[Persistence of Chlamydia pneumoniae in coronary plaque tissue. A contribution to infection and immune hypothesis in unstable angina pectoris]

Abstract

Background and objective: There is an increasing number of pointers towards a causative connection between Chlamydia pneumoniae and atherosclerosis. But the pathogenetic mechanism and intimal structures that are involved remain unclear. Starting with the hypothesis of a chronic infection, as demonstrated by the presence of the chlamydial stress (heat-shock) protein 60 (HSP 60), the presence and localization of these bacterial products in coronary atheromas was investigated.

Patients and methods: Coronary atheroma tissue from primary stenoses in 42 patients (36 men, 6 women, mean age 60.2 +/- 7.3 years) was studied immunohistochemically in the course of a retrospective analysis for chlamydial HSP 60. The findings in clinically acute coronary syndrome (Braunwald's classification) present in 27 patients were compared with those in 15 patients with acute angina and evaluated in relation to expression and site of predilection.

Results: An immune reaction to chlamydial HSP 60 was demonstrated in 27 of 42 atheromas (64%). Intact, non-atherosclerotic vessels, such as the mammary artery and sphenous vein, showed no such signals. Chlamydial HSP 60 was localized in maximally 23% of all plaque cells, mostly in macrophages/foam cells, more rarely in smooth muscle cells. Chlamydia in foam cells most often revealed ultrastructural patterns that pointed to the persistence of the pathogen. Sites of predilection of chlamydial HSP were predominantly foam cell areas and cell-poor regions, more rarely inflammatory infiltrates and areas of rupture. When comparing both types of lesion, signals for chlamydial HSP 60 were present in 21 of the 27 atheromas (78%) with unstable angina or acute myocardial infarction, but in only 6 of the 15 atheromas (40%) with stable angina. Within the group with the acute coronary syndrome, the prevalence of chronic chlamydial infection was independent of a previous myocardial infarction.

Conclusions: Chlamydial HSP 60 can often be demonstrated in primary coronary stenosis of symptomatic patients. It is most frequently found in macrophages/foam cells and is highly prevalent in the acute coronary syndrome. In-situ findings suggest a pathogenetically relevant role of chronic persistent infection of Chlamydia pneumoniae in unstable coronary plaques.