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【摘要】
Acute myocardial infarction (AMI) associated with unfavorable prognosis is likely to be the consequence of a diffuse active chronic inflammatory process that destabilizes the whole coronary tree and myocardium, suggesting a possible common causal agent underlying both conditions. The main objective of this study was to investigate whether Chlamydia pneumoniae (CP) infection occurred beyond the coronary plaques, namely in the myocardium of individuals who died of AMI. The presence of CP cell wall antigen (OMP-2) and CP-HSP60 was investigated in the myocardium and coronary plaques of 10 AMI and 10 age-matched control patients by immunohistochemistry, electron microscopy, and molecular biology. OMP-2 antigens were found in the unaffected myocardium of 9 of 10 AMI patients. Conversely, only 1 of 10 control patients exhibited a positive staining for CP. Moreover, OMP-2 and CP-HSP60 were detected in the whole coronary tree. CP presence was strongly associated with a T-cell inflammatory infiltrate. Our results suggest that CP may underlie both coronary and myocardial vulnerabilities in patients who died of AMI and corroborate the notion that CP may act by reducing cardiac reserves, thus worsening the ischemic burden of myocardium.
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Acute myocardial infarction (AMI) is, at present, the major cause of death in western countries.1 Despite the use of advanced medical and invasive procedures, the mortality rates are up to 17% in the first year.2 Recognition and treatment of common risk factors cannot fully explain and help to prevent the occurrence of acute coronary syndromes.1 Indeed, multiple pathogenetic components are likely to be involved in these events. Hence, a better understanding of the mechanisms underlying the disease process will be of help in optimizing patient treatment.
Clinicopathological and angiographical observations suggest that acute coronary syndromes do not reflect the vulnerability of a single atherosclerotic plaque but the burden of multiple vulnerable plaques studding the entire coronary tree and associated with its diffuse inflammatory infiltration.3-6 Moreover, we have recently demonstrated that activated T lymphocytes infiltrate the myocardium both in the peri-infarctual area and in remote unaffected myocardial regions in patients who died of a first myocardial infarction.7 The simultaneous occurrence of diffuse coronary and myocardial inflammation in these patients further supports the concept that both coronary and myocardial vulnerabilities concur in the pathogenesis of fatal AMI and suggests a possible common causal agent underlying both conditions. Several autoantigens expressed in the atherosclerotic plaque, including oxidized low-density lipoprotein1,8 and infectious and heat shock proteins (HSPs),9-11 are able to elicit an immune response.
In several epidemiological and experimental studies, Chlamydia pneumoniae (CP), among other infectious agents, has been associated with the risk of ischemic heart disease.12,13 Indeed, CP has been detected within the atherosclerotic lesions by immunohistochemistry, electron microscopy, polymerase chain reaction (PCR), and tissue culture.14-17 In fact, considerable evidence demonstrates the association of CP infection with atherosclerosis.18,19 In the light of these considerations, CP may be a potential agent involved not only in coronary vulnerability but also in myocardial vulnerability. Therefore, the main objective of this study was to investigate whether CP infection occurred beyond the coronary plaques, namely in the myocardium of individuals who died of AMI. To detect the presence of CP cell wall antigen (OMP-2)20 and chlamydial-HSP60 (CP-HSP60), an immunohistochemical study has been performed on coronary plaques and on remote unaffected myocardium. The presence of CP in the myocardium was also assessed by molecular biology techniques and electron microscopy.
【关键词】 persistent chlamydia pneumoniae infection cardiomyocytes correlated myocardial infarction
Materials and Methods
Patient Population
Two patient groups were prospectively collected, forming the study population: 10 patients who died of AMI (AMI group, six males/four females, mean age 72.1 ?? 2.1 years) and 10 age-matched control patients without clinical cardiac history (CTRL group, six males/four females, mean age 72.9 ?? 2.5 years) and who died of noncardiac causes (Table 1) . In the AMI group, the time lapse between symptom onset and death was less than or equal to 72 hours for all cases. Clinical history and standard electrocardiographic findings defined AMI.
Table 1. Clinical Data
Patients with chronic inflammatory diseases or tumors were excluded from the study to avoid bias attributable to immunological changes. No differences were observed among the three groups in the distribution of the major risk factors (hypertension, hyperlipidemia, smoke, diabetes). All autopsies were performed within 12 to 24 hours of death. This study was conducted in accordance with the Human Research Committee guidelines of our institution.
Tissue Handling and Processing
The hearts were weighed and fixed in 10% neutral-buffered formalin. The three major epicardial coronary arteries (left anterior descending, left circumflex, and right coronary arteries) were carefully dissected from the heart. Coronary segments from patients who died of AMI were subdivided into two additional groups: infarct-related coronary arteries (IRA) and noninfarct-related coronary arteries (non-IRA).
The following segments of the coronary tree were examined: AMI group: in the IRA coronary the culprit segment, including the thrombotic lesion, 2.5 cm long; in the non-IRA a segment 2.5 cm long, in which maximum stenosis was present; and CTRL group: a segment 2.5 cm long, in which maximum stenosis was present. All coronary segments were cut transversely at 5-mm intervals and decalcified if necessary. A total of 165 arterial segments were embedded in paraffin and serially sectioned: 110 from the AMI group (55 from IRA and 55 from non-IRA coronaries) and 55 from the CTRL group. For histopathological examination, arterial sections were stained with hematoxylin and eosin and Movat??s pentachrome stain.
Myocardial slices were then cut transversely at 1.0-cm intervals from apex to base. The myocardium was macroscopically examined to detect the presence and extent of the infarcted area. In all cases, at least one complete transverse heart slice was processed for histopathological examination and the infarction confirmed by light microscopy. We selected for study only those cases affected by infarct in a single coronary artery distribution and in which acute infarct region was correlated with the coronary artery containing the thrombus.
Histopathological and Morphometric Studies
Plaques were classified into three categories, according to the recent consensus document of the American Heart Association:21 1) plaque "culprit," characterized by the presence of an acute thrombus associated with plaque rupture or plaque erosion; 2) "vulnerable" plaques, including a) "thin fibrous cap atheromata," characterized by a lesion composed of a lipid-rich core covered by a less than 65-µm-thick fibrous cap containing many lipid-laden macrophage foam cells (>25 per high-power magnification),22 b) plaques with >90% stenosis, and c) superficial calcified nodules. 3) The remaining plaques were classified as "stable plaques."
Immunohistochemical Stains for Conventional Microscopy
An immunohistochemical study was performed in the unaffected regions of myocardium and coronaries of both experimental groups to evaluate the presence of CP, CP-HSP60, and the inflammatory infiltrate. The presence of CP cell wall antigen, namely OMP-2, was evaluated through an antibody synthesized by the Department of Infectious, Parasitic, and Immune-Mediated Diseases of Istituto Superiore di Sanit
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作者单位：From the Dipartimento di Biopatologia e Diagnostica per Immagini, Cattedra di Anatomia ed Istologia Patologica,* University of Rome Tor Vergata, Rome; and the Department of Infectious, Parasitic, and Immune-Mediated Diseases, Istituto Superiore di Sanit