Cell Stress and Chaperones (2011) 16:219–224
DOI 10.1007/s12192-010-0235-5
ORIGINAL PAPER
Impact of seropositivity to Chlamydia pneumoniae
and anti-hHSP60 on cardiovascular events
in hemodialysis patients
Pasquale Esposito & Carmine Tinelli & Carmelo Libetta &
Elisa Gabanti & Teresa Rampino & Antonio Dal Canton
Received: 27 July 2010 / Revised: 16 September 2010 / Accepted: 17 September 2010 / Published online: 5 October 2010
# Cell Stress Society International 2010
Abstract Autoimmunity to heat shock protein 60 (HSP60)
has been related to atherosclerosis. Chlamydia pneumoniae
(CP), the most studied infectious agent implicated in
promoting atherosclerosis, produces a form of HSP60,
which can induce an autoimmune response, due to high
antigenic homology with human HSP60 (hHSP60). In this
study, we evaluated the correlations among anti-hHSP60
antibodies, CP infection, and cardiovascular disease (CVD)
in a high-risk population, such as patients undergoing
hemodialysis (HD). Thirty-two patients (67.9±13.9 years;
male/female, 23:9) on regular HD were enrolled. Global
absolute cardiovascular risk (GCR) was assessed using the
Italian CUORE Project’s risk charts, which evaluate age,
gender, smoking habits, diabetes, systolic blood pressure,
and serum cholesterol. The occurrence of cardiovascular
events during a 24-month follow-up was recorded. Seropositivity to CP and the presence of anti-hHSP60 antibodies
were tested by specific enzyme-linked immunosorbent
assays. Inflammation was assessed by measurement of Creactive protein (CRP) serum levels. Fifteen healthy sex
and age-matched (61.9± 9.5 years; male/female, 11:4)
subjects were the control group. Fifteen of 32 patients
resulted seropositive for CP. CP+patients were older than
P. Esposito (*) : C. Libetta : E. Gabanti : T. Rampino :
A. Dal Canton
Nephrology, Dialysis and Transplantation Unit,
Fondazione IRCCS Policlinico “San Matteo” and
Univeristy of Pavia,
P.le Golgi, no. 2,
27100 Pavia, Italy
e-mail: pasqualeesposito@hotmail.com
C. Tinelli
Clinical Epidemiology and Biometric Unit, Fondazione IRCCS
Policlinico “San Matteo” and Univeristy of Pavia,
Pavia, Italy
CP−, while they did not differ for GCR, CRP, and dialytic
parameters. CVD incidence was significantly higher in CP+
(9 CP+ vs 2 CP−, p<0.05). Cox analysis recognized that
the incidence of CVD was independently correlated with
seropositivity to CP (HR, 7.59; p=0.01; 95% CI=1.63–
35.4). On the other hand, there were no significant
differences in anti-hHSP60 levels among CP+, CP− and
healthy subjects: 18.11 μg/mL (14.8–47.8), 31.4 μg/mL
(23.2–75.3), and 24.72 μg/mL (17.7–41.1), respectively.
Anti-hHSP60 did not correlate to GCR, CRP, and incidence
of CVD. In conclusion, our data suggest that anti-hHSP60
autoimmune response is not related to CP infection and CPrelated CVD risk in HD patients.
Keywords HSP60 . Anti-human HSP60 . Chlamydia
pneumoniae . Cardiovascular risk . Hemodialysis
Introduction
Heat shock protein 60 (HSP60) belongs to the HSPs family
or chaperonins, a group of highly conserved proteins
involved in protein folding and degrading of denaturated
proteins. HSP60 is mainly located in mitochondria, but
under stress conditions, changes in the intracellular location
and cell surface expression have been reported (Soltys and
Gupta 1997)
Autoimmunity against HSP60 has been related to
inflammation and cardiovascular diseases (CVD). In vitro
experiments showed that anti-HSP60 antibodies induce
complement and antibody-dependent cellular cytotoxicity
on heat stressed endothelial cells and peripheral blood
mononuclear cells (PBMC; Schett et al. 1997). Moreover, it
has been recently described that anti-HSP60 antibodies
mediate endothelial damage and exert prothrombotic
activity in a murine experimental model (Dieudé et al.
220
2009). In addition, clinical studies reported significantly
higher serum levels of anti-hHSP60 immunoglobulin G
(IgG) antibodies in acute coronary syndrome patients when
compared to patients with stable ischemic heart disease or
controls (Hoshida et al. 2005).
Interestingly, HSP60 autoimmunity has been also related
to chronic infections, in particular to Chlamydia pneumoniae (CP) infection.
CP, the most studied infectious agent implicated in
promoting atherosclerosis (Watson and Alp 2008), is a
Gram-negative obligate intracellular bacterium, which
accesses the organism via the respiratory tract, invades
circulation, where it may persist asymptomatically, and then
localizes in arteries and atherosclerotic tissues (Borel et al.
2008).
CP chronic infection, evaluated both by the presence of
IgG and immunoglobulin A (IgA) antibodies and, more
recently, by the measurement of CP DNA in PBMC, has
been related to increased risk of CVD (Gattone et al. 2001;
Mitusch et al. 2005). CP could have a direct and/or indirect
effect on the infected vessel wall, by the induction of
cytokines and adhesion molecules (Högdahl et al. 2008). It
has been also suggested that CP components or products,
such as lipopolysaccharide (LPS), LPS-like products and
chlamydial HSP60 (cHSP60), stimulate inflammation,
leading to atherosclerosis (Netea et al. 2000; Pesonen
et al. 2007). CP may establish a persistent infection, which
could be a source of cHSP60. The persistent expression
of this antigen in CP-infected patients can induce not only
an immune reaction against cHSP60 but also an autoimmune response against hHSP60, through the mechanism
of molecular mimicry; in fact, chlamydial and human
HSP60 share 85% homology (Xu 2003). It has been
demonstrated that anti-hHSP60 IgA, but not anti-hHSP60
IgG or anti-cHSP60 antibodies, are related to a significant
risk for coronary events, especially when associated to CP
seropositivity and high c-reactive protein (CRP) serum
levels (Huittinen et al. 2002). For these reasons, a pathogenetic role of anti-hHSP60 antibodies in course of CP
infection has been hypothesized but, so far, poorly investigated. In this study, we evaluated whether autoimmunity to
hHSP60 is associated to CP infection and CVD risk in a
high-risk population, such as patients undergoing hemodialysis (HD), who present an elevated risk of cardiovascular
morbidity and mortality.
Patients and methods
Patients
We enrolled 32 clinically stable uremic patients in regular
dialytic treatment for at least 1 year prior to the study [male/
P. Esposito et al.
female=23:9, mean age of 67.9 (13.9)years, mean dialytic
age of 62.8 (42.5)months]. Written informed consent was
obtained. All patients were dialysed three times a week
using low-flux synthetic AM-BIO-1000Wet membrane
(Asahi Kasei Medical Europe GmbH, Frankfurt, Germany).
Dialysis session time was of 3.5–4.0 h.
Patients with conditions influencing immune response,
such as acute infections, active immunological diseases,
immunosuppressive therapy, previous transplantation, or
history of malignancies, were excluded from the study.
Dialysis adequacy was assessed by the evaluation of
delivered dose of dialysis, using a single-pool urea kinetic
model (spKt/V urea). At baseline, cardiovascular risk was
assessed by global absolute cardiovascular risk (GCR),
using the validated risk charts of the Italian CUORE
Project.
The CUORE study is a large prospective cohort
followed up study, whose aim was to develop a 10-year
coronary risk predictive equation, specific to the Italian
population (Ferrario et al. 2005). It evaluates well-known
cardiovascular risk factors, such as age, gender, smoking
habits, diabetes, systolic blood pressure, and serum
cholesterol. On the basis of these factors, a GCR score
was generated (from 1 to 6), which corresponds to welldefined 10-year cardiovascular risk classes (from 1 to 6:
<5%, 5–9%, 10–14%, 15–19%, 20–29%, and ≥30%,
respectively).
After the initial assessment, patients were followed up
for 24 months. During the follow-up, the occurrence of
cardiovascular events (myocardial infarction, heart failure,
stroke, mesenteric infarction, and peripheral vascular
disease) was recorded. Fifteen healthy subjects matched
by sex and age [male/female=11:4, mean age of 61.9 (9.5)
years], were considered the control group.
Laboratory measurements
Blood samples were collected before the dialytic treatment.
Serum lipids and nitrogen measurements were performed
using standard methods in routine clinical laboratory. CRP
was measured by nephelometry. Anti-CP IgG and IgA
antibodies were determined using a commercially available
semi-quantitative kit (Labsystems OY, Helsinki, Finland),
which is 100% specific and 97% sensitive. IgG and IgA
seropositivity for CP was defined by the presence of
detectable antibodies at dilution of ≥1:64 and ≥1:32,
respectively. Anti-hHSP60 serum levels were measured
by an enzyme-linked immunosorbent assay (EIA), which
detected IgG, IgA, and IgM isotypes, with a sensitivity
of 2.88 ng/mL and a range of 7.81–250 ng/mL
(Stressgen Biotechnologies Corporation, Victoria, BC,
Canada). Briefly, samples from healthy subjects and HD
patients were added in duplicate to a pre-coated hHsp60
C. pneumoniae and anti-hHSP60 in hemodialysis
immunoassay plate and then incubated. Captured antihuman HSP60 antibodies were detected with a goat
polyclonal antibody conjugated with peroxidase (HRP),
specific for human IgG, IgA, and IgM isotypes. Color
intensity was measured in a microplate reader at 450 nm
and then plotted to a standard curve to determine sample
concentrations.
Data analysis
To summarize quantitative variables, we used means and
SD, or medians [interquartile range (IQR)] if they were not
normally distributed (Shapiro Test), and count and percentage for qualitative variables. Differences between infected
and non infected patients were assessed by the Student T
test or the Mann-Whitney’s U test for quantitative variables,
and by the chi-square (χ2) test or Fisher exact test for
qualitative ones. Kaplan–Meier method was used to
illustrate the incidence of CVD events. Univariate and
multivariate Cox’s proportional hazard models were fitted
to identify the most important predictors of CVD (GCR and
CRP serum levels). The proportional hazard assumption
was verified by means of Schoenfeld residuals. All tests
were two sides, and p<0.05 was considered statistically
significant. Data analysis was performed with the STATA
statistical package (ver. 10.0, 209, Stata Corporation,
College Station, TX, USA).
221
Results
Patient characteristics and CP infection
Table 1 shows characteristics of the patients enrolled.
Fifteen of 32 patients (47%) were seropositive for CP (CP+).
In particular, 11 patients were exclusively positive to IgG, one
patient to IgA, while three patients presented both IgG and
IgA class of antibodies.
CP+patients were older than seronegative (CP−) patients
[mean (SD), 74.2 (8.2) vs 61.7 (15.5)years, p=0.009),
whereas they did not present any difference in dialytic age,
duration of HD sessions, and dialytic adequacy, as well as
in cardiovascular risk factors. GCR, evaluated as reported
above, was also not different between CP+ and CP− [3.0
(1.3) vs 2.4 (1.4), p=0.115]. Furthermore, also CRP serum
median (IQR) also was not significantly different between the two groups: CP+, 0.53 (0.22–1.21) vs CP−,
0.34 (0.15–0.90)
CP infection and CVD events
The mean follow-up time was 23 months. During the
follow-up, 11 patients died (seven for cardiovascular
events, mean follow-up of 16 months; four for noncardiovascular diseases, mean follow-up of 15 months).
Eleven cardiovascular events occurred, and the prevalence
Table 1 Patients characteristics
Data are expressed as mean
[SD]
CP+ seropositive to Chlamydia
pneumoniae (IgA and/or IgG),
CP− seronegative to Chlamydia
pneumoniae (IgA and/or IgG),
HD hemodialysis, spKT/V urea
delivered HD dose, evaluated
according to single-pool urea
kinetic model, BP blood pressure, GCR global cardiovascular
risk score, evaluated according
to the CUORE Project (see text),
CRP C-reactive protein, antihHSP 60 anti-human heat shock
protein 60
*p<0.05 vs CP−
a
Median (25–75%)
CP+
CP−
N (%)
Age (years)
Gender (male/female)
Time on HD treatment (months)
Mean HD session duration (hours)
spKT/V urea
Systolic pre-dialysis BP (mmHg)
15 (47)
74.2 [8.2]*
12:3
65.6 [33.3]
3.83 [0.24]
1.3 [0.1]
129 [19.7]
17 (53)
61.7 [15.5]
11:6
60.4[50.1]
3.76 [0.25]
1.3 [0.1]
136.2 [21.7]
Diastolic pre-dialysis BP (mmHg)
Current smokers (N)
Diabetes (N)
Total cholesterol serum level (mg/dl)
GCR
CRP (mg/dl)a
68.7 [13.1]
4
5
161.5 [43.1]
3.3 [1.2]
73.2 [11.2]
3
3
158.5 [29.7]
2.4 [1.4]
0.53 (0.22–1.21)
9 (60)*
3
3
1
1
1
18.11 (14.8–47.8)
0.34 (0.15–0.90)
2 (11)
1
0
0
0
1
31.4 (23.2–75.3)
Cardiovascular events, N (%)
Myocardial infarction, N
Heart failure, N
Stroke, N
Mesenteric infarction, N
Peripheral vascular disease, N
Anti-hHSP 60 serum levels (μg/mL)a
222
of CVD was significantly higher in CP+ (9/15 CP+ vs 2/17
CP−, p=0.008). The number of patients suffering from
separate cardiovascular events is reported in Table 1. On
univariate Cox regression analysis, the incidence of CVD
was significantly associated to GCR [hazard ration (HR),
2.03; p=0.01; 95% CI, 1.38–2.99, for every point of the
score]. CVD incidence was also strongly associated to CP
seropositivity (HR, 7.59, p=0.01; 95% CI, 1.63–35.4;
Fig. 1). Moreover, on multivariate Cox analysis, the
strength of the association between CP seropositivity and
CVD incidence further increased after data adjustment for
GCR and CRP (HR, 16.77, p=0.05; 95% CI, 2.20/127.63).
We also evaluated the relationship between CVD incidence
and anti-CP antibodies titer, but we did not find any
association.
Anti-hHSP60 autoimmune response
Anti-hHSP60 antibodies were present in all analyzed
subjects; there were no significant differences in antibody
serum medians comparing CP seropositive (CP+) and CP
seronegative (CP−) HD patients [18.11 μg/mL (14.8–47.8)
vs 31.4 μg/mL (23.2–75.3), respectively], as well as to
healthy control subjects [−24.72 μg/mL (17.7–41.1)].
Moreover, anti-hHSP60 titer was not different between
patients affected and not by CVD events: 21.3 μg/mL
(IQR, 14.8–77.8) vs 31.3 μg/mL (IQR, 18.2–52.7), respectively. Correlations among anti-hHSP60 serum levels,
dialytic parameters, CRP levels, GCR, as well as incidence
of CVD during the follow-up were not found.
Discussion
HD patients present an increased risk of cardiovascular
diseases (Foley et al. 1998). Traditional cardiovascular risk
Fig. 1 Kaplan–Meier estimate survival for cardiovascular events
occurred during the follow-up (myocardial infarction, heart failure,
stroke, mesenteric infarction, and peripheral vascular disease) in
Chlamydia pneumoniae seropositive (CP+) and seronegative (CP−)
HD patients
P. Esposito et al.
factors cannot fully justify such an elevated risk; therefore,
new and non-traditional risk factors, such as inflammation
and chronic infections, have been evaluated (Kendrick and
Chonchol 2008). CP infection has been related to the
development and progression of atherosclerosis in HD
patients and, more recently, also in patients undergoing
peritoneal dialysis (Kim et al. 2008). In particular, both
anti-CP IgG and IgA antibodies titers have been associated
to progression of carotid atherosclerosis and ischemic heart
disease (Kato et al. 2004; Wszola et al. 2006). However, in
the clinical setting, together with a great deal of studies
reporting the close association between CP infection and
CVD, both in general and HD population (Lentine et al.
2006), conflicting evidence by observational and interventional studies also exists (Ieven and Hoymans 2005;
O’Connor et al. 2003). Some authors have proposed CP
infection only having a subsidiary role in atherosclerosis
development in HD patients (Kato et al. 2006). In
particular, it has been suggested that the link between CP
seropositivity and CVD risk is confounded by the presence
of other risk factors (Zoccali et al. 2003). Our data agree
with former studies, showing a significant association
between CP seropositivity and incidence of CVD, which
was also relevant after adjustment for the so-called
traditional risk factors, such as diabetes, hypertension,
hypercholestolemia, etc., as summarized in the GCR score.
The reasons for this discrepancy among the reported studies
could be due, first of all, to the different methods and
definitions of CP infection (seropositivity or DNA detection) and second, to individual differences of the evaluated
patients (Paldanius et al. 2006). For instance, regarding HD
patients, it is well known that different dialytic modalities
and membranes may affect immune response and inflammation. In fact, there is evidence that the use of
bioincompatible dialytic devices results both in increased
levels of pro-inflammatory cytokines (such as IL-1, IL-6,
and IL-12) and impaired ability of lymphocytes to respond
to antigenic stimuli (Libetta et al. 2004). In order to
minimize these potential confounding factors, we evaluated
a homogeneous sample of patients undergoing a regular HD
treatment, with similar dialytic prescriptions. On the basis
of our findings, we confirm the hypothesis that CP infection
could be considered an additional non-traditional risk factor
in HD patients, even if we admit that the real impact of CP
infection on clinical outcomes in HD should be better
elucidated in specific-designed studies. It has been supposed that in HD patients, as well as in general population,
there are several potential pathogenetic mechanisms to
explain the role of CP in atherosclerosis, but the exact
pathways are still unknown. In vitro experiments have
shown that the growth of CP in human monocytes induces
the production of pro-inflammatory cytokines (TNF-α, IL1, and IL-6) and chemokines (IL-8, monocyte chemotactic
C. pneumoniae and anti-hHSP60 in hemodialysis
protein-1) (Kern et al. 2009; Tsirpanlis et al. 2003;
Stenvinkel et al. 2002). In addition, CP invasion of
endothelial cells determines the expression of adhesion
molecules, such as intercellular adhesion molecule, and
stimulates transendothelial migration of neutrophils and
monocytes (Summersgill et al. 2000; Molestina et al. 1999).
In the present study, we tested the hypothesis that, in HD
patients, CP infection could promote an autoimmune
response to hHSP60, mediated by the mechanism of
molecular mimicry, due to the high antigenic homology
between human and chlamydial HSP60. We found that antihHSP60 antibodies levels were not different between
healthy subjects and HD patients and, in turn, between CP
seropositive and seronegative HD patients. Moreover, antihHSP60 antibodies were not related to CP infection,
cardiovascular risk factors, or incidence of CVD. These
data agree with a recent paper, which reports, in an ex vivo
model on coronary artery, the ability of CP to induce
arterial thickening without the presence of a host immune
response to HSP60 (Deniset et al. 2010). These findings let
us suppose that anti-hHSP60 autoimmunity does not play a
role in the pathogenesis of CP infection and CP-associated
cardiovascular risk. As above reported, previous studies
showed pro-inflammatory and pro-atherotrombotic effects
of anti-hHSP60 antibodies, but actually inconclusive results
have been also reported. In fact, while a strong correlation
between anti-hHSP60 and atherosclerosis has been found in
general population and in patients suffering from acute
myocardial infarction (Heltai et al. 2004), it has also been
demonstrated that anti-hHSP60 antibodies are not associated to CVD events in diabetic and cardiopathic patients
(Gruden et al. 2009; Hoymans et al. 2008). Regarding HD
patients, high serum levels of anti-hHSP60 antibodies were
reported in children and young HD patients, whereas adult
subjects did not show different serum levels of antihHSP60 when compared to healthy control group (Musial
et al. 2009; Esposito et al. 2010). Similar data resulted from
the present study confirms our previous report. However, it
is noteworthy that, in the specific setting of HD, regulation
of immune system is quite complex, and several factors
could influence antibody levels. It is well established that
HD patients present a state of immune system dysfunction
that makes them liable to infections and malignancies and
unresponsiveness to vaccinations (Eleftheriadis et al. 2007).
This immunodeficiency depends mainly on the altered
function of various types of immune cells, including
polymorphonuclear leukocytes, monocytes, and B and T
lymphocytes (Sardenberg et al. 2006; Lim et al. 2007). The
leading causes of this immune response impairment still are
not clear. It is believed that iron overload, HD treatment per
se, and metabolic disturbances linked to uremic status,
accompanied by the accumulation of numerous toxic
substances, could play a role in this immunity impairment
223
(Cohen et al. 1997). This immunodeficiency could explain,
at least in part, the low anti-hHSP60 titer we found in our
HD patients. At the same time, it is important to underline
that HD treatment by standard HD techniques and devices,
such as what we used in this study, is not able to remove
serum antibodies from the circulation. In fact, HD membranes are optimized for the removal of low molecular
weight solutes (<100 Da), while antibodies are too large
(~150 kDa) to cross dialysis membrane. Taken together,
these considerations remark that the evaluation of immune
response and antibodies production in the setting of HD is
difficult. Nevertheless, in our opinion, our data add a new
interesting contribution to the debate on the role of antihHSP60 in atherosclerosis, bringing into question the real
impact of HSP60 autoimmunity in the clinical setting.
However, our study presents some limitations, mainly due
to the limited number of studied subjects and the short-term
follow-up, which make us unable to perform in-depth
statistical and clinical analysis. Furthermore, we did not
completely evaluate factors potentially influencing antihHSP60 response, such as immune and nutritional status
and dialysis-specific factors, testing, for example, the
effects of different dialytic techniques and membranes. In
conclusion, our data suggest that in HD patients, while CP
seropositivity is associated to higher incidence of CVD, even
after adjustment for traditional risk factors, the autoimmune
response to hHSP60 is not related to CP infection. However,
because of the highly potential clinical impact of the
relationship among infections, autoimmunity, and cardiovascular disease, we think that larger prospective studies are
required to better evaluate the nature of this association,
mainly in high-risk populations, such as HD patients.
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