(Circulation. 2001;103:1503.)
© 2001 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Department of Medical Microbiology (K. Burian, Z.K., D.V., V.E., E.G.) and Department of Medical Informatics (K. Boda), Szeged University, Szeged, Hungary; 3rd Department of Internal Medicine, Faculty of Medicine, Semmelweis University (Z.P., L.H., L.R., G.F.) and Research Group of Metabolism, Genetics and Immunology, Hungarian Academy of Science (Z.P., L.R., G.F.), Budapest, Hungary; National Institute of Cardiology (J.D.), Budapest, Hungary; and The Wistar Institute, Philadelphia, Pa (K. Berencsi, E.G.).
Correspondence to Eva Gonczol, MD, PhD, Department of Medical Microbiology, University of Szeged, Dom ter 10, H6720 Szeged, Hungary. E-mail gonczol{at}comser.szote.u-szeged.hu
| Abstract |
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Methods and ResultsA total of 405 subjects (276 patients with CAD and 129 control individuals) were tested for serum antibodies to hHSP60, Cpn, and CMV immediate-early-1 (IE1) antigens. Patients were also assessed for serum cholesterol, triglyceride levels, and smoking habit. Significantly elevated levels of antibodies to hHSP60 and Cpn but not to CMV-IE1 antigens were documented in CAD patients. Multiple logistic regression analysis and subanalyses of selected subjects showed that these associations were independent of age, sex, smoking, and serum lipid levels. Antibodies to hHSP60 and Cpn did not correlate quantitatively; however, the relative risk of disease development was substantially increased in subjects with high antibody levels to both hHSP60 and Cpn, reaching an odds ratio of 82.0 (95% CI 10.6 to 625.0).
ConclusionsHigh levels of antibodies to hHSP60 and Cpn are independent risk factors for coronary atherosclerosis, but their simultaneous presence substantially increases the risk for disease development.
Key Words: coronary disease antibodies epidemiology Chlamydia pneumoniae
| Introduction |
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From 50% to 80% of adults worldwide have antibodies to Cpn, a common respiratory pathogen. Cpn replicates intracellularly and expresses various proteins, including the major outer membrane protein (MOMP) and chlamydial HSP60. Chronic infection with Cpn is common.4
CMV is among the infectious agents that usually cause
no symptoms in immunocompetent individuals but do establish latent
infection. From 50% to
100% of adults are seropositive. The
immediate-early (IE) proteins of CMV influence transcription from
cellular and viral promoters, are involved in escape from immune
surveillance and in establishment of virus latency, and are the first
proteins expressed after virus
reactivation.5
Numerous studies have reported increased Cpn antibody levels in atherosclerotic patients, although several prospective studies found no significant correlation between the presence of Cpn antibodies and incidence of myocardial infarction.6 The seroepidemiology of CMV infections in atherosclerotic and control individuals is even less clear, with results suggesting elevated CMV antibody levels in patients with primary atherosclerosis7 or with restenosis after angioplastic surgery,8 or no association.9 Human CMV-IE antigens have been implicated in the restenosis process, because IE proteins are locally reactivated in the coronary walls, and the IE2 protein binds to and suppresses the function of tumor-suppressor p53 in the infected vessel wall.10 No studies to date have included measurement of CMV-IE antibodies in seroepidemiological analyses of atherosclerosis or restenosis development.
Significantly increased levels of serum antibodies to HSP65 have been reported in patients with coronary and carotid atherosclerosis.11 12 13 Some bacteria contain HSPs, and some viruses induce overproduction of human (h) HSP60 by the infected cell, leading to immunogenicity of the protein due to structural alterations or posttranslational modifications.14 Thus, antigenic mimicry by HSPs may be the link between infections and atherosclerosis.
Most seroepidemiological studies have focused on measurement of antibodies against a single pathogen or against HSPs. A few studies have assessed antibodies to multiple pathogens, including CMV and Cpn,15 16 17 or to Cpn and HSPs18 in the same individuals. In the present study, we measured antibody levels against Cpn, CMV-IE1, and hHSP60 in the same case/control population to further examine the potential combined effects of these factors in the development of atherosclerotic disease.
| Methods |
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Cpn
Antibodies
Sera were tested at a 1:128 dilution for
Chlamydia-specific IgG
antibodies with a microimmunofluorescence assay
(ServiMif Chlamydia, SERVIBIO),
according to the manufacturers instructions. Sera were designated as
positive (titer
1:128) or negative (titer <1:128) based on typical
fluorescence associated with evenly distributed Chlamydia
organisms. Sera positive for Chlamydia
trachomatis or Chlamydia
psittaci antigens were excluded from the
study.
CMV-IE1 Antibodies
Serum IgG antibodies to CMV-IE1 antigen were
determined by in-housedeveloped ELISA. For antigen
production, chicken embryo fibroblasts were infected with a
recombinant canarypox virus expressing CMV-IE exon4
protein.20 Parental
canarypox virusinfected cell lysate served as control antigen. Serum
samples were tested in dilution of 1:100 in a standard ELISA. Optical
density (OD) values measured on parental canarypox antigen were
subtracted from OD values on canarypox CMV-IE exon4 antigen. Antibody
levels were considered "low" at a calculated OD <1.00 and
"high" at OD
1.00.
hHSP60 Antibodies
IgG reacting with recombinant hHSP60 (SPP-740,
StressGen) was quantified by ELISA at a serum dilution of 1:500 as
described previously.21
Serial dilutions of a control anti-hHSP60 rabbit polyclonal antiserum
(StressGen SPA-840) were used as standard. OD values were calculated in
arbitrary units per milliliter relative to the
standard.
Clinical Laboratory Procedures
Serum cholesterol and
triglyceride were measured PAP (peroxidase-anti-peroxidase)
by enzymatic colorimetric assay using enzachol-F and
ENZGlycid reagents (Diachem). LDL cholesterol was
calculated according to the Friedewald
formula.22 The level of
lipoprotein(a) [Lp(a)] was determined by
ELISA.23
Statistical Analyses
All statistical analyses were performed with
SPSS for Windows program version 9.0. Differences between groups in
continuous variables were estimated with independent-sample
t test,
nonparametric Mann-Whitney
U test, or Kruskal-Wallis test.
For dichotomous variables,
2 test or
Fishers exact test was used. ORs and 95% CIs were calculated. All
tests were 2-tailed. Logistic regression was used to evaluate potential
confounding by covariables and to calculate adjusted ORs. To assess
the effect of high hHSP60 antibody levels on CAD development,
dichotomous variables were created for hHSP60 antibody levels, ie,
high (highest quartile) versus low (lower 3 quartiles of the
distribution). This approach was selected because of skewed
distributions of hHSP60 antibodies and because the risk associated with
hHSP60 antibodies did not differ in the lower quartiles of
distribution. Sets of 4 binary indicators were created for each
interaction investigated. In the joint-effect analyses,
subjects with low levels of both antibodies of interest were used as
reference to estimate the relative risk of the other 3 combinations.
Differences were considered significant at
P<0.05.
| Results |
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1:128)
(Table 1
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Sera of subjects in the clinically more
homogeneous groups 1 and 3 were also compared for total
serum cholesterol, HDL, LDL, triglyceride, and
Lp(a) levels, and smoking habit was recorded.
Table 2
summarizes the results of these measurements, as
well as levels of hHSP60, Cpn,
and CMV-IE1 antibodies. Age, sex, and total and LDL
cholesterol levels, as well as CMV-IE1 antibody levels,
were similar in both groups. HDL cholesterol was lower and
triglyceride and Lp(a) levels were higher in group 1 than
in group 3. There was a borderline significant difference in the
percentage of smokers. Antibody levels to hHSP60 and
Cpn remained significantly
higher in group 1 than in group 3
(Table 2
). When data were adjusted for age, sex, smoking
habits, and HDL cholesterol, triglyceride, and
Lp(a) levels by logistic regression analysis, anti-hHSP60
levels (high or low, P=0.0037,
OR 9.8, 95% CI 2.1 to 45.9) and the percentage of
Cpn seropositives
(P=0.047, OR 2.4, 95% CI 1.01
to 5.72) were significantly higher in group 1 than group 3. The same
parameters were also compared in 35 patients (group 1) and
35 controls (group 3) selected on the basis of same age ±4.5 years,
same sex, and similar cholesterol values; CMV-IE1 antibody
levels were not significantly different, whereas statistically
significant differences were seen for
Cpn seropositivity
(P=0.009, OR 4.6, 95% CI 1.5
to 14.7) and for hHSP60 antibodies (high or low:
P=0.012, OR 3.4, 95% CI 1.0 to
12.5). Furthermore, in group 1, there were 40, 28, and 189 patients
undergoing treatment with statin, fibrate, and aspirin, respectively,
at the time of blood sampling. No differences in the percentage of
Cpn seropositives or serum
concentrations of hHSP60 antibodies were found between patients with or
without treatment (not shown).
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Lack of Correlation of
Cpn Seropositivity With hHSP60
Antibody Levels; Correlation With Smoking Habit
Comparison of hHSP60 antibody levels (continuous
variable) in Cpn-negative
and Cpn-positive individuals
revealed no statistical difference between the 2 groups in the total
study population, in either CAD group, or in either control group
(Table 3
). Moreover, in either CAD group, no statistical
difference was seen between Cpn
seropositives and seronegatives in the percentage of subjects with
high-level (highest quartile) hHSP60 antibodies
(P=0.260 to 0.869) (not shown).
By logistic regression analysis of data for
Cpn seropositivity adjusted for
sex, age, and hHSP60 antibodies (continuous variable), the
probability value remained significant in all combinations of case and
control groups, and ORs varied between 2.2 and 2.6
(Table 4
). No correlation between hHSP60 and HCMV-IE1
antibodies was observed (not shown).
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In groups 1, 2, and 3, Cpn seropositivity was significantly associated with smoking; 81.1% of smokers but only 68.4% of nonsmokers tested positive for Cpn antibodies (P=0.018).
Joint Effects of Microbial and hHSP60
Antibodies in the Development of
Atherosclerosis
The simultaneous occurrence of high hHSP60
and high microbial antibodies was analyzed in combined group A
versus combined group B with respect to the relative risk of CAD
(Table 5
). In subjects with
Cpn antibody titers
1:128 and
with high hHSP60 antibody levels (highest quartile), the risk of CAD
was dramatically increased relative to subjects with no or low levels
of Cpn antibodies and low
levels of hHSP60 antibodies (lower 3 quartiles) (nonadjusted OR 83.3;
adjusted for age and sex, OR 82.0)
(Table 5
). ORs for subjects with high hHSP60 antibodies and
Cpn seropositivity (titer
1:128) in group 1 were also high compared with group 3 (adjusted for
age and sex, P=0.0007, OR 38.3,
95% CI 4.7 to 312.5) (not shown). However, the
simultaneous presence of high CMV-IE1 and high hHSP60
antibody levels was not associated with increased risk. The
simultaneous presence of high levels of CMV-IE1 and
Cpn antibodies did not change
the ORs
(Table 5
).
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| Discussion |
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Cpn antibodies have been shown to be associated with increasing age, male sex, and smoking.6 In the present study, the Cpn antibody data were adjusted for age, sex, serum lipids [including Lp(a)], and smoking by logistic regression, and statistically significant differences and ORs suggest a 2- to 3-fold higher risk for CAD in individuals with elevated Cpn antibodies.
Our analysis of high and low
Cpn-specific antibody titers
did not distinguish between subjects with low titers (<1:128) and
those never infected but rather may distinguish subjects with frequent,
recent, or chronic infections from those with less frequent, less
recent, or milder infections. However, misclassification of prior
infection based on current high antibody status (
1:128) was probably
equal in the case and control groups. Also, blood donors were not
examined by angiography, so that some individuals with
asymptomatic CAD may have been incorrectly classified as
controls. However, such misclassification would be reflected in a lower
OR, making the reported OR a conservative estimate.
Bacterial and viral infections can induce immune reactivity against hHSP60, which may serve as a target for autoimmune reactions. Our results for elevated levels of hHSP60 in CAD patients are in agreement with previous observations for HSP65.11 12 Our study revealed no quantitative correlation between hHSP60 and Cpn antibodies as detected by a microimmunofluorescence assay that is most likely specific for MOMP,24 and the data suggest that hHSP60 and Cpn are independent risk factors in the development of the disease. Circulating hHSP60 antibodies might be maintained at higher levels through different mechanisms (for example, through infection with agents containing homologous HSPs). Other mechanisms, such as hypertension25 or oxidized LDL,26 might also stimulate HSP60/70 expression and, in turn, increased HSP60/70 antibody levels. The independent presence of hHSP60 and Cpn antibodies suggests that hHSP60 antibodies are predominantly induced by mechanisms other than Cpn infection. Alternatively, high levels of autoantibodies against hHSP60 may be a stable, genetically determined trait (Amarilla Veres, MD, and Tamas Szamosi, MD, unpublished observations, 2000) that predisposes to CAD by formation of abundant hHSP60anti-hHSP60 immune complexes21 and may result in intense in situ complement activation and endothelial cell dysfunction.
A previous study18 concluded that high-titer antibodies to mycobacterial HSP65 correlated with the presence of antibodies to Cpn in human sera obtained from atherosclerotic patients and that the HSP65 antibodies cross-reacted with hHSP60, chlamydial HSP, and Escherichia coli Gro-EL in ELISA. Our results contrast with this observation, possibly owing to differences in the study populations used, the evaluation of high or low levels of antibodies to Cpn, or the type of HSP antibodies investigated (antibodies to mycobacterial HSP65 or hHSP60). However, a recent report27 that CAD patients were more likely to have IgG antibodies to Cpn than were individuals without CAD but that CAD was not associated with antibody response to chlamydial HSP60 supports our observation. Furthermore, marked differences in the complement-activating ability and epitope specificity were found between HSP65 and hHSP60 antibodies present in CAD patients.21
We found no significant difference in the percentage of
individuals with high anti-CMV-IE1 levels in patients versus controls.
A problem throughout seroepidemiological studies of CMV is the high
infection rate of the population worldwide (50% to
100%).5 Based on the
detection of antibodies to whole CMV,
90% of the adult Hungarian
population is seropositive (K. Burian, MD, unpublished observation,
1999). Thus, these results do not exclude the possibility of the
involvement of CMV in the development of some forms of CAD.
Previous analyses of the simultaneous presence of elevated Cpn and CMV antibodies to whole virion in the same populations suggested an association between Cpn infection, but not CMV infection, and CAD.15 17 Our findings are in accord with those data on elevated Cpn seropositivity in patients with CAD, and the results obtained by detection of CMV-IE1 antibodies are also consistent with those findings.
We found that the simultaneous presence of hHSP60 antibodies and Cpn antibodies is associated with a striking increase in the risk (OR 38.3 to 82.0) for development of CAD. On the other hand, no joint effects of the simultaneous presence of high hHSP60 and high CMV-IE1 antibodies were revealed, indicating differences between microbial infections in the interaction with hHSP antibodies.
In patients with CAD, a potent joint effect has also been described for the simultaneous presence of C-reactive protein, an acute phase protein used as a marker for inflammation, and antibodies to herpes simplex virus 1 (HSV-1); the OR in subjects with high HSV-1 antibody and high C-reactive protein levels was 25.4 (95% CI 2.9 to 220.3).17 That finding, together with our results, supports the hypothesis that inflammatory reactions, infections with certain pathogens, and hHSP60 induced by various stimuli in endothelial or other cells act independently, but their simultaneous presence greatly increases the risk for disease development.
In summary, our present data indicate the independent
presence of elevated Cpn and
hHSP60 antibodies in CAD patients and the substantially increased OR
for CAD in individuals with the simultaneous presence of
Cpn antibodies at titers
1:128 and high levels of hHSP60 antibodies. These results might
provide direction in further studies on the mechanisms underlying
coronary artery
diseases.
| Acknowledgments |
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Received September 25, 2000; revision received December 1, 2000; accepted December 7, 2000.
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