staining of PDGF producing cells
We next clarified the cells producing PDGF in the coculture system by immunohistochemical staining. As shown in Fig. 5, PDGF-B protein was not clearly immunolocalized in unstimulated ECs, whereas it was clearly detected in ECs stimulated with IL-1β (10 ng/ml) for 18 h (positive control). In the coculture system, both ECs and monocytes were stained with anti-PDGF-B Abs.


Figure 5
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  		Fig. 5 Immunohistochemical staining of monocytes and ECs with PDGF-B Ab. After ECs were cultured for 18 h with IL-1β (10 ng/ml) or monocytes, immunohistochemistry was performed using anti-PDGF-B or control IgG. (Top left panel) unstimulated ECs, (top right panel) IL-1β-stimulated ECs (positive control), (bottom left panel) ECs and adherent monocytes, (bottom right panel) ECs and adherent monocytes with control IgG (negative control) (x200).

 
3.5 Involvement of matrix proteins in PDGF production
Recently, it has been shown that IL-8 and monocyte chemoattractant protein-1 (MCP-1) production by monocyte-EC interaction are mediated via the matrix protein binding mechanism [40]. To investigate the involvement of this pathway in PDGF production, matrix proteins, soluble collagen, fibronectin and laminin, were added to the coculture system to block the cellular interaction. However, no significant inhibition of PDGF production was observed with these matrix proteins (Fig. 6).


Figure 6
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  		Fig. 6 Effects of soluble matrix proteins on PDGF production upon coculture of monocytes with ECs. Monocytes (6.0x104 cells) were preincubated with soluble collagen (30 µg/ml), fibronectin (30 µg/ml), or laminin (30 µg/ml) for 30 min at 37°C, and then cocultured with ECs (6.0x104 cells) for 18 h. PDGF concentration in the supernatant was measured by an ELISA method. The control values were taken as 100% control, which represents 1040±102.6 pg/ml. Values represent means±SE of three samples.

 
3.6 Involvement of cytokines in PDGF production upon coculture
PDGF is produced by ECs exposed to proinflammatory cytokines such as IL-1{alpha}, IL-1β and TNF{alpha}. Since the coculture of monocytes and ECs secreted substantial amounts of IL-1{alpha}, IL-1β and TNF{alpha} in our assay system (IL-1{alpha}; 85.00±3.61 pg/ml, IL-1β; 1634.00±491.51 pg/ml, and TNF{alpha}; 317.00±121.33 pg/ml at 6 h), it is possible that the production of PDGF by the coculture was mediated by these soluble factors. As shown in Fig. 7, conditioned medium from the coculture of monocytes with ECs induced PDGF production by unstimulated ECs. We then examined the effect of neutralizing Abs against IL-1{alpha}, IL-1β, TNF{alpha} and IL-1ra on PDGF production. In comparison with the use of control Ab (rabbit IgG), PDGF production by coculture-conditioned medium was significantly inhibited in the presence of Abs against IL-1β, TNF{alpha} or IL-1ra. Furthermore, when the Abs were used in combination (anti-IL-1{alpha}, anti-IL-1β plus anti-TNF{alpha}, or anti-TNF{alpha} plus IL-1ra), PDGF production was completely inhibited. However, these antibodies could not significantly inhibit PDGF production by the coculture when they were added to EC culture media before the addition of monocytes (data not shown).


Figure 7
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  		Fig. 7 The inhibitory effect of antibodies against cytokines on PDGF induction. ECs (3.6x106 cells) were cocultured with monocytes (3.6x106 cells) for 6 h. The conditioned medium (CM) from the coculture system was preincubated with anti-IL-1{alpha} Ab (50 µg/ml), anti-IL-1β Ab (50 µg/ml), anti-TNF{alpha} Ab (50 µg/ml), IL-1ra (200 ng/ml), anti-IL-1{alpha} Ab plus anti-IL-1β Ab plus anti-TNF{alpha} Ab, anti-TNF{alpha} Ab plus IL-1ra, or control rabbit IgG (50 µg/ml) for 1 h at 37°C and incubated with ECs for 18 h. PDGF concentration in the supernatant was measured by an ELISA method. Each PDGF concentration after 18 h incubation was calculated by subtracting that of added 6 h conditioned medium. EC-CM; EC conditioned medium, CO-CM; coculture conditioned medium. Values represent means±SE of three samples. *p<.0001 compared with ECs treated with control rabbit IgG.

 

   4 Discussion
Top
 Abstract
 1 Introduction
 2 Methods
 3 Results
 4 Discussion
References
 
The adhesion of monocytes to the endothelium during the early stages of atherogenesis has been observed in several animal model systems [41, 42]. In addition, immunohistochemical analyses of human necropsy and carotid endoarterectomy specimens have demonstrated a similar involvement of monocytes in the early stages of atherogenesis [43, 44], indicating that adhesion of monocytes to the endothelium is an initial step in the development of atherosclerosis. We demonstrated here that PDGF, the major mitogen and chemoattractant for vascular smooth muscle cells, was expressed in both monocytes and ECs at the mRNA and protein levels as a result of their direct adhesive interaction.

Although the molecular mechanisms underlying adhesive interaction between monocytes and ECs is unclear, recent studies have shown that the direct adhesive interaction of cells would be regulated by various adhesion molecules on the surfaces of both interacting cells [45]. Recently, Lukacs et al. [46]reported that ICAM-1 mediated the expression of macrophage inflammatory protein-1 (MIP-1{alpha}) during monocyte-EC interaction. Huh et al. [47]and Lo et al. [48]demonstrated that adhesion of monocytes to TNF{alpha}-activated ECs via E-selectin was involved in the induction of CD36 and tissue factor on monocytes. In the present study, when Abs were used in the following combination; anti-E-selectin, anti-CD18, anti-VLA-4, anti-ICAM-1 and anti-VCAM-1, approximately 30% inhibition of monocyte adhesion was observed (data not shown). However, mAbs against these molecules did not inhibit, but rather increased, PDGF production resulting from monocyte-EC interaction. Although the reason for this discrepancy is unknown, partial inhibition of monocyte adhesion might not be enough to inhibit PDGF production. Another possibility is that PDGF production resulting from monocyte-EC adhesive interaction might be mediated by other, as yet unknown, adhesion molecules [22, 49]. In this regard, a novel monocyte-EC adhesion molecule recognized by mAb IG9 has been recently reported by Calderon et al. [50].

Additional interactions between monocytes with ECs include the binding via matrix proteins as well as other specific receptor-ligand interaction [51, 52]. Albelda et al. [53]reported that the production of IL-8 and MCP-1 by monocyte-EC adhesion was dependent on the interaction of monocytes with matrix proteins, possibly via β-integrins. Lukacs et al. [41]also demonstrated that IL-8 and MCP-1 production were increased during monocyte-EC interaction in part due to the matrix protein binding mechanism. However, in this study, we found that addition of matrix proteins had no effect on PDGF production by the coculture, and that mAbs against β1-integrins and GLY-ARG-GLY-ASP-SER-PRO peptide did not to inhibit PDGF production resulting from monocyte-EC interaction (data not shown).

It has been shown that proinflammatory cytokines such as IL-1 and TNF{alpha} stimulate PDGF production [10–18], and we found that substantial amounts of IL-1β and TNF{alpha} were produced upon coculture of monocytes with ECs. In this study, conditioned medium from the coculture had an effect on PDGF production by other cultured ECs. The blocking study using neutralizing Abs against IL-1β and TNF{alpha} revealed a significant inhibition of PDGF producing activity of coculture-conditioned medium, suggesting that these cytokines are at least partially involved in PDGF production induced by the cell-to-cell interaction. However, direct addition of IL-1β and TNF{alpha} Abs did not significantly abrogate the increase in PDGF production by the coculture, thus these cytokines can not explain all of the induction of PDGF.

Increased expression of PDGF gene is detected in human atherosclerotic arteries. Immunohistochemical and in situ hybridization analyses by Ross et al. [1, 20]indicated that smooth muscle cells were the main site of PDGF-A mRNA and macrophages were the major site of PDGF-B mRNA in atherosclerotic lesions. In situ hybridization studies by Wilcox et al. [19]showed that PDGF-A mRNA was associated with plaque mesenchymal cells (presumably of smooth muscle origin), whereas PDGF-B mRNA was associated with ECs of the plaque vasa vasorum. Monocytes tend to accumulate underneath EC monolayers for prolonged periods during the development of atherosclerotic lesions [17]. The consensus view is therefore emerging that during development of atherosclerotic lesions, monocytes and ECs release PDGF through their adhesive interaction, which acts as a chemoattractant for medial smooth muscle cells migrating into the intima and stimulates their proliferation. PDGF is also required for smooth muscle cell accumulation during restenosis after arterial balloon angioplasty [54, 55].

In conclusion, the present study indicates that the direct adhesion of monocytes to ECs induces PDGF synthesis in both types of cells, suggesting that PDGF produced locally by monocyte-EC adhesive interaction plays an important role in the pathogenesis of atherosclerosis and restenosis after angioplasty by promoting the migration and accumulation of vascular smooth muscle cells.

Time for primary review 24 days.


   Acknowledgements
 
We thank Ms. Toshiko Kambe and Taeko Inageta for their technical assistance. This study was supported by the Ministry of Education, Science, Sports and Culture, Japan (No. 5670632) and Mitsukoshi Grant-in-Aid 1996.


   References
Top
 Abstract
 1 Introduction
 2 Methods
 3 Results
 4 Discussion
 References
 

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H. Loppnow, K. Werdan, and M. Buerke
Invited review: Vascular cells contribute to atherosclerosis by cytokine- and innate-immunity-related inflammatory mechanisms
Innate Immunity, April 1, 2008; 14(2): 63 - 87.
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