Chlamydia pneumoniae in foci of “early” calcification of the tunica media in atherosclerotic arteries; an incidental presence?

Abstract

Conclusion: Chlamydia pneumoniae infection of medial smooth muscle cells may be crucial to calcification of the tunica media in atherosclerotic arteries. Summary: The role of C pneumoniae infection in the pathogenesis of atherosclerosis continues to be debated. This study investigated a possible association between C pneumoniae infection and medial calcification. The authors obtained carotid endarterectomy specimens from 60 patients. The plaques were examined by polymerase chain reaction (PCR) and immunohistochemistry to identify presence of C pneumoniae. In this study, specimens that were double-positive (positive by both PCR and immunohistochemistry) were considered positive for the presence of C pneumoniae. Double-negative and single-positive results were analyzed separately. There were 17 specimens that were double-positive for C Pneumoniae. Twenty-two specimens were negative with respect to both PCR and immunohistochemistry, and 21 specimens showed single-positive results, being positive with either PCR or immunohistochemistry for C pneumonia, but not with both. Medial calcification was present in 58.8% (10 of 17) specimens double-positive for C pneumoniae. There was no medial calcification observed in any of the 22 specimens double-negative for C pneumoniae. In areas of medial calcification, electron microscopy indicated the presence of C pneumoniae in smooth muscle cells. These smooth muscle cells showed damage to the cytoplasm and basement membrane associated with elementary reticulate and aberrant bodies of C pneumoniae. Immunohistocytochemistry techniques confirmed the presence of C pneumoniae in smooth muscle cells. Comment: There are two distinct forms of vascular calcification: intimal calcification, which occurs in the context of atherosclerosis, and medial calcification, which can occur without atherosclerosis. A variety of different mechanisms can contribute to vascular calcification. The present study suggests that the medial form of vascular calcification may be initiated by the infection of medial smooth muscle cells by C pneumoniae. Whether C pneumoniae is required for eventual narrowing of the arterial lumen or degeneration of the arterial wall is still unknown.