Host Ferritin Translocates into the Chlamydial Inclusion: A Clear Alteration in its Subcellular Distribution as a Result of Infection

In the present study, the subcellular distribution of the major iron storage protein ferritin was investigated in cell cultures infected for various times with Chlamydia trachomatis or Chlamydia pneumoniae. In C. trachomatisinfected cells, confocal microscopy showed that ferritin was localized in the cytoplasm and did not overlap with the chlamydial staining, when examined 2, 5 and 10 h post-infection (pi). Interestingly, 18 h pi, the immunostaining indicated translocation of ferritin to the chlamydial inclusion. At 44 h pi, the localization of ferritin indicated a dramatic cytoplasmic redistribution and recruitment to C. trachomatis inclusion. For C. pneumoniae, ferritin did not colocalize with the inclusion until 40 h pi, when it was reduced in the cytoplasm and superimposed strongly with the chlamydial staining. At late stage of C. pneumoniae infection (70 h pi), predominant ferritin staining colocalized with the inclusion. Serial optical sections made by the confocal microscopy and the immunogold labeling technique confirmed the presence of ferritin inside of the chlamydial vacuole. The evidence presented in this work indicates an existence of a translocation system used by Chlamydiales to attract and acquire host proteins as large as ferritin through the inclusion membrane.