Survival of Chlamydia pneumoniae-infected Mono Mac 6 cells is dependent onNF-kappa B binding activity

The respiratory tract pathogen Chlamydia pneumoniae has been associated wit h atherosclerosis. Monocytes are supposed to serve as a vehicle for systemi c dissemination of intracellular C pneumoniae from the lung to the artery v essel wall. We were therefore interested in pathogen-induced cellular event s associated with NF-kappaB, a crucial transcription factor for both inflam matory cytokines and antiapoptotic molecules. In this study we demonstrate by electrophoretic mobility shift assay that C. pneumoniae infection of the human monocytic cell line Mono Mae 6 induces activation of NF-kappaB over 48 h, with a maximum level at 1 h postinfection. As shown by supershift ass ay, the activated NF-kappaB complex consists of the subunits RelA (p65) and NF-kappa B1 (p50). Apoptotic host cells were not detected during the early stages of the infection when maximal activation of NF-kappaB was detected. Pretreatment of Mono Mac 6 with the antioxidant and NF-kappaB inhibitor PD TC (pyrrolidine dithiocarbamate) induced activation of caspase-3 and led to apoptotic cell death. The C. pneumoniae-induced activation of the NF-kappa B complex was reduced by PDTC, which in parallel resulted in an increased a poptosis, as quantified by annexin V labeling and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling reaction. In the complet e absence of activated NF-kappaB, when Mono Mae 6 cells were pretreated wit h the more potent NF-kappaB inhibitors MG-132 and parthenolide a C pneumoni ae-mediated rescue of cells from induced apoptosis could not be achieved. O ur results indicate that activation of NF-kappaB in C. pneumoniae-infected Mono Mac 6 cells is associated with protection of Mono Mae 6 cells against apoptosis and might thereby contribute to systemic spread of the pathogen.