Neutrophil Infiltration of Culprit Lesions in
Acute Coronary Syndromes
Takahiko Naruko, MD; Makiko Ueda, MD; Kazuo Haze, MD; Allard C. van der Wal, MD;
Chris M. van der Loos, PhD; Akira Itoh, MD; Ryushi Komatsu, MD; Yoshihiro Ikura, MD;
Masayuki Ogami, MD; Yoshihisa Shimada, MD; Shoichi Ehara, MD; Minoru Yoshiyama, MD;
Kazuhide Takeuchi, MD; Junichi Yoshikawa, MD; Anton E. Becker, MD
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Background—Neutrophils in unstable atherosclerotic lesions have not received much consideration, despite accumulating
evidence suggesting a link between systemic inflammation and acute coronary syndromes.
Methods and Results—Coronary artery segments were obtained at autopsy from 13 patients with acute myocardial
infarction (AMI); 8 had a ruptured and 5 an eroded plaque. Patients (n⫽45) who had died of noncardiovascular diseases
served as reference. Atherectomy specimens were obtained from 35 patients with stable angina pectoris (SAP) and from
32 patients with unstable angina pectoris (UAP). Antibodies against CD66b, elastase, myeloperoxidase, and CD11b
identified neutrophils; CD10 identified neutral endopeptidase (NEP). CD66b-positive and NEP-positive neutrophils
were counted and expressed as a number per square millimeter of tissue. All specimens with plaque rupture or erosion
showed distinct neutrophil infiltration; the number did not differ between ruptured and eroded plaques. However, the
number of NEP-positive neutrophils was significantly higher (P⬍0.0001) in ruptured plaques than in eroded plaques.
UAP patients showed neutrophils in 14 of 32 culprit lesions; in SAP only 2 of 35 lesions contained neutrophils. The
number of neutrophils and NEP-positive cells in patients with UAP was significantly higher (neutrophils, P⬍0.0005;
NEP-positive cells, P⬍0.005) than in patients with SAP.
Conclusions—The observations suggest that neutrophil infiltration is actively associated with acute coronary events. The
high number of NEP-positive neutrophils in ruptured plaques, compared with eroded plaques, may reflect differences
in the underlying pathophysiological mechanisms. (Circulation. 2002;106:2894-2900.)
Key Words: myocardial infarction 䡲 angina 䡲 inflammation 䡲 atherosclerosis
P
laque rupture or erosion with mural thrombus formation
is considered to represent the most important morphological changes that underlie the transformation of stable coronary lesions into clinically unstable lesions, causing unstable
angina pectoris (UAP) or acute myocardial infarction (AMI).1
The pathomorphological substrate underlying such complicated lesions is heterogeneous with respect to plaque architecture and cellular composition, but the presence of a
localized intraplaque inflammatory process is a common
denominator.2
Presently, a growing body of literature suggests a link
between systemic inflammation and acute coronary syndromes. It is of note, therefore, that the presence of neutrophils in unstable lesions has not received much consideration,
despite the fact that these cells have been identified at rupture
sites2 and, in general, are among the first phagocytic cells in
acute inflammatory responses to tissue injury. Epidemiolog-
ical studies, moreover, have shown that leukocyte counts in
peripheral blood correlated positively with coronary atherosclerotic risk3 and risk of AMI4; the strongest epidemiological
association is with neutrophil counts.4 Indeed, clinical studies
have demonstrated that neutrophils are activated in patients
with UAP and AMI,5–7 and accumulation of neutrophils, with
adherence of fibrin-platelet thrombus, occurs at the site of
endothelial cell denudation almost instantly after coronary
artery bypass grafting.8
The major function of neutrophils at sites of tissue injury is
complex but can be summarized by stating that they may
endocytose foreign material or secrete enzymes, such as
elastase and myeloperoxidase. Neutrophils also contain neutral endopeptidase 24.11 (NEP), a membrane protein known
to modulate inflammatory responses.9 NEP can be detected
on mature (segmented) neutrophils only. Immature neutrophils are NEP-negative but have a greater chemotactic re-
Received July 18, 2002; accepted September 11, 2002.
From the Department of Cardiology, Osaka City General Hospital (T.N., K.H., A.I.); Departments of Pathology (M.U., R.K., Y.I., M.O.) and Internal
Medicine and Cardiology (Y.S., S.E., M.Y., K.T., J.Y.), Osaka City University Graduate School of Medicine, Osaka; and the Department of
Cardiovascular Pathology (A.C.W., C.M.L., A.E.B.), Academic Medical Center, University of Amsterdam, the Netherlands.
Correspondence to Anton E. Becker, MD, Department of Cardiovascular Pathology, Academic Medical Center, University of Amsterdam, PO Box
22700, 1100 DE Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam, the Netherlands. E-mail [email protected]
© 2002 American Heart Association, Inc.
Circulation is available at http://www.circulationaha.org
DOI: 10.1161/01.CIR.0000042674.89762.20
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Naruko et al
TABLE 1.
Neutrophils in Acute Coronary Syndromes
2895
Human Coronary Specimens Used in the Study
Origin and Histological Classification of Lesions
AHA
Classification
No. of
Specimens
䡠䡠䡠
䡠䡠䡠
113
Autopsy
Specimens obtained from patients with noncardiovascular diseases
Diffuse intimal thickening
Hypercellular lesion
䡠䡠䡠
Type I
26
26
Fibrolipid plaque
䡠䡠䡠
Type Va
Fibrous plaque
Type Vc
30
Ruptured plaque
䡠䡠䡠
Type VI
13
Eroded plaque
Type VI
5
Specimens obtained from patients with AMI
Atherectomy
䡠䡠䡠
SAP (n⫽35)
䡠䡠䡠
UAP (n⫽32)
䡠䡠䡠
AHA Classification indicates the American Heart Association histological criteria.13,14
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sponse to activated complement than NEP-positive mature
neutrophils.9,10 Thus, the presence or absence of NEP on
neutrophils may provide some insight into their functional
capacity.
The present study has focused on the question of whether
there could be a role for neutrophils in the culprit lesions of
acute coronary syndromes. The study is based on frozen
tissue samples, because monoclonal antibodies against neutrophil markers, as well as the antibody against NEP, work
well on frozen sections only.
Methods
Coronary Tissue Specimens
This study is based on 3 different groups of specimens; the first and
second groups of specimens were obtained at autopsy, and the third
group of specimens was obtained by atherectomy (Table 1).
Autopsy
Coronary artery segments (n⫽126) were obtained at autopsy from 58
patients; 13 had died of AMI and 45 had died of noncardiovascular
diseases. The ages of the patients ranged from 21 to 77 years
(noncardiovascular diseases, 61⫾11; AMI, 51⫾19; mean⫾SD). Of
those with noncardiovascular diseases, 84% were men; for AMI,
77% were men. The following risk factors were evaluated: cigarette
smoking, hypertension as defined by the Joint National Committee
V,11 diabetes mellitus as defined by the WHO Study Group,12 and
hypercholesterolemia (cholesterol level ⬎220 mg/dL). Their distribution among patients with noncardiovascular diseases versus those
with AMI was as follows: cigarette smoking (27% versus 62%),
hypertension (18% versus 46%), diabetes mellitus (9% versus 39%),
and hypercholesterolemia (27% versus 38%).
Of the patients who had died of noncardiovascular diseases, 113
segments were obtained. Twenty-six of these contained normal
coronary artery with diffuse intimal thickening (AHA classification
type I).13,14 The other 87 segments contained atherosclerotic lesions
and were characterized histologically either as atherosclerotic lesions
with hypercellularity (n⫽26) or as advanced atherosclerotic lesions
(n⫽61), according to our classification described previously.15 The
hypercellular lesion was defined as a cell-rich intimal lesion,
predominantly composed of smooth muscle cells (SMCs) and
occasional macrophages, but without an extracellular lipid core
(“hypercellular lesions” are not recognized by the AHA classification).13,14 The advanced atherosclerotic lesions were additionally
31
8
䡠䡠䡠
35
32
divided into fibrolipid (type Va; n⫽31) and fibrous (type Vc; n⫽30).
In fibrous plaques, the fibrocellular tissue was the predominant
component and a lipid core was inconspicuous or absent. In
fibrolipid plaques, the ratio of fibrous cap tissue to a lipid core was
estimated as between 25% and 75%.
Of the patients who had died of AMI, 13 segments were obtained
from culprit lesions, divided into ruptured (type VI; n⫽8) and eroded
(type VI; n⫽5) plaques. In ruptured plaques, the fibrous cap had
ruptured completely, with the fissure extending into the lipid core,
additionally complicated by intraplaque hemorrhage and luminal
thrombosis. In eroded plaques, a “trans-cap” rupture was not found,
despite serial sectioning. The intimal plaque showed an eroded
surface, characterized by loss of the endothelial lining with lacerations of the superficial intimal layers and with thrombus overlying
the site of injury. Seven of the 13 AMI patients underwent emergency percutaneous transluminal coronary angioplasty (PTCA). The
time interval between onset of cardiac symptoms and death was well
documented in these patients and varied from 0 to 2 days (mean
interval ⬍1 day). Age, sex, and presence of risk factors did not differ
among patients with ruptured plaques or eroded plaques.
All autopsies were performed within 3 hours after death. The
coronary arteries were removed from the epicardial surface and
sectioned at ⬇2-mm intervals. The slices were snap-frozen and
stored at ⫺80°C.
Atherectomy
The atherectomy specimens were obtained from 67 patients, all of
whom underwent atherectomy of the target lesion considered responsible for either stable angina pectoris (SAP) (n⫽35) or UAP (n⫽32).
The demographic data (SAP versus UAP) were as follows: age
(58⫾11 versus 59⫾10), male sex (83% versus 81%), cigarette
smoking (67% versus 69%), hypertension (45% versus 45%), diabetes mellitus (26% versus 28%), and hypercholesterolemia (58%
versus 45%). There were no statistically significant differences
between patients with SAP or UAP. Immediately after atherectomy,
the tissue specimens were carefully oriented along their longest axis,
snap frozen, and stored at ⫺80°C.
The snap-frozen samples, obtained either by autopsy or atherectomy, were subsequently sectioned serially at 6-␮m thickness and
fixed in acetone. Every first section was stained with H&E; the other
sections were used for immunohistochemical staining.
Immunohistochemistry
Single Staining
The sources and specificity of all antibodies used in this study are
summarized in Table 2. Five different antibodies were used to
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Circulation
TABLE 2.
December 3, 2002
Antibody Used in the Study
Clone or
Catalog No.
Type
Cell Identified
Source
Working
Dilution
SS2/36
MAb (IgG1)
1:50
MAb (IgG2a)
䡠䡠䡠
Smooth muscle cells
DAKO
1A4
DAKO
1:100
CD68
EBM11
MAb (IgG1)
Macrophages
DAKO
1:100
von Willebrand factor
F8/86
MAb (IgG1)
Endothelial cells
DAKO
1:50
CD66b
80H3
MAb (IgG1)
Neutrophils
Coulter
1:50
CD11b
2LPM19c
MAb (IgG1)
Neutrophils, macrophages
DAKO
1:200
Elastase
NP57
MAb (IgG1)
Neutrophils, some monocytes
DAKO
1:200
MPO-7
MAb (IgG1)
Neutrophils, some monocytes
DAKO
1:500
K50891R
PAb (rabbit)
Neutrophils, some monocytes
Biodesign Inc
1:1000
Designation
NEP
␣-Smooth muscle actin
Myeloperoxidase (MPO-7)
Myeloperoxidase (MPO)
DAKO, Dako Laboratories (Glostrup, Denmark); Coulter (Hialeah, Fla); Biodesign Inc (Kennebunk, Maine).
MAb indicates monoclonal antibody; PAb, polyclonal antibody.
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identify neutrophils: anti-CD66b, elastase, myeloperoxidase (monoclonal [MPO-7] and polyclonal [MPO]), and CD11b. NEP was
identified by using anti-CALLA (CD10).16 Nonimmune mouse IgG
serum (DAKO, Glostrup, Denmark) served as negative control;
human kidney obtained at autopsy was used as positive control.
Sections were incubated at 4°C overnight and then subjected to a
3-step staining procedure, using the streptavidin-biotin complex
method (SABC) for detection. Peroxidase activity was visualized
with 3-amino-9-ethyl-carbazole (10 minutes, room temperature), and
the sections were faintly counterstained with hematoxylin.
Double Immunostaining
The simultaneous identification of SMCs and macrophages was
performed on the basis of 2 primary antibodies of a different IgG
subclass (1A4/CD68), as reported previously.17 The enzymatic
activity of ␤-galactosidase for 1A4 was visualized in turquoise
(BioGenex Kit, BioGenex) and that of alkaline phosphatase for
CD68 in red (New Fuchsin Kit, DAKO).
We also performed double immunostainings between macrophages (CD68) and each of the 5 neutrophil markers (CD66b,
elastase, myeloperoxidase MPO-7, myeloperoxidase MPO, and
CD11b), as well as between CD66b and each of the remaining 4
neutrophil markers, using modifications of procedures reported
previously.17 In both double immunostainings, alkaline phosphatase
was visualized with fast blue BB and peroxidase with 3-amino-9ethylcarbazole development.
To identify neutrophils that express NEP, double immunostainings
(NEP/CD66b; NEP/elastase) were performed, according to procedural modifications previously reported.17 Again, alkaline phosphatase was visualized with fast blue BB (blue: CD66b and elastase) and
peroxidase with 3-amino-9-ethylcarbazole development (red: NEP).
Quantitative Methods
Numbers of CD66b-positive neutrophils and NEP-positive cells were
counted in the entire tissue sections and expressed as the number of
cells per square millimeter of intimal tissue. In atherectomy specimens, neutrophils or NEP-positive cells within thrombi or tissueattached blood clots were excluded. The tissue area occupied by
immunostained macrophages was quantified, using computer-aided
planimetry and expressed as a percentage of the total surface area of
the tissue section. The morphometric analysis was performed by a
single investigator who was blinded to the patients’ characteristics
and histological classifications. Data are shown as mean⫾SD. The 2
groups were compared with an unpaired Student’s t test or with
Mann-Whitney U test when the variance was heterogeneous. Statistical comparisons between ⬎3 groups were performed with one-way
analysis of variance and post-hoc multiple comparison using Scheffe’s test. Values of P⬍0.05 were considered significant.
Results
Neutrophil Identification
The staining pattern of the 5 antibodies (CD66b, elastase,
myeloperoxidase MPO-7, myeloperoxidase MPO, and
CD11b) used to identify neutrophils in frozen sections differed slightly. Double immunostaining analysis revealed that
CD66b positivity was detected in neutrophils but not in
macrophages. In contrast, CD11b positivity was found in
neutrophils but occasionally also in macrophages. The double
immunostainings for CD66b/elastase, CD66b/MPO-7,
CD66b/MPO, macrophages/elastase, macrophages/MPO-7,
and macrophages/MPO demonstrated that most elastasepositive, MPO-7–positive, and MPO-positive cells within the
plaque are neutrophils (Figures 1 and 2).
Autopsy Specimens
Specimens Obtained From Patients With
Noncardiovascular Diseases
Normal coronary arteries with diffuse intimal thickening
contained no macrophages. In hypercellular lesions, 13 of the
26 lesions were composed almost solely of SMCs, whereas
the remaining 13 lesions contained foci of macrophages. In
advanced fibrous plaques, 12 of the 30 lesions had a small
number of macrophages. However, in advanced fibrolipid
plaques, all lesions contained macrophages, albeit to various
degrees: only 2 of the 31 lesions contained some neutrophils
at the shoulder region. Lesions that contained macrophages
but no neutrophils (CD66b and elastase-negative) did not
stain positive for MPO-7 or MPO.
NEP expression was not detected in normal coronary
arteries with diffuse intimal thickening, hypercellular lesions,
and advanced fibrous plaques. In the 2 fibrolipid plaques with
neutrophil infiltration, the neutrophils were negative for NEP
in one plaque, whereas in the other plaque, occasional
neutrophils were positive for NEP.
Specimens Obtained From AMI Patients
Macrophages were abundantly present in both ruptured and
eroded plaques (Figures 1A, 1B, 2A, and 2B). Distinct
neutrophil infiltration was detected in all specimens with
Naruko et al
Neutrophils in Acute Coronary Syndromes
2897
Morphometric Analysis
Morphometric results are shown in Figure 4. The macrophage-positive area was significantly higher (P⬍0.0001) in
ruptured and eroded plaques than in normal coronary arteries
with diffuse intimal thickening, hypercellular lesions, and
advanced fibrous plaques. The number of CD66b-positive
neutrophils did not differ between ruptured and eroded
plaques; the number of neutrophils in the culprit lesion was
not significantly different between AMI patients with PTCA
and those without PTCA. The number of NEP-positive cells
was significantly higher (P⬍0.0001) in ruptured plaques than
in eroded plaques.
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Figure 1. Micrographs of site of plaque rupture in an autopsied
patient with AMI. A, Double immunostaining (SMC, turquoise;
macrophage, red) reveals a lipid-rich plaque with abundant
macrophages and a thin fibrous cap with SMCs (arrow). L indicates lumen; M, media. The area indicated by the asterisk is
shown in higher magnification in adjacent serial sections labeled
B through H. B, Double immunostaining (SMC, turquoise; macrophage, red) shows part of the media (M) and adjacent atherosclerotic plaque tissue with abundant macrophages. C, The
anti-neutrophil CD66b antibody reveals large numbers of neutrophils at this same site. D, The anti-neutrophil elastase antibody
also shows neutrophils. E, The anti-MPO-7 antibody reveals
MPO-7 positivity of neutrophils. F, Double immunostaining for
MPO-7 (blue) and CD66b (red) reveals double staining (purple)
of almost all cells, indicating that the MPO-7–positive cells are
CD66b-positive neutrophils. G, Double immunostaining MPO-7
(blue) and macrophage (red) shows that only occasional macrophages show positivity for MPO-7; most MPO-7–positive cells
are neutrophils, and occasional macrophages also show staining positivity for MPO-7. H, Double immunostaining for MPO
(blue) and macrophage (red) also reveals colocalization of MPOpositive neutrophils and macrophages. Original magnification: A,
⫻18; B through H, ⫻212.
plaque rupture or erosion (Figures 1C through 1E and 2C
through 2E). Double immunostaining (MPO-7/CD66b) demonstrated that most MPO-7–positive cells were neutrophils
(Figures 1F and 2F). Double immunostainings for MPO-7 (or
MPO) and macrophages revealed that only occasional macrophages were positive (Figures 1G, 1H, 2G, and 2H).
In ruptured plaques, neutrophils were positive for NEP
(Figures 3A through 3C), whereas in eroded plaques,
most neutrophils lacked NEP positivity (Figures 3D
through 3F).
Figure 2. Micrographs of site of plaque erosion in an autopsied
patient with AMI. A, Double immunostaining (SMC, turquoise;
macrophage, red) reveals abundant macrophages within the
plaque. L indicates lumen; M, media. The area indicated by the
asterisk is shown in higher magnification in adjacent serial sections, labeled B through H. B, Double immunostaining (SMC,
turquoise; macrophage, red) reveals large numbers of macrophages. C, The anti-neutrophil CD66b antibody reveals the
presence of numerous neutrophils. D, The anti-neutrophil elastase antibody also shows abundant neutrophils. E, The antiMPO-7 antibody also reveals the presence of neutrophils. F,
Double immunostaining for MPO-7 (blue) and CD66b (red)
reveals that most cells show double staining (purple), indicating
that most MPO-7–positive cells are neutrophils. G, Double immunostaining for MPO-7 (blue) and macrophage (red) clearly
shows that only a few macrophages show double staining. H,
Double immunostaining for MPO (blue) and macrophage (red)
also shows that only a few macrophages are MPO-positive.
Original magnification: A, ⫻23; B through H, ⫻178.
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Circulation
December 3, 2002
Figure 5. Micrographs of an atherectomy specimen obtained
from a culprit lesion in a patient with UAP. A, Fragment of atherosclerotic plaque tissue. Double immunostaining (SMC, turquoise; macrophage, red) reveals areas containing abundant
macrophages. The area indicated by the asterisk is shown in
higher magnification in B. B, The anti-neutrophil CD66b antibody shows a large number of neutrophils. Original magnification: A, ⫻96; B, ⫻233.
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Figure 3. Serial sections taken immediately adjacent to the site
shown in Figure 1 (A through C; ruptured plaque) and Figure 2
(D through F; eroded plaque). A, Section adjacent to Figure 1B,
stained with anti-neutrophil CD66b antibody, reveals a large
number of neutrophils. B, The adjacent section stained with
anti-NEP antibody reveals the presence of abundant NEPpositive cells. C, Double immunostaining (neutrophil CD66b,
blue; NEP, red) reveals that almost all cells show double staining (purple), indicating that the NEP-positive cells are neutrophils. D, Section adjacent to Figure 2B, stained with antineutrophil CD66b antibody, reveals numerous neutrophils. E,
The adjacent section stained with anti-NEP antibody reveals
that most neutrophils lack NEP positivity. F, Double immunostaining (neutrophil CD66b, blue; NEP, red) shows that all cells
stain blue, indicating that these neutrophils are negative for
NEP. Original magnification: A and B, ⫻110; C, ⫻444; D and E,
⫻110; F, ⫻444.
Atherectomy Specimens
All 32 lesions obtained from patients with UAP contained
abundant macrophages, and 14 (44%) contained neutrophils (Figure 5). Double immunostaining for NEP and
neutrophils showed that both NEP-positive and NEPnegative neutrophils were present in the culprit lesions in
patients with UAP. In contrast, only 2 of 35 (6%) culprit
lesions obtained from patients with SAP contained neutrophils, and NEP positivity was found only occasionally.
Morphometric analysis demonstrated that the number of
neutrophils and NEP-positive cells in patients with UAP
was significantly higher (neutrophils; P⬍0.0005, and
NEP-positive cells; P⬍0.005) than in patients with SAP
(Figure 6).
Discussion
Intraplaque inflammation is presently widely acknowledged
to play a crucial role in the changing morphologies of
atherosclerotic plaques, with most interest focusing on macrophages and T lymphocytes. However, given the growing
notion that systemic inflammation could be involved also, the
question arises to what extent local neutrophil infiltration
could be involved. Previous studies, using conventional
formalin-fixed sections, documented occasional neutrophils
within plaques, but their functional significance was not
additionally elaborated.2 To the best of our knowledge, the
present study, based on frozen sections and using immunohistochemical single and double staining techniques, is the
first study systematically analyzing neutrophils in culprit
lesions of acute coronary syndromes.
All culprit lesions of patients who had died of AMI had
neutrophils within the plaques, although the number varied
widely. In contrast, neutrophils were extremely rare in coronary lesions obtained from patients who had died of noncardiovascular diseases; in only 2 of the 87 atherosclerotic
lesions neutrophils were identified. Similar observations were
made in patients in whom atherectomy material was studied.
In patients with UAP, neutrophils within the culprit lesion
were detected in 14 of 32 (44%), whereas this was the case in
only 2 of 35 (6%) patients with SAP. These observations
suggest that neutrophils are actively associated with acute
coronary events.
Figure 4. Graphs showing the macrophage-positive area, expressed as a percentage of the total surface area, the
number of neutrophils, and the number
of NEP-positive cells, both expressed as
absolute numbers per square millimeter
of intimal tissue, in diffuse intimal thickening (DIT, n⫽26), hypercellular lesions
(HC, n⫽26), fibrous plaques (FP, n⫽30),
fibrolipid plaques (FLP, n⫽31), ruptured
plaques (RP, n⫽8), and eroded plaques
(EP, n⫽5).
Naruko et al
Neutrophils in Acute Coronary Syndromes
2899
Figure 6. Graphs showing the number of
neutrophils/mm2 and that of NEPpositive cells/mm2 in the atherectomy
specimens obtained from the culprit
lesion in patients with SAP and UAP.
Downloaded from http://circ.ahajournals.org/ by guest on June 17, 2017
These findings contrast markedly with those recently
reported by Sugiyama et al.18 The authors reported that only
few neutrophils were found at sites of erosion or rupture.
However, they used formalin-fixed paraffin-embedded sections for the study of ruptured and eroded plaques, apparently
unaware of the fact that the CD66b antibody only works on
frozen samples (in accordance with the data sheet of Coulter,
endorsed by our own pilot studies; data not shown). It thus
seems that the negative findings by Sugiyama et al18 relate to
their handling of the tissue specimens.
Previous clinical studies have demonstrated intense in vivo
neutrophil activation in UAP and AMI.5-7 Mehta et al5
reported a 15-fold increase in plasma levels of peptide B␤, a
marker of elastase release, in patients with UAP compared
with those in patients with SAP. Biasucci et al7 measured the
index of intracellular neutrophil myeloperoxidase and
showed a significant release of myeloperoxidase from neutrophils related to their activation in patients with AMI and
UAP. Mazzone et al19 also revealed increased expression of
CD11b/CD18 integrins in neutrophils in UAP patients. These
clinical observations together with our present findings suggest that neutrophil activation may be one of the inflammatory components of acute coronary syndromes. Activated
neutrophils are known to release a variety of proteolytic
enzymes, all of which have the potential for tissue destruction. In particular, neutrophil elastase has been shown to
mediate both degradation of basement membrane constituents
and endothelial damage.6 Hence, it is conceivable that neutrophils contribute to the pathogenesis of plaque destabilization in human atherosclerotic plaques.
In this study, 7 of the 13 AMI patients underwent emergency PTCA, and, therefore, one could consider the presence
of neutrophils a result of PTCA-related injuries.20 However,
there were no significant differences in numbers of neutrophils within culprit lesions of patients with and without
PTCA. Moreover, neutrophils were found in the atherectomy
specimens in ⬇40% of the UAP patients, indicating that
neutrophils occur in culprit lesions in UAP and AMI patients,
irrespective of a PTCA procedure.
The present study also focused on the presence of NEP.9
The fact that NEP expression occurs primarily at the fully
mature polymorphonuclear stage of neutrophil development is of interest, given our observation that ruptured
plaques contain a significantly higher number of NEPpositive neutrophils than do eroded plaques. The pathobiology of this phenomenon remains unknown as yet. However, the observation that plaque erosions predominantly
contain NEP-negative neutrophils suggests a rapid and
relatively sudden outburst of neutrophils, like that seen in
acute and severe inflammatory states.
In conclusion, the distinct presence of neutrophils in
atherosclerotic plaques underlying UAP and AMI strongly
suggests that neutrophils play a role in mediating destabilization of atherosclerotic plaques.
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Neutrophil Infiltration of Culprit Lesions in Acute Coronary Syndromes
Takahiko Naruko, Makiko Ueda, Kazuo Haze, Allard C. van der Wal, Chris M. van der Loos,
Akira Itoh, Ryushi Komatsu, Yoshihiro Ikura, Masayuki Ogami, Yoshihisa Shimada, Shoichi
Ehara, Minoru Yoshiyama, Kazuhide Takeuchi, Junichi Yoshikawa and Anton E. Becker
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Circulation. 2002;106:2894-2900; originally published online November 18, 2002;
doi: 10.1161/01.CIR.0000042674.89762.20
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