RT Journal Article SR Electronic T1 Characterization of Antiapoptotic Activities ofChlamydia pneumoniae in Human Cells JF Infection and Immunity JO Infect. Immun. FD American Society for Microbiology SP 7121 OP 7129 DO 10.1128/IAI.69.11.7121-7129.2001 VO 69 IS 11 A1 Fischer, Silke F. A1 Schwarz, Claudia A1 Vier, Juliane A1 Häcker, Georg YR 2001 UL http://iai.asm.org/content/69/11/7121.abstract AB Chlamydia pneumoniae is an obligate intracellular bacterium which frequently causes airway infection in humans and has been implicated in atherosclerosis. Here we show that infection withC. pneumoniae protects HeLa human epithelioid cells against apoptosis induced by external stimuli. In infected HeLa cells, apoptosis induced by staurosporine and CD95-death-receptor signaling was strongly reduced. Upon treatment with staurosporine, generation of effector caspase activity, processing of caspase-3 and caspase-9 and cytochrome c redistribution were all profoundly inhibited in cells infected with C. pneumoniae. Bacterial protein synthesis during early infection was required for this inhibition. Furthermore, cytochrome c-induced processing and activation of caspases were inhibited in cytosolic extracts from infected cells, suggesting that a C. pneumoniae-dependent antiapoptotic factor was generated in the cytosol upon infection. Infection with C. pneumoniaefailed to induce significant NF-κB activation in HeLa cells, indicating that no NF-κB-dependent cellular factors were involved in the protection against apoptosis. These results show that C. pneumoniae is capable of interfering with the host cell's apoptotic apparatus at probably at least two steps in signal transduction and might explain the propensity of these bacteria to cause chronic infections in humans.