De Novo Induction of Atherosclerosis byChlamydia pneumoniae in a Rabbit Model

Chlamydia pneumoniae, a bacterial respiratory tract pathogen, has been associated with atherosclerosis in humans. C. pneumoniae infection of the respiratory tracts of rabbits fed a noncholesterol diet induced changes of atherosclerosis of the aorta in 6 (26.1%) of 23 animals after a single inoculum at 3 months. Multiple inocula given three times within 6 weeks resulted in grade III atherosclerosis in 8 (34.8%) of 23 rabbits, with an additional 5 (21. 7%) showing increased myxoid changes in the intima-media junction and exhibiting 8 (34.8%) focal periaortitis. Control animals inoculated with carrier broth (n = 24), HEp-2 cells (n = 12), or another respiratory pathogen, Mycoplasma pneumoniae (n = 32), produced no changes of atherosclerosis after 3 months. The histological changes were dissimilar (fewer foam cells) from those of rabbits fed a 0.5% cholesterol diet but were highly similar to or indistinguishable from changes in rabbits fed a 0.15% cholesterol diet (similar to that of humans). Proinflammatory cytokines and tissue growth factors were more consistently detected in cholesterol-induced aortic lesions than those induced by C. pneumoniae. These data are compatible with de novo induction of atherogenesis by C. pneumoniae in rabbits and suggest that C. pneumoniae may be important in the pathogenesis of atherosclerosis in humans.