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Infection and Immunity, February 2004, p. 1107-1115, Vol. 72, No. 2
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.2.1107-1115.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Protection against CD95-Induced Apoptosis by Chlamydial Infection at a Mitochondrial Step

Silke F. Fischer, Thomas Harlander, Juliane Vier, and Georg Häcker*

Institute for Medical Microbiology, Technische Universität München, D-81675 Munich, Germany

Received 7 August 2003/ Returned for modification 12 September 2003/ Accepted 28 October 2003

Chlamydiae are obligate intracellular bacteria that infect human epithelial and myeloid cells. Previous work has established that chlamydiae are able to protect a cell against apoptosis induced by certain experimentally applied stimuli. Here we provide an analysis of this protective activity against the signal transduction during CD95-induced apoptosis. In HeLa cells overexpressing CD95, infection with Chlamydia trachomatis inhibited the appearance of apoptotic morphology, effector caspase activity, the activation of caspase-9 and -3, and the release of cytochrome c from mitochondria. However, caspase-8-processing and activity (measured as cleavage of Bid) were unaffected by the chlamydial infection. Similarly, infection with the species C. pneumoniae did not prevent the activation of caspase-8 but inhibited the appearance of effector caspase activity upon signaling through CD95. Furthermore, infection with C. trachomatis was able to inhibit CD95-induced apoptosis in Jurkat lymphoid cells, where a mitochondrial contribution is required, but not in SKW6.4 lymphoid cells, where caspase-8 directly activates caspase-3. Taken together, these data show that chlamydial infection can protect cells against CD95-induced apoptosis but only where a mitochondrial signaling step is necessary for apoptotic signal transduction.

* Corresponding author. Mailing address: Institute for Medical Microbiology, Technische Universität München, Trogerstr. 9, D-81675 Munich, Germany. Phone: 49-89-4140-4121. Fax: 49-89-4140-4868. E-mail: hacker{at}lrz.tum.de.

Editor: J. T. Barbieri

Infection and Immunity, February 2004, p. 1107-1115, Vol. 72, No. 2
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.2.1107-1115.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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