The acute phase reactant response to respiratory infection with Chlamydia pneumoniae: implications for the pathogenesis of atherosclerosis

The acute phase response to Chlamydia pneumoniae infection was analyzed over a 72 h period post-infection in C57BL/6J mice. A single intra-nasal inoculation stimulated statistically significant increases in the plasma levels of IL-2, IL-5, IL-6, IL-10, IL-12, GM-CSF, IFN-γ, and serum amyloid A but not TNF-α, IL-1β, IL-4 and serum amyloid P. There was also a decrease in the activity of the HDL protective enzyme paraoxonase as well as a reduced ability of HDL to prevent oxidation of palmitoyl-2-arachidonyl-sn-glycerol-3-phosphocholine by hydroperoxyoctadecadienoic acid at 48 and 72 h post-infection. To determine whether the C. pneumoniae induced acute phase response had any effect on atherosclerotic plaque stability, we measured the frequency of intra-plaque hemorrhage as a marker of plaque disruption in the innominate arteries of apolipoprotein E deficient mice at 29–30 weeks and 1.5–2.0 years of age. There was an increased frequency of intra-plaque hemorrhage only in the older mice infected with the live organism (8/14) as compared to mice treated with killed C. pneumoniae (2/11) or sham inoculated with PBS (2/12). These results suggest that acute phase reactant proteins produced in response to pulmonary infection with C. pneumoniae may contribute to the progression and destabilization of atherosclerotic lesions.