© 2000 American Heart Association, Inc.
Vascular Biology |
Adhesion of Monocyte Very Late Antigen-4 to Endothelial Vascular Cell Adhesion Molecule-1 Induces Interleukin-1ß–Dependent Expression of Interleukin-6 in Endothelial Cells
From the 1. Medizinische Klinik and Deutsches Herzzentrum and Institut für Klinische Chemie und Pathobiochemie (K.B.), Technische Universität München, Germany.
Correspondence to Dietlind Zohlnhöfer, MD, Deutsches Herzzentrum und 1. Medizinische Klinik der Technischen Universität München, Lazarettstraße 36, D-80636 München, Germany. E-mail dietlind.zohlnhoefer{at}micromet.de
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Abstract |
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Abstract—In atheroma, T cell–derived interferon-
(INF-) stimulates
endothelial cells and facilitates recruitment of
monocytes. We investigated potential mechanisms by which these
interactions could contribute to local and systemic inflammatory
responses. Specifically, we analyzed the expression of
interleukin (IL)-1ß and IL-6 in both cell types after coculture, the
relevant adhesion molecules in this interaction, and transcriptional
control by NF-
B. We studied coculture of purified
peripheral blood monocytes with human umbilical vein
endothelial cells (HUVECs), which were stimulated with
INF- (106 U/L) to model the activated
endothelium of atherosclerotic lesions. Coculture of
monocytes with activated HUVECs resulted in release of IL-1ß
(40.6±3 pg/24 h, P=0.002) and IL-6 (46.6±7 ng/24 h,
P=0.0015). Electrophoretic mobility gel shift assay and
Northern blotting in each cell type separately revealed NF-B
activation in both cell types, IL-1ß mRNA expression predominantly in
monocytes, and IL-6 mRNA expression predominantly in HUVECs. The
endothelial IL-6 release was IL-1–dependent, because
it was suppressed by IL-1 receptor antagonist. Experiments
with blocking antibodies demonstrated that binding of monocyte very
late antigen-4 (VLA-4) to endothelial vascular cell
adhesion molecule-1 (VCAM-1) was necessary for the induction of IL-1ß
in monocytes. Binding of monocyte VLA-4 to endothelial
VCAM-1 induces NF-B activation in both cell types with expression
and release of IL-1ß by monocytes, which in turn stimulates
endothelial release of IL-6. The
ß1-integrin–mediated expression of IL-1ß and IL-6
could contribute to local and systemic inflammatory reactions in
atherosclerosis.
Key Words: monocyte • endothelial cell • ß1-integrin • interleukin-1ß • interleukin-6
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Introduction |
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Atherosclerosis is an inflammatory disease with both local vascular and systemic components.1 2 3 4 5 Systemic inflammatory responses in atherosclerosis carry an increased risk of ischemic complications, as indicated by several lines of evidence. The plasma level of C-reactive protein, the central inflammatory marker protein, is an independent predictor of the risk of major cardiac events in patients with unstable angina as well as in apparently healthy men.4 5 6 7 Likewise, leukocyte counts are important determinants of the risk of acute myocardial infarction and its recurrence.8 Moreover, fibrinogen, which is upregulated in inflammation, is an established cardiovascular risk factor.9 10 Clarification of the underlying mechanisms for systemic inflammatory responses may thus have important therapeutic implications.
Most of the systemic inflammatory responses in atherosclerosis can be explained by an action of interleukin (IL)-6. IL-6 is the main inducer of the hepatic synthesis of C-reactive protein, fibrinogen, and other acute-phase proteins and cooperates with various hemopoietic cytokines in elevating leukocyte and platelet counts.11 12 13 14 Several studies found increased concentrations of IL-6 in the peripheral blood of patients with advanced stages of atherosclerotic disease.15 16 17 IL-6 has also been recovered from atheroma.3 It is therefore generally believed that the systemic inflammatory responses in atherosclerosis are largely regulated by IL-6 released from plaques.
According to the response-to-injury hypothesis,
ß1- and
ß2-integrin–mediated recruitment of monocytes
and T cells to the subendothelial space sets the stage
for a variety of inflammatory interactions between blood cells and
vascular cells.2 18 19 20 Analysis of the
cytokine contents of atherosclerotic lesions suggests IL-1,
tumor necrosis factor-
, and interferon (INF)- as the key
mediators in this setting.1 The mechanisms for expression
and release of IL-6 in atheroma, however, are still
incompletely understood. Recently, Lukacs et al21 showed
that adhesion of monocytes to INF-–stimulated
endothelial cells induced expression of chemokines,
such as monocyte chemoattractant protein-1 (MCP-1) and IL-8. We
speculated that adhesion of monocytes to INF-–stimulated
endothelial cells could also induce expression of IL-6.
Such interactions could play an important role in atheroma,
because activated T lymphocytes within the lesion secrete large
amounts of INF-.2 3
To gain further insight into potential mechanisms that regulate IL-6 in
atherosclerosis, we studied the interaction of
monocytes with INF-–stimulated endothelial cells.
Specifically, we investigated the expression of IL-1ß and IL-6 in
both cell types after coculture, the role of selectin- or
integrin-supported adhesion in this interaction, and transcriptional
control by nuclear factor (NF)-B.
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Methods |
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Cell Isolation
Peripheral blood was drawn from healthy volunteers, and the mononuclear cell fraction was prepared by Ficoll-Hypaque gradient technique (Pharmacia).22 Neutrophil contamination was consistently <5%. To obtain purified peripheral blood monocytes, we performed an additional gradient centrifugation with Percoll (Pharmacia). The purity of monocytes was >85%, with >95% viable cells (trypan blue exclusion).23
Endothelial Cells
Primary human umbilical vein endothelial cells
(HUVECs) were harvested by collagenase (Worthington)
digestion as described.24 Cells were grown in 6-well
culture plates (NUNC) in endothelial cell growth medium
(modified MCBD 131 media, Boehringer Ingelheim) and were used
as confluent monolayers after 1 to 2 passages. ECV-304, an immortal
human endothelial cell line (American Type Culture
Collection, ATCC), was cultured in complete medium 199 (Sigma)
containing 10% FCS, 2 mmol/L glutamine, 100 U/L penicillin, and
100 mg/L streptomycin.
To obtain preactivated endothelial cells, we
incubated confluent monolayers for 16 hours with human recombinant
INF- at a concentration of 106 U/L (Pepro
Tech). Thereafter, INF- was removed by 3 gentle washes with 1 mL
prewarmed culture medium. The wash medium was carefully and completely
removed after each wash. INF- increased the surface expression of
intercellular adhesion molecule (ICAM)-1 by 273±15% on HUVECs and by
331±75% on ECV-304, whereas endothelial surface
expression of E-selectin or vascular cell adhesion molecule (VCAM)-1
was not altered significantly.
Coculture of Monocytes and HUVECs
Coculture experiments were performed in culture medium in the
presence of 1 mmol/L CaCl2 and 10 g/L
polymyxine (Sigma) with or without IL-1–receptor
antagonist (RA) at 100 g/L. We added 1 mL of suspension of
washed mononuclear cells or purified monocytes containing
5x106 or 1x106 cells,
respectively, to confluent monolayers of nonstimulated or
INF-–stimulated endothelial cells grown on 6-well
plates. Cocultures in transwell chambers (Costar, pore size
0.4 µm) served as controls. Culture supernatants were collected
at the times indicated and assayed for IL-1ß and IL-6 by ELISA
(Biermann) with detection limits of 3.9 ng/L for IL-1ß and 30 ng/L
for IL-6.
In some experiments, endothelial cells had been
preincubated for 1 hour with blocking anti–ICAM-1 monoclonal
antibodies (mAbs) (clone 84H10: reacts with extracellular part and
blocks adhesion; Immunotech), blocking anti–VCAM-1 mAbs (clone
BBJG-V1, blocks adhesion, R&D Systems, and clone 1G11, blocks adhesion,
Immunotech) at 5 mg/L, blocking anti–E-selectin mAbs (clone 1.2B6,
blocks adhesion, Immunotech), anti–L-selectin mAbs (clone Dreg 56,
blocks L-selectin–mediated binding, Immunotech) at 5 mg/L, or
anti–P-selectin mAbs (G1, blocks P-selectin–mediated adhesion,
Centocor) at 10 mg/L. In other experiments, purified monocytes had been
preincubated with blocking anti–4-integrin
mAbs (clone 2B4, blocks very late antigen [VLA]-4–dependent adhesion
of monocytes to VCAM-1, R&D Systems),
anti–ß1-integrin mAbs (clone Lia1/2, blocks
adhesion, Immunotech), or anti–CD 11b mAbs (clone 44; recognizes the
M-chain of Mac-1 and blocks adhesion, Cymbus Biotechnology) at 5
mg/L.
To eliminate endotoxin contamination, all crystalloid solutions were ultrafiltered (U2000, Gambro), and stock solutions of proteins were decontaminated by polymyxin columns (Pierce). In addition, we assayed potential endotoxin contamination of all cell suspensions at the end of each experiment by chromogenic limulus amoebocyte lysate assay (Schulz).
Flow Cytometry
Immunofluorescence staining and flow
cytometry were performed as described previously.15 In
brief, HUVECs were harvested and resuspended in fresh medium, and 40
µL of cell suspension was incubated with saturating concentrations of
FITC–conjugated anti–VCAM-1 mAbs (Immunotech), FITC-conjugated
anti–ICAM-1 mAbs (Immunotech), or FITC-conjugated anti–E-selectin
mAbs (Immunotech) for 30 minutes at 4°C. Cell suspension was washed 3
times and stored in 1% paraformaldehyde at 4°C until
flow cytometry analysis was performed within 12 hours.
RNA Preparation, Northern Blot Analysis, and
Electrophoretic Mobility Shift Assay
After coculture of ECV-304 and mononuclear cells for the times
indicated, mRNA and nuclear extracts were analyzed in each cell
type separately. To harvest the adherent mononuclear cells, we washed
the wells twice with ice-cold 0.02% EDTA/PBS, pH 7.4, for 3 minutes.
ECV-304 contamination in this cell fraction was <1%. Monocyte
contamination in the endothelial fraction was also
negligible, as shown by light microscopy. Likewise, we were unable to
detect mRNA expression of the monocyte-specific
ß2-integrin chain in the
endothelial cell fraction, whereas a strong signal was
found in the monocyte fraction.
As a positive control for Northern blot analysis, mononuclear cells were stimulated with lipopolysaccharide (0.1 mg/L) for 2 hours. Total RNA of 107 ECV-304 cells or 2.5x107 mononuclear cells was isolated with the RNeasy Mini Kit (Qiagen GmbH) and analyzed by Northern blotting as described previously.25 Briefly, 5 µg of total RNA of each sample was subjected to electrophoresis on a 1.2% agarose gel containing 100 mmol/L MOPS (Boehringer), 40 mmol/L sodium acetate (Boehringer), 5 mmol/L EDTA, and 6% formaldehyde (Boehringer). The RNA was transferred to nylon membrane (Hybond-N, Amersham) in 20x SSC (Merck) by capillary blotting overnight. Blots were baked and prehybridized at 42°C in 50% formamide (Merck), 5x Denhardt’s solution, 5x SSC, 0.5% SDS (Merck), and 20 mmol/L salmon sperm DNA (Gibco BRL). Blots were probed with the 1.06-kb PstI fragment of IL-1ß pBR322 (ATCC), the 1.0-kb EcoR1 fragment of IL-6 p91023(B) (ATCC), and the 0.6-kb EcoR1 fragment of ß2-integrin pGemTeasy (kindly provided by P. Baeuerle, Micromet) to assess contamination of the endothelial cell fraction with adherent or transmigrated monocytes and reprobed with the 1.3-kb PstI–Xba fragment of pUC19-GAPDH to ensure integrity of total RNA and comparable RNA loading in each lane.
The cDNA probes were radiolabeled by random priming with
[-P32]dCTP (>6000 Ci/mmol)
(Amersham). The blots were washed at 60°C in 1% SDS/2x SSC and
autoradiographed with Kodak X-omat film at -70°C with an
intensifying screen.
Nuclear extracts from 10x106 ECV-304
cells and 10x107 mononuclear cells per
sample were prepared and analyzed for NF-B and SP-1 binding
as described previously.26 27 The B consensus
oligonucleotide (5'-CAGAGGGACTTTCCGAGA-3') was used as
a probe and labeled by annealing of complementary primers followed by
primer extension with the Klenow fragment of DNA polymerase I
(Boehringer) in the presence of
[-32P]dCTP (>3000 Ci/mmol; DuPont) and
deoxynucleoside triphosphates (Boehringer). Nuclear extracts (5
µg protein) were incubated with radiolabeled DNA probes (10 ng;
105 cpm) for 30 minutes at room temperature in 20
µL of binding buffer [20 mmol/L HEPES, pH 7.9, 50 mmol/L
KCl, 1 mmol/L dithiothreitol, 0.5 mmol/L EDTA, 10% glycerol,
1 g/L BSA, 0.2% NP-40, 50 ng of poly(dI-dC)/µL]. Samples were run
in 0.25x TBE buffer (10x: 890 mmol/L Tris, 890 mmol/L boric
acid, 20 mmol/L EDTA, pH 8.0) on nondenaturing 4%
polyacrylamide gels. To control the nuclear protein content,
nuclear extracts were incubated with a
[-32P]ATP-labeled (>5000 Ci/mmol, DuPont)
Sp-1 oligonucleotide. Gels were dried and
analyzed by autoradiography.
Statistical Analysis
Results of the experimental studies are reported as mean±SEM,
unless otherwise indicated. For paired comparisons, we used the paired
t test, and differences between 
3 variables were
analyzed by ANOVA with the general linear model (SPSS version
8.0). A value of P<0.05 in the 2-tailed test was regarded
as significant.
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Results |
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Release of IL-6 and IL-1ß and Endothelial Surface Expression of VCAM-1 After Coculture of Endothelial Cells and Monocytes
Coculture of purified monocytes with INF-
–stimulated HUVECs
for 24 hours resulted in a time-dependent release of IL-1ß and IL-6
protein into the supernatant (Figure 1
).
After coculture with resting HUVECs, the release of IL-6 and IL-1ß
protein was significantly less, achieving only 20% or 34% of that
obtained with INF-–stimulated HUVECs, respectively (Figures 1 and 2). Resting and
INF-–activated HUVECs did not release detectable amounts of
IL-6 or IL-1ß when incubated alone. Likewise, monocytes incubated
alone did not liberate detectable amounts of IL-6 protein, and their
basal IL-1ß release was just above the detection limit (4.65±0.85
pg/24 hours).
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When resting or INF-–stimulated HUVECs and monocytes were placed in
different compartments of transwell chambers, the release of
IL-1ß and IL-6 was reduced to the expression level obtained after
interaction of monocytes with resting HUVECs (Figure 2
).
Likewise, the increase in IL-6 release after binding of monocytes to
INF-–stimulated HUVECs was completely abolished in the presence of
IL-1RA (Figure 2). IL-1RA, however, had no effect on the IL-1ß
release.
As with IL-6, coculture of monocytes with INF-–stimulated HUVECs
induced an upregulation of endothelial VCAM-1 surface
expression to 300±17% of the VCAM-1 expression on resting HUVECs
incubated with monocytes (P=0.02). Addition of IL-1RA
significantly (P=0.048) suppressed VCAM-1 surface expression
after coculture of monocytes with INF-–stimulated HUVECs to
123±18% of the level achieved with resting HUVECs. A small,
insignificant upregulation in VCAM-1 surface expression was found on
resting HUVECs after coculture with monocytes.
Blocking mAbs against endothelial VCAM-1 or either the
4- or ß1-subunit of
monocyte VLA-4 abolished the increase in IL-6 and IL-1ß protein
release by coculture of monocytes and activated HUVECs, while
blocking ICAM-1 mAbs had no such effect (Figure 3). Similarly, blocking mAbs against
E-selectin, P-selectin, or L-selectin given alone or in combination had
no inhibitory effect on IL-1ß and IL-6 release in our
model (data not shown).
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P<0.01 vs experiments in
the absence of mAbs.
Expression of IL-1ß mRNA and IL-6 mRNA and NF-B Activation
After Coculture
We investigated the cellular source of cytokines by
analyzing mRNA expression in each cell type separately. To facilitate
the recovery of large enough amounts of mRNA, we used mononuclear cells
and ECV-304 cells in these experiments. The pattern of IL-1ß and IL-6
protein expression after coculture of mononuclear cells with ECV-304
cells was similar to that after coculture of monocytes and HUVECs
(Table).
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Coculture of mononuclear cells with INF-–stimulated ECV-304 cells
substantially increased IL-1ß mRNA in mononuclear cells, reaching a
maximum after 2 hours, and IL-6 mRNA in ECV-304 cells, with a maximum
after 6 hours (Figure 4). Both IL-1ß
mRNA expression in mononuclear cells and IL-6 mRNA expression in
ECV-304 cells were markedly less pronounced when resting ECV-304 cells
had been used for the experiment. IL-1ß or IL-6 transcripts were not
detectable in isolated mononuclear cells or isolated ECV-304 cells,
with or without stimulation with INF-. After stimulation with
lipopolysaccharide for 2 hours, mononuclear cells expressed
both IL-1ß and IL-6 mRNA (data not shown).
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In mononuclear cells, coculture with INF-–stimulated ECV-304 cells
induced substantial NF-B activation (Figure 5); a weak NF-B activation was also
found after coculture with resting ECV-304 cells. We also found NF-B
activation in resting and INF-–stimulated ECV-304 cells after
adhesion of mononuclear cells. In pure mononuclear cells and in pure
nonstimulated or INF-–stimulated ECV-304 cells, no NF-B
activation was detectable.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Our study sought to investigate cellular mechanisms that could link local vascular to systemic inflammatory responses in atherosclerosis. Because the atheromatous inflammatory reaction is characterized by recruitment of monocytes and T lymphocytes to the vessel wall,2 we focused on interactions of monocytes with endothelial cells after activation by T cell–derived INF-
. Our major findings (Figure 6)
are as follows. (1) Adhesion of monocytes to activated
endothelial cells induces NF-B activation in both
cell types, predominantly monocyte-derived release of IL-1ß,
predominantly endothelium-derived release of IL-6, and
upregulation of VCAM-1 on the endothelial surface. (2)
The endothelial responses, IL-6 release, and
upregulation of VCAM-1 surface expression are IL-1–dependent. (3)
Binding of monocyte VLA-4 by endothelial VCAM-1 is
needed for the induction of IL-1ß in monocytes.
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IL-1ß and IL-6 Release by Coculture of Monocytes and
Activated HUVECs
As a model for the activated endothelium
in atherosclerosis, we used INF-–stimulated HUVECs.
The phenotypic changes in our INF-–stimulated HUVECs were similar
to those observed in the endothelium adjacent to
subendothelial infiltrates of T lymphocytes and
macrophages in atheromatous
plaques.18 T lymphocytes are known to secrete INF- at
the site of the atherosclerotic plaque.1 2 3 This induces
upregulation of the adhesion molecule ICAM-1 on the
endothelial surface28 29 and leads to
endothelial expression of such leukotactic agents as
IL-8 and MCP-1.21 This effect is mediated by Janus
kinase–dependent activation of signal transducer and
activator of transcription (JAK-STAT) transcription
factors.30 INF- itself, however, does not induce the
NF-B–dependent pattern of immediate-early gene expression, as shown
by others and by our study.30 31
Consistent with the fact that resting monocytes barely interact with resting endothelial cells,32 we found substantial release of IL-1ß and IL-6 only after coculture of monocytes with activated HUVECs. Likewise, prevention of adhesion by transwell chambers reduced cytokine production by adhesion of monocytes to activated HUVECs to the low level achieved by coculture with resting HUVECs. These findings demonstrate a central role of direct cellular interactions of monocytes with activated endothelium in the induction of IL-1ß and IL-6 expression.
Analysis of mRNA for IL-1ß and IL-6 in each cell type separately revealed monocytes as the major source for IL-1ß and endothelial cells as the predominant source for IL-6. The release of IL-1ß preceded the release of IL-6. Because it is known that IL-1ß can induce expression of IL-6 and VCAM-1 in endothelial cells,33 34 we analyzed the role of IL-1ß in the induction of the endothelial responses. IL-1RA almost completely inhibited endothelial VCAM-1 expression and IL-6 release induced by coculture of monocytes with activated HUVECs. These endothelial responses can thus be interpreted as an effect of monocyte-derived IL-1ß. IL-1RA, however, did not suppress IL-1ß release, suggesting that there was no autocrine effect.
As suggested by recent studies, integrin signaling may account for adhesion-induced inflammatory responses.21 22 35 36 37 We therefore investigated the role of integrin-mediated cell interactions in our experimental setup. Our finding suggests a key role of binding of monocyte VLA-4 to endothelial VCAM-1. Blocking mAbs against either subunit of VLA-4 on monocytes or against its endothelial counter-receptor VCAM-1 abolished the adhesion-induced IL-1ß release in monocytes as well as the resultant IL-6 release in endothelial cells. Conversely, blocking mAbs against ICAM-1 or selectins had no such effect. Thus, selectin-supported adhesion or ß2-integrin binding by ICAM-1 is not sufficient for the observed effects.
Our study shows that adhesion of mononuclear cells to
endothelial cells induces activation and nuclear
translocation of NF-B in both cell types. It is known that NF-B
activation is a critical element in the regulation of both IL-1ß and
IL-6.31 38 39 Our finding on NF-B activation is
consistent with a recent study showing that cross-linking of
VLA-4 induced NF-B activation in the monocytic cell lineage
THP-1.40 The early endothelial NF-B
activation can be interpreted as an effect of ligation of
endothelial surface receptors, such as VCAM-1, by
adhering monocytes. Similarly, it has recently been shown that VCAM-1
mediates endothelial stimulation after adhesion of
leukocytes, leading to a transient increase in
endothelial cytosolic free calcium
concentration.41
Comparison With Previous Studies
The results of our study are corroborated by previous studies in
the monocytic cell line THP-1, which showed expression of
IL-1ß42 and NF-B activation40
after mAb ligation of VLA-4. Our study substantially extends the
concept of ß1-integrin–regulated gene
expression. It demonstrates the relevance of this pathway for the
transcriptional regulation of NF-B–dependent genes in the
physiological setting of cell adhesion. Among the
various potential pathways of integrin-induced cell activation, our
study identifies VLA-4 signaling as the key mechanism for the induction
of IL-1ß after adhesion of monocytes to endothelial
cells.
Our finding of differential expression of IL-1ß and IL-6 mRNA in
monocytes and endothelial cells after adhesion-induced
NF-B activation is in accordance with other studies showing that
cytokine-induced differential gene expression involves the
synergistic interaction of a variable combinatorial set of
transcription factors that assemble in response to specific stimuli in
a unique complex.43
Limitations of the Study
Our study did not address the mechanisms of the weak stimulation
of IL-1ß and IL-6 release after coculture of monocytes with resting
endothelial cells. A recent study showed
platelet-derived growth factor expression as a consequence of
monocyte adhesion to resting endothelial
cells.44 In our study, cytokine expression after
coculture of monocytes with resting endothelial cells
was essentially the same in transwell chambers. Hence, we suggest
that as yet unidentified soluble factors were involved in this
effect.
Previous studies revealed macrophages to be a source of IL-6 in atheroma and in the border zone of reperfused myocardium.45 46 In our experimental setting, we were unable to demonstrate substantial IL-6 mRNA expression in monocytes, whereas a strong IL-6 mRNA signal was found in endothelial cells. We cannot fully exclude minor monocyte contamination of the endothelial fraction. Nevertheless, this could not account for the IL-6 mRNA signal in this fraction, because mRNA of the monocyte-specific ß2-integrin chain was not detectable. Our inability to detect substantial IL-6 mRNA in the monocyte fraction may be explained by the time frame of our study. We focused on early inflammatory responses after adhesion of monocytes to preactivated endothelium but did not address the late events after differentiation of monocytes to IL-6–expressing macrophages.
Potential Clinical and Therapeutic Implications
The cellular interactions we describe may play a major role in the
regulation of both local and systemic inflammatory responses in
atherosclerosis (Figure 6). When monocytes
adhere to the INF-–activated endothelium of
atherosclerotic lesions, binding of monocyte VLA-4 to
endothelial VCAM-1 may induce NF-B activation with
expression and release of IL-1ß by monocytes. This, in turn, could
enhance local inflammatory responses by promoting further monocyte
attachment through increased endothelial surface
expression of VCAM-1 and simultaneously induce systemic
inflammatory responses by stimulating the release of IL-6 from the
endothelium. Binding of monocytes to activated
endothelial cells by interaction of VLA-4 and VCAM-1
may thus represent one of the earliest events in the
inflammatory cascade of atherosclerosis.
The functional relevance of VLA-4/VCAM-1 interactions is underscored by animal studies showing that blockade of VLA-4 attenuates monocyte recruitment to atherosclerotic plaques.47 Our present study demonstrates that the interaction of VLA-4 with VCAM-1 induces IL-1ß–dependent local inflammatory responses promoting atherogenesis as well as IL-6–dependent systemic inflammatory responses. Inhibition of this interaction may constitute a novel therapeutic strategy for modification of inflammatory cardiovascular risk factors, such as fibrinogen upregulation.
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Acknowledgments |
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This study was supported by grants from the Deutsche Forschungsgemeinschaft (Ne 540/1-2, Br 1026/3-2), Bonn–Bad Godesberg, Germany. We gratefully acknowledge the large contribution made to this study through the technical expertise and assistance of Tanja Breustedt and Tamara Eisele.
Received April 15, 1999; accepted August 9, 1999.
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