184 M. Edvinsson et al. obtained from all patients, and the investigation con- formed to the principles outlined in the Declaration of Helsinki. Results Real-time PCR Of the biopsy samples, 6/23 (26%) aneurysm and 2/18 (11%) dissection patient samples were positive for C. pneumoniae DNA but none of the forensic control specimens were. Concentrations of C. pneumoniae in the positive samples were low, with only a few copies of C. pneumoniae per mg tissue. In the PBMC all patients tested negative for C. pneumoniae DNA. Throat swabs were positive in 2/25 aneurysm patients but in none of the 21 dissection patients. Nasopha- ryngeal swabs were positive in 1/21 dissection patients but in none of the 25 aneurysm patients. Those three positive patients were only positive in the nasopharynx or throat and not in the aorta. Moreover, all these samples contained few copies of C. pneumoniae. All aortic samples tested negative for C. pneumoniae mRNA. Human GAPDH mRNA was found in all cDNA, indicating that mRNA had not been degraded. All DNA samples tested positive for the presence of human beta-actin. Spiked samples showed no signs of inhibition. The present results of C. pneumoniae DNA in thoracic aortic aneurysm biopsies and in forensic control specimens have pre- viously been published (13). Serology IgG antibodies ‡1:64 against C. pneumoniae were found in 56% (14/25) of the aneurysm patients, in 43% (9/21) of the dissection patients, in 83% (5/6) of the aneurysm patients positive for C. pneumoniae in the aorta, and in 50% (1/2) of the dissection patients positive for C. pneumoniae in the aorta. Mean IgG titre was 1:123 in the aneurysm patients and 1:67 in the dissection patients. IgA antibodies ‡1:16 were found in 28% (7/25) of the aneurysm patients with a mean titre of 1:24. None of the dissection patients had any IgA antibodies against C. pneumoniae. Histopathology Samples for histopathological analyses were obtained from 23 thoracic aortic aneurysm patients and 17 aortic dissection patients. Among the eight patients positive for C. pneumoniae in the aorta, samples for histopathological analyses were obtained from 5/6 aneurysm patients and from both dissection patients. Cystic media necrosis, atherosclerotic changes, and inﬂammatory cells in the biopsies are shown in Table II. Discussion Chlamydophila pneumoniae (C. pneumoniae) DNA was found in thoracic aortic biopsies from 26% (6/23) of the patients undergoing surgery for thoracic aortic aneurysm and from 11% (2/18) of the patients with aortic dissection. C. pneumoniae-speciﬁc mRNA, a marker of metabolically active bacteria, could not be found in any of the biopsies, and none of the patients had C. pneumoniae in their PBMC. This may indicate that the acute phase of the C. pneumoniae infection occurred long before the patient was undergoing surgery and that the infection in the aortic wall had passed into a state of persistence. C. pneumoniae has been demonstrated by PCR in abdominal aortic aneurysm in several studies (15,16), and viable bacteria have been cultured from aneurys- matic tissue (7). We have previously demonstrated Table II. Histopathological analyses in aortic biopsies from thoracic aortic aneurysm and aortic dissection patients. Thoracic aortic aneurysm patients (n = 23) Aortic dissection patients (n = 17) C. pneumoniae- positive (n = 5) C. pneumoniae- negative (n = 18) C. pneumoniae- positive (n = 2) C. pneumoniae- negative (n = 15) Cystic medial necrosis Atherosclerotic changes Inﬂammatory cells Atherosclerotic changes and inﬂammatory cells Cystic medial necrosis and inﬂammatory cells 1/5 1/5 5/5 1/5 1/5 1/18 8/18 8/18 a 4/18 0/18 0/2 1/2 0/2 0/2 0/2 4/15 1/15 8/15 0/15 1/15 aP < 0.05, difference between Chlamydophila pneumoniae-positive and C. pneumoniae-negative aneurysm.