Chlamydia pneumoniae Infection and Atherosclerosis: Methodological Considerations

To the Editor:In contrast to several previously published studies,1–3⇓⇓ the one by Caligiuri et al4 failed to observe an accelerating effect of Chlamydia pneumoniae infection on atherosclerotic lesion development in apolipoprotein E–deficient mice. There are several critical differences in experimental design that likely account for these contrasting observations.In their initial studies, Caligiuri et al4 administered a single, nonpurified, low titer dose of C pneumoniae (1×106 ifu/mouse). This method is in contrast to the other studies where multiple inoculations of higher titers of purified C pneumoniae (5×106 to 3×107 ifu/mouse) were administered at intervals of 1 or 2 weeks. We have previously demonstrated that a single inoculation in animals at 8 weeks of age does not produce a sustained infection in the aorta, whereas multiple inoculations lead …