(Circulation. 1999;100:2135.)
© 1999 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Departments of Medicine (G.L., S.L.K., R.L.F., J.J.G., C.M.W.) and Biostatistics (W.M.O.), Mayo Clinic, Rochester, Minn; and the Division of Cardiology (A.M.), Catholic University, Rome, Italy.
Correspondence and reprint requests to C.M. Weyand, MD, Mayo Clinic and Foundation, 200 First Street SW, Rochester, MN 55905. E-mail weyand.cornelia{at}mayo.edu
| Abstract |
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is altered in UA, we compared cytokine
production by T lymphocytes in patients with UA (Braunwalds
class IIIB) and with stable angina (SA).
Methods and ResultsPeripheral blood lymphocytes were
collected at the time of hospitalization and after 2 and 12 weeks.
Cytokine-producing CD4+ and CD8+ T
cells were quantified by 3-color flow cytometry after stimulation with
phorbol myristate acetate and ionomycin. UA was associated with
an increased number of CD4+ and CD8+ T cells
producing IFN-
, whereas patients with SA had higher frequencies of
IL-2+ and IL-4+ CD4+ T cells.
Expansion of the IFN-
+ T-cell population in UA
persisted for at least 3 months. Increased production of
IFN-
in UA could be attributed to the expansion of an unusual subset
of T cells, CD4+CD28null T cells.
ConclusionsPatients with UA are characterized by a perturbation
of the functional T-cell repertoire with a bias toward IFN-
production, suggesting that monocyte activation and acute phase
responses are consequences of T-cell activation. IFN-
is produced by
CD4+CD28null T cells, which are expanded in UA
and distinctly low in SA and controls. The emergence of
CD4+CD28null T cells may result from persistent
antigenic stimulation.
Key Words: angina ischemia interleukins immune system lymphocytes
| Introduction |
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Monocyte activation can be mediated by several mechanisms,
including IFN-
released from activated T cells. To
investigate the role of T cells in UA, we examined the ability of
circulating CD4+ and CD8+ T
cells to produce IFN-
, IL-2, and IL-4. UA patients had an increased
frequency of CD4+ IFN-
+
and CD8+ IFN-
+ T cells.
Attempts to characterize the IFN-
producing T-cell subset led to
the identification of an unusual subpopulation of
CD4+ T cells,
CD4+CD28null T cells, in UA
patients. Such T cells were infrequent in patients with stable angina
(SA). We have recently demonstrated that
CD4+CD28null T cells
represent proinflammatory cells with a high tissue-damaging
potential.8 The expansion of
CD4+CD28null T cells in UA
suggests that these patients have a perturbation in the T-cell
repertoire toward the production of IFN-
, resulting in
increased inflammatory responsiveness.
| Materials and Methods |
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SA patients had no acute events or worsening of symptoms during the previous 6 months and no anginal episodes within the week preceding enrollment. UA patients had at least 2 episodes of angina at rest or 1 episode lasting >20 minutes during the preceding 48 hours, ST-segment shift diagnostic for myocardial ischemia during the angina attacks, and no elevation in serum creatinine kinase on admission and during the first 24 hours of hospitalization. UA and SA patients did not differ for demographic characteristics and for angiographic findings, except for a previous history of angina (data not shown).
Design of the Study
Blood
Peripheral blood samples were taken immediately
after hospitalization, 7 to 14 days after hospital discharge, and 3
months after the first sample. In 9 SA and 8 UA patients, blood samples
were obtained simultaneously from the aortic root and the
coronary sinus during diagnostic coronary
angiography before contrast medium injection and drug
administration.
Laboratory Assays
Flow Cytometry
Frequencies of
CD3+CD4+,
CD3+CD8+, and
CD4+CD28null T cells in
peripheral blood mononuclear cells (PBMC) were determined
by flow cytometry using the following monoclonal antibodies (mAb)
anti-CD3 (fluorescein isothiocyanate-conjugated), anti-CD4
(peridinin chlorophyll protein-conjugated), anti-CD8 (peridinin
chlorophyll protein-conjugated) (Becton Dickinson, San Jose, Calif),
and anti-CD28 (fluorescein isothiocyanate-conjugated)
(Pharmingen, San Diego, Calif) as described.9
Cytokine production by T-cell subsets was assessed
after 4-hour in vitro activation with 10 ng/mL phorbol
myristate acetate and 1 µg/mL ionomycin (Sigma Chemical Co,
St Louis, Mo) in the presence of 10 µg/mL Brefeldin A (Epicentre
Technologies, Madison, Wis). After staining for cell surface markers,
cells were fixed and cytoplasmic cytokines were stained with
phycoerythrin-labeled anti-cytokine mAb (anti-IFN-
,
anti-IL-2, and anti-IL-4) (R&D Systems, Minneapolis, Minn) as
recommended by the manufacturer. Nonspecific staining with
isotype-matched control mAb was <1%.
Monocyte Stimulation With IFN-
One million PBMC were incubated for 18 hours at 37°C with and
without 200 U/mL IFN-
(BioSource International, Camarillo, Calif).
Cell surface expression of HLA class I molecules or monocytes was
determined by flow cytometry using the mAb W6/32 (ATCC, Bethesda, Md)
and anti-CD14 mAb (Becton Dickinson, San Jose, Calif).
Statistical Analysis
The Mann-Whitney U test and the Kruskal Wallis 1-way
ANOVA were used for comparisons between groups. Correlations were
determined using Spearmans rank correlation test. The remaining
variables were compared using Students t test for
paired and unpaired variables or the Fisher exact test, as
appropriate. In addition, we used bootstrap sampling to estimate the
distribution of the differences between the medians of the groups of SA
and UA patients.
| Results |
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compared with
56% in patients with UA (median frequency 26.4%,
P<0.001) (Figure 1
expression in UA was also seen for CD8 T
cells. The frequencies of CD8+ cells that
synthesized IFN-
was higher in UA patients (58.2%) than in controls
(38.7%) and SA patients (38.5%, P<0.001). IL-2 and IL-4
expression by CD8 T cells was similar in all 3 study cohorts. Increased
frequencies of IFN-
producing cells in UA patients were not related
to passing through the coronary circulation. Frequencies in
samples harvested from the coronary sinus and from the aortic
root during coronary angiography failed to show a significant
difference (data not shown).
|
Expansion of IFN-
Producing T Cells Is Not a Consequence of
Acute Chest Pain
In SA patients, the frequencies of cytokine-producing T
cells were stable. In UA donors, the frequencies of
CD4+ IFN-
+ and
CD8+ IFN-
+ cells
declined 1 to 2 weeks after discharge but returned to their original
high levels after 3 months, although the patients were free of
symptoms. CD4+ IL-2+ and
CD4+ IL-4+ T cells were
characterized by a reciprocal course with an intermittent increase at 7
to 14 days after discharge and a return to initial frequencies after 3
months (Figure 2
).
|
Expansion of CD4+CD28null T Cells in
Patients With UA
Production of high amounts of IFN-
is typical for an
unusual subset of T cells,
CD4+CD28null T cells which
are infrequent in normals.8 9 To address the
question whether UA patients carry
CD4+CD28null T cells, PBMC
were analyzed by 2-color cytometry (Figure 3
). Median frequencies of
CD4+CD28null T cells were
9-fold higher (9.0%) in UA than in SA patients (P<0.001).
Analysis of the distribution of the differences of the medians
after bootstrap sampling yielded a 99% CI ranging from 4.1 to 19.4,
confirming that the medians differed significantly
(P<0.01). Frequencies of UA patients were also
significantly increased when compared with hospitalized control
patients (P=0.001). Also, the expansion of
CD4+CD28null T cells
persisted after hospital discharge. Thirteen UA and 14 SA patients were
reanalyzed 63 to 221 days after the initial visit. The
frequencies of CD4+CD28null
T cells at the 2 time points correlated highly (R=0.81,
P<0.001), indicating that the expansion was not related to
the acute event or the hospitalization.
|
The frequency of
CD4+CD28null T cells
correlated (R=0.64, P=0.002) with the number of
IFN-
secreting cells (Figure 4
). In
addition, analysis of cytoplasmic IFN-
in
CD4+CD28+ and
CD4+CD28null T cells by
3-color cytometry in 16 UA patients showed that the increased IFN-
production in UA could be attributed to the
CD4+CD28null T cells,
whereas the CD4+CD28+
subset produced normal amounts.
|
Monocytes of Patients With UA Remain Responsive to IFN-
Levels of HLA class I expression, a monocyte activation marker
upregulated by IFN-
, was determined in 10 patients (4 with SA and 6
with UA) following 18 hours of incubation with or without 200 U of
human recombinant IFN-
. Results of a representative
experiment are shown in Figure 5
. In all
donors, CD14+ cells expressed higher levels of
HLA class I molecules following stimulation (mean fluorescence
intensity 439.5 versus 296.5, P<0.01), demonstrating
that monocytes of UA patients remain responsive to IFN-
.
|
| Discussion |
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on stimulation. Circulating
CD4+CD28null cells might
infiltrate the coronary plaque and induce inflammation,
particularly if stimulatory antigen is locally expressed. Also, the
well established constitutive activation of circulating monocytes in UA
could be viewed as a consequence of excessive IFN-
production by these cells.
Emergence and expansion of
CD4+CD28null cells
indicates a defect in T-cell homeostasis in UA. Generation of these T
cells could be genetically controlled and/or result from long-term
antigenic stimulation. Accumulating data favor long-term antigen
recognition and thus provide indirect evidence for a role of antigen
persistence in UA. Expanded
CD4+CD28null cells are
highly oligoclonal, suggesting ongoing antigenic
stimulation.13 14 Obvious candidate antigens are derived
from microorganisms chronically infecting the host. Release of IFN-
by CD4+CD28null cells would
be in line with anti-microbial reactivity. As the interaction of T
cells with antigen is highly specific,
CD4+CD28null T-cell clones
should provide excellent reagents to search for relevant antigens in
UA.
The association of T-cell repertoire perturbations with UA but not with
SA raises the possibility that committing to certain immunopathways may
have detrimental effects for the host. Although responding to
persistent antigen should be beneficial, expansion of
CD4+CD28null cells appears
to be correlated with negative consequences.
CD28null cells lack transcription of CD40 and are
therefore unable to support B-cell differentiation and antibody
production.15 Concomitantly, they have acquired
expression of perforin and granzyme B equipping them with cytolytic
abilities.8 Independent from costimulatory signals
provided by their microenvironment,
CD4+CD28null cells produce
high amounts of the proinflammatory cytokine
IFN-
.16 And finally, these unusual lymphocytes have a
tendency to leave the circulation and infiltrate the tissue. We propose
that a subset of patients, developing instability of otherwise
benign and slowly progressing CAD, have systemic alterations in the
immune system manifesting as the emergence of unusual T cells, possibly
triggered by chronic microbial infection. The functional profile of
expanding T cells, however, is biased against antibody-mediated host
defense and favors tissue infiltration, cell-mediated cytotoxicity, and
secretion of high amounts of IFN-
. Migration of
CD4+CD28null T cells into
plaques, possibly initiated by the local deposition of microbial
antigens, would elicit tissue destructive immune pathways such as
IFN-
mediated activation of metalloproteinase-secreting
macrophages, cytolysis of smooth muscle cells, and damage of
endothelial cells. This model proposes a direct
relationship between plaque instability and effector functions of
CD4+CD28null T cells.
| Acknowledgments |
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Received June 2, 1999; revision received July 16, 1999; accepted July 20, 1999.
| References |
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