BACKGROUND

Chlamydia pneumoniue (C. pneumoniae), a recently discovered human pathogen, is a common cause of respiratory infections worldwide.'Seroepidemiological studies have indicated an association between chronic C. pneumoniae infection and coronary artery disease. The presence of C. pneumoniae has been demonstrated in about 50% of atherosclerotic lesions from autopsy and atherectomy tissue specimens, but not in normal-appearing arterial tissue, by electron microscopy, immunohistochemistry, and polymerase chain reaction (PCR). 2* 3 Moreover, persistent infection and multiplication of C. pneumoniae in endothelial cells have been demonstrated in~ itro.~

Inflammation may actually be an important factor in the formation of abdominal aortic aneurysms (AAA), although the initial triggers are obsc~ re.~ Because C. pneumoniae has been shown to be present in atherosclerotic lesions and it is capable of multiplying in the cells of the vessel wall, we studied the presence of C. pneumoniae in the walls of AAA by immunohistochemistry.