Transmission of Chlamydophila pneumoniae from dendritic cells to macrophages does not require cell-to-cell contact in vitro

Chlamydophila pneumoniae (C. pneumoniae) has been detected in macrophages (Mø) and dendritic cells (DC) in vascular diseases. To understand the importance of these cell types in C. pneumoniae infection and transmission, we infected DC and cultivated them with Mø in a coculture model system which precludes cell-to-cell contact during chlamydial infection. C. pneumoniae inside living DC were labeled and tracked with a red fluorescent ceramide dye. Subsequently, red-coloured chlamydial inclusions were detected 3 and 5 days later in cocultured Mø. Moreover, standard assays revealed infectious elementary bodies in infected DC and cocultured Mø. Assays for chlamydial gene expression indicated vital and dividing chlamydiae in both cell types. In summary, the results suggest that the transwell system employed here is a suitable model to investigate the transmission of C. pneumoniae from DC to Mø. Importantly, the observations presented demonstrate that transmission is independent of cell-to-cell contact.