Fate of Chlamydophila pneumoniae in human monocyte-derived dendritic cells: long lasting infection.

Earlier studies from this group demonstrated that Chlamydophila pneumoniae co-localized with dendritic cells (DC) in temporal artery biopsies from patients with giant cell arteritis (GCA). To investigate the interaction of DC with C. pneumoniae we employed an in vitro cell culture system of human monocyte derived DC. These DC were infected with C. pneumoniae and observed at regular time intervals up to 25 days post infection. Chlamydiae were visualized inside DC by both confocal and electron microscopy. Statistical analysis showed an increase in the number of chlamydial antigen during that period (p < 0.00005, chi2-test). Titration of DC lysates on HEp-2 cells showed that infectious progeny was recovered at various intervals but showed no exponential growth. Additionally, RT-PCR analyses of infected DC identified transcripts from dnaA, ftsK and tal throughout a period of 14 days, indicating viable chlamydiae. Thus, human monocyte-derived DC are susceptible to C. pneumoniae infection. These results indicate that C. pneumoniae-infected DC can play an important role in the transmission of these bacteria in GCA and other chlamydial diseases.