Chronic perivascular inoculation with Chlamydophila pneumoniae results in plaque formation in vivo

Abstract

Hypercholesterolemic and normocholesterolemic rabbit models of chronic arterial Chlamydophila (Chlamydia) pneumoniae (CPN) inoculation were established and the role of both viable and inactivated bacteria was investigated in atherogenesis. A total of 29 rabbits were randomized to four groups. Groups A and B were fed a cholesterol-enriched diet, and groups C and D were fed a normal diet. Arterial segments of group A and C animals were inoculated in vivo using viable CPN chronically using repeated perivascular applications. Contralateral arteries were treated using heat-inactivated CPN. Group B and D animals were treated with repeated perivascular injections of bacterial lipopolysaccharide (LPS) and saline (control). Additional hypercholesterolemic rabbits were treated by repeated injections using viable and inactivated CPN, each controlled by saline injections. To compare the effects of this chronic inoculation model, additional animals received single injections of either viable CPN, inactivated CPN, LPS, or saline. Vascular tissues (n=162 treated arteries of 29 rabbits) were analyzed using morphometry at histology. CPN was detected by fluorescence-immunohistochemistry and nested polymerase chain reaction. Only in hypercholesterolemic, but not in normocholesterolemic rabbits, chronic perivascular infection of all bacterial components, viable and heat-inactivated CPN, as well as LPS resulted in a significant increase in atheromatous lesion formation (lesion area index: 0.23±0.08, 0.25±0.09, and 0.15±0.05) when compared to controls (lesion area index 0.01±0.01, P=0.002). CPN persisted in atheromatous lesions and vascular tissues. Single perivascular infection using CPN or inactivated CPN was not able to induce lesion formation (lesion area index: 0.03±0.03, 0.03±0.02 vs 0.03±0.02 after single saline inoculation, P=0.965). In conclusion, chronic vascular infection with CPN or CPN components acts as a cofactor requiring other major atherogenic stimuli, rather than as a causative agent.