Endovascular presence of Chlamydia pneumoniae DNA is a generalized phenomenon in atherosclerotic vascular disease

Abstract

The common respiratory pathogen Chlamydia pneumoniae has been implicated in the pathogenesis of coronary artery disease and acute myocardial infarction. In order to verify the endovascular presence of potentially viable chlamydia by detection of genomic DNA, we examined atherosclerotic arteries from various vascular regions using a C. pneumoniae specific nested polymerase chain reaction (PCR). The samples were obtained during surgical revascularization procedures or at autopsy. Chlamydial DNA was detected in 51/238 (21%) atherosclerotic samples. A total of 17 non-atherosclerotic control samples were PCR-negative. Chlamydial presence was detected in 36/140 (26%) vascular samples obtained at coronary revascularization procedures, in 9/61 (15%) samples from carotid artery stenosis, 3/17 (18%) samples from the aorta, and 3/20 (15%) iliac artery samples. Histomorphological discrimination of infected and non-infected arterial samples was not possible. Antichlamydial IgG and IgM response as examined by microimmunofluorescence assay did not aid identification of individual endovascular infection. C. pneumoniae is present in a significant proportion of atherosclerotic arteries. Its occurrence in atheromatous plaques is not limited to coronary arteries and may be considered indicative of an infectious component in atherosclerosis. However, it remains unclear whether chlamydia actually initiates atherosclerotic injury, facilitates its progression, or merely colonizes pre-existing atheromata.

Introduction

Chlamydia pneumoniae has recently been established as a third species of the obligate intracellular Chlamydiae. Respiratory epithelium has been identified as its primary target and the pathogen is now recognized as an important cause of community-acquired pneumonia, pharyngitis, and bronchitis 1, 2, 3. C. pneumoniae is characterized by an extraordinarily high seroprevalence: seroepidemiological surveys indicate that virtually everybody has been infected with the organism at least once during their lifetime and re-infections are common [2]. As chlamydia are notorious for causing persistent disease with severe tissue destruction, concern regarding sequelae from recurrent chlamydial infection is justified [4]. In this respect, chronic coronary artery disease has been related to prior or persistent C. pneumoniae infection 5, 6, 7. Based on elevated levels of antichlamydial IgG and the presence of immune complexes containing chlamydial lipopolysaccharide in coronary heart disease patients, C. pneumoniae infection was first suggested as an independent cardiovascular risk factor in studies carried out in Finland 5, 6. These results have been reproduced in subsequent studies 8, 9, 10. However, indirect statistical associations do not provide evidence of causality.

Endovascular infection might provide an explanation for atherosclerosis phenomena that are as yet unclear, such as mesenchymal cell proliferation and the distinct inflammatory component [11]. For C. pneumoniae to contribute in this respect it must be present in diseased arteries, and several investigators have now reported an occurrence of pathogen-specific structures such as lipopolysaccharide epitopes and segments of genomic DNA in atheromatous plaques, though detection rates have varied widely with the techniques employed. In fact, reported endovascular occurrence of C. pneumoniae varies from 2 to 100% 12, 13, 14, 15. The actual rate of vessels potentially infected and the distribution of the organism in the vascular system is thus unknown. If an occurrence of chlamydia in atheromatous plaques is indeed a newly recognized general phenomenon of atherosclerotic disease, examination of peripheral arteries prone to atherosclerosis should also indicate the presence of the pathogen. Therefore, we examined arterial tissues from various vascular regions by a C. pneumoniae-specific polymerase chain reaction (PCR) using a nested protocol for enhanced sensitivity and specificity. Detection of genomic DNA avoids the specificity problems which might be potentially caused by altered tissue antigenicity in immunological detection protocols [16]and thus gives more specific evidence for the presence of intact pathogen than detection of single epitopes.