Demonstration of Chlamydia pneumoniae in the walls of abdominal aortic aneurysms

Background: Seroepidemiologic studies have indicated an association between chronic Chlamydia pneumoniae infection and coronary heart disease. The organism, which is a common respiratory pathogen, has been demonstrated in atherosclerotic lesions of the aorta and coronary arteries. Abdominal aortic aneurysms are frequently associated with atherosclerosis, and inflammation may actually be an important factor in aneurysmal dilatation. Hence it could be assumed that C. pneumoniae may play a role in maintaining an inflammation and triggering the development of aortic aneurysms. Methods and Results: Specimens from abdominal aortic aneurysm were examined for the presence of C. pneumoniae by immunohistochemical analysis, the polymerase chain reaction amplifying omp1 gene, transmission electron microscopy, and culture methods with histologically atherosclerosis-negative human aortic tissues used as a control group. Chlamydial lipopolysaccharide and C. pneumoniae specific antigens were found by immunohistochemistry in 12 and 8 of 12 aneurysm specimens, respectively, and C. pneumoniae DNA could be demonstrated in 6 of 6 aneurysm specimens studied. Furthermore electron microscopy revealed the presence of Chlamydia-like elementary bodies in three of four aneurysm specimens tested. None of the control samples gave positive reaction in the polymerase chain reaction, and C. pneumoniae antigens were not detected in any of them. Conclusions: C. pneumoniae is frequently found in the vessel wall of abdominal aortic aneurysm. The potential etiopathogenetic role of C. pneumoniae in the development of these aneurysms remains to be studied.