We examined 26 atherosclerotic lesions and 14 nondiseased aorta specimens to detect the periodontopathogenic part of the bacterial 16S rRNA locus by PCR. Treponema denticola sequence of the 16S rRNA locus was found in 6 out of 26 DNA samples (23.1%) from the formalin-fixed, paraffin-embeded atherosclerotic lesions obtained during surgery but not in any of the 14 nondiseased aorta samples from deceased persons. Utilizing immunofluorescence microscopy, we observed aggregated antigenic particles reacting with rabbit antiserum against T. denticola in thin sections of the PCR-positive samples, but we could not detect any reacting particles in the PCR-negative thin sections.Recent epidemiological studies have established that rheological and hemostatic factors are related to vascular diseases. These factors are potential biological effectors which may interact with known risk factors such as hyperlipidemia, smoking, and infections to promote vascular events. A number of studies have suggested that infectious organisms may play a role in the etiology and epidemiology of atherosclerosis and related diseases (5,6,9,29). For one such organism, Chlamydia pneumoniae, there is mounting evidence associating infections with a greater risk of atherosclerosis, myocardial infarction, and chronic coronary heart disease (3,20,26). Persistent infections by the obligate intracellular gram-negative bacteria are involved in a wide spectrum of respiratory diseases. It is now recognized that chronic oral infections, such as adult periodontitis, may have important long-term sequelae (2,7,10,16,19,(21)(22)(23)(24)28). An inflammatory response to endothelial cell injury and dysfunction caused by these infections may lead to atherosclerosis (26). Recently, Haraszthey et al. (11) reported that periodontal organisms such as Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Bacteroides forsythus, and Prevotella intermedia were detected in atheromatous plaque by PCR. In the present study, we attempted to detect periodontopathic bacterial DNA in atherosclerotic vascular lesions.To detect A. actinomycetemcomitans, P. gingivalis, B. forsythus, Campylobacter rectus, and Treponema denticola, we used the PCR and followed a double-blind protocol. The primers for detecting part of the bacterial 16S rRNA locus by PCR were synthesized in accordance with previously reported procedures (1, 30). Primer pairs for T. denticola (5Ј-TAATACCG AATGTGCTCATTTACAT-3Ј and 5-TCAAAGAAGCATTC CCTCTTCTTCTTA-3Ј), B. forsythus (5Ј-GCGTATGTAACC TGCCCGCA-3Ј and 5Ј-TGCTTCAGTGTCAGTTATACCT-3Ј), and C. rectus (5Ј-TTTCGGAGCGTAAAACTCCTTTTC-3Ј and 5Ј-TTTCTGCAAGCAGACACTTTT-3Ј) were designed on the basis of 16S rRNA (1). Primer pairs for P. gingivalis (5Ј-ATAATGGAGAACAGCAGGAA-3Ј and 5Ј-TCTTGCC AACCAGTTCCATTGC-3Ј) and A. actinomycetemcomitans (5Ј-CAGCAAGCTGCACAGTTTGCAAA-3Ј and 5Ј-CATTA GTTAATGCCGGGCCGTCT-3Ј) were designed on the basis of fimbriae and leukotoxin (30). Primer pairs for C. pneumoniae (5Ј-TGACAACTGTAGAAATACAGC-3Ј and 5Ј-GG TTGAGRTCAACGACTTAAGG-3Ј) were designe...