Delivery of Chlamydia pneumoniae to the vessel wall aggravates atherosclerosis in LDLr-/- mice

OBJECTIVE: The role of Chlamydia pneumoniae in atherosclerosis is still debated. In this study a novel mouse model was applied to determine the direct impact of C. pneumoniae on the arterial wall and the development of atherosclerosis. METHODS: Direct effects of C. pneumoniae on collar-induced atherosclerosis were studied after local delivery of C. pneumoniae to carotid arteries of LDL receptor-deficient (LDLr-/-) mice. RESULTS: The presence of C. pneumoniae in the vessel wall was quantified by RT-PCR (6.2 x 10(4) copies/artery) and resulted in a 2.0-fold increase in intima/media ratios (p<0.05) and a 1.7-fold increase in stenosis (p<0.05). Immunostaining revealed a 2.98-fold (p<0.01) increased macrophage content and a tendency towards lower numbers of smooth muscle cells and collagen in lesions of infected carotid arteries. Direct delivery of another respiratory pathogen, Mycoplasma pneumoniae, to the carotids did not affect size or composition of the atherosclerotic lesions. Presence of C. pneumoniae in the carotid arteries resulted within 7 days in a marked upregulation of the expression of MCP-1 (p<0.01) and ICAM-1 as determined on mRNA and protein levels. These in vivo data were in line with data obtained with in vitro infections of macrophages and endothelial cells with C. pneumoniae. CONCLUSIONS: We conclude that C. pneumoniae in carotid arteries leads to more pronounced atherosclerotic lesions with a more vulnerable morphology and that this model is suitable to monitor direct effects of C. pneumoniae on atherogenesis.